CN114526893A - Method and device for measuring stimulated emission cross section of laser crystal - Google Patents
Method and device for measuring stimulated emission cross section of laser crystal Download PDFInfo
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Abstract
The invention discloses a method and a device for measuring the stimulated emission cross section of a laser crystal, wherein the method comprises the following steps: measuring the intensity noise of the laser, and acquiring a relaxation oscillation frequency measured value of the laser from an intensity noise spectral line of the laser; according to the actual parameters of the laser when the intensity noise of the laser is measured, a function curve graph is made by using a theoretical function of relaxation oscillation frequency of the laser; the function curve graph takes the theoretical value of the stimulated emission cross section of the laser crystal of the laser as an independent variable and takes the theoretical value of the relaxation oscillation frequency of the laser as a dependent variable; when the measured value of the relaxation oscillation frequency is equal to the theoretical value of the relaxation oscillation frequency, the value of the abscissa corresponding to the measured value of the relaxation oscillation frequency in the function curve graph is the actual stimulated emission cross section of the laser crystal to be measured of the laser under the operation state of injecting pumping power. The method is accurate in measurement and suitable for measuring the actual stimulated emission cross section of the laser crystal of the all-solid-state laser under stable operation.
Description
Technical Field
The invention relates to the technical field of laser, in particular to a method and a device for measuring a stimulated emission cross section of a laser crystal.
Background
The all-solid-state laser has the characteristics of low noise, narrow line width, perfect beam quality and the like when realizing high-power output, and is widely applied to the fields of basic scientific research, industrial manufacturing and processing, national defense safety and the like, such as quantum information, cold atom physics, precise spectrum, precise measurement, laser processing, laser radar, laser remote sensing, photoelectric countermeasure and the like. The laser crystal is a carrier for generating oscillation laser and is one of three elements forming a laser, the stimulated emission cross section of the laser crystal is an important parameter of the laser crystal, and the stimulated emission cross section of the optical crystal directly determines the small-signal gain coefficient of the laser crystal and the saturation laser intensity of the laser, and finally influences the output power and the light-light conversion efficiency of the laser. In the development of all-solid-state lasers and all-solid-state laser amplifiers, the accurate acquisition of the stimulated emission cross section of a laser crystal under actual operating conditions is of great importance to the design of the parameter structures of the lasers and the laser amplifiers. Meanwhile, the stimulated emission cross section of the laser crystal under the actual running state of the laser can be accurately measured, reference basis can be provided for judging whether the crystal performance is good and whether the crystal temperature control element works normally in laser maintenance, and the method plays a key role in later-stage laser design optimization.
Currently, the measurement of the effective emission cross section of a laser crystal is mainly based on fluorescence spectroscopy, and is mainly based on measuring the fluorescence spectrum emitted by the laser crystal by using a monochromator or a fluorescence spectrometer to obtain the effective half-width of a fluorescence emission band, and the fluorescence life is obtained according to the decay characteristic of fluorescence intensity along with time. In order to avoid the effect of generating laser light in the process, the fluorescence spectrum emitted by the crystal is generally measured under the condition that low-pumping laser light is injected into the laser crystal and the laser crystal is in an incubator.
Although there are many reports on the measurement of the stimulated emission cross section of the laser crystal at present, the stimulated emission cross section listed in the same kind of laser crystal has a large difference due to different growth conditions of the crystal used in the measurement state. Meanwhile, the fluorescence spectroscopy can not be used for measuring the stimulated emission cross section of the laser crystal of the laser which is being debugged or is packaged. In the actual operating state of the laser, the pumping laser power is far higher than the laser threshold. And the stimulated emission cross section of the laser crystal is influenced by the temperature distribution characteristics of the crystal in the actual running state of the laser, which is specifically shown in that the stimulated emission cross section of the laser crystal is rapidly reduced along with the increase of the temperature of the crystal. The temperature distribution characteristics of the laser crystal are influenced by factors such as the heat load generated in the laser non-radiative transition process, the actual temperature control effect of the laser crystal temperature control device and the like. The real stimulated emission cross section of the laser crystal is affected by the doping concentration of the crystal and the pumping laser power of the injection crystal, the thermal load of the laser crystal is aggravated by the higher doping concentration and the pumping laser power, the actual stimulated emission cross section of the crystal is reduced, and the light-light conversion efficiency of a laser is reduced.
