WO2015001876A1 - Laser device, and photoacoustic measurement device - Google Patents

Laser device, and photoacoustic measurement device Download PDF

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Publication number
WO2015001876A1
WO2015001876A1 PCT/JP2014/064125 JP2014064125W WO2015001876A1 WO 2015001876 A1 WO2015001876 A1 WO 2015001876A1 JP 2014064125 W JP2014064125 W JP 2014064125W WO 2015001876 A1 WO2015001876 A1 WO 2015001876A1
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WIPO (PCT)
Prior art keywords
wavelength
mirror
resonator
light
laser
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PCT/JP2014/064125
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French (fr)
Japanese (ja)
Inventor
笠松　直史
覚 入澤
村越　大
裕康 石井
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富士フイルム株式会社
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Publication of WO2015001876A1 publication Critical patent/WO2015001876A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G01N29/2418—Probes using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/082—Construction or shape of optical resonators or components thereof comprising three or more reflectors defining a plurality of resonators, e.g. for mode selection or suppression
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/127—Plural Q-switches
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/162—Solid materials characterised by an active (lasing) ion transition metal
    • H01S3/1623—Solid materials characterised by an active (lasing) ion transition metal chromium, e.g. Alexandrite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/115—Q-switching using intracavity electro-optic devices

Definitions

  • the present invention relates to a laser device, and more particularly to a laser device capable of emitting light of a first wavelength and light of a second wavelength.
  • the present invention also relates to a photoacoustic measurement device including such a laser device.
  • Patent Document 1 and Non-Patent Document 1 a photoacoustic imaging apparatus that images the inside of a living body using a photoacoustic effect is known.
  • a living body is irradiated with pulsed light such as pulsed laser light.
  • pulsed light such as pulsed laser light.
  • the living tissue that has absorbed the energy of the pulsed light undergoes volume expansion due to heat, and an acoustic wave is generated.
  • This acoustic wave is detected by an ultrasonic probe or the like, and the inside of the living body can be visualized based on the detected signal (photoacoustic signal).
  • photoacoustic imaging method since an acoustic wave is generated in a specific light absorber, a specific tissue in a living body, such as a blood vessel, can be imaged.
  • FIG. 17 shows oxygenated hemoglobin (oxyhemoglobin combined with oxygen: oxy-Hb) abundant in human arteries and deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) abundantly contained in veins.
  • the molecular absorption coefficient for each light wavelength is shown.
  • the light absorption characteristic of the artery corresponds to that of oxygenated hemoglobin
  • the light absorption characteristic of the vein corresponds to that of deoxygenated hemoglobin.
  • a photoacoustic imaging method in which a blood vessel portion is irradiated with light of two different wavelengths using the difference in light absorption rate according to the wavelength, and an artery and a vein are distinguished and imaged. (For example, refer to Patent Document 2).
  • Patent Document 3 describes a laser device that oscillates a plurality of wavelengths by using a branching polarizer and a resonant optical path selector.
  • FIG. 18 shows a laser device described in Patent Document 3.
  • This laser device is an alexandrite laser using a flash lamp 1214 as an excitation source, and can oscillate at wavelengths of 755 nm and 800 nm.
  • the polarization direction of the oscillated light beam is in the plane of the paper and is p-polarized light.
  • a Pockels cell 1205 that constitutes a resonant optical path selection unit is arranged on the common optical path 1209.
  • a predetermined voltage is applied to the Pockels cell 1205.
  • the Pockels cell 1205 rotates the polarization direction of the incident linearly polarized light by 90 °.
  • no voltage is applied to the Pockels cell 1205.
  • a polarizer 1204 serving as an optical path branching unit transmits p-polarized light and reflects s-polarized light.
  • the light transmitted through the polarizer 1204 travels along the first branch optical path 1210 and is reflected by the first reflecting prism 1207.
  • the light reflected by the polarizer 1204 travels through the second branch optical path 1211 and is reflected by the second reflecting prism 1208.
  • the first reflecting prism 1207 is arranged to have a Brewster angle with respect to incident light.
  • the first reflecting prism 1207 has a dielectric reflecting film that selectively reflects light having a wavelength of 755 nm.
  • the second reflecting prism 1208 has a dielectric reflecting film that selectively reflects light having a wavelength of 800 nm.
  • the output mirror 1202 and the first reflecting prism 1207 constitute a resonator having a wavelength of 755 nm.
  • the output mirror 1202 and the second reflecting prism 1208 constitute a resonator having a wavelength of 800 nm.
  • a Q switch including a Pockels cell 1212 and a ⁇ / 4 wavelength plate 1213 is also arranged.
  • the flash lamp 1214 When the flash lamp 1214 is turned on, no voltage is applied to the Pockels cell 1212 constituting the Q switch, and the Q switch is off.
  • the Q switch After the flash lamp 1214 is turned on, the Q switch is turned on when the inversion distribution density in the alexandrite crystal 1203 becomes sufficiently high.
  • Laser oscillation occurs in the resonator constituted by the output mirror 1202 and the first reflecting prism 1207 or in the resonator constituted by the output mirror 1202 and the second reflecting prism 1208, and pulse laser light is emitted from the output mirror 1202. Exit.
  • the p-polarized light emitted from the alexandrite crystal 1203 is transmitted through the Pockels cell 1205 as p-polarized light and transmits p-polarized light. , Passes through the first branch optical path 1210, and is reflected by the first reflecting prism 1207.
  • the light reflected by the first reflecting prism 1207 passes through the polarizer 1204 and the Pockels cell 1205 in the opposite direction as p-polarized light and enters the alexandrite crystal 1203.
  • the output mirror 1202 and the first reflecting prism 1207 constitute a resonator, and laser oscillation occurs.
  • the first reflecting prism 1207 selectively reflects light having a wavelength of 755 nm, so that light having a wavelength of 755 nm oscillates.
  • the polarization direction of the p-polarized light emitted from the alexandrite crystal 1203 is changed when passing through the Pockels cell 1205. Rotates 90 ° to become s-polarized light.
  • the light that has become s-polarized light is reflected by the polarizer 1204, passes through the second branch optical path 1211, and is reflected by the second reflecting prism 1208.
  • the light reflected by the second reflecting prism 1208 passes through the polarizer 1204 in the reverse direction and enters the Pockels cell 1205 in the reverse direction.
  • the light incident on the Pockels cell 1205 as s-polarized light is rotated by 90 ° in the polarization direction when passing through the Pockels cell 1205, and becomes p-polarized light and enters the alexandrite crystal 1203.
  • the output mirror 1202 and the second reflecting prism 1208 constitute a resonator, and laser oscillation occurs.
  • the second reflecting prism 1208 selectively reflects light having a wavelength of 800 nm, so that light having a wavelength of 800 nm oscillates.
  • Patent Document 3 two Pockels cells are inserted in a common optical path common to a resonator having a wavelength of 755 nm and a resonator having a wavelength of 800 nm. That is, the Pockels cell 1212 for the Q switch and the Pockels cell 1205 for selecting the resonator optical path are inserted in the common optical path. Since light loss occurs when light passes through the Pockels cell, the laser described in Patent Document 3 is compared to a normal Q-switched laser in which only one Pockels cell for Q switching is arranged in the resonator. The optical loss is large.
  • the laser gain at the wavelength of 755 nm is compared with the laser gain at 800 nm, the laser gain is lower at the wavelength of 800 nm, and there is a demand for suppressing an extra output loss particularly at the wavelength of 800 nm where the laser output is low.
  • the intensity of the photoacoustic wave generated due to the irradiation of the pulsed light changes depending on the pulse width of the irradiated pulsed light.
  • the pulse width of the pulsed laser light changes depending on the resonator length, and a short wave pulse can be realized by shortening the resonator length.
  • Patent Document 3 since two Pockels cells are inserted in the common optical path common to both wavelengths, the resonator length cannot be shortened.
  • an object of the present invention is to provide a wavelength tunable laser device that can suppress a decrease in output at a wavelength having a low laser gain among a plurality of wavelengths and that can shorten the pulse.
  • the present invention also provides a photoacoustic measuring device including the laser device.
  • the present invention provides a solid laser medium having emission wavelengths at a first wavelength and a second wavelength, wherein the emission efficiency of the first wavelength is the emission efficiency of the second wavelength. And a first mirror and a second mirror facing each other with the laser medium interposed therebetween, and oscillates light of the first wavelength.
  • the second resonator having a common optical path which is a common portion and oscillating light of the second wavelength, the first resonator, and the second resonator are disposed on a common optical path, and
  • a first Q value changing unit for controlling the Q values of the first resonator and the second resonator, a second mirror, and a third mirror Disposed between the mirrors, to provide a laser apparatus and a second Q value control unit for controlling the Q value of the second resonator.
  • the laser apparatus drives the first Q value changing unit and the second Q value changing unit, and oscillates the Q values of the first resonator and the second resonator, respectively.
  • the first drive state in which the low Q state is lower than the threshold value the Q values of the first resonator and the second resonator are set to the high Q state in which the Q value of the resonator is higher than the oscillation threshold value.
  • a configuration may further include a control circuit for switching.
  • the control circuit may set the driving state of the first Q value changing unit and the second Q value changing unit as the first driving state when the laser medium is excited.
  • the control circuit changes the driving state of the first Q value changing unit and the second Q value changing unit from the first driving state to the third driving state.
  • the first Q value changing unit and the second Q value changing unit are preferably changed from the first driving state to the second driving state.
  • the control circuit drives the second Q value changing unit so that the Q value of the second resonator is in a high Q state, and at the same time, the control circuit of the first resonator
  • the first Q value changing unit may be driven so that the Q value becomes a high Q state. Instead, after driving the second Q value changing unit so that the Q value of the second resonator becomes the high Q state, the first resonator so that the Q value of the first resonator becomes the high Q state.
  • the Q value changing unit may be driven.
  • the first Q value changing unit is disposed on an optical path common to the first resonator and the second resonator, and sets the Q values of the first resonator and the second resonator according to the applied voltage.
  • a first Q switch to be changed may be included.
  • the control circuit may drive the first Q value changing unit by controlling the voltage applied to the first Q switch.
  • the first Q switch sets the first resonator and the second resonator to a low Q state when the applied voltage is the first voltage corresponding to the Q switch off, and the applied voltage has the absolute value of the first voltage.
  • the first resonator and the second resonator may be brought into a high-Q state when the second voltage is smaller than the absolute value of Q and the second voltage corresponds to Q switch-on.
  • the first voltage may be, for example, a voltage that acts as a quarter wavelength plate for light passing through the first Q switch.
  • the second voltage may be no voltage (0 V), for example.
  • the first Q value changing unit may further include a quarter-wave plate disposed between one of the first mirror and the second mirror and the first Q switch.
  • the first Q switch sets the first resonator and the second resonator to the low Q state when the applied voltage is the first voltage corresponding to the Q switch off, and the applied voltage is The first resonator and the second resonator may be brought into a high Q state when the second voltage corresponds to a Q switch-on whose absolute value is larger than the absolute value of the first voltage.
  • the first voltage may be no voltage (0 V), for example.
  • the second voltage may be a voltage at which the first Q switch works as a quarter wavelength plate, for example.
  • the second voltage corresponding to the Q switch on may be different between the oscillation at the first wavelength and the oscillation at the second wavelength.
  • the second Q value changing unit is disposed between the second mirror and the third mirror, and includes a second Q switch that changes the Q value of the second resonator according to the applied voltage. Also good.
  • the control circuit may drive the second Q value changing unit by controlling the voltage applied to the second Q switch.
  • the second Q value changing unit may further include a quarter wavelength plate disposed between the second Q switch and the third mirror.
  • the second Q switch sets the second resonator to a low Q state when the applied voltage is a third voltage corresponding to the Q switch off, and the applied voltage is an absolute value of the third voltage.
  • the second resonator may be brought into a high Q state at a fourth voltage corresponding to a larger Q switch-on.
  • the third voltage may be no voltage (0 V), for example.
  • the fourth voltage may be, for example, a voltage that causes the second Q switch to function as a quarter wave plate.
  • the second mirror may reflect light of the first wavelength and transmit light of the second wavelength.
  • the first mirror may be an output mirror of light having the first wavelength and light having the second wavelength.
  • the reflectance of the first mirror with respect to the first wavelength light may be set higher than the reflectance with respect to the second wavelength light.
  • the first mirror may be an output mirror for light of the first wavelength
  • the third mirror may be an output mirror for light of the second wavelength.
  • the reflectance of the first mirror with respect to the light of the second wavelength may be set higher than the reflectance of the third mirror with respect to the light of the second wavelength.
  • the reflectivity of the first mirror with respect to the light of the first wavelength is The reflectance of the third mirror with respect to the light of the second wavelength may be set higher.
  • the first mirror is light of the first wavelength and the third mirror as an output mirror of light of the second wavelength
  • the first mirror is light of the first wavelength and The output mirror of the light of the second wavelength may be used, and the third mirror may be the output mirror of the light of the second wavelength.
  • the reflectance with respect to the light of the first wavelength in the first mirror may be the same as the reflectance with respect to the light of the second wavelength.
  • At least one of the first mirror, the second mirror, and the third mirror may be configured to be movable along the optical axis direction.
  • the repetition frequency of the first wavelength oscillation may be higher than the repetition frequency of the second wavelength oscillation.
  • the laser apparatus of the present invention may further include a beam expander that expands a light beam in a direction away from the laser medium in at least one of the optical path of the first resonator and the optical path of the second resonator. .
  • the beam expander can be disposed, for example, between the laser medium and the second mirror.
  • a beam expander may be disposed between the second mirror and the second Q value control unit.
  • the beam expander may include a concave lens and a convex lens.
  • the second mirror may also serve as a concave lens of the beam expander.
  • the first mirror may be a plane mirror
  • the second mirror and the third mirror may be concave mirrors.
  • the radius of curvature of the third mirror located farther from the second mirror when viewed from the first mirror is shorter than the radius of curvature of the second mirror.
  • the first mirror may be a concave mirror
  • the second and third mirrors may be flat mirrors.
  • the excitation energy of the laser medium is individually set when the first wavelength is oscillated and when the second wavelength is oscillated.
  • the excitation energy at the second wavelength oscillation may be lower than the excitation energy at the first wavelength oscillation.
  • the laser device of the present invention may be configured to further include an optical filter that gives loss to the light of the second wavelength between the second mirror and the third mirror. Even in this case, the oscillation threshold value of the first wavelength in the first resonator is preferably higher than the oscillation threshold value of the second wavelength in the second resonator.
  • the present invention is also a solid-state laser medium having emission wavelengths at a first wavelength and a second wavelength, wherein the emission efficiency of the first wavelength is lower than the emission efficiency of the second wavelength;
  • a first resonator that oscillates light of the first wavelength, and is configured by an excitation unit that intermittently excites the laser medium, and a first mirror and a second mirror that are opposed to each other with the laser medium interposed therebetween.
  • the second resonator that oscillates light of the second wavelength, the first resonator, and the second resonator are disposed on a common optical path, and the first resonator and the second resonator
  • the first Q value changing unit that controls the Q value, the second resonance, and the second resonance are arranged between the second mirror and the third mirror.
  • a photoacoustic signal generated in the subject when the first and second wavelength laser beams are emitted to the subject is provided.
  • a photoacoustic measurement device comprising detection means for detecting and generating first and second photoacoustic data corresponding to the first and second wavelengths, respectively.
  • the laser apparatus of the present invention can suppress a decrease in output particularly at the first wavelength with low emission efficiency.
  • the pulsed light can be shortened for the first wavelength.
  • the block diagram which shows the structure of the laser light source unit which concerns on 1st Embodiment.
  • the graph which shows the gain of alexandrite.
  • the graph which shows the relationship between excitation energy and the pulse width of a pulsed laser beam.
  • the graph which shows the relationship between excitation energy and the output of a pulse laser beam.
  • the flowchart which shows the operation
  • FIG. 6 is a block diagram showing a laser device described in Patent Document 3.
  • FIG. 1 shows a photoacoustic measuring apparatus including a laser apparatus according to a first embodiment of the present invention.
  • the photoacoustic measurement device 10 includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, and a laser light source unit (laser device) 13.
  • the laser light source unit 13 emits pulsed laser light that irradiates the subject.
  • the laser light source unit 13 emits laser light having a plurality of wavelengths including the first wavelength and the second wavelength. In the wavelength characteristic of the laser gain coefficient (light emission efficiency), the gain coefficient at the second wavelength is higher than the gain coefficient at the first wavelength.
  • the molecular absorption coefficient at a wavelength of 755 nm of oxygenated hemoglobin (hemoglobin combined with oxygen: oxy-Hb) contained in a large amount in human arteries is lower than the molecular absorption coefficient at a wavelength of 800 nm.
  • the molecular absorption coefficient at a wavelength of 755 nm of deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) contained in a large amount in veins is higher than the molecular absorption coefficient at a wavelength of 800 nm.
  • the photoacoustic signal obtained by irradiating a laser beam having a wavelength of 755 nm is relatively large or small with respect to the photoacoustic signal obtained by irradiating a laser beam having a wavelength of 800 nm.
  • the photoacoustic signal from the artery and the photoacoustic signal from the vein can be discriminated.
  • the oxygen saturation can be measured.
  • any combination of two wavelengths may be used as long as there is a difference in the light absorption coefficient between the two selected wavelengths, and the above-described about 755 nm and about 800 nm.
  • the combination is not limited.
  • the two wavelengths selected are approximately 800 nm (exactly 798 nm) at which the light absorption coefficients of oxygenated hemoglobin and deoxygenated hemoglobin are the same, and the light of deoxygenated hemoglobin.
  • a combination with a wavelength of about 755 nm (more precisely, 757 nm) at which the absorption coefficient becomes a maximum is preferable.
  • the first wavelength does not need to be exactly 798 nm.
  • the second wavelength does not need to be exactly 757 nm.
  • the second wavelength is in the range of 748 to 770 nm which is the half-value width of the peak near the maximum value (757 nm), there is no practical problem.
  • FIG. 2 shows the configuration of the laser light source unit 13.
  • the laser light source unit 13 includes a laser rod 51, a flash lamp 52, a first mirror 53, a second mirror 54, a third mirror 55, a first Q value changing unit 56, a second Q value changing unit 57, And a control circuit 62.
  • the laser rod 51 is a laser medium.
  • the laser rod 51 has emission wavelengths at a first wavelength (800 nm) and a second wavelength (755 nm).
  • an alexandrite crystal can be used for the laser rod 51.
  • Fig. 3 shows the laser gain of alexandrite.
  • the laser gain of alexandrite peaks at a wavelength near 755 nm.
  • the laser gain monotonously decreases as the wavelength becomes shorter in the wavelength range shorter than the wavelength of 755 nm.
  • the laser gain coefficient of the alexandrite crystal at a wavelength of 800 nm is lower than the laser gain coefficient at a wavelength of 755 nm.
  • the flash lamp 52 is an excitation light source and is an excitation means for irradiating the laser rod 51 with excitation light.
  • the flash lamp 52 is driven intermittently. Thereby, the laser rod 51 is intermittently excited.
  • a light source other than the flash lamp 52 may be used as the excitation light source.
  • the first mirror 53, the second mirror 54, and the third mirror 55 are arranged along the optical axis of the laser rod 51.
  • the first mirror 53 and the second mirror 54 face each other with the laser rod 51 interposed therebetween.
  • the third mirror 55 is disposed on the side opposite to the laser rod 51 when viewed from the second mirror 54.
  • the first mirror 53 and the third mirror 55 face each other with the laser rod 51 and the second mirror 54 interposed therebetween.
  • the first mirror 53 is an output mirror of light having a wavelength of 800 nm and light having a wavelength of 755 nm.
  • the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm is higher than the reflectance with respect to light with a wavelength of 755 nm.
  • the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm is 80%
  • the reflectance with respect to light with a wavelength of 755 nm is 70%.
  • the second mirror 54 reflects light having a wavelength of 800 nm and transmits light having a wavelength of 755 nm.
  • the reflectance of the second mirror 54 with respect to light with a wavelength of 800 nm is 99.8% or more, and the reflectance with respect to light with a wavelength of 755 nm is 0.5% or less.
  • the third mirror 55 reflects light having a wavelength of 755 nm.
  • the reflectance of the third mirror 55 with respect to light having a wavelength of 755 nm is, for example, 99.8% or more.
  • the first mirror 53 and the second mirror 54 constitute a first resonator that oscillates light having a wavelength of 800 nm.
  • light having a wavelength of 755 nm emitted from the laser rod 51 passes through the second mirror 54 and is reflected by the third mirror 55, and reciprocates between the first mirror 53 and the third mirror 55.
  • the first mirror 53 and the third mirror 55 constitute a second resonator that oscillates light having a wavelength of 755 nm.
  • the resonator length of the first resonator is shorter than the resonator length of the second resonator.
  • the optical path from the first mirror 53 to the second mirror 54 is a common optical path for the first resonator and the second resonator. That is, a part of the optical path of the second resonator is common to the first resonator.
  • the first Q value changing unit 56 is disposed in a common part to the first resonator and the second resonator, and controls the Q values of the first resonator and the second resonator.
  • the first Q value changing unit 56 is disposed, for example, between the first mirror 53 and the laser rod 51 on a common optical path for the first resonator and the second resonator. Instead, the first Q value changing unit 56 is disposed on the optical path between the laser rod 51 and the second mirror 54 and common to the first resonator and the second resonator. May be.
  • the first Q value changing unit 56 includes a first Q switch 58 and a polarizer 59.
  • the first Q switch 58 is arranged on an optical path common to the first resonator and the second resonator.
  • the first Q switch 58 changes the Q values of the first resonator and the second resonator according to the applied voltage.
  • the first Q switch 58 can be an electro-optic element that changes the polarization state of the light passing therethrough according to the applied voltage.
  • the polarizer 59 is disposed between the laser rod 51 and the first Q switch 58.
  • the polarizer 59 transmits only linearly polarized light in a predetermined direction.
  • a beam splitter that transmits linearly polarized light (for example, p-polarized light) in a predetermined direction and reflects a direction orthogonal to the predetermined direction (for example, s-polarized light) can be used.
  • the polarizer 59 may be omitted if the light emitted from the laser rod 51 is p-polarized light, such as when an alexandrite crystal is used for the laser rod 51.
  • a Pockels cell is used for the first Q switch 58.
  • the first Q switch 58 sets the first resonator and the second resonator to a low Q state when the applied voltage is the first voltage corresponding to the Q switch off.
  • the low Q state refers to a state where the Q value of the resonator is lower than the laser oscillation threshold value.
  • the first voltage is, for example, a voltage at which the first Q switch 58 works as a quarter wavelength plate.
  • the first voltage may be a positive voltage or a negative voltage.
  • the first Q switch 58 sets the first resonator and the second resonator to a high Q state when the applied voltage is a second voltage corresponding to the Q switch being turned on.
  • the high Q state refers to a state where the Q value of the resonator is higher than the laser oscillation threshold value.
  • the absolute value of the second voltage is smaller than the absolute value of the first voltage.
  • the second voltage is, for example, 0 V (no voltage applied), and the polarization state of the light transmitted through the first Q switch 58 does not change at this time.
  • the first Q switch 58 When the first voltage is applied to the first Q switch 58, the first Q switch 58 functions as a quarter wave plate, and the p-polarized light incident on the first Q switch 58 from the polarizer 59 is Then, the light passes through the first Q switch 58 and becomes circularly polarized light, is reflected by the first mirror 53, and enters the first Q switch 58 in the reverse direction.
  • the circularly polarized light incident on the first Q switch 58 in the reverse direction becomes s-polarized light when passing through the first Q switch 58, and is reflected by the polarizer 59 that reflects the s-polarized light and is out of the optical path of the resonator. Is released.
  • the voltage applied to the first Q switch 58 is 0 V (second voltage)
  • the p-polarized light incident on the first Q switch 58 from the polarizer 59 remains p-polarized. 58 is reflected and reflected by the first mirror 53.
  • the p-polarized light reflected by the first mirror 53 passes through the first Q switch 58 without changing the polarization state, passes through the polarizer 59 that transmits p-polarized light, and enters the laser rod 51.
  • the second Q value changing unit 57 is disposed between the second mirror 54 and the third mirror 55, and controls the Q value of the second resonator.
  • the second Q value changing unit 57 includes a second Q switch 60 and a quarter wavelength plate 61.
  • the second Q switch 60 is disposed on the optical path of the second resonator and outside the optical path of the first resonator, that is, between the second mirror 54 and the third mirror 55.
  • the second Q switch 60 changes the Q value of the second resonator according to the applied voltage.
  • the second Q switch 60 can be an electro-optic element that changes the polarization state of light passing therethrough according to the applied voltage.
  • the quarter wavelength plate 61 is disposed between the second Q switch 60 and the third mirror 55.
  • a Pockels cell is used for the second Q switch 60.
  • the second Q switch 60 sets the second resonator in a low Q state when the applied voltage is a third voltage corresponding to the Q switch off.
  • the third voltage is, for example, 0 V (no voltage applied), and at this time, the polarization state of the light transmitted through the second Q switch 60 does not change.
  • the second Q switch 60 sets the second resonator to a high Q state when the applied voltage is a fourth voltage corresponding to the Q switch being turned on.
  • the absolute value of the fourth voltage is greater than the absolute value of the third voltage.
  • the fourth voltage is, for example, a voltage at which the second Q switch 60 works as a quarter wavelength plate.
  • the fourth voltage may be a positive voltage or a negative voltage.
  • the p-polarized light that has passed through the second mirror 54 and entered the second Q switch 60 from the laser rod 51 side is The polarization state does not change, passes through the second Q switch 60, passes through the quarter wavelength plate 61, becomes circularly polarized light, and is reflected by the third mirror 55.
  • the circularly polarized light reflected by the third mirror 55 passes through the quarter-wave plate 61 in the reverse direction to become s-polarized light, passes through the second Q switch 60 as s-polarized light, and returns to the laser rod 51.
  • the second mirror 54 reflects light having a wavelength of 800 nm and transmits light having a wavelength of 755 nm. Therefore, the light traveling between the second mirror 54 and the third mirror 55 is light having a wavelength of 755 nm, and the light having a wavelength of 800 nm does not travel from the second mirror 54 to the third mirror 55 side. .
  • the second Q switch 60 when a fourth voltage is applied to the second Q switch 60, the second Q switch 60 functions as a quarter wavelength plate, passes through the second mirror 54 from the laser rod 51 side, and passes through the second mirror 54.
  • the p-polarized light incident on the Q switch 60 becomes circularly polarized light when passing through the second Q switch 60, and further passes through the quarter wavelength plate 61 to become s-polarized light at the third mirror 55. reflect.
  • the light reflected by the third mirror 55 passes through the quarter-wave plate 61 in the reverse direction and becomes circularly polarized light, and further passes through the second Q switch 60 and becomes p-polarized light, and returns to the laser rod 51.
  • the control circuit 62 drives the first Q value changing unit 56 and the second Q value changing unit 57.
  • the control circuit 62 includes a first driving state, a first resonator in which the Q values of the first resonator and the second resonator are set to a low Q state in which the Q value of the resonator is lower than an oscillation threshold value.
  • the second driving state in which the Q value of the second resonator is set to a high Q state in which the Q value of the resonator is higher than the oscillation threshold value, and the Q value of the first resonator is set to a high Q state.
  • the driving state is switched between the third driving states in which the Q value of the second resonator is set to the low Q state.
  • the control circuit 62 drives the first Q value changing unit 56 by controlling the voltage applied to the first Q switch 58 and controls the second voltage by controlling the voltage applied to the second Q switch 60.
  • the Q value changing unit 57 is driven.
  • the control circuit 62 also drives the flash lamp 52.
  • the control circuit 62 applies a first voltage to the first Q switch 58 to make the first Q switch 58 work as a quarter wavelength plate. Further, the applied voltage to the second Q switch 60 is set to 0 V (third voltage), and the polarization state of the light passing through the second Q switch 60 is not changed. Since the first Q switch 58 functions as a quarter wavelength plate, the light reflected by the first mirror 53 does not enter the laser rod 51. Further, by not changing the polarization state of the light passing through the second Q switch 60, the light having a wavelength of 755 nm reflected by the third mirror 55 is incident on the laser rod 51 in the s-polarized state.
  • the Q values of the first resonator and the second resonator are in a low Q state, and laser oscillation does not occur for both the wavelength of 800 nm and the wavelength of 755 nm.
  • the first Q switch 58 is disposed on a common optical path for the first resonator and the second resonator, and the second voltage is applied by applying a first voltage to the first Q switch 58.
  • the Q value of each of the resonators can be set to a low Q state.
  • the voltage applied to the second Q switch 60 is not particularly limited to the third voltage
  • the fourth voltage is applied to the second Q switch 60
  • the second voltage The Q switch 60 may be used as a quarter wavelength plate.
  • the control circuit 62 sets the applied voltage to the first Q switch 58 to 0 V (second voltage) and does not change the polarization state of the light passing through the first Q switch 58.
  • a fourth voltage is applied to the second Q switch 60 to cause the second Q switch 60 to function as a quarter wavelength plate.
  • the Q values of the first resonator and the second resonator are in a high Q state, and laser oscillation occurs.
  • the laser gain at a wavelength of 755 nm is higher than the laser gain at a wavelength of 800 nm, so the oscillation wavelength is 755 nm, which has a higher laser gain.
  • the control circuit 62 sets the applied voltage to the first Q switch 58 to 0 V (second voltage) and does not change the polarization state of the light passing through the first Q switch 58. Further, the applied voltage to the second Q switch 60 is set to 0 V (third voltage), and the polarization state of the light passing through the second Q switch 60 is not changed. By not changing the polarization state of the light passing through the first Q switch 58, the light reflected by the first mirror 53 enters the laser rod 51 in a p-polarized state.
  • the Q value of the first resonator becomes a high Q state
  • the Q value of the second resonator becomes a low Q state
  • laser oscillation occurs in the first resonator.
  • the first resonator is a resonator having a wavelength of 800 nm
  • the oscillation wavelength is 800 nm.
  • the control circuit 62 sets the driving state of the first Q value changing unit 56 and the second Q value changing unit 57 to the first driving state when the laser rod 51 is excited. That is, the Q values of the first resonator and the second resonator are set to a low Q state, the flash lamp 52 is turned on, and the laser rod 51 is excited. After the excitation of the laser rod 51, the control circuit 62 changes the driving state of the first Q value changing unit 56 and the second Q value changing unit 57 from the first driving state to the third driving when the oscillation wavelength is 800 nm. Change to state. In the third driving state, since the first resonator is in the high Q state and the second resonator is in the low Q state, the oscillation wavelength is 800 nm. By rapidly changing the Q value of the first resonator from the low Q state to the high Q state, pulse laser light having a wavelength of 800 nm can be obtained.
  • the control circuit 62 changes the driving state of the first Q value changing unit 56 and the second Q value changing unit 57 from the first driving state to the second driving state. Change to state. At this time, the control circuit 62 drives the second Q value changing unit 57 so that the second resonator is in the high Q state, and at the same time, the first resonator is in the high Q state. The Q value changing unit 56 is driven. Alternatively, after driving the second Q value changing unit 57 so that the second resonator is in the high Q state, the first Q value changing unit 56 is driven so that the first resonator is in the high Q state. May be.
  • both resonators are in the high Q state, but the oscillation wavelength is 755 nm, which has a high laser gain, of the wavelength 800 nm and the wavelength 755 nm.
  • FIG. 4 shows the relationship between the excitation energy and the pulse width of the pulsed laser beam.
  • the figure shows the relationship between excitation energy and pulse width for two resonator lengths.
  • Graph (a) shows the relationship between excitation energy and pulse width when a resonator with a short resonator length is used
  • graph (b) shows excitation energy and pulse width when a resonator with a long resonator length is used. The relationship is shown. Referring to graphs (a) and (b), it can be seen that, when the excitation energy is constant, the pulse width can be shortened when the resonator length is shorter than when the resonator length is long.
  • the laser light source unit 13 see FIG.
  • the pulse width of the pulse laser beam having a wavelength of 800 nm is set to the pulse width of the pulse laser beam having a wavelength of 755 nm. Can be shorter than the width.
  • FIG. 5 shows the relationship between excitation energy and laser output.
  • the figure shows the relationship between excitation energy and laser output for two resonator lengths.
  • Graph (a) shows the relationship between excitation energy and laser output when a resonator with a short resonator length is used
  • graph (b) shows excitation energy and laser output when a resonator with a long resonator length is used. The relationship is shown. Referring to graphs (a) and (b), it can be seen that when the excitation energy is constant, the laser output can be increased when the resonator length is shorter than when the resonator length is longer.
  • the first resonator has a resonator length shorter than that of the second resonator, and the laser output of light having a wavelength of 800 nm can be obtained compared to the case where both resonators have the same resonator length. Can be raised.
  • FIG. 6 shows the relationship between the excitation energy and the pulse width of the pulse laser beam.
  • graph (a) shows the relationship between excitation energy and pulse width when the reflectance of the first mirror 53 as an output mirror is 80%
  • graph (b) shows the first mirror 53.
  • the relationship between the excitation energy and the pulse width when the reflectivity is 60% is shown. Referring to graphs (a) and (b), when the excitation energy is constant, it can be seen that the higher the output mirror reflectivity, the shorter the pulse width compared to the lower output mirror reflectivity. .
  • the pulse width of the pulse laser light with a wavelength of 800 nm is made larger than the pulse width of the pulse laser light with a wavelength of 755 nm. Can also be shortened.
  • FIG. 7 shows the relationship between excitation energy and laser output.
  • graph (a) shows the relationship between excitation energy and laser output when the reflectance of the first mirror 53 is 80%
  • graph (b) shows the reflectance of the first mirror 53.
  • the relationship between excitation energy and laser output when 60% is shown. Referring to graphs (a) and (b), when the excitation energy is constant, the higher the output mirror reflectivity, the higher the laser output compared to the lower output mirror reflectivity. I understand.
  • the laser of light with a wavelength of 800 nm is compared with the case where the reflectivity of both wavelengths is the same.
  • the output can be increased.
  • FIG. 8 shows operation waveforms of each part during laser oscillation.
  • the control circuit 62 turns on the flash lamp 52 at time t1 (a).
  • the control circuit 62 applies the first voltage to the first Q switch 58 (b) before turning on the flash lamp 52, and sets the applied voltage to the second Q switch 60 to 0 V (third voltage).
  • the time for applying the first voltage to the first Q switch 58 may be a time slightly before the time t1.
  • the first voltage may be continuously applied to the first Q switch 58 after the previous pulse laser beam emission.
  • the first Q switch 58 acts as a quarter wavelength plate.
  • the polarization state of the light passing through the second Q switch 60 does not change.
  • the laser rod 51 When the laser rod 51 is excited at time t1, p-polarized light is emitted from the laser rod 51.
  • the light emitted from the laser rod 51 in the direction of the first mirror 53 reciprocates through the first Q switch 58 that functions as a quarter-wave plate, and the polarization direction rotates by 90 ° and passes through the polarizer 59. Cannot be returned to the laser rod 51.
  • the light having a wavelength of 755 nm reciprocates through the quarter-wave plate 61 and the polarization direction is rotated by 90 °, and the laser has a predetermined polarization axis. It does not return to the rod 51. Therefore, the Q values of the first resonator and the second resonator are in a low Q state, and the first resonator and the second resonator do not oscillate.
  • the control circuit 62 changes the voltage applied to the first Q switch 58 from the first voltage to 0 V (second voltage) at time t2 (b). At this time, the applied voltage to the second Q switch 60 remains 0 V and is not changed (c). By changing the voltage applied to the first Q switch 58 to 0 V, the Q value of the first resonator changes from the low Q state to the high Q state. On the other hand, the Q value of the second resonator is kept in a low Q state. When only the first resonator enters the high Q state, laser oscillation with a wavelength of 800 nm occurs, and pulse laser light with a wavelength of 800 nm is emitted from the first mirror 53 (d).
  • the control circuit 62 turns on the flash lamp 52 at time t3 after emitting pulsed laser light having a wavelength of 800 nm (a).
  • the control circuit 62 applies the first voltage to the first Q switch 58 at a time before time t3 (b), and the Q values of the first resonator and the second resonator are low Q. It is in a state.
  • the control circuit 62 changes the applied voltage of the first Q switch 58 from the first voltage to 0V, and changes the applied voltage of the second Q switch 60 from 0V to the fourth voltage.
  • the applied voltage of the first Q switch 58 and the applied voltage of the second Q switch 60 are changed simultaneously, or the applied voltage of the second Q switch 60 is changed first and then the first Q switch 58
  • a wavelength 755 nm having a high laser gain of the wavelength 800 nm and the wavelength 755 nm oscillates, and pulse laser light having a wavelength 755 nm is emitted from the first mirror 53 (d).
  • the first Q value changing unit 56 and the second Q value changing unit 57 are such that the first resonator and the second resonator are both in the high Q state, and the first resonator and the second resonator are in the high Q state. It is only necessary to switch between the low Q state, the first resonator in the high Q state, and the second resonator in the low Q state, and the first Q value change unit 56 and the second Q value change.
  • the specific configuration of the unit 57 is not limited to the above.
  • the first Q value changing unit 56 may be configured by combining a Pockels cell and a quarter-wave plate in the same manner as the second Q value changing unit 57, or the second Q value changing unit 57 may be Similarly to the first Q value changing unit 56, a Pockels cell and a polarizer may be combined.
  • the quarter wavelength plate is interposed between the first mirror 53 and the Pockels cell. Be placed.
  • the Pockels cell sets the first resonator and the second resonator to a low Q state when the applied voltage is a first voltage corresponding to Q switch off, and the applied voltage is a second voltage corresponding to the Q switch on.
  • the first resonator and the second resonator are brought into a high Q state.
  • the first voltage is 0 V, for example
  • the second voltage is a voltage at which the Pockels cell works as a quarter-wave plate, for example.
  • the second voltage may be a positive voltage or a negative voltage.
  • the absolute value of the second voltage is greater than the absolute value of the first voltage.
  • the second voltage corresponding to the Q switch-on is different between the oscillation at the wavelength of 800 nm and the oscillation at the wavelength of 755 nm. . That is, the voltage applied to the Pockels cell differs depending on whether the wavelength is 800 nm or 755 nm.
  • the drive circuit of the Q switch and its control are somewhat complicated as compared with the configuration in which the applied voltage 0 V to the Pockels cell corresponds to the Q switch on. Therefore, as shown in FIG. 2, the first Q value changing unit 56 is preferably configured such that the applied voltage 0 V corresponds to the Q switch on.
  • the second Q value changing unit 57 preferably has a configuration in which the second resonator is placed in a high Q state by applying a voltage acting as a quarter wavelength plate to the Pockels cell. In this configuration, it is only necessary to apply a voltage that acts as a quarter-wave plate to the Pockels cell only when oscillating at a wavelength of 755 nm. Therefore, the time for applying a high voltage is short.
  • the voltage corresponding to the Q switch-off is a voltage that acts as a quarter wavelength plate. The time for applying the voltage becomes long, and the deterioration of the Pockels cell electrode portion due to migration proceeds. Since the second Q value changing unit 57 only needs to control light having a wavelength of 755 nm, it is not necessary to apply a different voltage depending on the wavelength when operating as a quarter wavelength plate.
  • At least one of the first mirror 53, the second mirror 54, and the third mirror 55 may be movable along the optical axis direction.
  • the relative distance between the mirrors can be adjusted, and the resonator length of the first resonator or the second resonator can be adjusted.
  • the resonator length of the resonator can be changed.
  • at least one of the resonator length of the first resonator and the resonator length of the second resonator at least one of the pulse width of the pulse laser beam having a wavelength of 800 nm and the pulse width of the pulse laser beam having a wavelength of 755 nm.
  • this mechanism for example, a change in pulse width due to the reflectance of the mirror can be corrected.
  • the laser light emitted from the laser light source unit 13 is guided to the probe 11 using light guide means such as an optical fiber, and is irradiated from the probe 11 toward the subject.
  • the irradiation position of the laser beam is not particularly limited, and the laser beam may be irradiated from a place other than the probe 11.
  • an ultrasonic wave photoacoustic wave
  • the probe 11 includes an ultrasonic detector.
  • the probe 11 has, for example, a plurality of ultrasonic detector elements (ultrasonic transducers) arranged in a one-dimensional manner, and an acoustic wave (light) from within the subject by the ultrasonic transducers arranged in a one-dimensional manner. Sound signal).
  • ultrasonic detector elements ultrasonic transducers
  • acoustic wave light
  • the ultrasonic unit 12 includes a reception circuit 21, an AD (Analog / Digital) conversion unit 22, a reception memory 23, a complex number conversion unit 24, a photoacoustic image reconstruction unit 25, a phase information extraction unit 26, an intensity information extraction unit 27, a detection / It has logarithmic conversion means 28, photoacoustic image construction means 29, trigger control circuit 30, and control means 31.
  • the receiving circuit 21 receives the photoacoustic signal detected by the probe 11.
  • the AD conversion unit 22 is a detection unit that samples the photoacoustic signal received by the receiving circuit 21 and generates photoacoustic data that is digital data.
  • the AD conversion means 22 samples the photoacoustic signal at a predetermined sampling period in synchronization with the AD clock signal.
  • the AD conversion means 22 stores the photoacoustic data in the reception memory 23.
  • the AD conversion means 22 stores photoacoustic data corresponding to each wavelength of the pulsed laser light emitted from the laser light source unit 13 in the reception memory 23. That is, the AD conversion means 22 has the first photoacoustic data obtained by sampling the photoacoustic signal detected by the probe 11 when the subject is irradiated with the pulse laser beam having the first wavelength, and the second wavelength.
  • the second photoacoustic data obtained by sampling the photoacoustic signal detected by the probe 11 when the pulse laser beam is irradiated is stored in the reception memory 23.
  • the complex number conversion means 24 reads the first photoacoustic data and the second photoacoustic data from the reception memory 23, and generates complex number data in which one is a real part and the other is an imaginary part. In the following description, it is assumed that the complex number converting means 24 generates complex number data having the first photoacoustic data as an imaginary part and the second photoacoustic data as a real part.
  • the photoacoustic image reconstruction unit 25 receives complex number data from the complex number conversion unit 24.
  • the photoacoustic image reconstruction means 25 performs image reconstruction from the input complex number data by the Fourier transform method (FTA method).
  • FFA method Fourier transform method
  • For image reconstruction using the Fourier transform method for example, the document “Photoacoustic Image Reconstruction-A Quantitative Analysis” Jonathan I. Sperl et al. SPIE-OSA Conventionally known methods described in Vol.6631, 663103, etc. can be applied.
  • the photoacoustic image reconstruction unit 25 inputs Fourier transform data indicating the reconstructed image to the phase information extraction unit 26 and the intensity information extraction unit 27.
  • the phase information extraction means 26 extracts the relative magnitude of the relative signal intensity between the photoacoustic data corresponding to each wavelength.
  • the phase information extraction unit 26 uses the reconstructed image reconstructed by the photoacoustic image reconstruction unit 25 as input data, and compares the real part and the imaginary part from the input data that is complex data. In comparison, phase information indicating which is relatively large is generated.
  • the intensity information extraction unit 27 generates intensity information indicating the signal intensity based on the photoacoustic data corresponding to each wavelength.
  • the intensity information extraction unit 27 uses the reconstructed image reconstructed by the photoacoustic image reconstruction unit 25 as input data, and generates intensity information from the input data that is complex number data. For example, when the complex number data is represented by X + iY, the intensity information extraction unit 27 extracts (X 2 + Y 2 ) 1/2 as the intensity information.
  • the detection / logarithm conversion means 28 generates an envelope of data indicating the intensity information extracted by the intensity information extraction means 27, and then logarithmically converts the envelope to widen the dynamic range.
  • the photoacoustic image construction unit 29 receives the phase information from the phase information extraction unit 26 and the intensity information after the detection / logarithmic conversion processing from the detection / logarithmic conversion unit 28.
  • the photoacoustic image construction unit 29 generates a photoacoustic image that is a distribution image of the light absorber based on the input phase information and intensity information.
  • the photoacoustic image construction unit 29 determines the luminance (gradation value) of each pixel in the distribution image of the light absorber based on the input intensity information.
  • the photoacoustic image construction means 29 determines the color (display color) of each pixel in the light absorber distribution image based on, for example, phase information.
  • the photoacoustic image construction unit 29 determines the color of each pixel based on the input phase information using, for example, a color map in which a phase range of 0 ° to 90 ° is associated with a predetermined color. To do.
  • the range of the phase from 0 ° to 45 ° is a range in which the second photoacoustic data is larger than the first photoacoustic data. Therefore, the source of the photoacoustic signal is 755 nm in wavelength rather than absorption for the wavelength of 798 nm. It is considered that this is a vein through which blood mainly containing deoxygenated hemoglobin flows.
  • the range of 45 ° to 90 ° is a range in which the first photoacoustic data is larger than the second photoacoustic data
  • the source of the photoacoustic signal is for the wavelength 755 nm rather than the absorption for the wavelength 798 nm. It is considered to be an artery through which blood mainly containing oxygenated hemoglobin is flowing.
  • the phase gradually changes so that the phase is 0 ° in blue and the phase becomes colorless (white) as the phase approaches 45 °, and the phase 90 ° is red and the phase is 45.
  • the portion corresponding to the artery can be represented in red
  • the portion corresponding to the vein can be represented in blue.
  • the gradation value may be constant and only the color classification of the portion corresponding to the artery and the portion corresponding to the vein may be performed according to the phase information.
  • the image display means 14 displays the photoacoustic image generated by the photoacoustic image construction means 29 on the display screen.
  • the control means 31 controls each part in the ultrasonic unit 12.
  • the trigger control circuit 30 outputs a flash lamp trigger signal for controlling the light emission of the flash lamp 52 (FIG. 2) to the laser light source unit 13.
  • the control circuit 62 of the laser light source unit 13 turns on the flash lamp 52 and irradiates the laser rod 51 with excitation light from the flash lamp 52.
  • the trigger control circuit 30 outputs a Q switch trigger signal to the control circuit 62 after outputting the flash lamp trigger signal.
  • the control circuit 62 changes the Q value of the first resonator from the low Q state to the high Q state when the oscillation wavelength is 800 nm. When the oscillation wavelength is 755 nm, the Q values of the first resonator and the second resonator are changed from the low Q state to the high Q state.
  • the trigger control circuit 30 outputs a sampling trigger signal (AD trigger signal) to the AD conversion means 22 in accordance with the timing of the Q switch trigger signal, that is, the emission timing of the pulse laser beam.
  • the AD conversion unit 22 starts sampling of the photoacoustic signal based on the sampling trigger signal.
  • FIG. 9 shows an operation procedure of the photoacoustic measurement apparatus 10.
  • the trigger control circuit 30 (FIG. 1) is ready to receive the photoacoustic signal
  • the trigger control circuit 30 (FIG. 1) outputs a flash lamp trigger signal to the laser light source unit 13 in order to emit pulsed laser light having the first wavelength (800 nm) ( Step S1).
  • the control circuit 62 (FIG. 2) of the laser light source unit 13 applies the first voltage to the first Q switch 58, and turns on the first resonator and the second resonator. Low Q state.
  • the control circuit 62 turns on the flash lamp 52 in response to the flash lamp trigger signal and excites the laser rod 51 (step S2).
  • the trigger control circuit 30 outputs the Q switch trigger signal to the laser light source unit 13 after the laser lamp 51 is sufficiently excited after the output of the flash lamp trigger signal.
  • the control circuit 62 changes the voltage applied to the first Q switch 58 from the first voltage to 0 V (step S3). At this time, the control circuit 62 applies 0 V to the second Q switch 60, and the first resonator is controlled to the high Q state and the second resonator is controlled to the low Q state. Of the first resonator and the second resonator, only the first resonator enters the high Q state, so that the laser light source unit 13 emits pulsed laser light having a wavelength of 800 nm.
  • the pulsed laser light having a wavelength of 800 nm emitted from the laser light source unit 13 is guided to, for example, the probe 11 and irradiated from the probe 11 to the subject.
  • a photoacoustic signal is generated by absorbing the energy of the pulsed laser light irradiated by the light absorber.
  • the probe 11 detects a photoacoustic signal generated in the subject.
  • the photoacoustic signal detected by the probe 11 is received by the receiving circuit 21.
  • the trigger control circuit 30 outputs a sampling trigger signal to the AD conversion means 22 in accordance with the timing of outputting the Q switch trigger signal.
  • the AD conversion means 22 samples the photoacoustic signal received by the receiving circuit 21 at a predetermined sampling period (step S4).
  • the photoacoustic signal sampled by the AD conversion means 22 is stored in the reception memory 23 as first photoacoustic data.
  • the trigger control circuit 30 When the trigger control circuit 30 is ready to receive the next photoacoustic signal, the trigger control circuit 30 outputs a flash lamp trigger signal to the laser light source unit 13 in order to emit pulsed laser light having the second wavelength (755 nm) (step S5). ). Before receiving the flash lamp trigger signal, the control circuit 62 applies a first voltage to the first Q switch 58 to bring the first resonator and the second resonator into a low Q state. The control circuit 62 turns on the flash lamp 52 in response to the flash lamp trigger signal, and excites the laser rod 51 (step S6).
  • the trigger control circuit 30 outputs a Q switch trigger signal to the laser light source unit 13 after the flash lamp 52 is lit and the laser rod 51 is sufficiently excited.
  • the control circuit 62 changes the voltage applied to the first Q switch 58 from the first voltage to 0V, and changes the voltage applied to the second Q switch 60 from 0V to the fourth voltage (step S7).
  • the control circuit 62 changes the applied voltage in the first Q switch 58 and the second Q switch 60 at the same time, or first changes the applied voltage of the second Q switch 60 and then changes the first applied voltage.
  • the applied voltage of the Q switch 58 is changed.
  • both the first resonator and the second resonator are in a high Q state.
  • the laser gain is oscillated at a wavelength of 755 nm, and the laser light source unit 13 emits a pulsed laser beam having a wavelength of 755 nm.
  • the pulsed laser beam having a wavelength of 755 nm emitted from the laser light source unit 13 is guided to, for example, the probe 11 and irradiated from the probe 11 to the subject.
  • a photoacoustic signal is generated by absorbing the energy of the pulsed laser light irradiated by the light absorber.
  • the probe 11 detects a photoacoustic signal generated in the subject.
  • the photoacoustic signal detected by the probe 11 is received by the receiving circuit 21.
  • the trigger control circuit 30 outputs a sampling trigger signal to the AD conversion means 22 in accordance with the timing of outputting the Q switch trigger signal.
  • the AD conversion means 22 samples the photoacoustic signal received by the receiving circuit 21 at a predetermined sampling period (step S88).
  • the photoacoustic signal sampled by the AD conversion means 22 is stored in the reception memory 23 as second photoacoustic data.
  • the complex numbering means 24 reads the first photoacoustic data and the second photoacoustic data from the reception memory 23, sets the first photoacoustic image data as an imaginary part, and sets the second photoacoustic image data as a real part.
  • the complex data is generated (step S9).
  • the photoacoustic image reconstruction means 25 performs image reconstruction from the complex number data converted into the complex number in step S9 by a Fourier transform method (FTA method) (step S10).
  • FFA method Fourier transform method
  • the intensity information extraction means 27 extracts intensity information from the reconstructed complex number data (step S12). For example, when the reconstructed complex number data is represented by X + iY, the intensity information extraction unit 27 extracts (X 2 + Y 2 ) 1/2 as the intensity information.
  • the detection / logarithmic conversion means 28 performs detection / logarithmic conversion processing on the intensity information extracted in step S12.
  • the photoacoustic image construction means 29 generates a photoacoustic image based on the phase information extracted in step S11 and the intensity information extracted in step S12 subjected to detection / logarithmic conversion processing ( Step S13). For example, the photoacoustic image construction unit 29 determines the luminance (gradation value) of each pixel in the distribution image of the light absorber based on the intensity information, and determines the color of each pixel based on the phase information. An acoustic image is generated. The generated photoacoustic image is displayed on the image display means 14.
  • the subject is irradiated with light having a wavelength of 800 nm and light having a wavelength of 755 nm alternately.
  • the repetition frequency of oscillation with a wavelength of 800 nm may be higher than the repetition frequency of oscillation with a wavelength of 755 nm.
  • light having a wavelength of 800 nm may be continuously emitted a plurality of times.
  • a photoacoustic signal for light having a wavelength of 800 nm may be acquired a plurality of times, and a process such as addition averaging may be performed on the plurality of photoacoustic signals.
  • the signal-to-noise ratio of a photoacoustic image having a wavelength of 800 nm can be increased.
  • the first mirror 53 and the second mirror 54 constitute a first resonator that oscillates light having a wavelength of 800 nm, and the first mirror 53 and the third mirror 55 have a wavelength of 755 nm.
  • a second resonator that oscillates light is formed.
  • the laser rod 51 has emission wavelengths at a wavelength of 800 nm and a wavelength of 755 nm, and the emission efficiency at a wavelength of 755 nm is higher than the emission efficiency at a wavelength of 800 nm.
  • a first Q value changing unit 56 is disposed on an optical path common to the first resonator and the second resonator, and a second Q value is provided between the second mirror 54 and the third mirror 55.
  • a change unit 57 is arranged.
  • the Q values of the first resonator and the second resonator can be controlled. Further, by driving the second Q value changing unit 57, it is possible to control only the Q value of the second resonator among the first resonator and the second resonator.
  • the first resonator and the second resonator are set to a low Q state to excite the laser rod 51, the first resonator is switched to a high Q state after excitation, and the second resonator is set to a low Q state.
  • a wavelength of 800 nm can be pulse-oscillated.
  • the laser resonator 51 is excited with the first resonator and the second resonator in the low Q state, and the first resonator and the second resonator are brought into the high Q state after the excitation, thereby increasing the light emission efficiency.
  • a high wavelength of 755 nm can be pulse-oscillated.
  • the first Q switch 58 is inserted in the resonator having a wavelength of 800 nm with a low laser gain.
  • the first Q switch 58 and the second Q switch 60 are inserted into a resonator having a high laser gain and a wavelength of 755 nm.
  • two Pockels cells are inserted in the resonators of both wavelengths, and a decrease in output becomes a problem particularly at a wavelength of 800 nm where the laser gain is low.
  • only one Pockels cell is inserted into the first resonator, and it is not necessary to arrange a plurality of elements that change the polarization state of light in the first resonator. For a low wavelength of 800 nm, it is possible to suppress a decrease in laser output due to the insertion of a plurality of Pockels cells.
  • the first resonator and the second resonator are configured on one axis so that the optical axes of the light having a wavelength of 800 nm and the light having a wavelength of 755 nm are parallel to each other.
  • the optical member of a mirror and a Q value change part can be used in common with respect to light with a wavelength of 800 nm and light with a wavelength of 755 nm.
  • the third mirror 55 is disposed on the side farther from the laser rod 51 than the second mirror 54, and the resonator length of the first resonator is the resonance of the second resonator. Shorter than the length of the instrument. By shortening the resonator length of the first resonator, the pulse laser beam can be shortened at a wavelength of 800 nm where the laser gain is low.
  • complex number data in which one of the first photoacoustic data and the second photoacoustic data obtained by irradiating laser beams of two wavelengths is a real part and the other is an imaginary part is obtained. Then, a reconstructed image is generated from the complex number data by the Fourier transform method. In this case, reconstruction can be performed more efficiently than when the first photoacoustic data and the second photoacoustic data are reconstructed separately.
  • photoacoustic signals photoacoustic data
  • Patent Document 4 describes a laser device including a He—Ne laser discharge tube, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, and a light modulation device.
  • the first reflecting mirror and the second reflecting mirror constitute a resonator having a wavelength of 632.8 nm
  • the first reflecting mirror and the third reflecting mirror constitute a resonator having a wavelength of 3.39 ⁇ m.
  • the light modulation device is disposed between the second reflecting mirror and the third reflecting mirror.
  • Patent Document 4 the purpose of Patent Document 4 is to perform optical modulation due to the necessity of signal processing in order to apply laser light to measurement equipment.
  • Patent Document 4 describes that the 632.8 nm line of the He—Ne laser has a small gain, and it is difficult to insert and modulate an optical modulation element in the resonator. It is applied in such a case. Therefore, in Patent Document 4, it is not possible to adopt a configuration in which an optical element for controlling the Q value is inserted into both resonators to form a Q-switched laser, in particular, two-wavelength Q-switched oscillation.
  • FIG. 10 shows a laser light source unit according to the second embodiment of the present invention.
  • the first mirror 53 is an output mirror for light having a wavelength of 800 nm
  • the third mirror 55 is an output mirror for light having a wavelength of 755 nm.
  • the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm is, for example, 80%
  • the reflectance with respect to light with a wavelength of 755 nm is, for example, 99.8 or more
  • the reflectance of the third mirror with respect to light having a wavelength of 755 nm is, for example, 60%.
  • Other points may be the same as in the first embodiment.
  • the reflectance of the first mirror 53 with respect to light with a wavelength of 755 nm is set higher than the reflectance of the third mirror 55 with respect to light with a wavelength of 755 nm.
  • the third mirror 55 is an output mirror for light having a wavelength of 755 nm.
  • light having a wavelength of 800 nm can be emitted from one side of the resonator, and light having a wavelength of 755 nm can be emitted from the other side.
  • the light having a wavelength of 800 nm emitted from the first mirror 53 and the light having a wavelength of 755 nm emitted from the third mirror 55 may be combined at the optical axis outside the resonator.
  • the reflectance of the first mirror 53 which is an output mirror of light having a wavelength of 800 nm, with respect to light of wavelength 800nm is the reflection of the third mirror 55, which is an output mirror of light having a wavelength of 755nm, with respect to light having a wavelength of 755nm.
  • the rate By setting the reflectivity of the output mirror for light with a wavelength of 800 nm with a low laser gain to be higher than the reflectivity of the output mirror for light with a wavelength of 755 nm, the oscillation (input) energy threshold is lowered and the laser gain is increased. Therefore, the pulse laser beam can be shortened. Other effects are the same as those of the first embodiment.
  • the first mirror 53 is an output mirror for light having a wavelength of 800 nm and the third mirror 55 is an output mirror for light having a wavelength of 755 nm.
  • the first mirror is light having a wavelength of 800 nm and light having a wavelength of 755 nm.
  • the third mirror 55 may be an output mirror for light having a wavelength of 755 nm.
  • light having a wavelength of 800 nm and wavelength 755 nm can be emitted from one side of the resonator, and light having a wavelength of 755 nm can be emitted from the other side.
  • the light having a wavelength of 800 nm and 755 nm emitted from the first mirror 53 and the light having a wavelength of 755 nm emitted from the third mirror 55 may be combined at the optical axis outside the resonator.
  • the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm may be set to the same setting as the reflectance with respect to light with a wavelength of 755 nm.
  • the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm and the reflectance with respect to light with a wavelength of 755 nm are both 80%.
  • the reflectance of the third mirror 55 with respect to light having a wavelength of 755 nm is, for example, 80%.
  • the light confinement in the first resonator is stronger than the light confinement in the second resonator, and the pulsed laser light having a wavelength of 800 nm can be shortened.
  • the first mirror 53 is an output mirror for light having a wavelength of 800 nm and light having a wavelength of 755 nm
  • the third mirror 55 is an output mirror for light having a wavelength of 755 nm
  • the first mirror 53 has a wavelength of 800 nm.
  • the reflectance for light and the reflectance for light having a wavelength of 755 nm can be made the same.
  • the third mirror 55 can be a mirror having the same reflectivity as the first mirror 53 with respect to light having a wavelength of 755 nm.
  • FIG. 11 shows a laser light source unit according to the third embodiment of the present invention.
  • the laser light source unit 13b according to the present embodiment, concave mirrors are used for the second mirror 54a and the third mirror 55a.
  • the first mirror 53 is a plane mirror. Other points may be the same as in the first embodiment or the second embodiment.
  • the control circuit 62 is not shown.
  • the focal length of the second mirror 54a which is a concave mirror, is longer than the resonator length of the first resonator.
  • the focal length of the third mirror 55a which is a concave mirror, is longer than the resonator length of the second resonator.
  • the radius of curvature of the concave mirror constituting the third mirror 55a is set shorter than the radius of curvature of the concave mirror constituting the second mirror 54a.
  • a concave mirror having a radius of curvature of 8 m is used as the second mirror 54a
  • the third mirror A concave mirror having a curvature radius of 4 m is used for 55a.
  • FIG. 12 shows a modified laser light source unit using a concave mirror as a resonator mirror.
  • a concave mirror is used for the first mirror 53a.
  • the second mirror 54 and the third mirror 55 are plane mirrors.
  • a concave mirror having a radius of curvature of 4 m can be used as the first mirror 53a.
  • the first resonator and the second resonator are stabilized as in the laser light source unit having the configuration shown in FIG. be able to.
  • FIG. 13 shows a laser light source unit according to the fourth embodiment of the present invention.
  • the laser light source unit 13d according to the present embodiment includes a beam expander 63 that expands a light beam in a direction away from the laser rod 51 on the optical path of the second resonator. More specifically, a beam expander 63 is provided between the second mirror 54 and the second Q switch 60. Other configurations may be the same as those in the first embodiment, the second embodiment, or the third embodiment.
  • the beam expander 63 includes, for example, a concave lens 63a and a convex lens 63b in this order from the second mirror 54 side. The beam expander 63 enlarges the diameter of the light beam incident from the second mirror 54 side and emits it to the second Q switch 60 side.
  • the beam expander 63 When the beam expander 63 enlarges the diameter of the light beam, the area energy density (J / cm 2 ) of the light beam incident on the various optical components arranged around the laser rod 51 can be lowered. Damage to the light incident surface can be reduced.
  • the beam expander 63 when the beam expander 63 is disposed between the second mirror 54 and the second Q switch 60 as in the example of FIG. 13, the second Q switch is transmitted through the second mirror 54.
  • the diameter of the light beam having a wavelength of 755 nm toward 60 can be enlarged, and the area energy density of the light beam incident on the second Q switch 60 can be reduced.
  • the laser gain at the wavelength 755 nm is higher than that at the wavelength 800 nm, the laser output tends to be stronger than that at the time of oscillation at the wavelength 800 nm.
  • the beam expander 63 By expanding the diameter of the laser beam having such strong energy using the beam expander 63, it is possible to reduce damage to the light incident surfaces of the respective parts constituting the second Q value changing unit 57. As a result, it is possible to extend the life of each part constituting the second Q value changing part 57.
  • the second mirror 54a when the second mirror 54a is constituted by a concave mirror, the second mirror 54a functions as a concave lens for light having a wavelength of 755 nm.
  • the second mirror 54 a when the second mirror 54 a is configured by a concave mirror, the second mirror 54 a may also serve as a part of the beam expander 63. That is, the concave lens 63a may be omitted, and the beam expander 63 may be configured by the second mirror 54a and the convex lens 63b. In this case, the number of necessary parts can be reduced.
  • the beam expander 63 may be inserted on the optical path of the first resonator.
  • the beam expander 63 may be disposed between the laser rod 51 and the second mirror 54, for example.
  • the beam expander 63 expands the beam diameter from the laser rod 51 toward the second mirror 54, whereby the area energy density of the light incident on the second mirror 54 can be reduced, and the second mirror The damage on the light incident surface 54 can be reduced. Further, damage to the light incident surface of the second Q value changing unit 57 at the tip of the second mirror 54 can also be reduced.