Therefore, the existing method for measuring the effective emission cross section of the laser crystal has the problem of inaccurate measurement, and the stimulated emission cross section of the laser crystal cannot be easily and accurately measured in the actual running state of the all-solid-state laser.
Disclosure of Invention
The invention aims to solve the technical problems that the existing method for measuring the effective emission cross section of the laser crystal has the problem of inaccurate measurement, and the stimulated emission cross section of the laser crystal cannot be accurately measured easily in the actual running state of an all-solid-state laser.
The invention aims to provide a method and a device for measuring the stimulated emission cross section of a laser crystal, which are simple to operate, accurate in result and easy to accurately measure the stimulated emission cross section of the laser crystal in the actual operation state of an all-solid-state laser. The method can accurately measure the stimulated emission cross section of the laser crystal in the actual running state of the laser, and is favorable for accurately predicting the output characteristic of the laser and optimizing the design of the structural parameters of the laser.
The invention is realized by the following technical scheme:
in a first aspect, the present invention provides a method of measuring a stimulated emission cross-section of a laser crystal, the method comprising the steps of;
measuring intensity noise of the laser, and reading relaxation oscillation frequency measurement value omega of the laser from intensity noise spectral line of the laserm；
According to the actual parameters of the laser when the intensity noise of the laser is measured, a function curve graph is made by using a theoretical function of relaxation oscillation frequency of the laser; the function curve diagram is a theoretical value sigma of stimulated emission cross section of laser crystal of a lasersAs independent variable and with the theoretical value omega of the relaxation oscillation frequency of the laseroffIs a function graph of the dependent variable;
when said relaxation oscillation frequency measures ωmEqual to said relaxation oscillation frequency theoretical value ωoffThen, the value of the abscissa corresponding to the relaxation oscillation frequency measurement value in the function curve graph is the pumping power p of the laser crystal to be measured during injectioninThe actual stimulated emission cross-section in this operating state.
The working principle is as follows: the existing method for measuring the effective emission cross section of the laser crystal is a direct measurement method, has the problem of inaccurate measurement, and is not easy to accurately measure the stimulated emission cross section of the laser crystal under the actual operation state of an all-solid-state laser. In the invention, in consideration of the full quantum noise theoretical function of the all-solid-state laser, the stimulated emission cross section of the laser crystal of the laser directly influences the stimulated radiation rate of the coupling of the laser crystal atomic transition and the laser cavity mode; the number of photons oscillated in the laser cavity is a function of the stimulated emission rate of atomic transition and laser cavity mode coupling; the relaxation oscillation frequency of the laser is a function of the stimulated emission rate associated with the coupling of the laser crystal atomic transitions to the laser cavity modes and the number of photons oscillating within the laser cavity. Therefore, there is a functional correlation characteristic between the laser relaxation oscillation frequency and the stimulated emission cross section of the laser crystal. In the invention, under the stable operation state of the laser, the intensity noise of the laser can be measured by using the self-homodyne noise detection device, and the measured value of the laser relaxation oscillation frequency can be obtained from the laser intensity noise spectral line. According to the actual parameters of the laser when measuring the intensity noise of the laser, the stimulated emission section sigma of the laser crystal of the laser is theoretically madesAs independent variable, with laser relaxation oscillation frequency ωoffIs a graph of the function of the dependent variable. And (3) making the measured value of the laser relaxation oscillation frequency identical to the theoretical value of the laser relaxation oscillation frequency of the theoretical function curve graph, and reading the corresponding value of the abscissa, namely the actual stimulated emission cross section of the laser crystal of the laser in the running state. The method is particularly suitable for measuring the stimulated emission cross section of the laser crystal of the stably-operating all-solid-state laser in the actual operation state.