  • the excitation energy for the laser rod 51 when the excitation energy for the laser rod 51 is the same at the time of oscillation at the first wavelength and at the time of oscillation at the second wavelength, the optical element in the resonator is generated at the time of oscillation at the low gain side wavelength. If an attempt is made to obtain a high output within an allowable range with respect to the damage threshold value, the energy in the resonator may exceed the damage threshold value of the optical element during oscillation at a wavelength on the high gain side. .
  • the excitation energy of the laser rod 51 (see FIG. 2) is set individually for the oscillation of the first wavelength and the oscillation of the second wavelength.
  • the excitation energy at the second wavelength oscillation is set lower than the excitation energy at the first wavelength oscillation.
  • the excitation energy at the time of oscillation at the first wavelength and the excitation energy at the time of oscillation at the second wavelength are set so that the laser output intensity is equal between the oscillation at the first wavelength and the oscillation at the second wavelength. And set.
  • the excitation energy is set by changing the voltage applied to the flash lamp 52, for example.
  • the voltage setting for the flash lamp 52 when oscillating at a wavelength of 800 nm, is set to the voltage V1 before the time t1, and the voltage V1 is applied to the flash lamp 52 at the time t1.
  • the voltage setting for the flash lamp 52 is set to a voltage V2 lower than the voltage V1 before time t3, and the voltage V2 is applied to the flash lamp 52 at time t3. In this way, the excitation energy can be set individually during oscillation of each wavelength.
  • FIG. 14 shows the relationship between excitation energy and laser output.
  • graph (a) Shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 800 nm
  • the graph (b) shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 755 nm.
  • E1 is the excitation energy when the oscillation wavelength is 800 nm.
  • the excitation energy is E1
  • the laser output with an oscillation wavelength of 800 nm does not exceed the damage threshold.
  • the laser gain coefficient at the wavelength 755 nm is higher than the laser gain coefficient at the wavelength 800 nm.
  • the energy in the resonator exceeds the damage threshold of the optical element.
  • the excitation energy is lowered to E2 when the oscillation wavelength is 755 nm.
  • the laser output with an oscillation wavelength of 755 nm can be made lower than the damage threshold. Further, the laser output can be made uniform at both oscillation wavelengths.
  • the excitation energy is individually set for both wavelengths so that the energy in the resonator during laser oscillation does not exceed the damage threshold of the optical element in the resonator. .
  • the light of the second wavelength on the high gain side is used.
  • a loss filter optical filter that gives a loss is used.
  • FIG. 15 shows a laser apparatus according to this embodiment.
  • the laser light source unit 13e according to this embodiment further includes a loss filter 64 between the second mirror 54 and the third mirror 55. More specifically, a loss filter (optical filter) 64 is provided between the second mirror 54 and the second Q switch 60.
  • the loss filter 64 is, for example, a neutral density filter (ND (Neutral Density) filter).
  • ND Neutral Density
  • FIG. 16 shows the relationship between excitation energy and laser output.
  • graph (a) shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 800 nm.
  • Graph (b) shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 755 nm without the loss filter 64, and
  • graph (c) shows the relationship when the oscillation wavelength is 755 nm with the loss filter 64. The relationship between the excitation energy E and the laser output is shown.
  • the loss filter 64 When the loss filter 64 is inserted in the second resonator, a loss is given to light having a wavelength of 755 nm in the second resonator. Therefore, if the excitation energy is constant, the laser output is It becomes lower than the case without the loss filter.
  • the relationship between the excitation energy and the laser output when the loss filter 64 is inserted is the relationship between the excitation energy and the laser output without the loss filter 64 shown in the graph (b) as shown in the graph (c). The relationship is a parallel movement to the higher energy side.
  • the laser output resonates at the oscillation of the wavelength of 755 nm even when the excitation energy is E1 which is the same as that at the oscillation of the wavelength of 800 nm.
  • the damage threshold of the optical elements in the vessel can be prevented from being exceeded. It is more preferable to adjust the loss that the loss filter 64 gives to the light having a wavelength of 755 nm so that the laser outputs of both wavelengths are equal at the same excitation energy.
  • the loss filter 64 gives a loss to the light with a wavelength of 755 nm so that the laser output is equal between the oscillation with the wavelength of 800 nm and the oscillation with the wavelength of 755 nm.
  • the loss that the loss filter 64 gives to the light with a wavelength of 755 nm is selected in a range where the oscillation threshold value of the wavelength of 800 nm in the first resonator is higher than the oscillation threshold value of the wavelength of 755 nm in the second resonator. It is preferable to do.
  • the loss filter 64 is inserted into the second resonator, but in addition to this, a loss filter may be inserted into the first resonator.
  • the excitation energy does not have to be the same when oscillating at a wavelength of 800 nm and 755 nm.
  • the excitation energy is individually set for the oscillation at the wavelength of 800 nm and the oscillation at the wavelength of 755 nm, as described in the fifth embodiment. Also good.
  • the example in which the first photoacoustic data and the second photoacoustic data are converted to complex numbers has been described.
  • the first photoacoustic data and the second photoacoustic data are not converted to complex numbers.
  • Data may be reconstructed separately.
  • the ratio between the first photoacoustic data and the second photoacoustic data is calculated using the complex number and the phase information, but the same effect can be obtained by calculating the ratio from the intensity information of both.
  • the obtained intensity information can also be generated based on the signal intensity in the first reconstructed image and the signal intensity in the second reconstructed image.
  • the number of wavelengths of the pulsed laser light applied to the subject is not limited to two, and the subject is irradiated with three or more pulsed laser lights, and photoacoustic data corresponding to each wavelength is generated.
  • a photoacoustic image may be generated based on this.
  • the phase information extracting unit 26 may generate a relative magnitude relationship between the photoacoustic data corresponding to each wavelength as the phase information.
  • the intensity information extraction unit 27 may generate, as intensity information, a collection of signal intensities in photoacoustic data corresponding to each wavelength, for example.
  • the alexandrite laser has been mainly described.
  • the laser medium used for the laser rod 51 (FIG. 2) is not limited to alexandrite.
  • Cr: LiSAF, Cr: LiCAF, and the like can oscillate in the wavelength range of 750 nm to 900 nm
  • the laser rod 51 may be Cr: LiSAF, Cr: LiCAF, or the like.
  • Ti: Sapphire can oscillate in the wavelength range of 700 nm to 1000 nm, and Ti: Sapphire may be used for the laser rod 51.
  • the present invention is not limited to this.
  • the laser device of the present invention can also be used for a device different from the photoacoustic measuring device.
  • the laser device and the photoacoustic measurement device of the present invention are not limited to the above embodiment, and various modifications can be made from the configuration of the above embodiment. Further, modifications and changes are also included in the scope of the present invention.
  • Photoacoustic measuring device 11 Probe 12: Ultrasonic unit 13: Laser light source unit 14: Image display means 21: Reception circuit 22: AD conversion means 23: Reception memory 24: Complex number conversion means 25: Photoacoustic image reconstruction means 26: Phase information extraction means 27: Intensity information extraction means 28: Detection / logarithmic conversion means 29: Photoacoustic image construction means 30: Trigger control circuit 31: Control means 51: Laser rod 52: Flash lamps 53, 54, 55: Mirror 56, 57: Q value changing unit 58, 60: Q switch 59: Polarizer 61: 1/4 wavelength plate 62: Control circuit 63: Beam expander 63a: Concave lens 63b: Convex lens 64: Loss filter

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Abstract

Provided are a laser device and a photoacoustic measurement device that are capable of suppressing reductions in output within a plurality of wavelengths, particularly low laser gain wavelengths, and enable pulse shortening. A laser rod (51) has emission wavelengths of a first wavelength and a second wavelength. The luminous efficacy of the first wavelength is lower than the luminous efficacy of the second wavelength. A first mirror (53) and a second mirror (54) constitute a first resonator which oscillates light of the first wavelength. The first mirror (53) and the second mirror (54) constitute a resonator which oscillates light of the second wavelength. A first Q value changing unit (56) is disposed on an optical path shared by the first resonator and the second resonator, and controls the Q values of the first resonator and the second resonator. A second Q value changing unit (57) is disposed between the second mirror (54) and a third mirror (55), and controls the Q value of the second resonator.

Description

レーザ装置及び光音響計測装置Laser apparatus and photoacoustic measuring apparatus
　本発明は、レーザ装置に関し、更に詳しくは、第１の波長の光及び第２の波長の光を出射可能なレーザ装置に関する。また、本発明は、そのようなレーザ装置を含む光音響計測装置に関する。 The present invention relates to a laser device, and more particularly to a laser device capable of emitting light of a first wavelength and light of a second wavelength. The present invention also relates to a photoacoustic measurement device including such a laser device.
　従来、例えば特許文献１や非特許文献１に示されているように、光音響効果を利用して生体の内部を画像化する光音響画像化装置が知られている。この光音響画像化装置においては、例えばパルスレーザ光等のパルス光が生体に照射される。このパルス光の照射を受けた生体内部では、パルス光のエネルギーを吸収した生体組織が熱によって体積膨張し、音響波が発生する。この音響波を超音波プローブなどにより検出し、検出された信号（光音響信号）に基づいて生体内部を可視像化することが可能となっている。光音響画像化方法では、特定の光吸収体において音響波が発生するため、生体における特定の組織、例えば血管等を画像化することができる。 Conventionally, as shown in Patent Document 1 and Non-Patent Document 1, for example, a photoacoustic imaging apparatus that images the inside of a living body using a photoacoustic effect is known. In this photoacoustic imaging apparatus, a living body is irradiated with pulsed light such as pulsed laser light. Inside the living body that has been irradiated with the pulsed light, the living tissue that has absorbed the energy of the pulsed light undergoes volume expansion due to heat, and an acoustic wave is generated. This acoustic wave is detected by an ultrasonic probe or the like, and the inside of the living body can be visualized based on the detected signal (photoacoustic signal). In the photoacoustic imaging method, since an acoustic wave is generated in a specific light absorber, a specific tissue in a living body, such as a blood vessel, can be imaged.
　ところで、生体組織の多くは光吸収特性が光の波長に応じて変わり、また一般に、その光吸収特性も組織ごとに特有のものとなっている。例えば図１７に、ヒトの動脈に多く含まれる酸素化ヘモグロビン(酸素と結合したヘモグロビン:oxy-Hb)と、静脈に多く含まれる脱酸素化ヘモグロビン（酸素と結合していないヘモグロビンdeoxy-Hb)の光波長ごとの分子吸収係数を示す。動脈の光吸収特性は、酸素化ヘモグロビンのそれに対応し、静脈の光吸収特性は、脱酸素化ヘモグロビンのそれに対応する。この波長に応じた光吸収率の違いを利用して、互いに異なる２種の波長の光を血管部分に照射し、動脈と静脈とを区別して画像化する光音響画像化方法が知られている（例えば特許文献２参照）。 By the way, in many living tissues, the light absorption characteristics vary depending on the wavelength of light, and generally, the light absorption characteristics are also unique to each tissue. For example, FIG. 17 shows oxygenated hemoglobin (oxyhemoglobin combined with oxygen: oxy-Hb) abundant in human arteries and deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) abundantly contained in veins. The molecular absorption coefficient for each light wavelength is shown. The light absorption characteristic of the artery corresponds to that of oxygenated hemoglobin, and the light absorption characteristic of the vein corresponds to that of deoxygenated hemoglobin. A photoacoustic imaging method is known in which a blood vessel portion is irradiated with light of two different wavelengths using the difference in light absorption rate according to the wavelength, and an artery and a vein are distinguished and imaged. (For example, refer to Patent Document 2).
　ここで、可変波長レーザに関して、特許文献３には、分岐用偏光子と共振光路選択部とを用いて複数波長の発振を行うレーザ装置が記載されている。図１８は、特許文献３に記載のレーザ装置を示す。このレーザ装置は、フラッシュランプ１２１４を励起源とするアレキサンドライトレーザであり、波長７５５ｎｍと波長８００ｎｍのレーザ発振が可能である。発振される光束の偏光方向は紙面面内でありｐ偏光である。 Here, regarding a variable wavelength laser, Patent Document 3 describes a laser device that oscillates a plurality of wavelengths by using a branching polarizer and a resonant optical path selector. FIG. 18 shows a laser device described in Patent Document 3. This laser device is an alexandrite laser using a flash lamp 1214 as an excitation source, and can oscillate at wavelengths of 755 nm and 800 nm. The polarization direction of the oscillated light beam is in the plane of the paper and is p-polarized light.
　共通光路１２０９上には、共振光路選択部を構成するポッケルスセル１２０５が配置される。波長８００ｎｍを発振する際には、所定の電圧がポッケルスセル１２０５に印加される。これにより、ポッケルスセル１２０５は、入射した直線偏光の偏光方向を９０°回転させる。波長７５５ｎｍを発振する際には、ポッケルスセル１２０５に電圧は印加されない。光路分岐部である偏光子１２０４は、ｐ偏光を透過しｓ偏光を反射する。偏光子１２０４を透過した光は、第１の分岐光路１２１０を進み、第１の反射プリズム１２０７で反射する。一方、偏光子１２０４で反射した光は、第２の分岐光路１２１１を進み、第２の反射プリズム１２０８で反射する。 On the common optical path 1209, a Pockels cell 1205 that constitutes a resonant optical path selection unit is arranged. When oscillating at a wavelength of 800 nm, a predetermined voltage is applied to the Pockels cell 1205. As a result, the Pockels cell 1205 rotates the polarization direction of the incident linearly polarized light by 90 °. When oscillating at a wavelength of 755 nm, no voltage is applied to the Pockels cell 1205. A polarizer 1204 serving as an optical path branching unit transmits p-polarized light and reflects s-polarized light. The light transmitted through the polarizer 1204 travels along the first branch optical path 1210 and is reflected by the first reflecting prism 1207. On the other hand, the light reflected by the polarizer 1204 travels through the second branch optical path 1211 and is reflected by the second reflecting prism 1208.
　第１の反射プリズム１２０７は、入射光に対してブリュースター角となるように配置される。第１の反射プリズム１２０７は、波長７５５ｎｍの光を選択的に反射する誘電体反射膜を有する。第２の反射プリズム１２０８は、波長８００ｎｍの光を選択的に反射する誘電体反射膜を有する。出力鏡１２０２と第１の反射プリズム１２０７とにより、波長７５５ｎｍの共振器が構成される。また、出力鏡１２０２と第２の反射プリズム１２０８とにより、波長８００ｎｍの共振器が構成される。 The first reflecting prism 1207 is arranged to have a Brewster angle with respect to incident light. The first reflecting prism 1207 has a dielectric reflecting film that selectively reflects light having a wavelength of 755 nm. The second reflecting prism 1208 has a dielectric reflecting film that selectively reflects light having a wavelength of 800 nm. The output mirror 1202 and the first reflecting prism 1207 constitute a resonator having a wavelength of 755 nm. The output mirror 1202 and the second reflecting prism 1208 constitute a resonator having a wavelength of 800 nm.
　共通光路１２０９上には、ポッケルスセル１２１２及びλ／４波長板１２１３により構成されるＱスイッチも配置されている。フラッシュランプ１２１４を点灯するとき、Ｑスイッチを構成するポッケルスセル１２１２には電圧が印加されず、Ｑスイッチはオフしている。フラッシュランプ１２１４の点灯後、アレキサンドライト結晶１２０３における反転分布密度が十分に高くなるタイミングでＱスイッチをオンにする。出力鏡１２０２と第１の反射プリズム１２０７とによって構成される共振器、又は出力鏡１２０２と第２の反射プリズム１２０８とによって構成される共振器においてレーザ発振が起こり、出力鏡１２０２からパルスレーザ光が出射する。 On the common optical path 1209, a Q switch including a Pockels cell 1212 and a λ / 4 wavelength plate 1213 is also arranged. When the flash lamp 1214 is turned on, no voltage is applied to the Pockels cell 1212 constituting the Q switch, and the Q switch is off. After the flash lamp 1214 is turned on, the Q switch is turned on when the inversion distribution density in the alexandrite crystal 1203 becomes sufficiently high. Laser oscillation occurs in the resonator constituted by the output mirror 1202 and the first reflecting prism 1207 or in the resonator constituted by the output mirror 1202 and the second reflecting prism 1208, and pulse laser light is emitted from the output mirror 1202. Exit.
　共振光路選択部を構成するポッケルスセル１２０５に電圧が印加されてない場合、アレキサンドライト結晶１２０３から出射したｐ偏光の光は、ポッケルスセル１２０５をｐ偏光のまま透過し、ｐ偏光を透過する偏光子１２０４を透過して第１の分岐光路１２１０を通り、第１の反射プリズム１２０７で反射する。第１の反射プリズム１２０７で反射した光は、偏光子１２０４及びポッケルスセル１２０５をｐ偏光のまま逆向きに通り、アレキサンドライト結晶１２０３に入射する。出力鏡１２０２と第１の反射プリズム１２０７とにより共振器が構成され、レーザ発振が起こる。第１の反射プリズム１２０７が波長７５５ｎｍの光を選択的に反射することにより、波長７５５ｎｍの光が発振する。 When no voltage is applied to the Pockels cell 1205 constituting the resonant optical path selector, the p-polarized light emitted from the alexandrite crystal 1203 is transmitted through the Pockels cell 1205 as p-polarized light and transmits p-polarized light. , Passes through the first branch optical path 1210, and is reflected by the first reflecting prism 1207. The light reflected by the first reflecting prism 1207 passes through the polarizer 1204 and the Pockels cell 1205 in the opposite direction as p-polarized light and enters the alexandrite crystal 1203. The output mirror 1202 and the first reflecting prism 1207 constitute a resonator, and laser oscillation occurs. The first reflecting prism 1207 selectively reflects light having a wavelength of 755 nm, so that light having a wavelength of 755 nm oscillates.
　ポッケルスセル１２０５に所定の電圧が印加され、ポッケルスセル１２０５が入射光の偏光方向を９０°回転させる場合、アレキサンドライト結晶１２０３から出射したｐ偏光の光は、ポッケルスセル１２０５を透過する際に偏光方向が９０°回転してｓ偏光となる。ｓ偏光となった光は、偏光子１２０４で反射して第２の分岐光路１２１１を通り、第２の反射プリズム１２０８で反射する。第２の反射プリズム１２０８で反射した光は、偏光子１２０４を逆向きに通り、ポッケルスセル１２０５に逆向きに入射する。ポッケルスセル１２０５にｓ偏光で入射した光は、ポッケルスセル１２０５を通過する際に偏光方向が９０°回転され、ｐ偏光となってアレキサンドライト結晶１２０３に入射する。出力鏡１２０２と第２の反射プリズム１２０８とにより共振器が構成され、レーザ発振が起こる。第２の反射プリズム１２０８が波長８００ｎｍの光を選択的に反射することにより、波長８００ｎｍの光が発振する。 When a predetermined voltage is applied to the Pockels cell 1205 and the Pockels cell 1205 rotates the polarization direction of the incident light by 90 °, the polarization direction of the p-polarized light emitted from the alexandrite crystal 1203 is changed when passing through the Pockels cell 1205. Rotates 90 ° to become s-polarized light. The light that has become s-polarized light is reflected by the polarizer 1204, passes through the second branch optical path 1211, and is reflected by the second reflecting prism 1208. The light reflected by the second reflecting prism 1208 passes through the polarizer 1204 in the reverse direction and enters the Pockels cell 1205 in the reverse direction. The light incident on the Pockels cell 1205 as s-polarized light is rotated by 90 ° in the polarization direction when passing through the Pockels cell 1205, and becomes p-polarized light and enters the alexandrite crystal 1203. The output mirror 1202 and the second reflecting prism 1208 constitute a resonator, and laser oscillation occurs. The second reflecting prism 1208 selectively reflects light having a wavelength of 800 nm, so that light having a wavelength of 800 nm oscillates.
特開２００５－２１３８０号公報JP 2005-21380 A 特開２０１０－０４６２１５号公報JP 2010-046215 A 特開２０１３－８９６８０号公報JP 2013-89680 A 特公昭５９－１７８７２号公報Japanese Patent Publication No.59-17872
　特許文献３では、波長７５５ｎｍの共振器と波長８００ｎｍの共振器とに共通の共通光路にポッケルスセルが２つ挿入されている。すなわち、Ｑスイッチ用のポッケルスセル１２１２と共振器光路選択用のポッケルスセル１２０５とが共通光路に挿入されている。光がポッケルスセルを通過する際に光のロスが発生するため、特許文献３に記載のレーザは、Ｑスイッチ用のポッケルスセルが共振器内に１つだけ配置される通常のＱスイッチレーザに比べて、光損失が大きい。アレキサンドライトレーザにおいて、波長７５５ｎｍのレーザ利得と８００ｎｍのレーザ利得とを比べると、波長８００ｎｍの方がレーザ利得が低く、特にレーザ出力が低い波長８００ｎｍにおいて、余分な出力ロスを抑制したいという要望がある。 In Patent Document 3, two Pockels cells are inserted in a common optical path common to a resonator having a wavelength of 755 nm and a resonator having a wavelength of 800 nm. That is, the Pockels cell 1212 for the Q switch and the Pockels cell 1205 for selecting the resonator optical path are inserted in the common optical path. Since light loss occurs when light passes through the Pockels cell, the laser described in Patent Document 3 is compared to a normal Q-switched laser in which only one Pockels cell for Q switching is arranged in the resonator. The optical loss is large. In the alexandrite laser, when the laser gain at the wavelength of 755 nm is compared with the laser gain at 800 nm, the laser gain is lower at the wavelength of 800 nm, and there is a demand for suppressing an extra output loss particularly at the wavelength of 800 nm where the laser output is low.
　また、光音響計測において、パルス光照射に起因して発生する光音響波の強度は、照射するパルス光のパルス幅に依存して変化する。強い光音響波を発生させるために、パルス幅が短いパルス光を照射することが好ましい。一般に、パルスレーザ光のパルス幅は共振器長に依存して変化し、共振器長を短くすることにより短波パルス化が可能である。しかし、特許文献３では、両波長に共通の共通光路にポッケルスセルが２つ挿入されているため、共振器長を短くできない。 In photoacoustic measurement, the intensity of the photoacoustic wave generated due to the irradiation of the pulsed light changes depending on the pulse width of the irradiated pulsed light. In order to generate a strong photoacoustic wave, it is preferable to irradiate pulsed light having a short pulse width. In general, the pulse width of the pulsed laser light changes depending on the resonator length, and a short wave pulse can be realized by shortening the resonator length. However, in Patent Document 3, since two Pockels cells are inserted in the common optical path common to both wavelengths, the resonator length cannot be shortened.
　本発明は、上記に鑑み、複数波長のうち、特にレーザ利得が低い波長において出力低下を抑制でき、かつ、短パルス化が可能な波長可変のレーザ装置を提供することを目的とする。 In view of the above, an object of the present invention is to provide a wavelength tunable laser device that can suppress a decrease in output at a wavelength having a low laser gain among a plurality of wavelengths and that can shorten the pulse.
　また、本発明は、上記レーザ装置を含む光音響計測装置を提供する。 The present invention also provides a photoacoustic measuring device including the laser device.
　上記目的を達成するために、本発明は、第１の波長と第２の波長とに発光波長を有する固体のレーザ媒質であって、第１の波長の発光効率が第２の波長の発光効率よりも低いレーザ媒質と、レーザ媒質を間欠的に励起する励起手段と、レーザ媒質を間に挟んで対向する第１のミラー及び第２のミラーによって構成され、第１の波長の光を発振する第１の共振器と、第１のミラーと、レーザ媒質及び第２のミラーを間に挟んで第１のミラーと対向する第３のミラーとによって構成され、第１の共振器と一部が共通の部分である共通の光路を有し、第２の波長の光を発振する第２の共振器と、第１の共振器と第２の共振器とに共通の光路上に配置され、第１の共振器及び第２の共振器のＱ値を制御する第１のＱ値変更部と、第２のミラーと第３のミラーとの間に配置され、第２の共振器のＱ値を制御する第２のＱ値制御部とを備えたレーザ装置を提供する。 In order to achieve the above object, the present invention provides a solid laser medium having emission wavelengths at a first wavelength and a second wavelength, wherein the emission efficiency of the first wavelength is the emission efficiency of the second wavelength. And a first mirror and a second mirror facing each other with the laser medium interposed therebetween, and oscillates light of the first wavelength. A first resonator, a first mirror, and a third mirror facing the first mirror with the laser medium and the second mirror in between, the first resonator and a part thereof The second resonator having a common optical path which is a common portion and oscillating light of the second wavelength, the first resonator, and the second resonator are disposed on a common optical path, and A first Q value changing unit for controlling the Q values of the first resonator and the second resonator, a second mirror, and a third mirror Disposed between the mirrors, to provide a laser apparatus and a second Q value control unit for controlling the Q value of the second resonator.
　本発明のレーザ装置は、第１のＱ値変更部及び第２のＱ値変更部を駆動し、第１の共振器及び第２の共振器のＱ値を、それぞれ共振器のＱ値が発振しきい値よりも低い低Ｑ状態にする第１の駆動状態、第１の共振器及び第２の共振器のＱ値を、それぞれ共振器のＱ値が発振しきい値よりも高い高Ｑ状態にする第２の駆動状態、及び、第１の共振器のＱ値を高Ｑ状態にし、かつ第２の共振器のＱ値を低Ｑ状態にする第３の駆動状態の間で駆動状態を切り替える制御回路を更に備えた構成であってもよい。 The laser apparatus according to the present invention drives the first Q value changing unit and the second Q value changing unit, and oscillates the Q values of the first resonator and the second resonator, respectively. The first drive state in which the low Q state is lower than the threshold value, the Q values of the first resonator and the second resonator are set to the high Q state in which the Q value of the resonator is higher than the oscillation threshold value. Between the second driving state and the third driving state in which the Q value of the first resonator is set to the high Q state and the Q value of the second resonator is set to the low Q state. A configuration may further include a control circuit for switching.
　制御回路は、レーザ媒質の励起時は第１のＱ値変更部及び第２のＱ値変更部の駆動状態を第１の駆動状態としてもよい。 The control circuit may set the driving state of the first Q value changing unit and the second Q value changing unit as the first driving state when the laser medium is excited.
　制御回路は、レーザ媒質の励起後、発振波長が第１の波長のときは第１のＱ値変更部及び第２のＱ値変更部の駆動状態を第１の駆動状態から第３の駆動状態へと変化させ、発振波長が第２の波長のときは第１のＱ値変更部及び第２のＱ値変更部を第１の駆動状態から第２の駆動状態へと変化させることが好ましい。 When the oscillation wavelength is the first wavelength after the excitation of the laser medium, the control circuit changes the driving state of the first Q value changing unit and the second Q value changing unit from the first driving state to the third driving state. Preferably, when the oscillation wavelength is the second wavelength, the first Q value changing unit and the second Q value changing unit are preferably changed from the first driving state to the second driving state.
　制御回路は、発振波長が第２の波長のときは、第２の共振器のＱ値が高Ｑ状態となるように第２のＱ値変更部を駆動するのと同時に第１の共振器のＱ値が高Ｑ状態となるように第１のＱ値変更部を駆動することとすればよい。これに代えて、第２の共振器のＱ値が高Ｑ状態となるように第２のＱ値変更部を駆動した後に第１の共振器のＱ値が高Ｑ状態となるように第１のＱ値変更部を駆動してもよい。 When the oscillation wavelength is the second wavelength, the control circuit drives the second Q value changing unit so that the Q value of the second resonator is in a high Q state, and at the same time, the control circuit of the first resonator The first Q value changing unit may be driven so that the Q value becomes a high Q state. Instead, after driving the second Q value changing unit so that the Q value of the second resonator becomes the high Q state, the first resonator so that the Q value of the first resonator becomes the high Q state. The Q value changing unit may be driven.
　第１のＱ値変更部は、第１の共振器と第２の共振器とに共通の光路上に配置され、印加電圧に応じて第１の共振器及び第２の共振器のＱ値を変化させる第１のＱスイッチを含んでいてもよい。この場合、制御回路は、第１のＱスイッチの印加電圧を制御することにより第１のＱ値変更部を駆動すればよい。 The first Q value changing unit is disposed on an optical path common to the first resonator and the second resonator, and sets the Q values of the first resonator and the second resonator according to the applied voltage. A first Q switch to be changed may be included. In this case, the control circuit may drive the first Q value changing unit by controlling the voltage applied to the first Q switch.
　第１のＱスイッチは、印加電圧がＱスイッチオフに対応した第１の電圧のとき第１の共振器及び第２の共振器を低Ｑ状態にし、印加電圧が、絶対値が第１の電圧の絶対値よりもが小さく、Ｑスイッチオンに対応した第２の電圧のとき第１の共振器及び第２の共振器を高Ｑ状態にするものであってよい。第１の電圧は、例えば第１のＱスイッチが通過する光に対して１／４波長板として働く電圧であってよい。第２の電圧は例えば無電圧（０Ｖ）であってよい。 The first Q switch sets the first resonator and the second resonator to a low Q state when the applied voltage is the first voltage corresponding to the Q switch off, and the applied voltage has the absolute value of the first voltage. The first resonator and the second resonator may be brought into a high-Q state when the second voltage is smaller than the absolute value of Q and the second voltage corresponds to Q switch-on. The first voltage may be, for example, a voltage that acts as a quarter wavelength plate for light passing through the first Q switch. The second voltage may be no voltage (0 V), for example.
　第１のＱ値変更部は、第１のミラー及び第２のミラーのいずれか一方と、第１のＱスイッチとの間に配置された１／４波長板を更に含んでいてもよい。この場合、第１のＱスイッチは、上記とは異なり、印加電圧がＱスイッチオフに対応した第１の電圧のとき第１の共振器及び第２の共振器を低Ｑ状態にし、印加電圧が、絶対値が第１の電圧の絶対値よりも大きいＱスイッチオンに対応した第２の電圧のとき第１の共振器及び第２の共振器を高Ｑ状態にするものであってよい。第１の電圧は例えば無電圧（０Ｖ）であってよい。第２の電圧は、例えば第１のＱスイッチが１／４波長板として働く電圧であってよい。 The first Q value changing unit may further include a quarter-wave plate disposed between one of the first mirror and the second mirror and the first Q switch. In this case, unlike the above, the first Q switch sets the first resonator and the second resonator to the low Q state when the applied voltage is the first voltage corresponding to the Q switch off, and the applied voltage is The first resonator and the second resonator may be brought into a high Q state when the second voltage corresponds to a Q switch-on whose absolute value is larger than the absolute value of the first voltage. The first voltage may be no voltage (0 V), for example. The second voltage may be a voltage at which the first Q switch works as a quarter wavelength plate, for example.
　上記の場合、Ｑスイッチオンに対応した第２の電圧が、第１の波長の発振時と第２の波長の発振時とで異なっていてもよい。 In the above case, the second voltage corresponding to the Q switch on may be different between the oscillation at the first wavelength and the oscillation at the second wavelength.
　第２のＱ値変更部は、第２のミラーと第３のミラーとの間に配置され、印加電圧に応じて第２の共振器のＱ値を変化させる第２のＱスイッチを含んでいてもよい。この場合、制御回路は、第２のＱスイッチの印加電圧を制御することにより第２のＱ値変更部を駆動すればよい。 The second Q value changing unit is disposed between the second mirror and the third mirror, and includes a second Q switch that changes the Q value of the second resonator according to the applied voltage. Also good. In this case, the control circuit may drive the second Q value changing unit by controlling the voltage applied to the second Q switch.
　第２のＱ値変更部が、第２のＱスイッチと第３のミラーとの間に配置された１／４波長板を更に含んでいてもよい。この場合、第２のＱスイッチは、印加電圧がＱスイッチオフに対応した第３の電圧のとき第２の共振器を低Ｑ状態にし、印加電圧が、絶対値が第３の電圧の絶対値よりも大きいＱスイッチオンに対応した第４の電圧のとき第２の共振器を高Ｑ状態にするものであってよい。第３の電圧は例えば無電圧（０Ｖ）であってよい。第４の電圧は、例えば第２のＱスイッチを１／４波長板として働かせる電圧であってよい。 The second Q value changing unit may further include a quarter wavelength plate disposed between the second Q switch and the third mirror. In this case, the second Q switch sets the second resonator to a low Q state when the applied voltage is a third voltage corresponding to the Q switch off, and the applied voltage is an absolute value of the third voltage. The second resonator may be brought into a high Q state at a fourth voltage corresponding to a larger Q switch-on. The third voltage may be no voltage (0 V), for example. The fourth voltage may be, for example, a voltage that causes the second Q switch to function as a quarter wave plate.
　第２のミラーは、第１の波長の光を反射し、第２の波長の光を透過するものであってよい。 The second mirror may reflect light of the first wavelength and transmit light of the second wavelength.
　第１のミラーを、第１の波長の光及び第２の波長の光の出力ミラーとしてもよい。 The first mirror may be an output mirror of light having the first wavelength and light having the second wavelength.
　第１のミラーの第１の波長の光に対する反射率は、第２の波長の光に対する反射率よりも高く設定されていてもよい。 The reflectance of the first mirror with respect to the first wavelength light may be set higher than the reflectance with respect to the second wavelength light.
　上記に代えて、第１のミラーを第１の波長の光の出力ミラーとし、かつ第３のミラーを第２の波長の光の出力ミラーとしてもよい。その場合、第１のミラーの第２の波長の光に対する反射率を第３のミラーの第２の波長の光に対する反射率よりも高く設定してもよい。 Alternatively, the first mirror may be an output mirror for light of the first wavelength, and the third mirror may be an output mirror for light of the second wavelength. In that case, the reflectance of the first mirror with respect to the light of the second wavelength may be set higher than the reflectance of the third mirror with respect to the light of the second wavelength.
　第１のミラーを第１の波長の光の出力ミラーとし、かつ第３のミラーを第２の波長の光の出力ミラーとした場合、第１のミラーの第１の波長の光に対する反射率を、第３のミラーの第２の波長の光に対する反射率よりも高く設定してもよい。 When the first mirror is an output mirror for light of the first wavelength and the third mirror is an output mirror for light of the second wavelength, the reflectivity of the first mirror with respect to the light of the first wavelength is The reflectance of the third mirror with respect to the light of the second wavelength may be set higher.
　第１のミラーを第１の波長の光の出力ミラーとし、かつ第３のミラーを第２の波長の光の出力ミラーとするのに代えて、第１のミラーを第１の波長の光及び第２の波長の光の出力ミラーとし、かつ第３のミラーを第２の波長の光の出力ミラーとしてもよい。その場合、第１のミラーにおける第１の波長の光に対する反射率は第２の波長の光に対する反射率と同じであってもよい。 Instead of the first mirror as an output mirror of light of the first wavelength and the third mirror as an output mirror of light of the second wavelength, the first mirror is light of the first wavelength and The output mirror of the light of the second wavelength may be used, and the third mirror may be the output mirror of the light of the second wavelength. In that case, the reflectance with respect to the light of the first wavelength in the first mirror may be the same as the reflectance with respect to the light of the second wavelength.
　第１のミラー、第２のミラー、及び第３のミラーのうちの少なくとも１つが光軸方向に沿って移動可能に構成されていてもよい。 At least one of the first mirror, the second mirror, and the third mirror may be configured to be movable along the optical axis direction.
　第１の波長の発振の繰り返し周波数は、第２の波長の発振の繰り返し周波数よりも高くてもよい。 The repetition frequency of the first wavelength oscillation may be higher than the repetition frequency of the second wavelength oscillation.
　本発明のレーザ装置は、第１の共振器の光路と第２の共振器の光路との少なくとも一方に、レーザ媒質から離れる方向に向かって光束を拡大するビームエキスパンダを更に備える構成としてもよい。 The laser apparatus of the present invention may further include a beam expander that expands a light beam in a direction away from the laser medium in at least one of the optical path of the first resonator and the optical path of the second resonator. .
　ビームエキスパンダは、例えばレーザ媒質と第２のミラーとの間に配置できる。 The beam expander can be disposed, for example, between the laser medium and the second mirror.
　上記に代えて、ビームエキスパンダを、第２のミラーと第２のＱ値制御部との間に配置してもよい。 Instead of the above, a beam expander may be disposed between the second mirror and the second Q value control unit.
　ビームエキスパンダは凹レンズと凸レンズとを含んでいてもよい。第２のミラーが凹面ミラーであるとき、第２のミラーはビームエキスパンダの凹レンズを兼ねてもよい。 The beam expander may include a concave lens and a convex lens. When the second mirror is a concave mirror, the second mirror may also serve as a concave lens of the beam expander.
　本発明のレーザ装置では、第１のミラーを平面ミラーとし、第２のミラー及び第３のミラーを凹面ミラーとしてもよい。この場合において、第１のミラーから見て第２のミラーよりも遠方にある第３のミラーの曲率半径は、第２のミラーの曲率半径よりも短いことが好ましい。 In the laser apparatus of the present invention, the first mirror may be a plane mirror, and the second mirror and the third mirror may be concave mirrors. In this case, it is preferable that the radius of curvature of the third mirror located farther from the second mirror when viewed from the first mirror is shorter than the radius of curvature of the second mirror.
　上記に代えて、第１のミラーを凹面ミラーとし、第２のミラー及び第３のミラーを平面ミラーとしてもよい。 Instead of the above, the first mirror may be a concave mirror, and the second and third mirrors may be flat mirrors.
　本発明のレーザ装置では、第１の波長の発振時と第２の波長の発振時とにおいてレーザ媒質の励起エネルギーが個別に設定されることが好ましい。例えば、第２の波長の発振時における励起エネルギーを、第１の波長の発振時における励起エネルギーよりも低くするとよい。 In the laser apparatus of the present invention, it is preferable that the excitation energy of the laser medium is individually set when the first wavelength is oscillated and when the second wavelength is oscillated. For example, the excitation energy at the second wavelength oscillation may be lower than the excitation energy at the first wavelength oscillation.
　本発明のレーザ装置は、第２のミラーと第３のミラーとの間に、第２の波長の光に対して損失を与える光学フィルタを更に備える構成としてもよい。この場合でも、第１の共振器における第１の波長の発振しきい値は、第２の共振器における第２の波長の発振しきい値よりも高いことが好ましい。 The laser device of the present invention may be configured to further include an optical filter that gives loss to the light of the second wavelength between the second mirror and the third mirror. Even in this case, the oscillation threshold value of the first wavelength in the first resonator is preferably higher than the oscillation threshold value of the second wavelength in the second resonator.
　本発明は、また、第１の波長と第２の波長とに発光波長を有する固体のレーザ媒質であって、第１の波長の発光効率が第２の波長の発光効率よりも低いレーザ媒質と、レーザ媒質を間欠的に励起する励起手段と、レーザ媒質を間に挟んで対向する第１のミラー及び第２のミラーによって構成され、第１の波長の光を発振する第１の共振器と、第１のミラーと、レーザ媒質及び第２のミラーを間に挟んで第１のミラーと対向する第３のミラーとによって構成され、第１の共振器と一部が共通の光路を有し、第２の波長の光を発振する第２の共振器と、第１の共振器と第２の共振器とに共通の光路上に配置され、第１の共振器及び第２の共振器のＱ値を制御する第１のＱ値変更部と、第２のミラーと第３のミラーとの間に配置され、第２の共振器のＱ値を制御する第２のＱ値制御部とを備えたレーザ装置と、第１及び第２の波長のレーザ光が被検体に出射されたときに被検体内において生じた光音響信号を検出し、第１及び第２の波長のそれぞれに対応した第１及び第２の光音響データを生成する検出手段とを備えたことを特徴とする光音響計測装置を提供する。 The present invention is also a solid-state laser medium having emission wavelengths at a first wavelength and a second wavelength, wherein the emission efficiency of the first wavelength is lower than the emission efficiency of the second wavelength; A first resonator that oscillates light of the first wavelength, and is configured by an excitation unit that intermittently excites the laser medium, and a first mirror and a second mirror that are opposed to each other with the laser medium interposed therebetween. The first mirror and a third mirror facing the first mirror with the laser medium and the second mirror in between, and a part of the first resonator and a common optical path. The second resonator that oscillates light of the second wavelength, the first resonator, and the second resonator are disposed on a common optical path, and the first resonator and the second resonator The first Q value changing unit that controls the Q value, the second resonance, and the second resonance are arranged between the second mirror and the third mirror. And a photoacoustic signal generated in the subject when the first and second wavelength laser beams are emitted to the subject. Provided is a photoacoustic measurement device comprising detection means for detecting and generating first and second photoacoustic data corresponding to the first and second wavelengths, respectively.
　本発明のレーザ装置は、特に発光効率が低い第１の波長において出力低下を抑制できる。また、本発明のレーザ装置では、第１の波長についてパルス光の短パルス化が可能である。 The laser apparatus of the present invention can suppress a decrease in output particularly at the first wavelength with low emission efficiency. In the laser device of the present invention, the pulsed light can be shortened for the first wavelength.
本発明の第１実施形態に係る光音響画像計測装置を示すブロック図。The block diagram which shows the photoacoustic image measuring device which concerns on 1st Embodiment of this invention. 第１実施形態に係るレーザ光源ユニットの構成を示すブロック図。The block diagram which shows the structure of the laser light source unit which concerns on 1st Embodiment. アレキサンドライトの利得を示すグラフ。The graph which shows the gain of alexandrite. 励起エネルギーとパルスレーザ光のパルス幅との関係を示すグラフ。The graph which shows the relationship between excitation energy and the pulse width of a pulsed laser beam. 励起エネルギーとパルスレーザ光の出力との関係を示すグラフ。The graph which shows the relationship between excitation energy and the output of a pulse laser beam. 励起エネルギーとパルスレーザ光のパルス幅との関係を示すグラフ。The graph which shows the relationship between excitation energy and the pulse width of a pulsed laser beam. 励起エネルギーとパルスレーザ光の出力との関係を示すグラフ。The graph which shows the relationship between excitation energy and the output of a pulse laser beam. 各部の動作波形を示すタイミングチャート。The timing chart which shows the operation waveform of each part. 光音響計測装置の動作手順を示すフローチャート。The flowchart which shows the operation | movement procedure of a photoacoustic measuring device. 本発明の第２実施形態に係るレーザ光源ユニットを示すブロック図。The block diagram which shows the laser light source unit which concerns on 2nd Embodiment of this invention. 本発明の第３実施形態に係るレーザ光源ユニットを示すブロック図The block diagram which shows the laser light source unit which concerns on 3rd Embodiment of this invention. 共振器ミラーに凹面ミラーを用いた変形例のレーザ光源ユニットを示すブロック図。The block diagram which shows the laser light source unit of the modification which used the concave mirror for the resonator mirror. 本発明の第４実施形態に係るレーザ光源ユニットを示すブロック図。The block diagram which shows the laser light source unit which concerns on 4th Embodiment of this invention. 励起エネルギーとレーザ出力との関係を示すグラフ。The graph which shows the relationship between excitation energy and a laser output. 本発明の第５実施形態に係るレーザ光源ユニットを示すブロック図。The block diagram which shows the laser light source unit which concerns on 5th Embodiment of this invention. 励起エネルギーとレーザ出力との関係を示すグラフ。The graph which shows the relationship between excitation energy and a laser output. 酸素化ヘモグロビンと脱酸素化ヘモグロビンの光波長ごとの分子吸収係数を示すグラフ。The graph which shows the molecular absorption coefficient for every light wavelength of oxygenated hemoglobin and deoxygenated hemoglobin. 特許文献３に記載のレーザ装置を示すブロック図。FIG. 6 is a block diagram showing a laser device described in Patent Document 3.
　以下、図面を参照し、本発明の実施の形態を詳細に説明する。図１は、本発明の第１実施形態に係るレーザ装置を含む光音響計測装置を示す。光音響計測装置１０は、超音波探触子（プローブ）１１と、超音波ユニット１２と、レーザ光源ユニット（レーザ装置）１３とを備える。レーザ光源ユニット１３は、被検体に照射されるパルスレーザ光を出射する。レーザ光源ユニット１３は、第１の波長及び第２の波長を含む複数の波長のレーザ光を出射する。レーザの利得係数（発光効率）の波長特性において、第２の波長における利得係数は第１の波長における利得係数よりも高い。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a photoacoustic measuring apparatus including a laser apparatus according to a first embodiment of the present invention. The photoacoustic measurement device 10 includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, and a laser light source unit (laser device) 13. The laser light source unit 13 emits pulsed laser light that irradiates the subject. The laser light source unit 13 emits laser light having a plurality of wavelengths including the first wavelength and the second wavelength. In the wavelength characteristic of the laser gain coefficient (light emission efficiency), the gain coefficient at the second wavelength is higher than the gain coefficient at the first wavelength.
　例えば、第１の波長（中心波長）として約８００ｎｍを用い、第２の波長として約７５５ｎｍを用いた場合を検討する。先に説明した図１７を参照すると、ヒトの動脈に多く含まれる酸素化ヘモグロビン(酸素と結合したヘモグロビン:oxy-Hb)の波長７５５ｎｍにおける分子吸収係数は、波長８００ｎｍにおける分子吸収係数よりも低い。一方、静脈に多く含まれる脱酸素化ヘモグロビン（酸素と結合していないヘモグロビンdeoxy-Hb)の波長７５５ｎｍにおける分子吸収係数は、波長８００ｎｍにおける分子吸収係数よりも高い。この性質を利用し、波長８００ｎｍのレーザ光を照射して得られた光音響信号に対して、波長７５５ｎｍのレーザ光を照射して得られた光音響信号が相対的に大きいのか小さいのかを調べることにより、動脈からの光音響信号と静脈からの光音響信号とを判別することができる。あるいは、酸素飽和度を計測することができる。 For example, consider the case where about 800 nm is used as the first wavelength (center wavelength) and about 755 nm is used as the second wavelength. Referring to FIG. 17 described above, the molecular absorption coefficient at a wavelength of 755 nm of oxygenated hemoglobin (hemoglobin combined with oxygen: oxy-Hb) contained in a large amount in human arteries is lower than the molecular absorption coefficient at a wavelength of 800 nm. On the other hand, the molecular absorption coefficient at a wavelength of 755 nm of deoxygenated hemoglobin (hemoglobin deoxy-Hb not bound to oxygen) contained in a large amount in veins is higher than the molecular absorption coefficient at a wavelength of 800 nm. Using this property, it is investigated whether the photoacoustic signal obtained by irradiating a laser beam having a wavelength of 755 nm is relatively large or small with respect to the photoacoustic signal obtained by irradiating a laser beam having a wavelength of 800 nm. Thus, the photoacoustic signal from the artery and the photoacoustic signal from the vein can be discriminated. Alternatively, the oxygen saturation can be measured.
　なお、第１の波長と第２の波長の選択に関しては、理論上、選択される二波長において光吸収係数に差があればどのような二波長の組み合わせでもよく、上記した約７５５ｎｍと約８００ｎｍの組み合わせには限定されない。扱いやすさなどを考えると、選択される２つの波長は、酸素化ヘモグロビンと脱酸素化ヘモグロビンとの光吸収係数が同じになる波長約８００ｎｍ（正確には７９８ｎｍ）と、脱酸素化ヘモグロビンの光吸収係数が極大値となる波長約７５５ｎｍ（正確には７５７ｎｍ）との組み合わせが好ましい。第１の波長は、正確に７９８ｎｍである必要はなく、例えば７９３ｎｍ～８０２ｎｍの範囲にあれば実用上問題はない。また、第２の波長は、正確に７５７ｎｍである必要はなく、例えば極大値（７５７ｎｍ）付近のピークの半値幅である７４８～７７０ｎｍの範囲にあれば実用上問題はない。 Regarding the selection of the first wavelength and the second wavelength, theoretically, any combination of two wavelengths may be used as long as there is a difference in the light absorption coefficient between the two selected wavelengths, and the above-described about 755 nm and about 800 nm. The combination is not limited. Considering ease of handling and the like, the two wavelengths selected are approximately 800 nm (exactly 798 nm) at which the light absorption coefficients of oxygenated hemoglobin and deoxygenated hemoglobin are the same, and the light of deoxygenated hemoglobin. A combination with a wavelength of about 755 nm (more precisely, 757 nm) at which the absorption coefficient becomes a maximum is preferable. The first wavelength does not need to be exactly 798 nm. For example, if it is in the range of 793 nm to 802 nm, there is no practical problem. The second wavelength does not need to be exactly 757 nm. For example, if the second wavelength is in the range of 748 to 770 nm which is the half-value width of the peak near the maximum value (757 nm), there is no practical problem.
　図２は、レーザ光源ユニット１３の構成を示す。レーザ光源ユニット１３は、レーザロッド５１、フラッシュランプ５２、第１のミラー５３、第２のミラー５４、第３のミラー５５、第１のＱ値変更部５６、第２のＱ値変更部５７、及び制御回路６２を有する。レーザロッド５１は、レーザ媒質である。レーザロッド５１は、第１の波長（８００ｎｍ）と第２の波長（７５５ｎｍ）に発光波長を有する。レーザロッド５１には、例えばアレキサンドライト結晶を用いることができる。 FIG. 2 shows the configuration of the laser light source unit 13. The laser light source unit 13 includes a laser rod 51, a flash lamp 52, a first mirror 53, a second mirror 54, a third mirror 55, a first Q value changing unit 56, a second Q value changing unit 57, And a control circuit 62. The laser rod 51 is a laser medium. The laser rod 51 has emission wavelengths at a first wavelength (800 nm) and a second wavelength (755 nm). For the laser rod 51, for example, an alexandrite crystal can be used.
　図３に、アレキサンドライトのレーザ利得を示す。アレキサンドライトのレーザ利得は、波長７５５ｎｍ付近でピークとなる。レーザ利得は、波長７５５ｎｍよりも短い波長の範囲では波長が短くなるに連れて単調に減少していく。また、波長７５５ｎｍよりも長い波長の範囲では波長が長くなるに連れて単調に減少していく。アレキサンドライト結晶の波長８００ｎｍにおけるレーザ利得係数は、波長７５５ｎｍにおけるレーザ利得係数よりも低い。 Fig. 3 shows the laser gain of alexandrite. The laser gain of alexandrite peaks at a wavelength near 755 nm. The laser gain monotonously decreases as the wavelength becomes shorter in the wavelength range shorter than the wavelength of 755 nm. Moreover, in the wavelength range longer than 755 nm, it decreases monotonously as the wavelength becomes longer. The laser gain coefficient of the alexandrite crystal at a wavelength of 800 nm is lower than the laser gain coefficient at a wavelength of 755 nm.
　フラッシュランプ５２は、励起光源であり、レーザロッド５１に励起光を照射する励起手段である。フラッシュランプ５２は間欠的に駆動される。これにより、レーザロッド５１は、間欠的に励起される。フラッシュランプ５２以外の光源を、励起光源として用いてもよい。 The flash lamp 52 is an excitation light source and is an excitation means for irradiating the laser rod 51 with excitation light. The flash lamp 52 is driven intermittently. Thereby, the laser rod 51 is intermittently excited. A light source other than the flash lamp 52 may be used as the excitation light source.
　第１のミラー５３、第２のミラー５４、及び第３のミラー５５は、レーザロッド５１の光軸上に沿って並べられている。第１のミラー５３及び第２のミラー５４は、レーザロッド５１を挟んで対向する。第３のミラー５５は、第２のミラー５４から見てレーザロッド５１とは反対側に配置される。第１のミラー５３及び第３のミラー５５は、レーザロッド５１及び第２のミラー５４を挟んで対向する。 The first mirror 53, the second mirror 54, and the third mirror 55 are arranged along the optical axis of the laser rod 51. The first mirror 53 and the second mirror 54 face each other with the laser rod 51 interposed therebetween. The third mirror 55 is disposed on the side opposite to the laser rod 51 when viewed from the second mirror 54. The first mirror 53 and the third mirror 55 face each other with the laser rod 51 and the second mirror 54 interposed therebetween.
　第１のミラー５３は、波長８００ｎｍの光及び波長７５５ｎｍの光の出力ミラーである。第１のミラー５３の波長８００ｎｍの光に対する反射率は、波長７５５ｎｍの光に対する反射率よりも高い。例えば、第１のミラー５３の波長８００ｎｍの光に対する反射率は８０％であり、波長７５５ｎｍの光に対する反射率は７０％である。レーザ利得が低い波長８００ｎｍの光に対する反射率を高く設定することにより、発振（投入）エネルギーしきい値が下がり、レーザ利得が増加する。これにより、パルスレーザ光の短パルス化が可能である。 The first mirror 53 is an output mirror of light having a wavelength of 800 nm and light having a wavelength of 755 nm. The reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm is higher than the reflectance with respect to light with a wavelength of 755 nm. For example, the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm is 80%, and the reflectance with respect to light with a wavelength of 755 nm is 70%. By setting the reflectivity for light having a wavelength of 800 nm with a low laser gain to be high, the oscillation (input) energy threshold is lowered and the laser gain is increased. As a result, the pulse laser beam can be shortened.
　第２のミラー５４は、波長８００ｎｍの光を反射し、波長７５５ｎｍの光を透過する。例えば、第２のミラー５４の波長８００ｎｍの光に対する反射率は９９．８％以上であり、波長７５５ｎｍの光に対する反射率は０．５％以下である。第３のミラー５５は、波長７５５ｎｍの光を反射する。第３のミラー５５の波長７５５ｎｍの光に対する反射率は例えば９９．８％以上である。 The second mirror 54 reflects light having a wavelength of 800 nm and transmits light having a wavelength of 755 nm. For example, the reflectance of the second mirror 54 with respect to light with a wavelength of 800 nm is 99.8% or more, and the reflectance with respect to light with a wavelength of 755 nm is 0.5% or less. The third mirror 55 reflects light having a wavelength of 755 nm. The reflectance of the third mirror 55 with respect to light having a wavelength of 755 nm is, for example, 99.8% or more.
　レーザロッド５１から出射した光のうち、波長８００ｎｍの光は第２のミラー５４によって反射され、第１のミラー５３と第２のミラー５４との間を往復する。第１のミラー５３と第２のミラー５４とにより、波長８００ｎｍの光を発振する第１の共振器が構成される。一方、レーザロッド５１から出射した波長７５５ｎｍの光は第２のミラー５４を透過して第３のミラー５５によって反射され、第１のミラー５３と第３のミラー５５との間を往復する。第１のミラー５３と第３のミラー５５とにより、波長７５５ｎｍの光を発振する第２の共振器が構成される。第１の共振器の共振器長は、第２の共振器の共振器長よりも短い。第１のミラー５３から第２のミラー５４までの光路は、第１の共振器と第２の共振器とに共通の光路である。すなわち、第２の共振器の光路の一部は、第１の共振器と共通である。 Of the light emitted from the laser rod 51, light having a wavelength of 800 nm is reflected by the second mirror 54 and reciprocates between the first mirror 53 and the second mirror 54. The first mirror 53 and the second mirror 54 constitute a first resonator that oscillates light having a wavelength of 800 nm. On the other hand, light having a wavelength of 755 nm emitted from the laser rod 51 passes through the second mirror 54 and is reflected by the third mirror 55, and reciprocates between the first mirror 53 and the third mirror 55. The first mirror 53 and the third mirror 55 constitute a second resonator that oscillates light having a wavelength of 755 nm. The resonator length of the first resonator is shorter than the resonator length of the second resonator. The optical path from the first mirror 53 to the second mirror 54 is a common optical path for the first resonator and the second resonator. That is, a part of the optical path of the second resonator is common to the first resonator.
　第１のＱ値変更部５６は、第１の共振器と第２の共振器とに共通の部分に配置され、第１の共振器及び第２の共振器のＱ値を制御する。第１のＱ値変更部５６は、例えば第１のミラー５３とレーザロッド５１との間であって、第１の共振器と第２の共振器とに共通の光路上に配置される。これに代えて、レーザロッド５１と第２のミラー５４との間であって、第１の共振器と第２の共振器とに共通の光路上に第１のＱ値変更部５６を配置してもよい。第１のＱ値変更部５６は、第１のＱスイッチ５８と偏光子５９とを含む。第１のＱスイッチ５８は、第１の共振器と第２の共振器とに共通の光路上に配置される。第１のＱスイッチ５８は、印加電圧に応じて、第１の共振器及び第２の共振器のＱ値を変化させる。第１のＱスイッチ５８には、印加電圧に応じて通過する光の偏光状態を変化させる電気光学素子を用いることができる。 The first Q value changing unit 56 is disposed in a common part to the first resonator and the second resonator, and controls the Q values of the first resonator and the second resonator. The first Q value changing unit 56 is disposed, for example, between the first mirror 53 and the laser rod 51 on a common optical path for the first resonator and the second resonator. Instead, the first Q value changing unit 56 is disposed on the optical path between the laser rod 51 and the second mirror 54 and common to the first resonator and the second resonator. May be. The first Q value changing unit 56 includes a first Q switch 58 and a polarizer 59. The first Q switch 58 is arranged on an optical path common to the first resonator and the second resonator. The first Q switch 58 changes the Q values of the first resonator and the second resonator according to the applied voltage. The first Q switch 58 can be an electro-optic element that changes the polarization state of the light passing therethrough according to the applied voltage.
　偏光子５９は、レーザロッド５１と第１のＱスイッチ５８との間に配置される。偏光子５９は、所定方向の直線偏光のみを透過させる。偏光子５９には、例えば、所定の方向の直線偏光（例えばｐ偏光）を透過し、所定の方向に直交する方向（例えばｓ偏光）を反射するビームスプリッタを用いることができる。なお、レーザロッド５１にアレキサンドライト結晶を用いた場合など、レーザロッド５１が出射する光がｐ偏光であれば、偏光子５９は省略してもよい。 The polarizer 59 is disposed between the laser rod 51 and the first Q switch 58. The polarizer 59 transmits only linearly polarized light in a predetermined direction. As the polarizer 59, for example, a beam splitter that transmits linearly polarized light (for example, p-polarized light) in a predetermined direction and reflects a direction orthogonal to the predetermined direction (for example, s-polarized light) can be used. Note that the polarizer 59 may be omitted if the light emitted from the laser rod 51 is p-polarized light, such as when an alexandrite crystal is used for the laser rod 51.
　第１のＱスイッチ５８には例えばポッケルスセルが用いられる。第１のＱスイッチ５８は、印加電圧がＱスイッチオフに対応した第１の電圧のとき第１の共振器及び第２の共振器を低Ｑ状態にする。低Ｑ状態とは、共振器のＱ値がレーザ発振しきい値よりも低い状態を指す。第１の電圧は、例えば第１のＱスイッチ５８が１／４波長板として働く電圧である。第１の電圧は正の電圧であっても、負の電圧であってもよい。第１のＱスイッチ５８は、印加電圧がＱスイッチオンに対応した第２の電圧のとき、第１の共振器及び第２の共振器を高Ｑ状態にする。高Ｑ状態とは、共振器のＱ値がレーザ発振しきい値よりも高い状態を指す。第２の電圧の絶対値は、第１の電圧の絶対値よりも小さい。第２の電圧は、例えば０Ｖ（電圧印加なし）であり、このとき第１のＱスイッチ５８を透過する光の偏光状態は変化しない。 For example, a Pockels cell is used for the first Q switch 58. The first Q switch 58 sets the first resonator and the second resonator to a low Q state when the applied voltage is the first voltage corresponding to the Q switch off. The low Q state refers to a state where the Q value of the resonator is lower than the laser oscillation threshold value. The first voltage is, for example, a voltage at which the first Q switch 58 works as a quarter wavelength plate. The first voltage may be a positive voltage or a negative voltage. The first Q switch 58 sets the first resonator and the second resonator to a high Q state when the applied voltage is a second voltage corresponding to the Q switch being turned on. The high Q state refers to a state where the Q value of the resonator is higher than the laser oscillation threshold value. The absolute value of the second voltage is smaller than the absolute value of the first voltage. The second voltage is, for example, 0 V (no voltage applied), and the polarization state of the light transmitted through the first Q switch 58 does not change at this time.
　第１のＱスイッチ５８に第１の電圧が印加されるとき、第１のＱスイッチ５８は１／４波長板として働き、偏光子５９から第１のＱスイッチ５８に入射したｐ偏光の光は、第１のＱスイッチ５８を通過して円偏光となり、第１のミラー５３で反射して第１のＱスイッチ５８に逆向きに入射する。第１のＱスイッチ５８に逆向きに入射した円偏光の光は、第１のＱスイッチ５８を通過する際にｓ偏光となり、ｓ偏光を反射する偏光子５９で反射して共振器の光路外へ放出される。一方、第１のＱスイッチ５８への印加電圧が０Ｖ（第２の電圧）のとき、偏光子５９から第１のＱスイッチ５８に入射したｐ偏光の光はｐ偏光のまま第１のＱスイッチ５８を透過し、第１のミラー５３で反射する。第１のミラー５３で反射したｐ偏光の光は、偏光状態を変化させずに第１のＱスイッチ５８を透過し、ｐ偏光を透過する偏光子５９を透過してレーザロッド５１に入射する。 When the first voltage is applied to the first Q switch 58, the first Q switch 58 functions as a quarter wave plate, and the p-polarized light incident on the first Q switch 58 from the polarizer 59 is Then, the light passes through the first Q switch 58 and becomes circularly polarized light, is reflected by the first mirror 53, and enters the first Q switch 58 in the reverse direction. The circularly polarized light incident on the first Q switch 58 in the reverse direction becomes s-polarized light when passing through the first Q switch 58, and is reflected by the polarizer 59 that reflects the s-polarized light and is out of the optical path of the resonator. Is released. On the other hand, when the voltage applied to the first Q switch 58 is 0 V (second voltage), the p-polarized light incident on the first Q switch 58 from the polarizer 59 remains p-polarized. 58 is reflected and reflected by the first mirror 53. The p-polarized light reflected by the first mirror 53 passes through the first Q switch 58 without changing the polarization state, passes through the polarizer 59 that transmits p-polarized light, and enters the laser rod 51.
　第２のＱ値変更部５７は、第２のミラー５４と第３のミラー５５との間に配置され、第２の共振器のＱ値を制御する。第２のＱ値変更部５７は、第２のＱスイッチ６０と１／４波長板６１とを含む。第２のＱスイッチ６０は、第２の共振器の光路上、かつ第１の共振器の光路外、すなわち第２のミラー５４と第３のミラー５５との間に配置される。第２のＱスイッチ６０は、印加電圧に応じて第２の共振器のＱ値を変化させる。第２のＱスイッチ６０には、印加電圧に応じて通過する光の偏光状態を変化させる電気光学素子を用いることができる。１／４波長板６１は、第２のＱスイッチ６０と第３のミラー５５との間に配置される。 The second Q value changing unit 57 is disposed between the second mirror 54 and the third mirror 55, and controls the Q value of the second resonator. The second Q value changing unit 57 includes a second Q switch 60 and a quarter wavelength plate 61. The second Q switch 60 is disposed on the optical path of the second resonator and outside the optical path of the first resonator, that is, between the second mirror 54 and the third mirror 55. The second Q switch 60 changes the Q value of the second resonator according to the applied voltage. The second Q switch 60 can be an electro-optic element that changes the polarization state of light passing therethrough according to the applied voltage. The quarter wavelength plate 61 is disposed between the second Q switch 60 and the third mirror 55.