Compared with the prior art direct measurement method, the method has the following advantages:
1. the invention is an indirect measurement method, which is easy to accurately measure the stimulated emission cross section of a laser crystal under the actual operation state of an all-solid-state laser; when the stimulated emission cross section of the laser crystal of the all-solid-state laser is measured, the device is simple, the operation is convenient, and the cost is low.
2. The invention has universal applicability, and is suitable for measuring stimulated emission cross sections of visible light and near infrared lasers pumped by laser diodes, mid-infrared lasers pumped by all-solid-state lasers and mid-infrared laser crystals pumped by fiber lasers in actual states.
3. The method is suitable for measuring the stimulated emission cross section of the laser crystal in the high-power, medium-power and low-power stably-operated laser.
4. The stimulated emission cross section of the laser crystal of the all-solid-state laser device obtained by measurement is a stimulated emission cross section value of the laser crystal in an actual running state of the laser device, and the influence of the temperature distribution characteristic of the laser crystal on the stimulated emission cross section of the laser crystal is included.
5. The method is suitable for measuring the stimulated emission cross section of the packaged all-solid-state laser crystal which is debugged in the actual operation state.
Further, the measuring of the intensity noise of the laser is measuring the intensity noise of the laser by using a self-homodyne noise detection device.
Further, the laser is an all-solid-state laser.
Furthermore, the laser crystal to be measured is arranged in the all-solid-state laser, and the laser is in a stable operation state in the noise measurement process of the laser.
Further, the relaxation oscillation frequency theoretical value ωoffThe calculation formula of (2) is as follows:
in the formula, k is the total cavity attenuation rate of the laser, g is the stimulated emission rate of the coupling between the laser crystal atomic transition and the laser cavity mode, and alpha is the number of photons in the cavity.
Further, the calculation formula of the total cavity attenuation rate of the laser is as follows:
κ＝κm+κl (2)
in the formula (I), the compound is shown in the specification,
the cavity decay rate caused by the laser output coupling mirror,
the cavity decay rate caused by the loss in the laser cavity,
for the lifetime of the oscillating laser in the laser resonator, L2The cavity length to which light travels a single round trip in the cavity.
Further, the calculation formula of the stimulated emission rate of the coupling between the laser crystal atomic transition and the laser cavity mode is as follows:
in the formula, σsFor stimulated emission cross section of laser, plm＝ρc*cwIs the density of doping atoms in the gain medium, pcAn atomic density corresponding to a doping atom concentration of 1.0%, cwIs the doping concentration of the gain medium, c is the speed of light, L1Doping the length, L, for laser crystal atoms2Which is the length of the cavity to which light is going back and forth a single time in the cavity, and n is the refractive index of the laser crystal.
Further, the calculation formula of the number of photons in the cavity is as follows:
in the formula (I), the compound is shown in the specification,
the spontaneous emission rate at the lower energy level,
for upper level spontaneous emission rate, τfThe fluorescence lifetime of the upper-level-inversion particles, j2Probability of distribution of number of particles being ground state, j2Expressed as:
where Γ is the pump rate, Γ is expressed as:
wherein p isinFor measuring the laser diode pumping power, eta, of the laser in response to intensity noisetEta (pump optical power ratio) for pumping optical transmission efficiency (ratio of pump optical power into gain medium to pump optical power output from laser diode)a＝1-exp(-αL1) To the absorption efficiency of the gain medium, α is the absorption coefficient of the gain medium for the pump laser light,
to quantum efficiency, vlTo output laser frequency, vpFor the pumping laser frequency, h is the Planck constant, NlmThe number of doping ions utilized in the lasing medium is expressed as: n is a radical oflm＝ρlm*VmWherein V ismThe mode volume at the laser crystal for pumping the laser is expressed as:
wherein, ω ispFor pumping laser light at the beam waist radius, λ, of the laser crystal centerpThe wavelength of the pump laser.