　第２のＱスイッチ６０には例えばポッケルスセルが用いられる。第２のＱスイッチ６０は、印加電圧がＱスイッチオフに対応した第３の電圧のとき第２の共振器を低Ｑ状態にする。第３の電圧は、例えば０Ｖ（電圧印加なし）であり、このとき第２のＱスイッチ６０を透過する光の偏光状態は変化しない。第２のＱスイッチ６０は、印加電圧がＱスイッチオンに対応した第４の電圧のとき第２の共振器を高Ｑ状態にする。第４の電圧の絶対値は第３の電圧の絶対値よりも大きい。第４の電圧は、例えば第２のＱスイッチ６０が１／４波長板として働く電圧である。第４の電圧は、正の電圧であっても、負の電圧であってもよい。 For example, a Pockels cell is used for the second Q switch 60. The second Q switch 60 sets the second resonator in a low Q state when the applied voltage is a third voltage corresponding to the Q switch off. The third voltage is, for example, 0 V (no voltage applied), and at this time, the polarization state of the light transmitted through the second Q switch 60 does not change. The second Q switch 60 sets the second resonator to a high Q state when the applied voltage is a fourth voltage corresponding to the Q switch being turned on. The absolute value of the fourth voltage is greater than the absolute value of the third voltage. The fourth voltage is, for example, a voltage at which the second Q switch 60 works as a quarter wavelength plate. The fourth voltage may be a positive voltage or a negative voltage.
　第２のＱスイッチ６０への印加電圧が０Ｖ（第３の電圧）のとき、レーザロッド５１側から第２のミラー５４を通過して第２のＱスイッチ６０に入射したｐ偏光の光は、偏光状態が変化せずに第２のＱスイッチ６０を通過し、１／４波長板６１を通過して円偏光となって第３のミラー５５で反射する。第３のミラー５５で反射した円偏光は、１／４波長板６１を逆向きに通ってｓ偏光となり、第２のＱスイッチ６０をｓ偏光のまま通過してレーザロッド５１へ戻る。ここで、第２のミラー５４は波長８００ｎｍの光を反射し、波長７５５ｎｍの光を透過する。このため、第２のミラー５４と第３のミラー５５との間を進行する光は波長７５５ｎｍの光であり、波長８００ｎｍの光は第２のミラー５４から第３のミラー５５側には進行しない。 When the applied voltage to the second Q switch 60 is 0 V (third voltage), the p-polarized light that has passed through the second mirror 54 and entered the second Q switch 60 from the laser rod 51 side is The polarization state does not change, passes through the second Q switch 60, passes through the quarter wavelength plate 61, becomes circularly polarized light, and is reflected by the third mirror 55. The circularly polarized light reflected by the third mirror 55 passes through the quarter-wave plate 61 in the reverse direction to become s-polarized light, passes through the second Q switch 60 as s-polarized light, and returns to the laser rod 51. Here, the second mirror 54 reflects light having a wavelength of 800 nm and transmits light having a wavelength of 755 nm. Therefore, the light traveling between the second mirror 54 and the third mirror 55 is light having a wavelength of 755 nm, and the light having a wavelength of 800 nm does not travel from the second mirror 54 to the third mirror 55 side. .
　一方、第２のＱスイッチ６０に第４の電圧が印加されるとき、第２のＱスイッチ６０は１／４波長板として働き、レーザロッド５１側から第２のミラー５４を通過して第２のＱスイッチ６０に入射したｐ偏光の光は、第２のＱスイッチ６０を通過する際に円偏光となり、更に１／４波長板６１を通過してｓ偏光となって第３のミラー５５で反射する。第３のミラー５５で反射した光は、１／４波長板６１を逆向きに通って円偏光となり、更に第２のＱスイッチ６０を通過してｐ偏光となって、レーザロッド５１へ戻る。 On the other hand, when a fourth voltage is applied to the second Q switch 60, the second Q switch 60 functions as a quarter wavelength plate, passes through the second mirror 54 from the laser rod 51 side, and passes through the second mirror 54. The p-polarized light incident on the Q switch 60 becomes circularly polarized light when passing through the second Q switch 60, and further passes through the quarter wavelength plate 61 to become s-polarized light at the third mirror 55. reflect. The light reflected by the third mirror 55 passes through the quarter-wave plate 61 in the reverse direction and becomes circularly polarized light, and further passes through the second Q switch 60 and becomes p-polarized light, and returns to the laser rod 51.
　制御回路６２は、第１のＱ値変更部５６及び第２のＱ値変更部５７を駆動する。制御回路６２は、第１の共振器及び第２の共振器のＱ値を、共振器のＱ値が発振しきい値よりも低い低Ｑ状態にする第１の駆動状態、第１の共振器及び第２の共振器のＱ値を、共振器のＱ値が発振しきい値よりも高い高Ｑ状態にする第２の駆動状態、及び、第１の共振器のＱ値を高Ｑ状態にし、かつ第２の共振器のＱ値を低Ｑ状態にする第３の駆動状態の間で駆動状態を切り替える。制御回路６２は、第１のＱスイッチ５８への印加電圧を制御することにより第１のＱ値変更部５６を駆動し、第２のＱスイッチ６０への印加電圧を制御することにより第２のＱ値変更部５７を駆動する。制御回路６２は、フラッシュランプ５２の駆動も行う。 The control circuit 62 drives the first Q value changing unit 56 and the second Q value changing unit 57. The control circuit 62 includes a first driving state, a first resonator in which the Q values of the first resonator and the second resonator are set to a low Q state in which the Q value of the resonator is lower than an oscillation threshold value. And the second driving state in which the Q value of the second resonator is set to a high Q state in which the Q value of the resonator is higher than the oscillation threshold value, and the Q value of the first resonator is set to a high Q state. The driving state is switched between the third driving states in which the Q value of the second resonator is set to the low Q state. The control circuit 62 drives the first Q value changing unit 56 by controlling the voltage applied to the first Q switch 58 and controls the second voltage by controlling the voltage applied to the second Q switch 60. The Q value changing unit 57 is driven. The control circuit 62 also drives the flash lamp 52.
　制御回路６２は、第１の駆動状態では、第１のＱスイッチ５８に第１の電圧を印加して、第１のＱスイッチ５８を１／４波長板として働かせる。また、第２のＱスイッチ６０への印加電圧を０Ｖ（第３の電圧）とし、第２のＱスイッチ６０を通過する光の偏光状態を変化させない。第１のＱスイッチ５８が１／４波長板として働くことにより、第１のミラー５３で反射した光はレーザロッド５１に入射しない。また、第２のＱスイッチ６０を通過する光の偏光状態を変化させないことにより、第３のミラー５５で反射した波長７５５ｎｍの光をｓ偏光の状態でレーザロッド５１へ入射させる。その結果、第１の共振器及び第２の共振器のＱ値は低Ｑ状態となり、波長８００ｎｍと波長７５５ｎｍの双方について、レーザ発振が起こらない。なお、第１のＱスイッチ５８は第１の共振器と第２の共振器とに共通の光路上に配置されており、第１のＱスイッチ５８に第１の電圧を印加することにより第２の共振器のＱ値を低Ｑ状態にすることができる。このため、第１の駆動状態において、第２のＱスイッチ６０への印加電圧は特に第３の電圧には限定されず、第２のＱスイッチ６０に第４の電圧を印加し、第２のＱスイッチ６０を１／４波長板として働かせていてもよい。 In the first driving state, the control circuit 62 applies a first voltage to the first Q switch 58 to make the first Q switch 58 work as a quarter wavelength plate. Further, the applied voltage to the second Q switch 60 is set to 0 V (third voltage), and the polarization state of the light passing through the second Q switch 60 is not changed. Since the first Q switch 58 functions as a quarter wavelength plate, the light reflected by the first mirror 53 does not enter the laser rod 51. Further, by not changing the polarization state of the light passing through the second Q switch 60, the light having a wavelength of 755 nm reflected by the third mirror 55 is incident on the laser rod 51 in the s-polarized state. As a result, the Q values of the first resonator and the second resonator are in a low Q state, and laser oscillation does not occur for both the wavelength of 800 nm and the wavelength of 755 nm. The first Q switch 58 is disposed on a common optical path for the first resonator and the second resonator, and the second voltage is applied by applying a first voltage to the first Q switch 58. The Q value of each of the resonators can be set to a low Q state. For this reason, in the first driving state, the voltage applied to the second Q switch 60 is not particularly limited to the third voltage, the fourth voltage is applied to the second Q switch 60, and the second voltage The Q switch 60 may be used as a quarter wavelength plate.
　制御回路６２は、第２の駆動状態では、第１のＱスイッチ５８への印加電圧を０Ｖ（第２の電圧）とし、第１のＱスイッチ５８を通過する光の偏光状態を変化させない。また、第２のＱスイッチ６０に第４の電圧を印加して、第２のＱスイッチ６０を１／４波長板として働かせる。第１のＱスイッチ５８を通過する光の偏光状態を変化させないことにより、第１のミラー５３で反射した光はｐ偏光の状態でレーザロッド５１に入射する。また、第２のＱスイッチ６０を１／４波長板として働かせることにより、第３のミラー５５で反射した波長７５５ｎｍの光はｐ偏光でレーザロッド５１へ入射する。その結果、第１の共振器及び第２の共振器のＱ値は高Ｑ状態となり、レーザ発振が起こる。波長８００ｎｍと波長７５５ｎｍとでは、波長７５５ｎｍのレーザ利得の方が波長８００ｎｍのレーザ利得よりも高いため、発振波長はレーザ利得が高い７５５ｎｍとなる。 In the second driving state, the control circuit 62 sets the applied voltage to the first Q switch 58 to 0 V (second voltage) and does not change the polarization state of the light passing through the first Q switch 58. In addition, a fourth voltage is applied to the second Q switch 60 to cause the second Q switch 60 to function as a quarter wavelength plate. By not changing the polarization state of the light passing through the first Q switch 58, the light reflected by the first mirror 53 enters the laser rod 51 in a p-polarized state. Further, by making the second Q switch 60 act as a quarter wavelength plate, the light having a wavelength of 755 nm reflected by the third mirror 55 is incident on the laser rod 51 as p-polarized light. As a result, the Q values of the first resonator and the second resonator are in a high Q state, and laser oscillation occurs. At a wavelength of 800 nm and a wavelength of 755 nm, the laser gain at a wavelength of 755 nm is higher than the laser gain at a wavelength of 800 nm, so the oscillation wavelength is 755 nm, which has a higher laser gain.
　制御回路６２は、第３の駆動状態では、第１のＱスイッチ５８への印加電圧を０Ｖ（第２の電圧）とし、第１のＱスイッチ５８を通過する光の偏光状態を変化させない。また、第２のＱスイッチ６０への印加電圧を０Ｖ（第３の電圧）とし、第２のＱスイッチ６０を通過する光の偏光状態を変化させない。第１のＱスイッチ５８を通過する光の偏光状態を変化させないことにより、第１のミラー５３で反射した光はｐ偏光の状態でレーザロッド５１に入射する。また、第２のＱスイッチ６０を通過する光の偏光状態を変化させないことにより、第３のミラー５５で反射した波長７５５ｎｍの光をｓ偏光の状態でレーザロッド５１へ入射させる。その結果、第１の共振器のＱ値は高Ｑ状態となり、かつ第２の共振器のＱ値は低Ｑ状態となり、第１の共振器においてレーザ発振が起こる。第１の共振器は波長８００ｎｍの共振器であり、発振波長は８００ｎｍとなる。 In the third driving state, the control circuit 62 sets the applied voltage to the first Q switch 58 to 0 V (second voltage) and does not change the polarization state of the light passing through the first Q switch 58. Further, the applied voltage to the second Q switch 60 is set to 0 V (third voltage), and the polarization state of the light passing through the second Q switch 60 is not changed. By not changing the polarization state of the light passing through the first Q switch 58, the light reflected by the first mirror 53 enters the laser rod 51 in a p-polarized state. Further, by not changing the polarization state of the light passing through the second Q switch 60, the light having a wavelength of 755 nm reflected by the third mirror 55 is incident on the laser rod 51 in the s-polarized state. As a result, the Q value of the first resonator becomes a high Q state, and the Q value of the second resonator becomes a low Q state, and laser oscillation occurs in the first resonator. The first resonator is a resonator having a wavelength of 800 nm, and the oscillation wavelength is 800 nm.
　制御回路６２は、レーザロッド５１の励起時は、第１のＱ値変更部５６及び第２のＱ値変更部５７の駆動状態を第１の駆動状態とする。すなわち、第１の共振器及び第２の共振器のＱ値を低Ｑ状態にしてフラッシュランプ５２を点灯し、レーザロッド５１の励起を行う。制御回路６２は、レーザロッド５１の励起後、発振波長が８００ｎｍのときは第１のＱ値変更部５６及び第２のＱ値変更部５７の駆動状態を第１の駆動状態から第３の駆動状態へと変化させる。第３の駆動状態では、第１の共振器が高Ｑ状態であり、かつ第２の共振器が低Ｑ状態であるため、発振波長は波長８００ｎｍとなる。第１の共振器のＱ値を低Ｑ状態から高Ｑ状態へ急激に変化させることにより、波長８００ｎｍのパルスレーザ光を得ることができる。 The control circuit 62 sets the driving state of the first Q value changing unit 56 and the second Q value changing unit 57 to the first driving state when the laser rod 51 is excited. That is, the Q values of the first resonator and the second resonator are set to a low Q state, the flash lamp 52 is turned on, and the laser rod 51 is excited. After the excitation of the laser rod 51, the control circuit 62 changes the driving state of the first Q value changing unit 56 and the second Q value changing unit 57 from the first driving state to the third driving when the oscillation wavelength is 800 nm. Change to state. In the third driving state, since the first resonator is in the high Q state and the second resonator is in the low Q state, the oscillation wavelength is 800 nm. By rapidly changing the Q value of the first resonator from the low Q state to the high Q state, pulse laser light having a wavelength of 800 nm can be obtained.
　制御回路６２は、レーザロッド５１の励起後、発振波長が７５５ｎｍのときは第１のＱ値変更部５６及び第２のＱ値変更部５７の駆動状態を第１の駆動状態から第２の駆動状態へと変化させる。このとき制御回路６２は、第２の共振器が高Ｑ状態となるように第２のＱ値変更部５７を駆動するのと同時に第１の共振器が高Ｑ状態となるように第１のＱ値変更部５６を駆動する。あるいは、第２の共振器が高Ｑ状態となるように第２のＱ値変更部５７を駆動した後に第１の共振器が高Ｑ状態となるように第１のＱ値変更部５６を駆動してもよい。第２の駆動状態では、双方の共振器が高Ｑ状態となるが、発振波長は、波長８００ｎｍと波長７５５ｎｍとのうちレーザ利得が高い７５５ｎｍとなる。第１の共振器及び第２の共振器のＱ値を低Ｑ状態から高Ｑ状態へ急激に変化させることにより、波長７５５ｎｍのパルスレーザ光を得ることができる。 When the oscillation wavelength is 755 nm after the excitation of the laser rod 51, the control circuit 62 changes the driving state of the first Q value changing unit 56 and the second Q value changing unit 57 from the first driving state to the second driving state. Change to state. At this time, the control circuit 62 drives the second Q value changing unit 57 so that the second resonator is in the high Q state, and at the same time, the first resonator is in the high Q state. The Q value changing unit 56 is driven. Alternatively, after driving the second Q value changing unit 57 so that the second resonator is in the high Q state, the first Q value changing unit 56 is driven so that the first resonator is in the high Q state. May be. In the second driving state, both resonators are in the high Q state, but the oscillation wavelength is 755 nm, which has a high laser gain, of the wavelength 800 nm and the wavelength 755 nm. By rapidly changing the Q values of the first resonator and the second resonator from the low Q state to the high Q state, pulse laser light having a wavelength of 755 nm can be obtained.
　図４は、励起エネルギーとパルスレーザ光のパルス幅との関係を示す。同図には、２つの共振器長について、励起エネルギーとパルス幅との関係を示している。グラフ（ａ）は共振器長が短い共振器を用いた場合の励起エネルギーとパルス幅との関係を示し、グラフ（ｂ）は共振器長が長い共振器を用いた場合の励起エネルギーとパルス幅との関係を示す。グラフ（ａ）とグラフ（ｂ）を参照すると、励起エネルギーを一定とした場合、共振器長が短い方が、共振器長が長い場合に比べてパルス幅を短くできることがわかる。レーザ光源ユニット１３（図２参照）では、第１の共振器は第２の共振器よりも共振器長が短いため、波長８００ｎｍのパルスレーザ光のパルス幅を、波長７５５ｎｍのパルスレーザ光のパルス幅よりも短くできる。 FIG. 4 shows the relationship between the excitation energy and the pulse width of the pulsed laser beam. The figure shows the relationship between excitation energy and pulse width for two resonator lengths. Graph (a) shows the relationship between excitation energy and pulse width when a resonator with a short resonator length is used, and graph (b) shows excitation energy and pulse width when a resonator with a long resonator length is used. The relationship is shown. Referring to graphs (a) and (b), it can be seen that, when the excitation energy is constant, the pulse width can be shortened when the resonator length is shorter than when the resonator length is long. In the laser light source unit 13 (see FIG. 2), since the first resonator has a shorter resonator length than the second resonator, the pulse width of the pulse laser beam having a wavelength of 800 nm is set to the pulse width of the pulse laser beam having a wavelength of 755 nm. Can be shorter than the width.
　図５は、励起エネルギーとレーザ出力との関係を示す。同図には、２つの共振器長について、励起エネルギーとレーザ出力との関係を示す。グラフ（ａ）は共振器長が短い共振器を用いた場合の励起エネルギーとレーザ出力との関係を示し、グラフ（ｂ）は共振器長が長い共振器を用いた場合の励起エネルギーとレーザ出力との関係を示す。グラフ（ａ）とグラフ（ｂ）を参照すると、励起エネルギーを一定とした場合、共振器長が短い方が、共振器長が長い場合に比べてレーザ出力を上げることができることがわかる。レーザ光源ユニット１３では、第１の共振器は第２の共振器よりも共振器長が短く、双方の共振器の共振器長を同じにした場合に比べて、波長８００ｎｍの光のレーザ出力を上げることができる。 FIG. 5 shows the relationship between excitation energy and laser output. The figure shows the relationship between excitation energy and laser output for two resonator lengths. Graph (a) shows the relationship between excitation energy and laser output when a resonator with a short resonator length is used, and graph (b) shows excitation energy and laser output when a resonator with a long resonator length is used. The relationship is shown. Referring to graphs (a) and (b), it can be seen that when the excitation energy is constant, the laser output can be increased when the resonator length is shorter than when the resonator length is longer. In the laser light source unit 13, the first resonator has a resonator length shorter than that of the second resonator, and the laser output of light having a wavelength of 800 nm can be obtained compared to the case where both resonators have the same resonator length. Can be raised.
　図６は、励起エネルギーとパルスレーザ光のパルス幅との関係を示す。同図において、グラフ（ａ）は、出力ミラーである第１のミラー５３の反射率を８０％とした場合の励起エネルギーとパルス幅との関係を示し、グラフ（ｂ）は第１のミラー５３の反射率を６０％とした場合の励起エネルギーとパルス幅との関係を示す。グラフ（ａ）とグラフ（ｂ）を参照すると、励起エネルギーを一定とした場合、出力ミラーの反射率が高い方が、出力ミラーの反射率を低くした場合に比べてパルス幅を短くできることがわかる。第１のミラー５３の波長８００ｎｍの光に対する反射率を、波長７５５ｎｍの光に対する反射率よりも高くすることにより、波長８００ｎｍのパルスレーザ光のパルス幅を、波長７５５ｎｍのパルスレーザ光のパルス幅よりも短くできる。 FIG. 6 shows the relationship between the excitation energy and the pulse width of the pulse laser beam. In the figure, graph (a) shows the relationship between excitation energy and pulse width when the reflectance of the first mirror 53 as an output mirror is 80%, and graph (b) shows the first mirror 53. The relationship between the excitation energy and the pulse width when the reflectivity is 60% is shown. Referring to graphs (a) and (b), when the excitation energy is constant, it can be seen that the higher the output mirror reflectivity, the shorter the pulse width compared to the lower output mirror reflectivity. . By making the reflectance of the first mirror 53 with respect to the light with a wavelength of 800 nm higher than the reflectance with respect to the light with a wavelength of 755 nm, the pulse width of the pulse laser light with a wavelength of 800 nm is made larger than the pulse width of the pulse laser light with a wavelength of 755 nm. Can also be shortened.
　図７は、励起エネルギーとレーザ出力との関係を示す。同図において、グラフ（ａ）は、第１のミラー５３の反射率を８０％とした場合の励起エネルギーとレーザ出力との関係を示し、グラフ（ｂ）は第１のミラー５３の反射率を６０％とした場合の励起エネルギーとレーザ出力との関係を示す。グラフ（ａ）とグラフ（ｂ）を参照すると、励起エネルギーを一定とした場合、出力ミラーの反射率が高い方が、出力ミラーの反射率を低くした場合に比べてレーザ出力を上げることができることがわかる。第１のミラー５３の波長８００ｎｍの光に対する反射率を、波長７５５ｎｍの光に対する反射率よりも高くすることにより、双方の波長の反射率を同じにした場合に比べて、波長８００ｎｍの光のレーザ出力を上げることができる。 FIG. 7 shows the relationship between excitation energy and laser output. In the figure, graph (a) shows the relationship between excitation energy and laser output when the reflectance of the first mirror 53 is 80%, and graph (b) shows the reflectance of the first mirror 53. The relationship between excitation energy and laser output when 60% is shown. Referring to graphs (a) and (b), when the excitation energy is constant, the higher the output mirror reflectivity, the higher the laser output compared to the lower output mirror reflectivity. I understand. By making the reflectivity of the first mirror 53 with respect to light with a wavelength of 800 nm higher than the reflectivity with respect to light with a wavelength of 755 nm, the laser of light with a wavelength of 800 nm is compared with the case where the reflectivity of both wavelengths is the same. The output can be increased.
　図８は、レーザ発振時の各部の動作波形を示す。制御回路６２は、時刻ｔ１にフラッシュランプ５２を点灯する（ａ）。制御回路６２は、フラッシュランプ５２を点灯する前に、第１のＱスイッチ５８に第１の電圧を印加し（ｂ）、第２のＱスイッチ６０への印加電圧を０Ｖ（第３の電圧）とする（ｃ）。第１のＱスイッチ５８に第１の電圧を印加する時刻は、時刻ｔ１よりも少し前の時刻でよい。あるいは、前回のパルスレーザ光出射の後から第１のＱスイッチ５８に第１の電圧を印加し続けてもよい。第１のＱスイッチ５８に第１の電圧を印加することにより、第１のＱスイッチ５８は１／４波長板として働く。また、第２のＱスイッチ６０への電圧印加を行わないことにより、第２のＱスイッチ６０を通過する光の偏光状態は変化しない。 FIG. 8 shows operation waveforms of each part during laser oscillation. The control circuit 62 turns on the flash lamp 52 at time t1 (a). The control circuit 62 applies the first voltage to the first Q switch 58 (b) before turning on the flash lamp 52, and sets the applied voltage to the second Q switch 60 to 0 V (third voltage). (C). The time for applying the first voltage to the first Q switch 58 may be a time slightly before the time t1. Alternatively, the first voltage may be continuously applied to the first Q switch 58 after the previous pulse laser beam emission. By applying a first voltage to the first Q switch 58, the first Q switch 58 acts as a quarter wavelength plate. Further, by not applying a voltage to the second Q switch 60, the polarization state of the light passing through the second Q switch 60 does not change.
　時刻ｔ１にレーザロッド５１が励起されると、レーザロッド５１からはｐ偏光の光が出射する。しかしながら、レーザロッド５１から第１のミラー５３方向に出射した光は、１／４波長板として働く第１のＱスイッチ５８を往復して偏光方向が９０°回転し、偏光子５９を通過することができず、レーザロッド５１に帰還しない。また、レーザロッド５１から第２のミラー５４方向に出射した光のうち、波長７５５ｎｍの光は、１／４波長板６１を往復して偏光方向が９０°回転し、所定の偏光軸を持つレーザロッド５１に帰還しない。従って、第１の共振器及び第２の共振器のＱ値は低Ｑ状態となり、第１の共振器及び第２の共振器は発振しない。 When the laser rod 51 is excited at time t1, p-polarized light is emitted from the laser rod 51. However, the light emitted from the laser rod 51 in the direction of the first mirror 53 reciprocates through the first Q switch 58 that functions as a quarter-wave plate, and the polarization direction rotates by 90 ° and passes through the polarizer 59. Cannot be returned to the laser rod 51. Of the light emitted from the laser rod 51 in the direction of the second mirror 54, the light having a wavelength of 755 nm reciprocates through the quarter-wave plate 61 and the polarization direction is rotated by 90 °, and the laser has a predetermined polarization axis. It does not return to the rod 51. Therefore, the Q values of the first resonator and the second resonator are in a low Q state, and the first resonator and the second resonator do not oscillate.
　制御回路６２は、時刻ｔ２に第１のＱスイッチ５８への印加電圧を第１の電圧から０Ｖ（第２の電圧）に変化させる（ｂ）。このとき、第２のＱスイッチ６０への印加電圧は０Ｖのまま変化させない（ｃ）。第１のＱスイッチ５８への印加電圧を０Ｖに変化させることにより、第１の共振器のＱ値は低Ｑ状態から高Ｑ状態へと変化する。一方で、第２の共振器のＱ値は低Ｑ状態に保たれる。第１の共振器のみが高Ｑ状態となることにより、波長８００ｎｍのレーザ発振が起こり、第１のミラー５３から、波長８００ｎｍのパルスレーザ光が出射する（ｄ）。 The control circuit 62 changes the voltage applied to the first Q switch 58 from the first voltage to 0 V (second voltage) at time t2 (b). At this time, the applied voltage to the second Q switch 60 remains 0 V and is not changed (c). By changing the voltage applied to the first Q switch 58 to 0 V, the Q value of the first resonator changes from the low Q state to the high Q state. On the other hand, the Q value of the second resonator is kept in a low Q state. When only the first resonator enters the high Q state, laser oscillation with a wavelength of 800 nm occurs, and pulse laser light with a wavelength of 800 nm is emitted from the first mirror 53 (d).
　制御回路６２は、波長８００ｎｍのパルスレーザ光の出射後、時刻ｔ３にフラッシュランプ５２を点灯する（ａ）。制御回路６２は、時刻ｔ３よりも前の時刻に第１のＱスイッチ５８に第１の電圧を印加しており（ｂ）、第１の共振器及び第２の共振器のＱ値は低Ｑ状態となっている。制御回路６２は、時刻ｔ４に、第１のＱスイッチ５８の印加電圧を第１の電圧から０Ｖに変化させ、第２のＱスイッチ６０の印加電圧を０Ｖから第４の電圧に変化させる。第１のＱスイッチ５８の印加電圧と第２のＱスイッチ６０の印加電圧とを同時に変化させるか、又は第２のＱスイッチ６０の印加電圧を先に変化させてから第１のＱスイッチ５８の印加電圧を変化させると、波長８００ｎｍと波長７５５ｎｍとのうち、レーザ利得が高い波長７５５ｎｍが発振し、第１のミラー５３から、波長７５５ｎｍのパルスレーザ光が出射する（ｄ）。 The control circuit 62 turns on the flash lamp 52 at time t3 after emitting pulsed laser light having a wavelength of 800 nm (a). The control circuit 62 applies the first voltage to the first Q switch 58 at a time before time t3 (b), and the Q values of the first resonator and the second resonator are low Q. It is in a state. At time t4, the control circuit 62 changes the applied voltage of the first Q switch 58 from the first voltage to 0V, and changes the applied voltage of the second Q switch 60 from 0V to the fourth voltage. The applied voltage of the first Q switch 58 and the applied voltage of the second Q switch 60 are changed simultaneously, or the applied voltage of the second Q switch 60 is changed first and then the first Q switch 58 When the applied voltage is changed, a wavelength 755 nm having a high laser gain of the wavelength 800 nm and the wavelength 755 nm oscillates, and pulse laser light having a wavelength 755 nm is emitted from the first mirror 53 (d).
　なお、第１のＱ値変更部５６及び第２のＱ値変更部５７は、第１の共振器及び第２の共振器が共に高Ｑ状態、第１の共振器及び第２の共振器が共に低Ｑ状態、及び第１の共振器が高Ｑ状態かつ第２の共振器が低Ｑ状態の３つの状態を切り替えられればよく、第１のＱ値変更部５６及び第２のＱ値変更部５７の具体的な構成は上記したものには限定されない。例えば第１のＱ値変更部５６を、第２のＱ値変更部５７と同様に、ポッケルスセルと１／４波長板とを組み合わせた構成としてもよいし、第２のＱ値変更部５７を、第１のＱ値変更部５６と同様に、ポッケルスセルと偏光子とを組み合わせた構成としてもよい。 The first Q value changing unit 56 and the second Q value changing unit 57 are such that the first resonator and the second resonator are both in the high Q state, and the first resonator and the second resonator are in the high Q state. It is only necessary to switch between the low Q state, the first resonator in the high Q state, and the second resonator in the low Q state, and the first Q value change unit 56 and the second Q value change. The specific configuration of the unit 57 is not limited to the above. For example, the first Q value changing unit 56 may be configured by combining a Pockels cell and a quarter-wave plate in the same manner as the second Q value changing unit 57, or the second Q value changing unit 57 may be Similarly to the first Q value changing unit 56, a Pockels cell and a polarizer may be combined.
　第１のＱ値変更部５６を、ポッケルスセル（第１のＱスイッチ）と１／４波長板とによって構成した場合、１／４波長板は、第１のミラー５３とポッケルスセルとの間に配置される。ポッケルスセルは、印加電圧がＱスイッチオフに対応した第１の電圧のとき第１の共振器及び第２の共振器を低Ｑ状態にし、印加電圧がＱスイッチオンに対応した第２の電圧のとき第１の共振器及び第２の共振器を高Ｑ状態にする。この場合の第１の電圧は例えば０Ｖであり、第２の電圧は例えばポッケルスセルが１／４波長板として働く電圧である。第２の電圧は、正の電圧であっても負の電圧であってもよい。第２の電圧の絶対値は、第１の電圧の絶対値よりも大きい。ここで、ポッケルスセルが１／４波長板として働く電圧は波長に依存して変化するため、Ｑスイッチオンに対応した第２の電圧は、波長８００ｎｍの発振時と波長７５５ｎｍの発振時とで異なる。すなわち、波長８００ｎｍの発振時と波長７５５ｎｍの発振時とで、ポッケルスセルへの印加電圧が異なる。このため、ポッケルスセルへの印加電圧０ＶがＱスイッチオンに対応する構成に比べて、Ｑスイッチのドライブ回路やその制御がやや複雑になる。従って、第１のＱ値変更部５６は、図２に示したように、印加電圧０ＶがＱスイッチオンに対応する構成とすることが好ましい。 When the first Q value changing unit 56 is configured by a Pockels cell (first Q switch) and a quarter wavelength plate, the quarter wavelength plate is interposed between the first mirror 53 and the Pockels cell. Be placed. The Pockels cell sets the first resonator and the second resonator to a low Q state when the applied voltage is a first voltage corresponding to Q switch off, and the applied voltage is a second voltage corresponding to the Q switch on. Sometimes the first resonator and the second resonator are brought into a high Q state. In this case, the first voltage is 0 V, for example, and the second voltage is a voltage at which the Pockels cell works as a quarter-wave plate, for example. The second voltage may be a positive voltage or a negative voltage. The absolute value of the second voltage is greater than the absolute value of the first voltage. Here, since the voltage at which the Pockels cell functions as a quarter-wave plate varies depending on the wavelength, the second voltage corresponding to the Q switch-on is different between the oscillation at the wavelength of 800 nm and the oscillation at the wavelength of 755 nm. . That is, the voltage applied to the Pockels cell differs depending on whether the wavelength is 800 nm or 755 nm. For this reason, the drive circuit of the Q switch and its control are somewhat complicated as compared with the configuration in which the applied voltage 0 V to the Pockels cell corresponds to the Q switch on. Therefore, as shown in FIG. 2, the first Q value changing unit 56 is preferably configured such that the applied voltage 0 V corresponds to the Q switch on.
　第２のＱ値変更部５７については、ポッケルスセルに１／４波長板として働く電圧を印加することにより第２の共振器を高Ｑ状態とする構成が好ましい。この構成では、波長７５５ｎｍの発振時にのみポッケルスセルに１／４波長板として働く電圧を印加すればよいため、高電圧を印加する時間が短くて済む。第２のＱ値変更部５７を、第１のＱ値変更部５６と同様な構成した場合は、Ｑスイッチオフに対応した電圧が１／４波長板として働く電圧であるため、ポッケルスセルに高電圧を印加する時間が長くなり、マイグレーションによるポッケルスセルの電極部の劣化が進行する。第２のＱ値変更部５７は、波長７５５ｎｍの光のみを制御すればよいため、１／４波長板として働かせるときに波長に応じて異なる電圧を印加する必要はない。 The second Q value changing unit 57 preferably has a configuration in which the second resonator is placed in a high Q state by applying a voltage acting as a quarter wavelength plate to the Pockels cell. In this configuration, it is only necessary to apply a voltage that acts as a quarter-wave plate to the Pockels cell only when oscillating at a wavelength of 755 nm. Therefore, the time for applying a high voltage is short. When the second Q value changing unit 57 is configured in the same manner as the first Q value changing unit 56, the voltage corresponding to the Q switch-off is a voltage that acts as a quarter wavelength plate. The time for applying the voltage becomes long, and the deterioration of the Pockels cell electrode portion due to migration proceeds. Since the second Q value changing unit 57 only needs to control light having a wavelength of 755 nm, it is not necessary to apply a different voltage depending on the wavelength when operating as a quarter wavelength plate.
　第１のミラー５３、第２のミラー５４、及び第３のミラー５５のうちの少なくとも１つを、光軸方向に沿って移動可能としてもよい。３つのミラーのうちの少なくとも１つを光軸方向に沿って移動可能とすることにより、ミラー間の相対間隔が調整可能であり、第１の共振器の共振器長又は第２の共振器の共振器の共振器長が変更可能である。第１の共振器の共振器長及び第２の共振器の共振器長の少なくとも一方を変更することにより、波長８００ｎｍのパルスレーザ光のパルス幅及び波長７５５ｎｍのパルスレーザ光のパルス幅の少なくとも一方を変更することができる。この仕組みにより、例えば、ミラーの反射率によるパルス幅の変化を補正することもできる。 At least one of the first mirror 53, the second mirror 54, and the third mirror 55 may be movable along the optical axis direction. By making at least one of the three mirrors movable along the optical axis direction, the relative distance between the mirrors can be adjusted, and the resonator length of the first resonator or the second resonator can be adjusted. The resonator length of the resonator can be changed. By changing at least one of the resonator length of the first resonator and the resonator length of the second resonator, at least one of the pulse width of the pulse laser beam having a wavelength of 800 nm and the pulse width of the pulse laser beam having a wavelength of 755 nm. Can be changed. With this mechanism, for example, a change in pulse width due to the reflectance of the mirror can be corrected.
　図１に戻り、レーザ光源ユニット１３から出射したレーザ光は、例えば光ファイバなどの導光手段を用いてプローブ１１まで導光され、プローブ１１から被検体に向けて照射される。レーザ光の照射位置は特に限定されず、プローブ１１以外の場所からレーザ光の照射を行ってもよい。被検体内では、光吸収体が照射されたレーザ光のエネルギーを吸収することにより超音波（光音響波）が生じる。プローブ１１は、超音波検出器を含む。プローブ１１は、例えば一次元的に配列された複数の超音波検出器素子（超音波振動子）を有し、その一次元配列された超音波振動子により、被検体内からの音響波（光音響信号）を検出する。 Returning to FIG. 1, the laser light emitted from the laser light source unit 13 is guided to the probe 11 using light guide means such as an optical fiber, and is irradiated from the probe 11 toward the subject. The irradiation position of the laser beam is not particularly limited, and the laser beam may be irradiated from a place other than the probe 11. In the subject, an ultrasonic wave (photoacoustic wave) is generated by absorbing the energy of the laser beam irradiated by the light absorber. The probe 11 includes an ultrasonic detector. The probe 11 has, for example, a plurality of ultrasonic detector elements (ultrasonic transducers) arranged in a one-dimensional manner, and an acoustic wave (light) from within the subject by the ultrasonic transducers arranged in a one-dimensional manner. Sound signal).
　超音波ユニット１２は、受信回路２１、ＡＤ（Analog Digital）変換手段２２、受信メモリ２３、複素数化手段２４、光音響画像再構成手段２５、位相情報抽出手段２６、強度情報抽出手段２７、検波・対数変換手段２８、光音響画像構築手段２９、トリガ制御回路３０、及び制御手段３１を有する。受信回路２１は、プローブ１１が検出した光音響信号を受信する。ＡＤ変換手段２２は検出手段であり、受信回路２１が受信した光音響信号をサンプリングし、デジタルデータである光音響データを生成する。ＡＤ変換手段２２は、ＡＤクロック信号に同期して、所定のサンプリング周期で光音響信号のサンプリングを行う。 The ultrasonic unit 12 includes a reception circuit 21, an AD (Analog / Digital) conversion unit 22, a reception memory 23, a complex number conversion unit 24, a photoacoustic image reconstruction unit 25, a phase information extraction unit 26, an intensity information extraction unit 27, a detection / It has logarithmic conversion means 28, photoacoustic image construction means 29, trigger control circuit 30, and control means 31. The receiving circuit 21 receives the photoacoustic signal detected by the probe 11. The AD conversion unit 22 is a detection unit that samples the photoacoustic signal received by the receiving circuit 21 and generates photoacoustic data that is digital data. The AD conversion means 22 samples the photoacoustic signal at a predetermined sampling period in synchronization with the AD clock signal.
　ＡＤ変換手段２２は、光音響データを受信メモリ２３に格納する。ＡＤ変換手段２２は、レーザ光源ユニット１３から出射されるパルスレーザ光の各波長に対応した光音響データを受信メモリ２３に格納する。つまり、ＡＤ変換手段２２は、被検体に第１の波長のパルスレーザ光が照射されたときにプローブ１１によって検出された光音響信号をサンプリングした第１の光音響データと、第２の波長のパルスレーザ光が照射されたときにプローブ１１によって検出された光音響信号をサンプリングした第２の光音響データとを、受信メモリ２３に格納する。 The AD conversion means 22 stores the photoacoustic data in the reception memory 23. The AD conversion means 22 stores photoacoustic data corresponding to each wavelength of the pulsed laser light emitted from the laser light source unit 13 in the reception memory 23. That is, the AD conversion means 22 has the first photoacoustic data obtained by sampling the photoacoustic signal detected by the probe 11 when the subject is irradiated with the pulse laser beam having the first wavelength, and the second wavelength. The second photoacoustic data obtained by sampling the photoacoustic signal detected by the probe 11 when the pulse laser beam is irradiated is stored in the reception memory 23.
　複素数化手段２４は、受信メモリ２３から第１の光音響データと第２の光音響データとを読み出し、何れか一方を実部、他方を虚部とした複素数データを生成する。以下では、複素数化手段２４が、第１の光音響データを虚部とし、第２の光音響データを実部とした複素数データを生成するものとして説明する。 The complex number conversion means 24 reads the first photoacoustic data and the second photoacoustic data from the reception memory 23, and generates complex number data in which one is a real part and the other is an imaginary part. In the following description, it is assumed that the complex number converting means 24 generates complex number data having the first photoacoustic data as an imaginary part and the second photoacoustic data as a real part.
　光音響画像再構成手段２５は、複素数化手段２４から複素数データを入力する。光音響画像再構成手段２５は、入力された複素数データから、フーリエ変換法（ＦＴＡ法）により画像再構成を行う。フーリエ変換法による画像再構成には、例えば文献”Photoacoustic Image Reconstruction-A Quantitative Analysis”Jonathan I.Sperl et al. SPIE-OSA
Vol.6631 663103　等に記載されている従来公知の方法を適用することができる。光音響画像再構成手段２５は、再構成画像を示すフーリエ変換のデータを位相情報抽出手段２６と強度情報抽出手段２７とに入力する。 The photoacoustic image reconstruction unit 25 receives complex number data from the complex number conversion unit 24. The photoacoustic image reconstruction means 25 performs image reconstruction from the input complex number data by the Fourier transform method (FTA method). For image reconstruction using the Fourier transform method, for example, the document “Photoacoustic Image Reconstruction-A Quantitative Analysis” Jonathan I. Sperl et al. SPIE-OSA
Conventionally known methods described in Vol.6631, 663103, etc. can be applied. The photoacoustic image reconstruction unit 25 inputs Fourier transform data indicating the reconstructed image to the phase information extraction unit 26 and the intensity information extraction unit 27.
　位相情報抽出手段２６は、各波長に対応した光音響データ間の相対的な信号強度の大小関係を抽出する。本実施形態では、位相情報抽出手段２６は、光音響画像再構成手段２５によって再構成された再構成画像を入力データとし、複素数データである入力データから、実部と虚部とを比較したときに、相対的に、どちらがどれくらい大きいかを示す位相情報を生成する。位相情報抽出手段２６は、例えば複素数データがＸ＋ｉＹによって表わされるとき、θ＝ｔａｎ－１（Ｙ／Ｘ）を位相情報として生成する。なお、Ｘ＝０の場合はθ＝９０°とする。実部を構成する第２の光音響データ（Ｘ）と虚部を構成する第１の光音響データ（Ｙ）とが等しいとき、位相情報はθ＝４５°となる。位相情報は、相対的に第２の光音響データが大きいほどθ＝０°に近づいていき、第１の光音響データが大きいほどθ＝９０°に近づいていく。 The phase information extraction means 26 extracts the relative magnitude of the relative signal intensity between the photoacoustic data corresponding to each wavelength. In the present embodiment, the phase information extraction unit 26 uses the reconstructed image reconstructed by the photoacoustic image reconstruction unit 25 as input data, and compares the real part and the imaginary part from the input data that is complex data. In comparison, phase information indicating which is relatively large is generated. The phase information extraction unit 26 generates θ = tan −1 (Y / X) as phase information, for example, when complex number data is represented by X + iY. When X = 0, θ = 90 °. When the second photoacoustic data (X) constituting the real part is equal to the first photoacoustic data (Y) constituting the imaginary part, the phase information is θ = 45 °. The phase information approaches θ = 0 ° as the second photoacoustic data is relatively large, and approaches θ = 90 ° as the first photoacoustic data increases.
　強度情報抽出手段２７は、各波長に対応した光音響データに基づいて信号強度を示す強度情報を生成する。本実施形態では、強度情報抽出手段２７は、光音響画像再構成手段２５によって再構成された再構成画像を入力データとし、複素数データである入力データから、強度情報を生成する。強度情報抽出手段２７は、例えば複素数データがＸ＋ｉＹによって表わされるとき、（Ｘ２＋Ｙ２）１／２を、強度情報として抽出する。検波・対数変換手段２８は、強度情報抽出手段２７によって抽出された強度情報を示すデータの包絡線を生成し、次いでその包絡線を対数変換してダイナミックレンジを広げる。 The intensity information extraction unit 27 generates intensity information indicating the signal intensity based on the photoacoustic data corresponding to each wavelength. In the present embodiment, the intensity information extraction unit 27 uses the reconstructed image reconstructed by the photoacoustic image reconstruction unit 25 as input data, and generates intensity information from the input data that is complex number data. For example, when the complex number data is represented by X + iY, the intensity information extraction unit 27 extracts (X 2 + Y 2 ) 1/2 as the intensity information. The detection / logarithm conversion means 28 generates an envelope of data indicating the intensity information extracted by the intensity information extraction means 27, and then logarithmically converts the envelope to widen the dynamic range.
　光音響画像構築手段２９は、位相情報抽出手段２６から位相情報を入力し、検波・対数変換手段２８から検波・対数変換処理後の強度情報を入力する。光音響画像構築手段２９は、入力された位相情報と強度情報とに基づいて、光吸収体の分布画像である光音響画像を生成する。光音響画像構築手段２９は、例えば入力された強度情報に基づいて、光吸収体の分布画像における各画素の輝度（階調値）を決定する。また、光音響画像構築手段２９は、例えば位相情報に基づいて、光吸収体の分布画像における各画素の色（表示色）を決定する。具体的には、光音響画像構築手段２９は、例えば位相０°から９０°の範囲を所定の色に対応させたカラーマップを用いて、入力された位相情報に基づいて各画素の色を決定する。 The photoacoustic image construction unit 29 receives the phase information from the phase information extraction unit 26 and the intensity information after the detection / logarithmic conversion processing from the detection / logarithmic conversion unit 28. The photoacoustic image construction unit 29 generates a photoacoustic image that is a distribution image of the light absorber based on the input phase information and intensity information. For example, the photoacoustic image construction unit 29 determines the luminance (gradation value) of each pixel in the distribution image of the light absorber based on the input intensity information. Moreover, the photoacoustic image construction means 29 determines the color (display color) of each pixel in the light absorber distribution image based on, for example, phase information. Specifically, the photoacoustic image construction unit 29 determines the color of each pixel based on the input phase information using, for example, a color map in which a phase range of 0 ° to 90 ° is associated with a predetermined color. To do.
　ここで、位相０°から４５°の範囲は、第２の光音響データが第１の光音響データよりも大きい範囲であるため、光音響信号の発生源は、波長７９８ｎｍに対する吸収よりも波長７５５ｎｍに対する吸収の方が大きい脱酸素化ヘモグロビンを主に含む血液が流れている静脈であると考えられる。一方、位相４５°から９０°の範囲は、第１の光音響データが第２の光音響データよりも大きい範囲であるため、光音響信号の発生源は、波長７９８ｎｍに対する吸収よりも波長７５５ｎｍに対する吸収の方が小さい酸素化ヘモグロビンを主に含む血液が流れている動脈であると考えられる。 Here, the range of the phase from 0 ° to 45 ° is a range in which the second photoacoustic data is larger than the first photoacoustic data. Therefore, the source of the photoacoustic signal is 755 nm in wavelength rather than absorption for the wavelength of 798 nm. It is considered that this is a vein through which blood mainly containing deoxygenated hemoglobin flows. On the other hand, since the range of 45 ° to 90 ° is a range in which the first photoacoustic data is larger than the second photoacoustic data, the source of the photoacoustic signal is for the wavelength 755 nm rather than the absorption for the wavelength 798 nm. It is considered to be an artery through which blood mainly containing oxygenated hemoglobin is flowing.
　そこで、カラーマップとして、例えば位相が０°が青色で、位相が４５°に近づくに連れて無色（白色）になるように色が徐々に変化すると共に、位相９０°が赤色で、位相が４５°に近づくに連れて白色になるように色が徐々に変化するようなカラーマップを用いる。この場合、光音響画像上に、動脈に対応した部分を赤色によって表わし、静脈に対応した部分を青色によって表わすことができる。強度情報を用いずに、階調値は一定として、位相情報に従って動脈に対応した部分と静脈に対応した部分との色分けを行うだけでもよい。画像表示手段１４は、光音響画像構築手段２９が生成した光音響画像を表示画面上に表示する。 Therefore, as a color map, for example, the phase gradually changes so that the phase is 0 ° in blue and the phase becomes colorless (white) as the phase approaches 45 °, and the phase 90 ° is red and the phase is 45. Use a color map that gradually changes its color to become white as it approaches °. In this case, on the photoacoustic image, the portion corresponding to the artery can be represented in red, and the portion corresponding to the vein can be represented in blue. Instead of using the intensity information, the gradation value may be constant and only the color classification of the portion corresponding to the artery and the portion corresponding to the vein may be performed according to the phase information. The image display means 14 displays the photoacoustic image generated by the photoacoustic image construction means 29 on the display screen.
　制御手段３１は、超音波ユニット１２内の各部の制御を行う。トリガ制御回路３０は、レーザ光源ユニット１３に、フラッシュランプ５２（図２）の発光を制御するためのフラッシュランプトリガ信号を出力する。レーザ光源ユニット１３の制御回路６２は、フラッシュランプトリガ信号を受けるとフラッシュランプ５２を点灯し、フラッシュランプ５２からレーザロッド５１に励起光を照射させる。トリガ制御回路３０は、フラッシュランプトリガ信号の出力後、制御回路６２にＱスイッチトリガ信号を出力する。制御回路６２は、発振波長が８００ｎｍのときは第１の共振器のＱ値を低Ｑ状態から高Ｑ状態に変化させる。発振波長が７５５ｎｍのときは第１の共振器及び第２の共振器のＱ値を低Ｑ状態から高Ｑ状態に変化させる。 The control means 31 controls each part in the ultrasonic unit 12. The trigger control circuit 30 outputs a flash lamp trigger signal for controlling the light emission of the flash lamp 52 (FIG. 2) to the laser light source unit 13. When receiving the flash lamp trigger signal, the control circuit 62 of the laser light source unit 13 turns on the flash lamp 52 and irradiates the laser rod 51 with excitation light from the flash lamp 52. The trigger control circuit 30 outputs a Q switch trigger signal to the control circuit 62 after outputting the flash lamp trigger signal. The control circuit 62 changes the Q value of the first resonator from the low Q state to the high Q state when the oscillation wavelength is 800 nm. When the oscillation wavelength is 755 nm, the Q values of the first resonator and the second resonator are changed from the low Q state to the high Q state.
　トリガ制御回路３０は、Ｑスイッチトリガ信号のタイミング、すなわちパルスレーザ光の出射タイミングに合わせて、ＡＤ変換手段２２にサンプリングトリガ信号（ＡＤトリガ信号）を出力する。ＡＤ変換手段２２は、サンプリングトリガ信号にと基づいて光音響信号のサンプリングを開始する。 The trigger control circuit 30 outputs a sampling trigger signal (AD trigger signal) to the AD conversion means 22 in accordance with the timing of the Q switch trigger signal, that is, the emission timing of the pulse laser beam. The AD conversion unit 22 starts sampling of the photoacoustic signal based on the sampling trigger signal.
　次いで動作手順について説明する。図９は、光音響計測装置１０の動作手順を示す。トリガ制御回路３０（図１）は、光音響信号の受信準備が整うと、第１の波長（８００ｎｍ）のパルスレーザ光を出射させるために、レーザ光源ユニット１３にフラッシュランプトリガ信号を出力する（ステップＳ１）。レーザ光源ユニット１３の制御回路６２（図２）は、フラッシュランプトリガ信号を受け取る前に、第１のＱスイッチ５８に第１の電圧を印加し、第１の共振器及び第２の共振器を低Ｑ状態にしている。制御回路６２は、フラッシュランプトリガ信号に応答してフラッシュランプ５２を点灯し、レーザロッド５１を励起させる（ステップＳ２）。 Next, the operation procedure will be described. FIG. 9 shows an operation procedure of the photoacoustic measurement apparatus 10. When the trigger control circuit 30 (FIG. 1) is ready to receive the photoacoustic signal, the trigger control circuit 30 (FIG. 1) outputs a flash lamp trigger signal to the laser light source unit 13 in order to emit pulsed laser light having the first wavelength (800 nm) ( Step S1). Before receiving the flash lamp trigger signal, the control circuit 62 (FIG. 2) of the laser light source unit 13 applies the first voltage to the first Q switch 58, and turns on the first resonator and the second resonator. Low Q state. The control circuit 62 turns on the flash lamp 52 in response to the flash lamp trigger signal and excites the laser rod 51 (step S2).
　トリガ制御回路３０は、フラッシュランプトリガ信号の出力後、レーザロッド５１が十分に励起された後にＱスイッチトリガ信号をレーザ光源ユニット１３に出力する。制御回路６２は、第１のＱスイッチ５８の印加電圧を第１の電圧から０Ｖに変化させる（ステップＳ３）。このとき制御回路６２は、第２のＱスイッチ６０には０Ｖを印加しており、第１の共振器は高Ｑ状態、第２の共振器は低Ｑ状態に制御される。第１の共振器及び第２の共振器のうち、第１の共振器のみが高Ｑ状態となることにより、レーザ光源ユニット１３は、波長８００ｎｍのパルスレーザ光を出射する。 The trigger control circuit 30 outputs the Q switch trigger signal to the laser light source unit 13 after the laser lamp 51 is sufficiently excited after the output of the flash lamp trigger signal. The control circuit 62 changes the voltage applied to the first Q switch 58 from the first voltage to 0 V (step S3). At this time, the control circuit 62 applies 0 V to the second Q switch 60, and the first resonator is controlled to the high Q state and the second resonator is controlled to the low Q state. Of the first resonator and the second resonator, only the first resonator enters the high Q state, so that the laser light source unit 13 emits pulsed laser light having a wavelength of 800 nm.
　レーザ光源ユニット１３から出射した波長８００ｎｍのパルスレーザ光は、例えばプローブ１１まで導光され、プローブ１１から被検体に照射される。被検体内では、光吸収体が照射されたパルスレーザ光のエネルギーを吸収することにより、光音響信号が発生する。プローブ１１は、被検体内で発生した光音響信号を検出する。プローブ１１によって検出された光音響信号は、受信回路２１にて受信される。 The pulsed laser light having a wavelength of 800 nm emitted from the laser light source unit 13 is guided to, for example, the probe 11 and irradiated from the probe 11 to the subject. In the subject, a photoacoustic signal is generated by absorbing the energy of the pulsed laser light irradiated by the light absorber. The probe 11 detects a photoacoustic signal generated in the subject. The photoacoustic signal detected by the probe 11 is received by the receiving circuit 21.
　トリガ制御回路３０は、Ｑスイッチトリガ信号を出力するタイミングに合わせて、ＡＤ変換手段２２にサンプリングトリガ信号を出力する。ＡＤ変換手段２２は、受信回路２１によって受信された光音響信号を、所定のサンプリング周期でサンプリングする（ステップＳ４）。ＡＤ変換手段２２によってサンプリングされた光音響信号は、受信メモリ２３に第１の光音響データとして格納される。 The trigger control circuit 30 outputs a sampling trigger signal to the AD conversion means 22 in accordance with the timing of outputting the Q switch trigger signal. The AD conversion means 22 samples the photoacoustic signal received by the receiving circuit 21 at a predetermined sampling period (step S4). The photoacoustic signal sampled by the AD conversion means 22 is stored in the reception memory 23 as first photoacoustic data.
　トリガ制御回路３０は、次の光音響信号の受信準備が整うと、第２の波長（７５５ｎｍ）のパルスレーザ光を出射させるために、レーザ光源ユニット１３にフラッシュランプトリガ信号を出力する（ステップＳ５）。制御回路６２は、フラッシュランプトリガ信号を受け取る前に、第１のＱスイッチ５８に第１の電圧を印加し、第１の共振器及び第２の共振器を低Ｑ状態にしている。制御回路６２は、フラッシュランプトリガ信号に応答してフラッシュランプ５２を点灯し、レーザロッド５１を励起させる（ステップＳ６）。 When the trigger control circuit 30 is ready to receive the next photoacoustic signal, the trigger control circuit 30 outputs a flash lamp trigger signal to the laser light source unit 13 in order to emit pulsed laser light having the second wavelength (755 nm) (step S5). ). Before receiving the flash lamp trigger signal, the control circuit 62 applies a first voltage to the first Q switch 58 to bring the first resonator and the second resonator into a low Q state. The control circuit 62 turns on the flash lamp 52 in response to the flash lamp trigger signal, and excites the laser rod 51 (step S6).
　トリガ制御回路３０は、フラッシュランプ５２の点灯後、レーザロッド５１が十分に励起された後にＱスイッチトリガ信号をレーザ光源ユニット１３に出力する。制御回路６２は、第１のＱスイッチ５８の印加電圧を第１の電圧から０Ｖに変化させ、第２のＱスイッチ６０への印加電圧を０Ｖから第４の電圧に変化させる（ステップＳ７）。このとき制御回路６２は、第１のＱスイッチ５８と第２のＱスイッチ６０とにおいて同時に印加電圧を変化させるか、又は、先に第２のＱスイッチ６０の印加電圧を変化させてから第１のＱスイッチ５８の印加電圧を変化させる。第１のＱスイッチ５８及び第２のＱスイッチ６０の印加電圧を変化させることにより、第１の共振器及び第２の共振器は共に高Ｑ状態となる。双方の共振器が高Ｑ状態のときレーザ利得が高い波長７５５ｎｍで発振し、レーザ光源ユニット１３は、波長７５５ｎｍのパルスレーザ光を出射する。 The trigger control circuit 30 outputs a Q switch trigger signal to the laser light source unit 13 after the flash lamp 52 is lit and the laser rod 51 is sufficiently excited. The control circuit 62 changes the voltage applied to the first Q switch 58 from the first voltage to 0V, and changes the voltage applied to the second Q switch 60 from 0V to the fourth voltage (step S7). At this time, the control circuit 62 changes the applied voltage in the first Q switch 58 and the second Q switch 60 at the same time, or first changes the applied voltage of the second Q switch 60 and then changes the first applied voltage. The applied voltage of the Q switch 58 is changed. By changing the voltage applied to the first Q switch 58 and the second Q switch 60, both the first resonator and the second resonator are in a high Q state. When both resonators are in a high Q state, the laser gain is oscillated at a wavelength of 755 nm, and the laser light source unit 13 emits a pulsed laser beam having a wavelength of 755 nm.
　レーザ光源ユニット１３から出射した波長７５５ｎｍのパルスレーザ光は、例えばプローブ１１まで導光され、プローブ１１から被検体に照射される。被検体内では、光吸収体が照射されたパルスレーザ光のエネルギーを吸収することにより、光音響信号が発生する。プローブ１１は、被検体内で発生した光音響信号を検出する。プローブ１１によって検出された光音響信号は、受信回路２１にて受信される。 The pulsed laser beam having a wavelength of 755 nm emitted from the laser light source unit 13 is guided to, for example, the probe 11 and irradiated from the probe 11 to the subject. In the subject, a photoacoustic signal is generated by absorbing the energy of the pulsed laser light irradiated by the light absorber. The probe 11 detects a photoacoustic signal generated in the subject. The photoacoustic signal detected by the probe 11 is received by the receiving circuit 21.
　トリガ制御回路３０は、Ｑスイッチトリガ信号を出力するタイミングに合わせて、ＡＤ変換手段２２にサンプリングトリガ信号を出力する。ＡＤ変換手段２２は、受信回路２１によって受信された光音響信号を、所定のサンプリング周期でサンプリングする（ステップＳ８８）。ＡＤ変換手段２２によってサンプリングされた光音響信号は、受信メモリ２３に第２の光音響データとして格納される。 The trigger control circuit 30 outputs a sampling trigger signal to the AD conversion means 22 in accordance with the timing of outputting the Q switch trigger signal. The AD conversion means 22 samples the photoacoustic signal received by the receiving circuit 21 at a predetermined sampling period (step S88). The photoacoustic signal sampled by the AD conversion means 22 is stored in the reception memory 23 as second photoacoustic data.
　第１及び第２の光音響データが受信メモリに格納されることにより、１フレーム分の光音響画像の生成に必要なデータが揃う。なお、光音響画像を生成する範囲が複数の部分領域に分割されているような場合は、部分領域ごとに、ステップＳ１からＳ８までの処理を実行すればよい。 By storing the first and second photoacoustic data in the reception memory, data necessary for generating a photoacoustic image for one frame is prepared. In addition, when the range which produces | generates a photoacoustic image is divided | segmented into the some partial area | region, what is necessary is just to perform the process from step S1 to S8 for every partial area | region.
　複素数化手段２４は、受信メモリ２３から第１の光音響データと第２の光音響データとを読み出し、第１の光音響画像データを虚部とし、第２の光音響画像データを実部とした複素数データを生成する（ステップＳ９）。光音響画像再構成手段２５は、ステップＳ９において複素数化された複素数データから、フーリエ変換法（ＦＴＡ法）により画像再構成を行う（ステップＳ１０）。 The complex numbering means 24 reads the first photoacoustic data and the second photoacoustic data from the reception memory 23, sets the first photoacoustic image data as an imaginary part, and sets the second photoacoustic image data as a real part. The complex data is generated (step S9). The photoacoustic image reconstruction means 25 performs image reconstruction from the complex number data converted into the complex number in step S9 by a Fourier transform method (FTA method) (step S10).
　位相情報抽出手段２６は、再構成された複素数データ（再構成画像）から位相情報を抽出する（ステップＳ１１）。位相情報抽出手段２６は、例えば再構成された複素数データがＸ＋ｉＹによって表わされるとき、θ＝ｔａｎ－１（Ｙ／Ｘ）を位相情報として抽出する（ただし、Ｘ＝０の場合はθ＝９０°）。強度情報抽出手段２７は、再構成された複素数データから強度情報を抽出する（ステップＳ１２）。強度情報抽出手段２７は、例えば再構成された複素数データがＸ＋ｉＹによって表わされるとき、（Ｘ２＋Ｙ２）１／２を強度情報として抽出する。 The phase information extraction unit 26 extracts phase information from the reconstructed complex number data (reconstructed image) (step S11). For example, when the reconstructed complex data is represented by X + iY, the phase information extraction unit 26 extracts θ = tan −1 (Y / X) as phase information (provided that θ = 90 ° when X = 0). ). The intensity information extraction means 27 extracts intensity information from the reconstructed complex number data (step S12). For example, when the reconstructed complex number data is represented by X + iY, the intensity information extraction unit 27 extracts (X 2 + Y 2 ) 1/2 as the intensity information.
　検波・対数変換手段２８は、ステップＳ１２において抽出された強度情報に対して検波・対数変換処理を施す。光音響画像構築手段２９は、ステップＳ１１において抽出された位相情報と、ステップＳ１２において抽出された強度情報に対して検波・対数変換処理を施したものとに基づいて、光音響画像を生成する（ステップＳ１３）。光音響画像構築手段２９は、例えば強度情報に基づいて光吸収体の分布画像における各画素の輝度（階調値）を決定し、位相情報に基づいて各画素の色を決定することにより、光音響画像を生成する。生成された光音響画像は、画像表示手段１４に表示される。 The detection / logarithmic conversion means 28 performs detection / logarithmic conversion processing on the intensity information extracted in step S12. The photoacoustic image construction means 29 generates a photoacoustic image based on the phase information extracted in step S11 and the intensity information extracted in step S12 subjected to detection / logarithmic conversion processing ( Step S13). For example, the photoacoustic image construction unit 29 determines the luminance (gradation value) of each pixel in the distribution image of the light absorber based on the intensity information, and determines the color of each pixel based on the phase information. An acoustic image is generated. The generated photoacoustic image is displayed on the image display means 14.
　なお、上記実施形態では波長８００ｎｍの光と波長７５５ｎｍの光とを交互に被検体に照射することとしているが、これには限定されない。波長８００ｎｍの発振の繰り返し周波数を、波長７５５ｎｍの発振の繰り返し周波数よりも高くしてもよい。例えばレーザ光源ユニット１３から波長７５５ｎｍの光を出射した後、波長８００ｎｍの光を複数回続けて出射してもよい。この場合、波長８００ｎｍの光に対する光音響信号を複数回取得し、複数回の光音響信号に対して加算平均などの処理を行ってもよい。そのようにすることにより、波長８００ｎｍの光音響画像の信号対雑音比を高めることができる。結果として、波長７５５ｎｍの光に対する光音響信号とのコントラスト差を利用して得られる動脈／静脈の分離描出の画質を向上でき、或いは酸素飽和度の演算精度を向上できる。 In the above embodiment, the subject is irradiated with light having a wavelength of 800 nm and light having a wavelength of 755 nm alternately. However, the present invention is not limited to this. The repetition frequency of oscillation with a wavelength of 800 nm may be higher than the repetition frequency of oscillation with a wavelength of 755 nm. For example, after emitting light having a wavelength of 755 nm from the laser light source unit 13, light having a wavelength of 800 nm may be continuously emitted a plurality of times. In this case, a photoacoustic signal for light having a wavelength of 800 nm may be acquired a plurality of times, and a process such as addition averaging may be performed on the plurality of photoacoustic signals. By doing so, the signal-to-noise ratio of a photoacoustic image having a wavelength of 800 nm can be increased. As a result, it is possible to improve the image quality of the articulated / venous separation obtained by using the contrast difference between the light of wavelength 755 nm and the photoacoustic signal, or to improve the calculation accuracy of the oxygen saturation.