As can be seen from the formulas (1), (2), (3) and (4), under the condition that the pump power of the laser and the cavity structure parameters are determined, the relaxation oscillation frequency of the laser is the function of the stimulated emission cross section of the laser crystalAnd (4) counting. Therefore, when the laser is operating stably (p)inTo a determined value), the stimulated emission cross section sigma of the laser crystal of the laser can be obtained according to the actual parameters of the lasersAs independent variable, with the relaxation oscillation frequency ω of the laseroffIs a graph of the function of the dependent variable.
When the laser is operating steadily (p)inFor determining value), the intensity noise of the laser is measured by a self-zero beat noise detection device, and the true relaxation oscillation frequency measured value omega of the laser can be read from the laser intensity noise linem。
When actually measured intensity noise linesmTheoretical value omega of oscillation frequency in curve graph of and functionoffWhen the same, ω in the function graphmThe corresponding value of the abscissa is the pumping power p of the laser crystal in the injection processinThe actual stimulated emission cross-section in this operating state.
In a second aspect, the present invention further provides an apparatus for measuring a stimulated emission cross section of a laser crystal, wherein the apparatus supports the method for measuring a stimulated emission cross section of a laser crystal, and the apparatus comprises:
a measuring unit for measuring the intensity noise of the laser and reading the relaxation oscillation frequency measured value omega of the laser from the intensity noise line of the laserm；
The theoretical plotting unit is used for drawing a function curve graph by using a theoretical function of relaxation oscillation frequency of the laser according to actual parameters of the laser when the intensity noise of the laser is measured; the function curve diagram is a theoretical value sigma of stimulated emission cross section of laser crystal of a lasersAs independent variable and with the theoretical value omega of the relaxation oscillation frequency of the laseroffIs a function graph of the dependent variable;
a judgment calculation unit for calculating the relaxation oscillation frequency measurement value ωmEqual to said relaxation oscillation frequency theoretical value ωoffThen, the value of the abscissa corresponding to the relaxation oscillation frequency measurement value in the function curve graph is the pumping power p of the laser crystal to be measured during injectioninActual receiving under the operating conditionThe emission cross section is excited.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the invention is an indirect measurement method, which is easy to accurately measure the stimulated emission cross section of a laser crystal under the actual operation state of an all-solid-state laser; when the stimulated emission cross section of the laser crystal of the all-solid-state laser is measured, the device is simple, the operation is convenient, and the cost is low.
2. The invention has universal applicability, and is suitable for measuring stimulated emission cross sections of visible light and near infrared lasers pumped by laser diodes, mid-infrared lasers pumped by all-solid-state lasers and mid-infrared laser crystals pumped by fiber lasers in actual states.
3. The method is suitable for measuring the stimulated emission cross section of the laser crystal in the high-power, medium-power and low-power stably-operated laser.
4. The stimulated emission cross section of the laser crystal of the all-solid-state laser device obtained by measurement is a stimulated emission cross section value of the laser crystal in an actual running state of the laser device, and the influence of the temperature distribution characteristic of the laser crystal on the stimulated emission cross section of the laser crystal is included.
5. The method is suitable for measuring the stimulated emission cross section of the packaged all-solid-state laser crystal which is debugged in the actual operation state.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
fig. 1 is a flow chart of a method for measuring a stimulated emission cross section of a laser crystal according to the invention.
Fig. 2 is a diagram of an embodiment of a method for measuring a stimulated emission cross section of a laser crystal according to the invention.
Fig. 3 is a schematic structural diagram of a device for measuring the stimulated emission cross section of a laser crystal of an all-solid-state laser in an embodiment.
Fig. 4 is a plot of the intensity noise spectrum obtained with the laser measured with a homodyne noise detection device.
FIG. 5 shows the intensity noise spectrum and the theoretical value σ of the stimulated emission cross section of the laser crystal according to the measurementsAnd laser relaxation oscillation frequency theoretical value omegaoffThe function curve diagram of the laser crystal obtains a demonstration diagram of a stimulated emission section of the laser crystal under an actual operation state.