　本実施形態では、第１のミラー５３と第２のミラー５４とにより波長８００ｎｍの光を発振する第１の共振器を構成し、第１のミラー５３と第３のミラー５５とにより波長７５５ｎｍの光を発振する第２の共振器を構成する。レーザロッド５１は波長８００ｎｍと波長７５５ｎｍとに発光波長を有し、波長７５５ｎｍの発光効率は波長８００ｎｍの発光効率よりも高い。第１の共振器と第２の共振器とに共通の光路上に第１のＱ値変更部５６を配置し、第２のミラー５４と第３のミラー５５との間に第２のＱ値変更部５７を配置する。第１のＱ値変更部５６を駆動することにより、第１の共振器及び第２の共振器のＱ値を制御することができる。また、第２のＱ値変更部５７を駆動することにより、第１の共振器及び第２の共振器のうち第２の共振器のＱ値のみを制御することができる。 In the present embodiment, the first mirror 53 and the second mirror 54 constitute a first resonator that oscillates light having a wavelength of 800 nm, and the first mirror 53 and the third mirror 55 have a wavelength of 755 nm. A second resonator that oscillates light is formed. The laser rod 51 has emission wavelengths at a wavelength of 800 nm and a wavelength of 755 nm, and the emission efficiency at a wavelength of 755 nm is higher than the emission efficiency at a wavelength of 800 nm. A first Q value changing unit 56 is disposed on an optical path common to the first resonator and the second resonator, and a second Q value is provided between the second mirror 54 and the third mirror 55. A change unit 57 is arranged. By driving the first Q value changing unit 56, the Q values of the first resonator and the second resonator can be controlled. Further, by driving the second Q value changing unit 57, it is possible to control only the Q value of the second resonator among the first resonator and the second resonator.
　例えば、第１の共振器及び第２の共振器を低Ｑ状態としてレーザロッド５１の励起を行い、励起後に第１の共振器を高Ｑ状態に切り替え、かつ第２の共振器は低Ｑ状態のままとすることにより、波長８００ｎｍをパルス発振させることができる。また、第１の共振器及び第２の共振器を低Ｑ状態としてレーザロッド５１の励起を行い、励起後に第１の共振器及び第２の共振器を高Ｑ状態とすることにより、発光効率が高いが高い波長７５５ｎｍをパルス発振させることができる。 For example, the first resonator and the second resonator are set to a low Q state to excite the laser rod 51, the first resonator is switched to a high Q state after excitation, and the second resonator is set to a low Q state. By keeping it as it is, a wavelength of 800 nm can be pulse-oscillated. In addition, the laser resonator 51 is excited with the first resonator and the second resonator in the low Q state, and the first resonator and the second resonator are brought into the high Q state after the excitation, thereby increasing the light emission efficiency. However, a high wavelength of 755 nm can be pulse-oscillated.
　本実施形態では、レーザ利得が低い波長８００ｎｍの共振器には第１のＱスイッチ５８が挿入される。一方で、レーザ利得が高い波長７５５ｎｍの共振器には、第１のＱスイッチ５８と第２のＱスイッチ６０とが挿入される。特許文献３では、双方の波長の共振器にポッケルスセルが２つ挿入されており、特にレーザ利得が低い波長８００ｎｍにおいて出力の低下が問題となった。本実施形態では、第１の共振器に挿入されるポッケルスセルは１つでよく、第１の共振器内に光の偏光状態を変化させる素子を複数個配置する必要がないため、特にレーザ出力が低い波長８００ｎｍについて、複数のポッケルスセルが挿入されることに伴うレーザ出力の低下を抑制することができる。 In the present embodiment, the first Q switch 58 is inserted in the resonator having a wavelength of 800 nm with a low laser gain. On the other hand, the first Q switch 58 and the second Q switch 60 are inserted into a resonator having a high laser gain and a wavelength of 755 nm. In Patent Document 3, two Pockels cells are inserted in the resonators of both wavelengths, and a decrease in output becomes a problem particularly at a wavelength of 800 nm where the laser gain is low. In this embodiment, only one Pockels cell is inserted into the first resonator, and it is not necessary to arrange a plurality of elements that change the polarization state of light in the first resonator. For a low wavelength of 800 nm, it is possible to suppress a decrease in laser output due to the insertion of a plurality of Pockels cells.
　また、本実施形態では、波長８００ｎｍの光及び波長７５５ｎｍの光の光軸が平行となるよう、第１の共振器と第２の共振器とを一軸上に構成している。このようにすることにより、ミラーやＱ値変更部の光学部材を波長８００ｎｍの光及び波長７５５ｎｍの光に対して共通に用いることができる。更に本実施形態では、第２のミラー５４よりもレーザロッド５１から見て遠い側に第３のミラー５５が配置されており、第１の共振器の共振器長が第２の共振器の共振器長よりも短い。第１の共振器の共振器長を短くすることにより、レーザ利得が低い波長８００ｎｍにおいてパルスレーザ光の短パルス化が可能である。 Further, in the present embodiment, the first resonator and the second resonator are configured on one axis so that the optical axes of the light having a wavelength of 800 nm and the light having a wavelength of 755 nm are parallel to each other. By doing in this way, the optical member of a mirror and a Q value change part can be used in common with respect to light with a wavelength of 800 nm and light with a wavelength of 755 nm. Furthermore, in the present embodiment, the third mirror 55 is disposed on the side farther from the laser rod 51 than the second mirror 54, and the resonator length of the first resonator is the resonance of the second resonator. Shorter than the length of the instrument. By shortening the resonator length of the first resonator, the pulse laser beam can be shortened at a wavelength of 800 nm where the laser gain is low.
　本実施形態では、２つの波長のレーザ光を照射して得られた第１の光音響データと、第２の光音響データとの何れか一方を実部、他方を虚部とした複素数データを生成し、その複素数データからフーリエ変換法により再構成画像を生成している。このようにする場合、第１の光音響データと第２の光音響データとを別々に再構成する場合に比して、再構成を効率的に行うことができる。複数の波長のパルスレーザ光を照射し、各波長のパルスレーザ光を照射したときの光音響信号（光音響データ）を用いることにより、各光吸収体の光吸収特性が波長に応じて異なることを利用した機能イメージングを行うことができる。 In the present embodiment, complex number data in which one of the first photoacoustic data and the second photoacoustic data obtained by irradiating laser beams of two wavelengths is a real part and the other is an imaginary part is obtained. Then, a reconstructed image is generated from the complex number data by the Fourier transform method. In this case, reconstruction can be performed more efficiently than when the first photoacoustic data and the second photoacoustic data are reconstructed separately. By irradiating pulse laser light of multiple wavelengths and using photoacoustic signals (photoacoustic data) when irradiating pulse laser light of each wavelength, the light absorption characteristics of each light absorber differ depending on the wavelength Can be used for functional imaging.
　ここで、特許文献４には、Ｈｅ－Ｎｅレーザ放電管と、第１反射鏡、第２反射鏡、第３反射鏡、及び光変調装置を備えたレーザ装置が記載されている。第１反射鏡と第２反射鏡は波長６３２．８ｎｍの共振器を構成し、第１反射鏡と第３反射鏡は波長３．３９μｍの共振器を構成する。光変調装置は、第２反射鏡と第３反射鏡との間に配置される。特許文献４では、Ｈｅ－Ｎｅレーザでは高利得を有する３．３９μ線と低利得の６３２．８ｎｍ線とがレーザの上順位を共有する競合関係にあることに着目し、３．３９μ線を変調することにより、結果的に６３２．８ｎｍ線の変調を可能にする。 Here, Patent Document 4 describes a laser device including a He—Ne laser discharge tube, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, and a light modulation device. The first reflecting mirror and the second reflecting mirror constitute a resonator having a wavelength of 632.8 nm, and the first reflecting mirror and the third reflecting mirror constitute a resonator having a wavelength of 3.39 μm. The light modulation device is disposed between the second reflecting mirror and the third reflecting mirror. In Patent Document 4, focusing on the fact that the He-Ne laser has a competitive relationship in which the high gain 3.39 μ line and the low gain 632.8 nm line share the upper rank of the laser, the 3.39 μ line is modulated. As a result, the 632.8 nm line can be modulated.
　しかしながら、特許文献４の目的は、レーザ光を計測機器に応用するために信号処理上の必要性から光変調するところにある。また、特許文献４には、Ｈｅ－Ｎｅレーザの６３２．８ｎｍ線は利得が小さく、共振器内に光変調素子を挿入して変調することは困難であると記載されており、特許文献４はそのような場合に適用されるものである。従って、特許文献４において、双方の共振器内部にＱ値を制御するための光学素子を挿入し、Ｑスイッチレーザとする、特に二波長をＱスイッチ発振させる構成は採り得ない。 However, the purpose of Patent Document 4 is to perform optical modulation due to the necessity of signal processing in order to apply laser light to measurement equipment. Patent Document 4 describes that the 632.8 nm line of the He—Ne laser has a small gain, and it is difficult to insert and modulate an optical modulation element in the resonator. It is applied in such a case. Therefore, in Patent Document 4, it is not possible to adopt a configuration in which an optical element for controlling the Q value is inserted into both resonators to form a Q-switched laser, in particular, two-wavelength Q-switched oscillation.
　次いで、本発明の第２実施形態を説明する。図１０は、本発明の第２実施形態に係るレーザ光源ユニットを示す。本実施形態に係るレーザ光源ユニット１３ａでは、第１のミラー５３が波長８００ｎｍの光の出力ミラーであり、第３のミラー５５が波長７５５ｎｍの光の出力ミラーである。第１のミラー５３の波長８００ｎｍの光に対する反射率は例えば８０％であり、波長７５５ｎｍの光に対する反射率は例えば９９．８以上である。第３のミラーの波長７５５ｎｍの光に対する反射率は例えば６０％である。その他の点は第１実施形態と同様でよい。 Next, a second embodiment of the present invention will be described. FIG. 10 shows a laser light source unit according to the second embodiment of the present invention. In the laser light source unit 13a according to the present embodiment, the first mirror 53 is an output mirror for light having a wavelength of 800 nm, and the third mirror 55 is an output mirror for light having a wavelength of 755 nm. The reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm is, for example, 80%, and the reflectance with respect to light with a wavelength of 755 nm is, for example, 99.8 or more. The reflectance of the third mirror with respect to light having a wavelength of 755 nm is, for example, 60%. Other points may be the same as in the first embodiment.
　本実施形態では、波長７５５ｎｍの光に対する第１のミラー５３の反射率が、波長７５５ｎｍの光に対する第３のミラー５５の反射率よりも高く設定される。この場合、第３のミラー５５が波長７５５ｎｍの光の出力ミラーとなる。本実施形態では、共振器の一方の側から波長８００ｎｍの光を出射し、他方の側から波長７５５ｎｍの光を出射できる。第１のミラー５３から出射する波長８００ｎｍの光と第３のミラー５５から出射する波長７５５ｎｍの光は、共振器の外部において光軸を合流させればよい。 In this embodiment, the reflectance of the first mirror 53 with respect to light with a wavelength of 755 nm is set higher than the reflectance of the third mirror 55 with respect to light with a wavelength of 755 nm. In this case, the third mirror 55 is an output mirror for light having a wavelength of 755 nm. In this embodiment, light having a wavelength of 800 nm can be emitted from one side of the resonator, and light having a wavelength of 755 nm can be emitted from the other side. The light having a wavelength of 800 nm emitted from the first mirror 53 and the light having a wavelength of 755 nm emitted from the third mirror 55 may be combined at the optical axis outside the resonator.
　本実施形態では、波長８００ｎｍの光の出力ミラーである第１のミラー５３の波長８００ｎｍの光に対する反射率は、波長７５５ｎｍの光の出力ミラーである第３のミラー５５の波長７５５ｎｍの光に対する反射率よりも高い。レーザ利得が低い波長８００ｎｍの光に対する出力ミラーの反射率を、波長７５５ｎｍの光に対する出力ミラーの反射率よりも高く設定することにより、発振（投入）エネルギーしきい値を下げ、レーザ利得を増加することができ、パルスレーザ光の短パルス化が可能である。その他の効果は第１実施形態と同様である。 In the present embodiment, the reflectance of the first mirror 53, which is an output mirror of light having a wavelength of 800 nm, with respect to light of wavelength 800nm is the reflection of the third mirror 55, which is an output mirror of light having a wavelength of 755nm, with respect to light having a wavelength of 755nm. Higher than the rate. By setting the reflectivity of the output mirror for light with a wavelength of 800 nm with a low laser gain to be higher than the reflectivity of the output mirror for light with a wavelength of 755 nm, the oscillation (input) energy threshold is lowered and the laser gain is increased. Therefore, the pulse laser beam can be shortened. Other effects are the same as those of the first embodiment.
　上記では、第１のミラー５３を波長８００ｎｍの光の出力ミラーとし、かつ第３のミラー５５を波長７５５ｎｍの光の出力ミラーとしたが、第１のミラーを波長８００ｎｍの光及び波長７５５ｎｍの光の出力ミラーとし、かつ第３のミラー５５を波長７５５ｎｍの光の出力ミラーとしてもよい。この場合、共振器の一方の側から波長８００ｎｍ及び波長７５５ｎｍの光を出射し、他方の側から波長７５５ｎｍの光を出射できる。第１のミラー５３から出射する波長８００ｎｍ及び波長７５５ｎｍの光と第３のミラー５５から出射する波長７５５ｎｍの光は、共振器の外部において光軸を合流させればよい。 In the above description, the first mirror 53 is an output mirror for light having a wavelength of 800 nm and the third mirror 55 is an output mirror for light having a wavelength of 755 nm. However, the first mirror is light having a wavelength of 800 nm and light having a wavelength of 755 nm. The third mirror 55 may be an output mirror for light having a wavelength of 755 nm. In this case, light having a wavelength of 800 nm and wavelength 755 nm can be emitted from one side of the resonator, and light having a wavelength of 755 nm can be emitted from the other side. The light having a wavelength of 800 nm and 755 nm emitted from the first mirror 53 and the light having a wavelength of 755 nm emitted from the third mirror 55 may be combined at the optical axis outside the resonator.
　上記構成の場合、第１のミラー５３における波長８００ｎｍの光に対する反射率を波長７５５ｎｍの光に対する反射率と同じ設定としてもよい。例えば、第１のミラー５３の波長８００ｎｍの光に対する反射率と波長７５５ｎｍの光に対する反射率は共に８０％とする。第３のミラー５５の波長７５５ｎｍの光に対する反射率は例えば８０％とする。このようにした場合、第１の共振器における光の閉じ込めが、第２の共振器における光の閉じ込めよりも強くなり、波長８００ｎｍのパルスレーザ光を短パルス化できる。 In the case of the above configuration, the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm may be set to the same setting as the reflectance with respect to light with a wavelength of 755 nm. For example, the reflectance of the first mirror 53 with respect to light with a wavelength of 800 nm and the reflectance with respect to light with a wavelength of 755 nm are both 80%. The reflectance of the third mirror 55 with respect to light having a wavelength of 755 nm is, for example, 80%. In this case, the light confinement in the first resonator is stronger than the light confinement in the second resonator, and the pulsed laser light having a wavelength of 800 nm can be shortened.
　上記した第１のミラー５３を波長８００ｎｍの光及び波長７５５ｎｍの光の出力ミラーとし、かつ第３のミラー５５を波長７５５ｎｍの光の出力ミラーとする構成では、第１のミラー５３における波長８００ｎｍの光に対する反射率と波長７５５ｎｍの光に対する反射率とを同じ反射率にできる。第１のミラー５３の双方の波長の光に対する反射率を同じにする場合、第１のミラー５３の作製が比較的容易になる。また、上記構成の場合、第３のミラー５５に、波長７５５ｎｍの光に対して第１のミラー５３と同じ反射率のミラーを用いることができる。 In the configuration in which the first mirror 53 is an output mirror for light having a wavelength of 800 nm and light having a wavelength of 755 nm, and the third mirror 55 is an output mirror for light having a wavelength of 755 nm, the first mirror 53 has a wavelength of 800 nm. The reflectance for light and the reflectance for light having a wavelength of 755 nm can be made the same. When the reflectances of the first mirror 53 with respect to light of both wavelengths are the same, the first mirror 53 can be manufactured relatively easily. In the case of the above configuration, the third mirror 55 can be a mirror having the same reflectivity as the first mirror 53 with respect to light having a wavelength of 755 nm.
　続いて、本発明の第３実施形態を説明する。図１１は、本発明の第３実施形態に係るレーザ光源ユニットを示す。本実施形態に係るレーザ光源ユニット１３ｂでは、第２のミラー５４ａ及び第３のミラー５５ａに凹面ミラーが用いられる。第１のミラー５３は平面ミラーである。その他の点は、第１実施形態又は第２実施形態と同様でよい。なお、図１１では、制御回路６２は図示を省略している。 Subsequently, a third embodiment of the present invention will be described. FIG. 11 shows a laser light source unit according to the third embodiment of the present invention. In the laser light source unit 13b according to the present embodiment, concave mirrors are used for the second mirror 54a and the third mirror 55a. The first mirror 53 is a plane mirror. Other points may be the same as in the first embodiment or the second embodiment. In FIG. 11, the control circuit 62 is not shown.
　凹面ミラーである第２のミラー５４ａの焦点距離は第１の共振器の共振器長よりも長い。また、凹面ミラーである第３のミラー５５ａの焦点距離は第２の共振器の共振器長よりも長い。第３のミラー５５ａを構成する凹面ミラーの曲率半径は、第２のミラー５４ａを構成する凹面ミラーの曲率半径よりも短く設定される。例えば、第２の共振器の共振器長が、第１の共振器の共振器長の２倍のとき、第２のミラー５４ａには曲率半径が８ｍの凹面ミラーが用いられ、第３のミラー５５ａには曲率半径が４ｍの凹面ミラーが用いられる。第２のミラー５４ａ及び第３のミラー５５ａに凹面ミラーを用い、共振器ミラーに集光力を持たせることにより、角度広がりを有する光束が共振器内を周回するたびに拡がることを防ぐことができ、第１の共振器及び第２の共振器を安定化させることができる。 The focal length of the second mirror 54a, which is a concave mirror, is longer than the resonator length of the first resonator. The focal length of the third mirror 55a, which is a concave mirror, is longer than the resonator length of the second resonator. The radius of curvature of the concave mirror constituting the third mirror 55a is set shorter than the radius of curvature of the concave mirror constituting the second mirror 54a. For example, when the resonator length of the second resonator is twice the resonator length of the first resonator, a concave mirror having a radius of curvature of 8 m is used as the second mirror 54a, and the third mirror A concave mirror having a curvature radius of 4 m is used for 55a. By using concave mirrors for the second mirror 54a and the third mirror 55a, and concentrating the resonator mirror, it is possible to prevent the light beam having an angular spread from spreading every time it circulates in the resonator. The first resonator and the second resonator can be stabilized.
　図１２は、共振器ミラーに凹面ミラーを用いた変形例のレーザ光源ユニットを示す。この変形例のレーザ光源ユニット１３ｂでは、第１のミラー５３ａに凹面ミラーが用いられる。第２のミラー５４及び第３のミラー５５は平面ミラーである。第１のミラー５３ａには、例えば曲率半径が４ｍの凹面ミラーを用いることができる。図１２に示すように、第１のミラー５３ａに凹面ミラーを用いた場合も、図１１に示す構成のレーザ光光源ユニットと同様に、第１の共振器及び第２の共振器を安定化することができる。 FIG. 12 shows a modified laser light source unit using a concave mirror as a resonator mirror. In the laser light source unit 13b of this modification, a concave mirror is used for the first mirror 53a. The second mirror 54 and the third mirror 55 are plane mirrors. For example, a concave mirror having a radius of curvature of 4 m can be used as the first mirror 53a. As shown in FIG. 12, even when a concave mirror is used for the first mirror 53a, the first resonator and the second resonator are stabilized as in the laser light source unit having the configuration shown in FIG. be able to.
　引き続き、本発明の第４実施形態を説明する。図１３は、本発明の第４実施形態に係るレーザ光源ユニットを示す。本実施形態に係るレーザ光源ユニット１３ｄは、第２の共振器の光路上に、レーザロッド５１から離れる方向に向かって光束を拡大するビームエキスパンダ６３を有する。より詳細には、第２のミラー５４と第２のＱスイッチ６０との間にビームエキスパンダ６３を有する。その他の構成は第１実施形態、第２実施形態、又は第３実施形態と同様でよい。ビームエキスパンダ６３は、例えば第２のミラー５４側から、凹レンズ６３ａと凸レンズ６３ｂとを順に有する。ビームエキスパンダ６３は、第２のミラー５４側から入射した光線の径を拡大して第２のＱスイッチ６０側に出射する。 Subsequently, a fourth embodiment of the present invention will be described. FIG. 13 shows a laser light source unit according to the fourth embodiment of the present invention. The laser light source unit 13d according to the present embodiment includes a beam expander 63 that expands a light beam in a direction away from the laser rod 51 on the optical path of the second resonator. More specifically, a beam expander 63 is provided between the second mirror 54 and the second Q switch 60. Other configurations may be the same as those in the first embodiment, the second embodiment, or the third embodiment. The beam expander 63 includes, for example, a concave lens 63a and a convex lens 63b in this order from the second mirror 54 side. The beam expander 63 enlarges the diameter of the light beam incident from the second mirror 54 side and emits it to the second Q switch 60 side.
　ビームエキスパンダ６３が光線の径を拡大することにより、レーザロッド５１の周囲に配置されている各種光学部品に入射する光線の面積エネルギー密度（Ｊ／ｃｍ２）を下げることができ、各種光学部品の光入射面のダメージを低減できる。例えば、図１３の例のように、ビームエキスパンダ６３を第２のミラー５４と第２のＱスイッチ６０との間に配置した場合は、第２のミラー５４を透過して第２のＱスイッチ６０に向かう波長７５５ｎｍの光線の径を拡大することができ、第２のＱスイッチ６０に入射する光線の面積エネルギー密度を下げることができる。 When the beam expander 63 enlarges the diameter of the light beam, the area energy density (J / cm 2 ) of the light beam incident on the various optical components arranged around the laser rod 51 can be lowered. Damage to the light incident surface can be reduced. For example, when the beam expander 63 is disposed between the second mirror 54 and the second Q switch 60 as in the example of FIG. 13, the second Q switch is transmitted through the second mirror 54. The diameter of the light beam having a wavelength of 755 nm toward 60 can be enlarged, and the area energy density of the light beam incident on the second Q switch 60 can be reduced.
　特に、波長７５５ｎｍは波長８００ｎｍに比べてレーザ利得が高いため、波長８００ｎｍの発振時に比べてレーザ出力が強くなりやすい。ビームエキスパンダ６３を用いてそのような強いエネルギーのレーザ光線の径を拡大することにより、第２のＱ値変更部５７を構成する各部の光入射面のダメージを低減できる。これにより、第２のＱ値変更部５７を構成する各部の長寿命化などを図ることが可能である。 Particularly, since the laser gain at the wavelength 755 nm is higher than that at the wavelength 800 nm, the laser output tends to be stronger than that at the time of oscillation at the wavelength 800 nm. By expanding the diameter of the laser beam having such strong energy using the beam expander 63, it is possible to reduce damage to the light incident surfaces of the respective parts constituting the second Q value changing unit 57. As a result, it is possible to extend the life of each part constituting the second Q value changing part 57.
　なお、図１１に示したように第２のミラー５４ａが凹面ミラーによって構成される場合、第２のミラー５４ａは波長７５５ｎｍの光に対しては凹レンズとして働く。第２のミラー５４ａが凹面ミラーによって構成される場合は、第２のミラー５４ａがビームエキスパンダ６３の一部を兼ねることとしてもよい。すなわち、凹レンズ６３ａを省略し、第２のミラー５４ａと凸レンズ６３ｂとによってビームエキスパンダ６３を構成してもよい。この場合は、必要な部品点数を削減できる。 As shown in FIG. 11, when the second mirror 54a is constituted by a concave mirror, the second mirror 54a functions as a concave lens for light having a wavelength of 755 nm. When the second mirror 54 a is configured by a concave mirror, the second mirror 54 a may also serve as a part of the beam expander 63. That is, the concave lens 63a may be omitted, and the beam expander 63 may be configured by the second mirror 54a and the convex lens 63b. In this case, the number of necessary parts can be reduced.
　上記では、ビームエキスパンダ６３を第２の共振器の光路上に有する例について説明したが、これには限定されず、ビームエキスパンダ６３を第１の共振器の光路上に挿入してもよい。具体的には、ビームエキスパンダ６３は、例えばレーザロッド５１と第２のミラー５４との間に配置されていてもよい。その場合、ビームエキスパンダ６３がレーザロッド５１から第２のミラー５４に向かうビーム径を拡大することにより、第２のミラー５４に入射する光線の面積エネルギー密度を下げることができ、第２のミラー５４の光入射面のダメージを低減できる。また、第２のミラー５４の先にある第２のＱ値変更部５７の光入射面のダメージも低減できる。 In the above, an example in which the beam expander 63 is provided on the optical path of the second resonator has been described. However, the present invention is not limited to this, and the beam expander 63 may be inserted on the optical path of the first resonator. . Specifically, the beam expander 63 may be disposed between the laser rod 51 and the second mirror 54, for example. In this case, the beam expander 63 expands the beam diameter from the laser rod 51 toward the second mirror 54, whereby the area energy density of the light incident on the second mirror 54 can be reduced, and the second mirror The damage on the light incident surface 54 can be reduced. Further, damage to the light incident surface of the second Q value changing unit 57 at the tip of the second mirror 54 can also be reduced.
　続いて、本発明の第５実施形態を説明する。上記各実施形態において、第１の波長の発振時と第２の波長の発振時とでレーザロッド５１に対する励起エネルギーが等しいとき、低利得側の波長の発振の際に、共振器内の光学素子の損傷しきい値に対して許容できる範囲で高い出力を得ようとすると、高利得側の波長の発振の際に、共振器内のエネルギーが光学素子の損傷しきい値を越える可能性がある。本実施形態では、第１の波長の発振時と第２の波長の発振時とで、レーザロッド５１（図２を参照）の励起エネルギーを個別に設定する。例えば、第２の波長の発振時における励起エネルギーを、第１の波長の発振時における励起エネルギーよりも低く設定する。好ましくは、第１の波長の発振時と第２の波長の発振時とでレーザ出力強度が等しくなるように、第１の波長の発振時における励起エネルギーと第２の波長の発振時における励起エネルギーとを設定する。 Subsequently, a fifth embodiment of the present invention will be described. In each of the above embodiments, when the excitation energy for the laser rod 51 is the same at the time of oscillation at the first wavelength and at the time of oscillation at the second wavelength, the optical element in the resonator is generated at the time of oscillation at the low gain side wavelength. If an attempt is made to obtain a high output within an allowable range with respect to the damage threshold value, the energy in the resonator may exceed the damage threshold value of the optical element during oscillation at a wavelength on the high gain side. . In the present embodiment, the excitation energy of the laser rod 51 (see FIG. 2) is set individually for the oscillation of the first wavelength and the oscillation of the second wavelength. For example, the excitation energy at the second wavelength oscillation is set lower than the excitation energy at the first wavelength oscillation. Preferably, the excitation energy at the time of oscillation at the first wavelength and the excitation energy at the time of oscillation at the second wavelength are set so that the laser output intensity is equal between the oscillation at the first wavelength and the oscillation at the second wavelength. And set.
　励起エネルギーの設定は、例えばフラッシュランプ５２に印加する電圧を変更することによって行う。例えば図８において、波長８００ｎｍで発振するときは、時刻ｔ１よりも以前にフラッシュランプ５２に対する電圧設定を電圧Ｖ１とし、時刻ｔ１にフラッシュランプ５２に対して電圧Ｖ１を印加する。波長７５５ｎｍで発振するときは、時刻ｔ３よりも以前にフラッシュランプ５２に対する電圧設定を電圧Ｖ１よりも低い電圧Ｖ２とし、時刻ｔ３にフラッシュランプ５２に対して電圧Ｖ２を印加する。このようにすることにより、各波長の発振時に、励起エネルギーを個別に設定可能である。 The excitation energy is set by changing the voltage applied to the flash lamp 52, for example. For example, in FIG. 8, when oscillating at a wavelength of 800 nm, the voltage setting for the flash lamp 52 is set to the voltage V1 before the time t1, and the voltage V1 is applied to the flash lamp 52 at the time t1. When oscillating at a wavelength of 755 nm, the voltage setting for the flash lamp 52 is set to a voltage V2 lower than the voltage V1 before time t3, and the voltage V2 is applied to the flash lamp 52 at time t3. In this way, the excitation energy can be set individually during oscillation of each wavelength.
　図１４は、励起エネルギーとレーザ出力との関係を示す。同図において、グラフ（ａ）
は発振波長が８００ｎｍのときの励起エネルギーＥとレーザ出力との関係を示し、グラフ（ｂ）は発振波長が７５５ｎｍのときの励起エネルギーＥとレーザ出力との関係を示す。発振波長が８００ｎｍのときの励起エネルギーをＥ１とする。励起エネルギーをＥ１としたとき、発振波長８００ｎｍのレーザ出力は損傷しきい値を超えない。 FIG. 14 shows the relationship between excitation energy and laser output. In the figure, graph (a)
Shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 800 nm, and the graph (b) shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 755 nm. E1 is the excitation energy when the oscillation wavelength is 800 nm. When the excitation energy is E1, the laser output with an oscillation wavelength of 800 nm does not exceed the damage threshold.
　発振波長が７５５ｎｍのとき、発振波長が８００ｎｍのときと同様に励起エネルギーをＥ１とすると、波長７５５ｎｍのレーザ利得係数は波長８００ｎｍのレーザ利得係数よりも高いため、レーザ出力が波長８００ｎｍの発振時よりも高くなり、共振器内のエネルギーが光学素子の損傷しきい値を超える。発振波長７５５ｎｍ時のレーザ出力を抑えるために、発振波長が７５５ｎｍのときは励起エネルギーをＥ２まで下げる。励起エネルギーをＥ２まで下げることにより、発振波長７５５ｎｍのレーザ出力を損傷しきい値よりも低くすることができる。また、双方の発振波長においてレーザ出力を揃えることができる。 When the oscillation wavelength is 755 nm and the excitation energy is E1 as in the case where the oscillation wavelength is 800 nm, the laser gain coefficient at the wavelength 755 nm is higher than the laser gain coefficient at the wavelength 800 nm. And the energy in the resonator exceeds the damage threshold of the optical element. In order to suppress the laser output when the oscillation wavelength is 755 nm, the excitation energy is lowered to E2 when the oscillation wavelength is 755 nm. By reducing the excitation energy to E2, the laser output with an oscillation wavelength of 755 nm can be made lower than the damage threshold. Further, the laser output can be made uniform at both oscillation wavelengths.
　さらに、本発明の第６実施形態を説明する。上記第５実施形態では、双方の波長に対して励起エネルギーを個別に設定することにより、レーザ発振時の共振器内のエネルギーが共振器内の光学素子の損傷しきい値を超えないようにした。本実施形態では、高利得側のレーザ発振時の共振器内のエネルギーが共振器内の光学素子の損傷しきい値を超えないようにするために、高利得側である第２の波長の光に対して損失を与えるロスフィルタ（光学フィルタ）を用いる。 Further, a sixth embodiment of the present invention will be described. In the fifth embodiment, the excitation energy is individually set for both wavelengths so that the energy in the resonator during laser oscillation does not exceed the damage threshold of the optical element in the resonator. . In the present embodiment, in order to prevent the energy in the resonator during laser oscillation on the high gain side from exceeding the damage threshold value of the optical element in the resonator, the light of the second wavelength on the high gain side is used. A loss filter (optical filter) that gives a loss is used.
　図１５に、本実施形態に係るレーザ装置を示す。本実施形態に係るレーザ光源ユニット１３ｅは、第２のミラー５４と第３のミラー５５との間にロスフィルタ６４を更に備える。より詳細には、第２のミラー５４と第２のＱスイッチ６０との間にロスフィルタ（光学フィルタ）６４を有する。ロスフィルタ６４は、例えば減光フィルタ（ＮＤ（Neutral Density）フィルタ）である。その他の構成は第１実施形態、第２実施形態、第３実施形態、第４実施形態、又は第５実施形態と同様でよい。 FIG. 15 shows a laser apparatus according to this embodiment. The laser light source unit 13e according to this embodiment further includes a loss filter 64 between the second mirror 54 and the third mirror 55. More specifically, a loss filter (optical filter) 64 is provided between the second mirror 54 and the second Q switch 60. The loss filter 64 is, for example, a neutral density filter (ND (Neutral Density) filter). Other configurations may be the same as those of the first embodiment, the second embodiment, the third embodiment, the fourth embodiment, or the fifth embodiment.
　図１６は、励起エネルギーとレーザ出力との関係を示す。同図において、グラフ（ａ）は発振波長が８００ｎｍのときの励起エネルギーＥとレーザ出力との関係を示す。グラフ（ｂ）はロスフィルタ６４なしの場合の発振波長が７５５ｎｍのときの励起エネルギーＥとレーザ出力との関係を示し、グラフ（ｃ）はロスフィルタ６４ありの場合の発振波長が７５５ｎｍのときの励起エネルギーＥとレーザ出力との関係を示す。 FIG. 16 shows the relationship between excitation energy and laser output. In the figure, graph (a) shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 800 nm. Graph (b) shows the relationship between the excitation energy E and the laser output when the oscillation wavelength is 755 nm without the loss filter 64, and graph (c) shows the relationship when the oscillation wavelength is 755 nm with the loss filter 64. The relationship between the excitation energy E and the laser output is shown.
　グラフ（ａ）を参照すると、発振波長が８００ｎｍであり、かつ励起エネルギーがＥ１のとき、レーザ出力は共振器内の光学素子の損傷しきい値を超えない。発振波長が７５５ｎｍであり、かつロスフィルタなしの場合、励起エネルギーをＥ１とすると、グラフ（ｂ）に示すように、レーザ出力は共振器内の光学素子の損傷しきい値を超える。 Referring to graph (a), when the oscillation wavelength is 800 nm and the excitation energy is E1, the laser output does not exceed the damage threshold of the optical element in the resonator. When the oscillation wavelength is 755 nm and there is no loss filter, if the excitation energy is E1, the laser output exceeds the damage threshold of the optical element in the resonator as shown in the graph (b).
　第２の共振器内にロスフィルタ６４が挿入されると、第２の共振器内において波長７５５ｎｍの光に対して損失が与えられるため、励起エネルギーが一定であるとすれば、レーザ出力は、ロスフィルタなしの場合に比べて低くなる。ロスフィルタ６４が挿入されたときの励起エネルギーとレーザ出力との関係は、グラフ（ｂ）に示すロスフィルタ６４なしの場合の励起エネルギーとレーザ出力の関係を、グラフ（ｃ）に示すように励起エネルギーが高い側に平行移動した関係となる。 When the loss filter 64 is inserted in the second resonator, a loss is given to light having a wavelength of 755 nm in the second resonator. Therefore, if the excitation energy is constant, the laser output is It becomes lower than the case without the loss filter. The relationship between the excitation energy and the laser output when the loss filter 64 is inserted is the relationship between the excitation energy and the laser output without the loss filter 64 shown in the graph (b) as shown in the graph (c). The relationship is a parallel movement to the higher energy side.
　第２の共振器内にロスフィルタ６４が挿入された場合、グラフ（ｃ）に示すように、励起エネルギーを波長８００ｎｍの発振時と同じＥ１としたときでも、波長７５５ｎｍの発振時にレーザ出力が共振器内の光学素子の損傷しきい値を超えないようにすることができる。ロスフィルタ６４が波長７５５ｎｍの光に与える損失を調整し、同じ励起エネルギーにおいて、双方の波長のレーザ出力が等しくなるようにすることが更に好ましい。言い換えれば、ロスフィルタ６４が、波長８００ｎｍの発振時と波長７５５ｎｍの発振時とでレーザ出力が等しくなるように、波長７５５ｎｍの光に対して損失を与えることが更に好ましい。 When the loss filter 64 is inserted in the second resonator, as shown in the graph (c), the laser output resonates at the oscillation of the wavelength of 755 nm even when the excitation energy is E1 which is the same as that at the oscillation of the wavelength of 800 nm. The damage threshold of the optical elements in the vessel can be prevented from being exceeded. It is more preferable to adjust the loss that the loss filter 64 gives to the light having a wavelength of 755 nm so that the laser outputs of both wavelengths are equal at the same excitation energy. In other words, it is more preferable that the loss filter 64 gives a loss to the light with a wavelength of 755 nm so that the laser output is equal between the oscillation with the wavelength of 800 nm and the oscillation with the wavelength of 755 nm.
　ここで、ロスフィルタ６４により波長７５５ｎｍの光に対して与える損失が大きいほど、レーザ発振に必要な励起エネルギーが高くなる。つまり、第２の共振器における波長７５５ｎｍの発振しきい値は高くなる。第１のミラー５３から第２のミラー５４までの間は双方の共振器に共通であるため、第２の共振器における波長７５５ｎｍの発振しきい値が第１の共振器における波長８００ｎｍの発振しきい値よりも高くなると、第１の共振器において波長８００ｎｍが先に発振することになる。従って、ロスフィルタ６４が波長７５５ｎｍの光に対して与える損失は、第１の共振器における波長８００ｎｍの発振しきい値が第２の共振器における波長７５５ｎｍの発振しきい値よりも高い範囲で選定することが好ましい。 Here, the greater the loss given to the light of wavelength 755 nm by the loss filter 64, the higher the excitation energy necessary for laser oscillation. That is, the oscillation threshold value of the wavelength 755 nm in the second resonator is increased. Since the interval from the first mirror 53 to the second mirror 54 is common to both resonators, the oscillation threshold of the wavelength 755 nm in the second resonator oscillates in the wavelength of 800 nm in the first resonator. If it becomes higher than the threshold value, the wavelength of 800 nm first oscillates in the first resonator. Therefore, the loss that the loss filter 64 gives to the light with a wavelength of 755 nm is selected in a range where the oscillation threshold value of the wavelength of 800 nm in the first resonator is higher than the oscillation threshold value of the wavelength of 755 nm in the second resonator. It is preferable to do.
　上記では、第２の共振器内にロスフィルタ６４が挿入される例を説明したが、これに加えて、第１の共振器内にロスフィルタを挿入することとしてもよい。また、波長８００ｎｍの発振時と波長７５５ｎｍの発振時とで励起エネルギーは同一である必要はない。第２の共振器内にロスフィルタ６４を挿入した上で、第５実施形態において説明したものと同様に、波長８００ｎｍの発振時と波長７５５ｎｍの発振時とで、励起エネルギーを個別に設定してもよい。 In the above description, the example in which the loss filter 64 is inserted into the second resonator has been described, but in addition to this, a loss filter may be inserted into the first resonator. Further, the excitation energy does not have to be the same when oscillating at a wavelength of 800 nm and 755 nm. After inserting the loss filter 64 in the second resonator, the excitation energy is individually set for the oscillation at the wavelength of 800 nm and the oscillation at the wavelength of 755 nm, as described in the fifth embodiment. Also good.
　なお、上記各実施形態では、第１の光音響データと第２の光音響データとを複素数化する例について説明したが、複素数化せずに、第１の光音響データと第２の光音響データとを別々に再構成してもよい。さらに、ここでは、複素数化して位相情報を用いて第１の光音響データと第２の光音響データの比を計算しているが、両者の強度情報から比を計算しても同様の効果が得られるまた、強度情報は、第１の再構成画像における信号強度と、第２の再構成画像における信号強度とに基づいて生成できる。 In each of the above embodiments, the example in which the first photoacoustic data and the second photoacoustic data are converted to complex numbers has been described. However, the first photoacoustic data and the second photoacoustic data are not converted to complex numbers. Data may be reconstructed separately. Further, here, the ratio between the first photoacoustic data and the second photoacoustic data is calculated using the complex number and the phase information, but the same effect can be obtained by calculating the ratio from the intensity information of both. The obtained intensity information can also be generated based on the signal intensity in the first reconstructed image and the signal intensity in the second reconstructed image.
　光音響画像の生成に際して、被検体に照射されるパルスレーザ光の波長の数は２つには限られず、３以上のパルスレーザ光を被検体に照射し、各波長に対応する光音響データに基づいて光音響画像を生成してもよい。その場合、例えば位相情報抽出手段２６は、各波長に対応する光音響データ間での相対的な信号強度の大小関係を位相情報として生成すればよい。また、強度情報抽出手段２７は、例えば各波長に対応する光音響データにおける信号強度を１つにまとめたものを強度情報として生成すればよい。 When generating a photoacoustic image, the number of wavelengths of the pulsed laser light applied to the subject is not limited to two, and the subject is irradiated with three or more pulsed laser lights, and photoacoustic data corresponding to each wavelength is generated. A photoacoustic image may be generated based on this. In that case, for example, the phase information extracting unit 26 may generate a relative magnitude relationship between the photoacoustic data corresponding to each wavelength as the phase information. Further, the intensity information extraction unit 27 may generate, as intensity information, a collection of signal intensities in photoacoustic data corresponding to each wavelength, for example.
　上記各実施形態では、主にアレキサンドライトレーザについて説明したが、レーザロッド５１（図２）に用いられるレーザ媒質はアレキサンドライトには限定されない。例えばＣｒ：ＬｉＳＡＦやＣｒ：ＬｉＣＡＦなどは７５０ｎｍ－９００ｎｍの波長範囲でレーザ発振が可能であり、レーザロッド５１に、Ｃｒ：ＬｉＳＡＦやＣｒ：ＬｉＣＡＦなどを用いてもよい。また、Ｔｉ：Ｓａｐｐｈｉｒｅは７００ｎｍ－１０００ｎｍの波長範囲でレーザ発振が可能であり、レーザロッド５１にＴｉ：Ｓａｐｐｈｉｒｅを用いてよい。 In the above embodiments, the alexandrite laser has been mainly described. However, the laser medium used for the laser rod 51 (FIG. 2) is not limited to alexandrite. For example, Cr: LiSAF, Cr: LiCAF, and the like can oscillate in the wavelength range of 750 nm to 900 nm, and the laser rod 51 may be Cr: LiSAF, Cr: LiCAF, or the like. Ti: Sapphire can oscillate in the wavelength range of 700 nm to 1000 nm, and Ti: Sapphire may be used for the laser rod 51.
　上記各実施形態では、レーザ装置が光音響計測装置の一部を構成する例について説明したが、これには限定されない。本発明のレーザ装置を、光音響計測装置とは異なる装置に用いることも可能である。 In each of the above embodiments, an example in which the laser device forms part of the photoacoustic measurement device has been described, but the present invention is not limited to this. The laser device of the present invention can also be used for a device different from the photoacoustic measuring device.
　以上、本発明をその好適な実施形態に基づいて説明したが、本発明のレーザ装置及び光音響計測装置は、上記実施形態にのみ限定されるものではなく、上記実施形態の構成から種々の修正及び変更を施したものも、本発明の範囲に含まれる。 Although the present invention has been described based on the preferred embodiment, the laser device and the photoacoustic measurement device of the present invention are not limited to the above embodiment, and various modifications can be made from the configuration of the above embodiment. Further, modifications and changes are also included in the scope of the present invention.
１０：光音響計測装置
１１：プローブ
１２：超音波ユニット
１３：レーザ光源ユニット
１４：画像表示手段
２１：受信回路
２２：ＡＤ変換手段
２３：受信メモリ
２４：複素数化手段
２５：光音響画像再構成手段
２６：位相情報抽出手段
２７：強度情報抽出手段
２８：検波・対数変換手段
２９：光音響画像構築手段
３０：トリガ制御回路
３１：制御手段
５１：レーザロッド
５２：フラッシュランプ
５３、５４、５５：ミラー
５６、５７：Ｑ値変更部
５８、６０：Ｑスイッチ
５９：偏光子
６１：１／４波長板
６２：制御回路
６３：ビームエキスパンダ
６３ａ：凹レンズ
６３ｂ：凸レンズ
６４：ロスフィルタ 10: Photoacoustic measuring device 11: Probe 12: Ultrasonic unit 13: Laser light source unit 14: Image display means 21: Reception circuit 22: AD conversion means 23: Reception memory 24: Complex number conversion means 25: Photoacoustic image reconstruction means 26: Phase information extraction means 27: Intensity information extraction means 28: Detection / logarithmic conversion means 29: Photoacoustic image construction means 30: Trigger control circuit 31: Control means 51: Laser rod 52: Flash lamps 53, 54, 55: Mirror 56, 57: Q value changing unit 58, 60: Q switch 59: Polarizer 61: 1/4 wavelength plate 62: Control circuit 63: Beam expander 63a: Concave lens 63b: Convex lens 64: Loss filter

Claims (31)

  1. 　第１の波長と第２の波長とに発光波長を有する固体のレーザ媒質であって、前記第１の波長の発光効率が前記第２の波長の発光効率よりも低いレーザ媒質と、
    　前記レーザ媒質を間欠的に励起する励起手段と、
    　前記レーザ媒質を間に挟んで対向する第１のミラー及び第２のミラーによって構成され、前記第１の波長の光を発振する第１の共振器と、
    　前記第１のミラーと、前記レーザ媒質及び前記第２のミラーを間に挟んで前記第１のミラーと対向する第３のミラーとによって構成され、前記第１の共振器と一部が共通の光路を有し、前記第２の波長の光を発振する第２の共振器と、
    　前記第１の共振器と前記第２の共振器とに共通の光路上に配置され、前記第１の共振器及び前記第２の共振器のＱ値を制御する第１のＱ値変更部と、
    　前記第２のミラーと第３のミラーとの間に配置され、前記第２の共振器のＱ値を制御する第２のＱ値制御部とを備えたレーザ装置。     A solid-state laser medium having a light emission wavelength at a first wavelength and a second wavelength, wherein the light emission efficiency of the first wavelength is lower than the light emission efficiency of the second wavelength;
    Excitation means for intermittently exciting the laser medium;
    A first resonator composed of a first mirror and a second mirror facing each other with the laser medium interposed therebetween, and oscillating light of the first wavelength;
    The first mirror and a third mirror facing the first mirror with the laser medium and the second mirror in between, and partly in common with the first resonator A second resonator having an optical path and oscillating light of the second wavelength;
    A first Q value changing unit disposed on a common optical path for the first resonator and the second resonator, and controlling a Q value of the first resonator and the second resonator; ,
    A laser apparatus comprising: a second Q value control unit that is disposed between the second mirror and the third mirror and controls a Q value of the second resonator.
  2. 　前記第１のＱ値変更部及び前記第２のＱ値変更部を駆動し、前記第１の共振器及び前記第２の共振器のＱ値を、それぞれ共振器のＱ値が発振しきい値よりも低い低Ｑ状態にする第１の駆動状態、前記第１の共振器及び前記第２の共振器のＱ値を、それぞれ共振器のＱ値が発振しきい値よりも高い高Ｑ状態にする第２の駆動状態、及び、前記第１の共振器のＱ値を高Ｑ状態にし、かつ前記第２の共振器のＱ値を低Ｑ状態にする第３の駆動状態の間で駆動状態を切り替える制御回路を更に備えた請求項１に記載のレーザ装置。 The first Q value changing unit and the second Q value changing unit are driven, and the Q values of the first resonator and the second resonator are respectively set to the oscillation threshold values. The Q value of the first driving state, the first resonator, and the second resonator that are lower than the low Q state is set to the high Q state where the Q value of the resonator is higher than the oscillation threshold value, respectively. A second driving state, and a driving state between a third driving state in which the Q value of the first resonator is set to a high Q state and the Q value of the second resonator is set to a low Q state. The laser device according to claim 1, further comprising a control circuit for switching between the two.
  3. 　前記制御回路は、前記レーザ媒質の励起時は前記第１のＱ値変更部及び前記第２のＱ値変更部の駆動状態を前記第１の駆動状態とする請求項２に記載のレーザ装置。 3. The laser apparatus according to claim 2, wherein the control circuit sets the driving state of the first Q value changing unit and the second Q value changing unit to the first driving state when the laser medium is excited.
  4. 　前記制御回路は、レーザ媒質の励起後、発振波長が前記第１の波長のときは前記第１のＱ値変更部及び前記第２のＱ値変更部の駆動状態を前記第１の駆動状態から前記第３の駆動状態へと変化させ、発振波長が前記第２の波長のときは前記第１のＱ値変更部及び前記第２のＱ値変更部を前記第１の駆動状態から前記第２の駆動状態へと変化させる請求項３に記載のレーザ装置。 When the oscillation wavelength is the first wavelength after the excitation of the laser medium, the control circuit changes the driving state of the first Q value changing unit and the second Q value changing unit from the first driving state. When the oscillation wavelength is the second wavelength, the first Q value changing unit and the second Q value changing unit are changed from the first driving state to the second driving state. The laser device according to claim 3, wherein the laser device is changed to a driving state of
  5. 　前記制御回路は、発振波長が第２の波長のときは、前記第２の共振器のＱ値が高Ｑ状態となるように前記第２のＱ値変更部を駆動するのと同時に前記第１の共振器のＱ値が高Ｑ状態となるように前記第１のＱ値変更部を駆動し、又は前記第２の共振器のＱ値が高Ｑ状態となるように前記第２のＱ値変更部を駆動した後に前記第１の共振器のＱ値が高Ｑ状態となるように前記第１のＱ値変更部を駆動する請求項４に記載のレーザ装置。 When the oscillation wavelength is the second wavelength, the control circuit drives the second Q value changing unit simultaneously with driving the second Q value changing unit so that the Q value of the second resonator is in a high Q state. The first Q value changing unit is driven so that the Q value of the resonator of the second resonator is in a high Q state, or the second Q value is set so that the Q value of the second resonator is in a high Q state. The laser apparatus according to claim 4, wherein the first Q value changing unit is driven so that a Q value of the first resonator becomes a high Q state after driving the changing unit.
  6. 　前記第１のＱ値変更部は、前記第１の共振器と前記第２の共振器とに共通の光路上に配置され、印加電圧に応じて前記第１の共振器及び前記第２の共振器のＱ値を変化させる第１のＱスイッチを含み、前記制御回路が、前記第１のＱスイッチの印加電圧を制御することにより前記第１のＱ値変更部を駆動する請求項２から５何れか１項に記載のレーザ装置。 The first Q-value changing unit is disposed on an optical path common to the first resonator and the second resonator, and the first resonator and the second resonance according to an applied voltage. 6. A first Q switch for changing a Q value of the device, wherein the control circuit drives the first Q value changing unit by controlling an applied voltage of the first Q switch. The laser device according to any one of the above.
  7. 　前記第１のＱスイッチは、印加電圧がＱスイッチオフに対応した第１の電圧のとき前記第１の共振器及び前記第２の共振器を低Ｑ状態にし、印加電圧が、絶対値が前記第１の電圧の絶対値よりも小さく、Ｑスイッチオンに対応した第２の電圧のとき前記第１の共振器及び前記第２の共振器を高Ｑ状態にする請求項６に記載のレーザ装置。 The first Q switch sets the first resonator and the second resonator to a low Q state when the applied voltage is a first voltage corresponding to Q switch off, and the applied voltage has the absolute value of the first Q switch. 7. The laser device according to claim 6, wherein the first resonator and the second resonator are set to a high Q state when the second voltage is smaller than the absolute value of the first voltage and corresponds to Q switch-on. .
  8. 　前記第１のＱ値変更部は、前記第１のミラー及び前記第２のミラーのいずれか一方と、前記第１のＱスイッチとの間に配置された１／４波長板を更に含み、前記第１のＱスイッチは、印加電圧がＱスイッチオフに対応した第１の電圧のとき前記第１の共振器及び前記第２の共振器を低Ｑ状態にし、印加電圧が、絶対値が前記第１の電圧の絶対値よりも大きいＱスイッチオンに対応した第２の電圧のとき前記第１の共振器及び前記第２の共振器を高Ｑ状態にする請求項６に記載のレーザ装置。 The first Q value changing unit further includes a quarter wave plate disposed between one of the first mirror and the second mirror and the first Q switch, The first Q switch sets the first resonator and the second resonator to a low Q state when the applied voltage is a first voltage corresponding to Q switch off, and the applied voltage has an absolute value of the first voltage. The laser device according to claim 6, wherein the first resonator and the second resonator are set to a high Q state when the second voltage corresponding to the Q switch-on larger than the absolute value of the voltage of 1 is set.
  9. 　前記第２の電圧は、前記第１の波長の発振時と前記第２の波長の発振時とで異なる請求項８に記載のレーザ装置。 9. The laser device according to claim 8, wherein the second voltage is different between the oscillation of the first wavelength and the oscillation of the second wavelength.
  10. 　前記第２のＱ値変更部は、前記第２のミラーと前記第３のミラーとの間に配置され、印加電圧に応じて前記第２の共振器のＱ値を変化させる第２のＱスイッチを含み、前記制御回路が、前記第２のＱスイッチの印加電圧を制御することにより前記第２のＱ値変更部を駆動する請求項２から９何れか１項に記載のレーザ装置。 The second Q value changing unit is disposed between the second mirror and the third mirror, and changes a Q value of the second resonator according to an applied voltage. The laser device according to claim 2, wherein the control circuit drives the second Q value changing unit by controlling an applied voltage of the second Q switch.
  11. 　前記第２のＱ値変更部は、前記第２のＱスイッチと前記第３のミラーとの間に配置された１／４波長板を更に含み、前記第２のＱスイッチは、印加電圧がＱスイッチオフに対応した第３の電圧のとき前記第２の共振器を低Ｑ状態にし、印加電圧が、絶対値が前記第３の電圧の絶対値よりも大きいＱスイッチオンに対応した第４の電圧のとき前記第２の共振器を高Ｑ状態にする請求項１０に記載のレーザ装置。 The second Q value changing unit further includes a ¼ wavelength plate disposed between the second Q switch and the third mirror, and the second Q switch has an applied voltage of Q When the third voltage corresponds to the switch-off, the second resonator is set to a low Q state, and the applied voltage has a fourth value corresponding to the Q-switch-on whose absolute value is larger than the absolute value of the third voltage. The laser device according to claim 10, wherein when the voltage is applied, the second resonator is brought into a high Q state.
  12. 　前記第２のミラーは、前記第１の波長の光を反射し、前記第２の波長の光を透過する請求項１から１１何れか１項に記載のレーザ装置。 The laser device according to claim 1, wherein the second mirror reflects light having the first wavelength and transmits light having the second wavelength.
  13. 　前記第１のミラーは、前記第１の波長の光及び前記第２の波長の光の出力ミラーである請求項１から１２何れか１項に記載のレーザ装置。 The laser device according to any one of claims 1 to 12, wherein the first mirror is an output mirror of light having the first wavelength and light having the second wavelength.
  14. 　前記第１のミラーの前記第１の波長の光に対する反射率は前記第２の波長の光に対する反射率よりも高い請求項１から１３何れか１項に記載のレーザ装置。 The laser device according to any one of claims 1 to 13, wherein a reflectance of the first mirror with respect to the light having the first wavelength is higher than a reflectance with respect to the light having the second wavelength.
  15. 　前記第１のミラーが前記第１の波長の光の出力ミラーであり、かつ前記第３のミラーが前記第２の波長の光の出力ミラーであり、前記第１のミラーの前記第２の波長の光に対する反射率が前記第３のミラーの前記第２の波長の光に対する反射率よりも高い請求項１から１２何れか１項に記載のレーザ装置。 The first mirror is an output mirror for light of the first wavelength, and the third mirror is an output mirror for light of the second wavelength, and the second wavelength of the first mirror The laser device according to claim 1, wherein a reflectance of the third mirror is higher than a reflectance of the third mirror with respect to the light of the second wavelength.
  16. 　前記第１のミラーが前記第１の波長の光の出力ミラーであり、かつ前記第３のミラーが前記第２の波長の光の出力ミラーであり、前記第１のミラーの前記第１の波長の光に対する反射率が前記第３のミラーの前記第２の波長の光に対する反射率よりも高い請求項１から１２何れか１項に記載のレーザ装置。 The first mirror is an output mirror of light of the first wavelength, and the third mirror is an output mirror of light of the second wavelength, and the first wavelength of the first mirror The laser device according to claim 1, wherein a reflectance of the third mirror is higher than a reflectance of the third mirror with respect to the light of the second wavelength.
  17. 　前記第１のミラーが前記第１の波長の光及び前記第２の波長の光の出力ミラーであり、かつ前記第３のミラーが前記第２の波長の光の出力ミラーであり、前記第１のミラーにおける前記第１の波長の光に対する反射率が前記第２の波長の光に対する反射率と同じである請求項１から１２何れか１項に記載のレーザ装置。 The first mirror is an output mirror of the light of the first wavelength and the light of the second wavelength, and the third mirror is an output mirror of the light of the second wavelength, and the first mirror The laser device according to claim 1, wherein a reflectance of the first mirror with respect to the light with the first wavelength is the same as a reflectance with respect to the light with the second wavelength.
  18. 　前記第１のミラー、前記第２のミラー、及び前記第３のミラーのうちの少なくとも１つは光軸方向に沿って移動可能である請求項１から１７何れか１項に記載のレーザ装置。 The laser device according to any one of claims 1 to 17, wherein at least one of the first mirror, the second mirror, and the third mirror is movable along an optical axis direction.
  19. 　前記第１の波長の発振の繰り返し周波数は、前記第２の波長の発振の繰り返し周波数よりも高い請求項１から１８何れか１項に記載のレーザ装置。 The laser device according to any one of claims 1 to 18, wherein a repetition frequency of oscillation of the first wavelength is higher than a repetition frequency of oscillation of the second wavelength.
  20. 　前記第１の共振器の光路と第２の共振器の光路との少なくとも一方に、前記レーザ媒質から離れる方向に向かって光束を拡大するビームエキスパンダを更に備える請求項１から１９何れか１項に記載のレーザ装置。 20. The beam expander according to claim 1, further comprising a beam expander that expands a light beam in a direction away from the laser medium in at least one of the optical path of the first resonator and the optical path of the second resonator. The laser device described in 1.
  21. 　前記ビームエキスパンダは、前記レーザ媒質と前記第２のミラーとの間に配置される請求項２０に記載のレーザ装置。 The laser apparatus according to claim 20, wherein the beam expander is disposed between the laser medium and the second mirror.
  22. 　前記ビームエキスパンダは、前記第２のミラーと前記第２のＱ値制御部との間に配置される請求項２０に記載のレーザ装置。 The laser device according to claim 20, wherein the beam expander is disposed between the second mirror and the second Q value control unit.
  23. 　前記ビームエキスパンダは凹レンズと凸レンズとを含み、前記第２のミラーは凹面ミラーであり前記ビームエキスパンダの凹レンズを兼ねる請求項２２に記載のレーザ装置。 23. The laser apparatus according to claim 22, wherein the beam expander includes a concave lens and a convex lens, and the second mirror is a concave mirror and also serves as a concave lens of the beam expander.
  24. 　前記第１のミラーが平面ミラーであり、前記第２のミラー及び前記第３のミラーが凹面ミラーである請求項１から２２何れか１項に記載のレーザ装置。 The laser device according to any one of claims 1 to 22, wherein the first mirror is a plane mirror, and the second mirror and the third mirror are concave mirrors.
  25. 　前記第３のミラーの曲率半径が、前記第２のミラーの曲率半径よりも短い請求項２４に記載のレーザ装置。 The laser device according to claim 24, wherein a radius of curvature of the third mirror is shorter than a radius of curvature of the second mirror.
  26. 　前記第１のミラーが凹面ミラーであり、前記第２のミラー及び前記第３のミラーが平面ミラーである請求項１から２２何れか１項に記載のレーザ装置。 The laser device according to any one of claims 1 to 22, wherein the first mirror is a concave mirror, and the second mirror and the third mirror are flat mirrors.
  27. 　前記第１の波長の発振時と前記第２の波長の発振時とで前記レーザ媒質の励起エネルギーが個別に設定される請求項１から２６何れか１項に記載のレーザ装置。 27. The laser device according to claim 1, wherein excitation energy of the laser medium is set individually for oscillation of the first wavelength and oscillation of the second wavelength.
  28. 　前記第２の波長の発振時における励起エネルギーは前記第１の波長の発振時における励起エネルギーよりも低い請求項２７に記載のレーザ装置。 28. The laser device according to claim 27, wherein excitation energy at the time of oscillation of the second wavelength is lower than excitation energy at the time of oscillation of the first wavelength.
  29. 　前記第２のミラーと前記第３のミラーとの間に、前記第２の波長の光に対して損失を与える光学フィルタを更に備える請求項１から２８何れか１項に記載のレーザ装置。 The laser device according to any one of claims 1 to 28, further comprising an optical filter that gives a loss to the light of the second wavelength between the second mirror and the third mirror.
  30. 　前記第１の共振器における前記第１の波長の発振しきい値は、前記第２の共振器における前記第２の波長の発振しきい値よりも高い請求項２９に記載のレーザ装置。 30. The laser device according to claim 29, wherein an oscillation threshold value of the first wavelength in the first resonator is higher than an oscillation threshold value of the second wavelength in the second resonator.
  31. 　第１の波長と第２の波長とに発光波長を有する固体のレーザ媒質であって、前記第１の波長の発光効率が前記第２の波長の発光効率よりも低いレーザ媒質と、
    該レーザ媒質を間欠的に励起する励起手段と、
    前記レーザ媒質を間に挟んで対向する第１のミラー及び第２のミラーによって構成され、前記第１の波長の光を発振する第１の共振器と、
    前記第１のミラーと、前記レーザ媒質及び前記第２のミラーを間に挟んで前記第１のミラーと対向する第３のミラーとによって構成され、前記第１の共振器と一部が共通の光路を有し、前記第２の波長の光を発振する第２の共振器と、
    前記第１の共振器と前記第２の共振器とに共通の光路上に配置され、前記第１の共振器及び前記第２の共振器のＱ値を制御する第１のＱ値変更部と、
    前記第２のミラーと第３のミラーとの間に配置され、前記第２の共振器のＱ値を制御する第２のＱ値制御部とを備えたレーザ装置と、
    　前記第１の波長及び前記第２の波長のレーザ光が被検体に出射されたときに被検体内で生じた光音響信号を検出し、前記第１の波長及び前記第２の波長のそれぞれに対応した第１の光音響データ及び第２の光音響データを生成する検出手段とを備えたことを特徴とする光音響計測装置。     A solid-state laser medium having a light emission wavelength at a first wavelength and a second wavelength, wherein the light emission efficiency of the first wavelength is lower than the light emission efficiency of the second wavelength;
    Excitation means for intermittently exciting the laser medium;
    A first resonator composed of a first mirror and a second mirror facing each other with the laser medium interposed therebetween, and oscillating light of the first wavelength;
    The first mirror and a third mirror facing the first mirror with the laser medium and the second mirror in between, and partly in common with the first resonator A second resonator having an optical path and oscillating light of the second wavelength;
    A first Q value changing unit disposed on a common optical path for the first resonator and the second resonator, and controlling a Q value of the first resonator and the second resonator; ,
    A laser device including a second Q value control unit that is disposed between the second mirror and the third mirror and controls a Q value of the second resonator;
    A photoacoustic signal generated in the subject when the laser light of the first wavelength and the second wavelength is emitted to the subject is detected, and each of the first wavelength and the second wavelength is detected. A photoacoustic measuring device comprising: detection means for generating corresponding first photoacoustic data and second photoacoustic data.
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