Fig. 6 is a schematic structural diagram of a device for measuring a stimulated emission cross section of a laser crystal according to the present invention.
Reference numbers and corresponding part names:
the system comprises a pump source 1, a self-homodyne noise detection device 2, a coupling system 3, an input coupling mirror 4, a concave-convex lens 5, a plano-concave lens 6, an output coupling mirror 7, a laser crystal 8 and an optical isolator 9.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
As shown in FIG. 1, the method for measuring the stimulated emission cross section of the laser crystal comprises the following steps;
measuring intensity noise of the laser, and reading relaxation oscillation frequency measurement value omega of the laser from intensity noise spectral line of the laserm；
According to the actual parameters of the laser when measuring the intensity noise of the laser (the actual parameters of the laser comprise the laser single round-trip cavity length L2Laser crystal doping length L1Refractive index n of laser crystal, and fluorescence lifetime τ of inverse particle numberfLower energy level particle lifetime tau, laser crystal doping ion concentration cwPumping power PinWavelength λ of pump laserpFrequency v of pumping laserpFrequency v of laser lightlBeam waist radius omega of pump laser at laser crystal centerpTransmittance t of output coupling mirror, laser cavity loss delta and laser wavelength lambdalIs pumped toLaser transmission efficiency etaaQuantum efficiency etaqAbsorption coefficient alpha of the gain medium to the pump laser, and atomic density rho corresponding to the doping atomic concentration of 1.0%c) Making a function curve graph by using a theoretical function of relaxation oscillation frequency of the laser; the function curve diagram is a theoretical value sigma of stimulated emission cross section of laser crystal of a lasersAs independent variable and with the theoretical value omega of the relaxation oscillation frequency of the laseroffIs a function graph of the dependent variable;
when said relaxation oscillation frequency measures ωmEqual to said relaxation oscillation frequency theoretical value ωoffThen, the value of the abscissa corresponding to the relaxation oscillation frequency measurement value in the function curve graph is the injection pumping power p of the measured laser crystal of the laserinThe actual stimulated emission cross section in this operating state.
The working principle is as follows: in the invention, in consideration of the full quantum noise theoretical function of the all-solid-state laser, the stimulated emission cross section of the laser crystal of the laser directly influences the stimulated radiation rate of the coupling of the laser crystal atomic transition and the laser cavity mode; the number of photons oscillated in the laser cavity is a function of the stimulated emission rate of atomic transition and laser cavity mode coupling; the relaxation oscillation frequency of the laser is a function of the stimulated emission rate associated with the coupling of the laser crystal atomic transitions to the laser cavity modes and the number of photons oscillating within the laser cavity. Therefore, there is a functional correlation characteristic between the laser relaxation oscillation frequency and the stimulated emission cross section of the laser crystal. In the invention, under the stable operation state of the laser, the intensity noise of the laser can be measured by using the self-homodyne noise detection device, and the measured value of the laser relaxation oscillation frequency can be obtained from the laser intensity noise spectral line. According to the actual parameters of the laser when measuring the intensity noise of the laser, the stimulated emission section sigma of the laser crystal of the laser is theoretically madesAs independent variable, with laser relaxation oscillation frequency ωoffIs a graph of the function of the dependent variable. The measured value of the laser relaxation oscillation frequency obtained by measurement is the same as the theoretical value of the laser relaxation oscillation frequency of the theoretical function curve graph, and the corresponding value of the abscissa is read, namely the actual value of the laser crystal of the laser in the running stateStimulated emission cross section. The method is particularly suitable for measuring the stimulated emission cross section of the laser crystal of the stably-operating all-solid-state laser in the actual operation state.
Example 2
As shown in fig. 2 to fig. 5, this embodiment is different from embodiment 1 in that, in the specific implementation, the invention is further described below with reference to fig. 2 to fig. 5, but the application scope of the invention is not limited to this embodiment. Fig. 2 shows a general embodiment of the present invention, which uses a self-homodyne noise detection device to measure the intensity noise of an all-solid-state laser in a steady operation state. Fig. 3 is a schematic structural diagram of a device for measuring the stimulated emission cross section of a laser crystal of a specific measured all-solid-state laser in an embodiment. The specific implementation scheme of the laser crystal stimulated emission cross section measurement is carried out in an all-solid-state continuous 1064nm continuous laser with a four-mirror annular cavity structure.
As can be seen from fig. 3, the device for measuring the stimulated emission cross section of the measured all-solid-state laser crystal includes a pump source 1, a coupling system 3, an input coupling mirror 4, a plano-convex lens 5, a plano-concave lens 6, an output coupling mirror 7, a laser crystal 8, an optical isolator 9, and a self-homodyne noise detection device 2; the laser resonator is a butterfly ring cavity formed by four mirrors, namely an input coupling mirror 4, a planoconvex lens 5, a planoconcave lens 6 and an output coupling mirror 7, wherein the input coupling mirror 4 is a concave-convex lens with the curvature radius R being 1500mm, the planoconvex lens 5 is 1500mm, and the planoconcave lens 6 and the output coupling mirror 7 are two planoconcave lenses with the curvature radius R being-100 mm. The input coupling mirror 4 is plated with a high-transmittance film (T) with the wavelength of 808nm808nm> 99.5%) and 1064nm high-reflection film (R)1064nm> 99.7%). A high reflection film (R) of 1064nm is plated on the plano-convex lens 5 and the plano-concave lens 61064nm> 99.7%). The output coupling mirror 7 is coated with a film with 1064nm transmittance T1064nm20% of film. The pump source 1 is a 808nm fiber coupled laser diode, and the core diameter and numerical aperture of the coupled fiber are 400 μm and 0.22, respectively. The waist spot of the pump laser 1 focused at the center of the laser crystal 8 by the coupling system 3 is 0.510 mm. The laser crystal 8 is composed of a 3mm undoped end and 15mm composite YVO doped with Nd at 0.2 at%4/Nd：YVO4(S1，S2：AR808nm；1064nm). The rear end of the laser crystal 8 is cut at a small angle of 1.5 degrees to ensure stable polarization of the laser. To eliminate the spatial hole burning effect and to achieve unidirectional propagation of the laser, an optical isolator 9 consisting of a 6mm long Terbium Gallium Garnet (TGG) crystal and a half-wave plate is used in the resonator. The cavity length of the butterfly-shaped annular cavity is 450 mm. The pumping laser power of 808nm is injected to be 52W under the stable operation state. The intensity noise spectrum obtained by the laser measured by the homodyne noise detection device is shown in FIG. 4, and the relaxation oscillation frequency measured value ω of the laser is shown in FIG. 4m594.752 kHz. Under the condition that the 808nm pumping laser power is 52W, according to the actual parameters of the laser: laser crystal length L1＝1.5×10-2m, laser single round-trip cavity length L20.45m, refractive index n of laser crystal 1.976, and fluorescence lifetime tauf＝1×10-4s, lower level particle lifetime τ of 3 × 10-8s, laser crystal doping Nd+3Ion concentration cw0.2 at.%, Avogastron constant na＝6.02×1023The light speed c is 2.997 × 10m/s, and the Planck constant h is 6.63 × 10-34Beam waist radius omega of pump laser at laser crystal centerpThe absorption coefficient alpha of the gain medium to the pump laser is 320/m, the transmittance t of the output coupling mirror is 0.2, the loss delta in the laser cavity is 0.035, etat0.98 (pumping laser transmission efficiency η)a0.98, quantum efficiency ηq0.76, pump power P of the laser diodein52W, pump laser wavelength λp＝808×10-9m, pumping laser frequency
Frequency of laser light
Density of doping atoms in gain medium plm＝ρc*cw＝1.26*1026*cw. According to the actual parameters of the laser, the stimulated emission section sigma of the laser crystal of the laser is madesAs independent variable, with the relaxation oscillation frequency ω of the laseroffIs a graph of the function of the dependent variable, as shown in fig. 5. In FIG. 5, let ω bem＝ωoffDuring the process, an intersection point is generated by a relaxation oscillation frequency straight line of the laser and a function curve graph which are actually measured, and an abscissa corresponding to the intersection point is an actual stimulated emission cross section of a laser crystal in the butterfly annular cavity laser when 808nm pumping laser power is injected into the laser crystal and is 52W: sigmas＝2.42275593*10- 22m2。
Therefore, the method is an indirect measurement method, and the measurement is accurate; the stimulated emission cross section of the laser crystal can be accurately measured easily in the actual running state of the all-solid-state laser; when the stimulated emission cross section of the laser crystal of the all-solid-state laser is measured, the device is simple, the operation is convenient, and the cost is low. The invention has universal applicability, and is applicable to the measurement of the stimulated emission cross section of a visible light and near infrared laser pumped by a laser diode, a mid-infrared laser pumped by an all-solid-state laser and a mid-infrared laser crystal pumped by a fiber laser in an actual state. The stimulated emission cross section of the laser crystal of the all-solid-state laser device obtained by measurement is a stimulated emission cross section value of the laser crystal in an actual running state of the laser device, and the influence of the temperature distribution characteristic of the laser crystal on the stimulated emission cross section of the laser crystal is included.
Meanwhile, the method is suitable for measuring the stimulated emission cross section of the packaged all-solid-state laser crystal which is debugged in the actual operation state.
Example 3
As shown in fig. 6, the present embodiment is different from embodiment 1 in that the present embodiment provides an apparatus for measuring a stimulated emission cross section of a laser crystal, which supports the method for measuring a stimulated emission cross section of a laser crystal described in embodiment 1, and the apparatus includes:
a measuring unit for measuring the intensity noise of the laser and reading the relaxation oscillation frequency measurement value omega of the laser from the intensity noise spectrum of the laserm；
A theoretical drawing unit for utilizing the relaxation oscillation frequency of the laser according to the actual parameters of the laser when measuring the intensity noise of the laserMaking a function curve graph of a theoretical function of the rate; the function curve diagram is a theoretical value sigma of stimulated emission cross section of laser crystal of a lasersAs independent variable and with the theoretical value omega of the relaxation oscillation frequency of the laseroffIs a function graph of the dependent variable;
a judgment calculation unit for calculating the relaxation oscillation frequency measurement value ωmEqual to said relaxation oscillation frequency theoretical value ωoffThen, the value of the abscissa corresponding to the relaxation oscillation frequency measurement value in the function curve graph is the injection pumping power p of the measured laser crystal of the laserinThe actual stimulated emission cross-section in this operating state.
The method is suitable for measuring the actual stimulated emission cross section of the laser crystal of the all-solid-state laser under stable operation.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A method for measuring the stimulated emission cross section of a laser crystal is characterized by comprising the following steps:
measuring the intensity noise of the laser, and acquiring a relaxation oscillation frequency measured value of the laser from an intensity noise spectral line of the laser;
according to the actual parameters of the laser when the intensity noise of the laser is measured, a function curve graph is made by using a theoretical function of relaxation oscillation frequency of the laser; the function curve graph takes a laser crystal stimulated emission cross section theoretical value of a laser as an independent variable and takes a relaxation oscillation frequency theoretical value of the laser as a dependent variable;
when the measured value of the relaxation oscillation frequency is equal to the theoretical value of the relaxation oscillation frequency, the value of the abscissa corresponding to the measured value of the relaxation oscillation frequency in the function curve graph is the actual stimulated emission cross section of the laser crystal to be measured of the laser in the operation state of injecting pumping power.
2. The method of claim 1, wherein the measuring the laser intensity noise is measuring the laser intensity noise by a self-homodyne noise detector.
3. The method of claim 1, wherein the laser is an all-solid-state laser.
4. The method for measuring the stimulated emission cross section of the laser crystal as claimed in claim 3, wherein the laser crystal to be measured is installed in an all-solid-state laser, so that the laser is in a stable operation state during the measurement of the noise of the laser.
5. The method for measuring the stimulated emission cross section of the laser crystal according to claim 1, wherein the formula for calculating the theoretical value of the relaxation oscillation frequency is as follows:
in the formula, ωoffFor the theoretical value of relaxation oscillation frequency, kappa is the total cavity attenuation rate of the laser, g is the stimulated emission rate of the coupling between the laser crystal atomic transition and the laser cavity mode, and alpha is the number of photons in the cavity.
6. The method for measuring the stimulated emission cross section of the laser crystal according to claim 5, wherein the calculation formula of the total cavity decay rate of the laser is as follows:
κ＝κm+κl
in the formula (I), the compound is shown in the specification,
the cavity decay rate caused by the laser output mirror coupling mirror,
the cavity decay rate caused by the loss in the laser cavity,
for the lifetime of the oscillating laser in the laser resonator, L2The cavity length to which light travels a single round trip in the cavity.
7. The method for measuring the stimulated emission cross section of the laser crystal as claimed in claim 5, wherein the calculation formula of the stimulated emission rate of the coupling between the laser crystal atomic transition and the laser cavity mode is as follows:
in the formula, σsFor stimulated emission cross section of laser, plm＝ρc*cwFor doping the density of atoms in the gain medium, pcAn atomic density corresponding to a doping atom concentration of 1.0%, cwIs the doping concentration of the gain medium, c is the speed of light, L1Doping the length, L, for laser crystal atoms2Which is the length of the cavity to which light is going back and forth a single time in the cavity, and n is the refractive index of the laser crystal.
8. The method for measuring the stimulated emission cross section of the laser crystal according to claim 5, wherein the calculation formula of the number of photons in the cavity is as follows:
in the formula (I), the compound is shown in the specification,
the spontaneous emission rate at the lower energy level,
for upper level spontaneous emission rate, τfThe fluorescence lifetime of the upper-level-inversion particles, j2Probability of distribution of number of particles being ground state, j2Expressed as:
where Γ is the pump rate, Γ is expressed as:
wherein p isinFor measuring the laser diode pumping power, eta, of the laser in response to intensity noisetTo pump the light transmission efficiency, ηa＝1-exp(-αL1) In order to obtain the absorption efficiency of the gain medium, α is the absorption coefficient of the gain medium for the pump laser light,
to quantum efficiency, vlTo output laser frequency, vpFor the pumping laser frequency, h is the Planck constant, NlmThe number of doping ions utilized in the lasing medium is expressed as: n is a radical oflm＝ρlm*VmWherein V ismThe mode volume at the laser crystal for pumping the laser is expressed as:
wherein, ω ispFor pumping laser light at the beam waist radius, λ, of the laser crystal centerpThe wavelength of the pump laser.
9. The method for measuring the stimulated emission cross section of the laser crystal according to claim 1, wherein the method is suitable for the stimulated emission cross section measurement of the laser crystal of the debugged or packaged all-solid-state laser in the actual operation state.
10. An apparatus for measuring a stimulated emission cross section of a laser crystal, the apparatus supporting a method of measuring a stimulated emission cross section of a laser crystal according to any one of claims 1 to 9, the apparatus comprising:
the measuring unit is used for measuring the intensity noise of the laser and acquiring a relaxation oscillation frequency measured value of the laser from an intensity noise spectral line of the laser;
the theoretical plotting unit is used for drawing a function curve graph by using a theoretical function of relaxation oscillation frequency of the laser according to actual parameters of the laser when the intensity noise of the laser is measured; the function curve graph takes a laser crystal stimulated emission cross section theoretical value of a laser as an independent variable and takes a relaxation oscillation frequency theoretical value of the laser as a dependent variable;
and the judgment calculation unit is used for obtaining the value of the abscissa corresponding to the relaxation oscillation frequency measured value in the function curve graph when the relaxation oscillation frequency measured value is equal to the theoretical value of the relaxation oscillation frequency, namely the actual stimulated emission cross section of the laser crystal to be tested in the operation state of injecting pumping power.
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