WO1994021012A1 - Dispositif acousto-optique - Google Patents

Dispositif acousto-optique Download PDF

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Publication number
WO1994021012A1
WO1994021012A1 PCT/GB1994/000371 GB9400371W WO9421012A1 WO 1994021012 A1 WO1994021012 A1 WO 1994021012A1 GB 9400371 W GB9400371 W GB 9400371W WO 9421012 A1 WO9421012 A1 WO 9421012A1
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WO
WIPO (PCT)
Prior art keywords
laser
acousto
medium
optic
ring
Prior art date
Application number
PCT/GB1994/000371
Other languages
English (en)
Inventor
David Colin Hanna
William Andrew Clarkson
Original Assignee
University Of Southampton
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University Of Southampton filed Critical University Of Southampton
Publication of WO1994021012A1 publication Critical patent/WO1994021012A1/fr

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Classifications

    • 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
    • H01S3/083—Ring lasers
    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • 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
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0606—Crystal lasers or glass lasers with polygonal cross-section, e.g. slab, prism
    • 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
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/1068—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using an acousto-optical device

Definitions

  • This invention relates to a device for enforcing
  • Enforcing unidirectional operation of a ring solid-state laser and thereby avoiding spatial hole burning as described in "single-frequency travelling-wave NdrYAG laser" can be an efficient way to achieve narrow-linewidth, single-frequency output radiation.
  • Such solid-state ring laser devices have potential applications in a number of important areas including remote sensing, coherent laser radar, metrology, coherent communications and high-resolution spectroscopy.
  • the most common technique makes use of an intracavity Faraday isolator which, in its most basic form, consists of three separate components; a Faraday rotator (to provide a non-reciprocal polarization rotation), a reciprocal rotator, and a polariser.
  • the effect of the reciprocal and non- reciprocal rotators is to produce different eigenpolarisations for the two counter-propagation directions which subsequently experience different amounts of attenuation at the polariser. The result is unidirectional lasing in the lower loss direction.
  • the resonator can be made monolithic. Unfortunately, this approach is only applicable to those laser materials which have a large enough Verdet constant at the lasing wavelength and, since the technique relies on polarisation discrimination, can only be used reliably with laser materials which are not birefringent.
  • a second technique for A-0 induced unidirectional operation can be adopted, which involves feeding back the diffracted beams via a feedback resonator.
  • This method is described in detail in Clarkson, W.A., Neilson, A.B. and Hanna, D.C., "Acousto-optically induced unidirectional operation of a ring laser: a feedback mechanism," Opt. Comm., 91, 365 [1992] and is known as the feedback technique.
  • the basic principle relies on the fact that the counter-propagating diffracted beams in the feedback path have different frequencies, since one is upshifted by the acoustic frequency and the other downshifted.
  • the round-trip phase shifts experienced by these beams along the feedback path are different, hence the effective diffraction losses experienced by counter-propagating beams in the main laser cavity are also different, and unidirectional lasing occurs preferentially in the lower loss direction.
  • the choice of which of the two A-0 techniques is most suitable depends on the details of the particular laser, the resonator and modulator design, and on the desired mode of operation (i.e. continuous wave or Q-switched). In many situations either technique works perfectly well.
  • Acousto-optic techniques for enforcing unidirectional operation of ring lasers offer a number of benefits over the Faraday isolator approach. In particular, since they do not rely on polarisation discrimination they can readily be used with birefringent laser materials.
  • the acousto-optic approach to unidirectional operation also offers the advantages of relatively low insertion loss (since only a single extra intracavity component is required) and unidirectional operation over a wide spectral range.
  • the acousto-optic modulator can also be operated as a Q-switch to obtain high peak power, pulsed, single frequency operation.
  • an acousto-optic device for enforcing unidrectional operation in a ring laser, the device comprising a medium in which travelling acoustic waves " are induced, in use, in order to effect deflection of light transmitted therethrough, the device being characterised in that the said medium is a laser-active medium which, in use, acts as the gain medium of the laser.
  • the acousto-optic unidirectional device is fabricated from the laser material itself. This is a novel and very useful extension of existing acousto-optic techniques, which avoids the problems outlined above, and is therefore expected to have far-reaching consequences for the improved design of miniature single-frequency ring lasers and therefore will have important industrial applications.
  • Many solid-state laser materials are themselves not considered as suitable candidates for most acousto-optic applications since their acousto-optic figure of merit is generally small, and therefore they cannot provide sufficient diffraction loss at reasonable radio frequency powers.
  • Figure 1 shows a side view of a travelling-wave acousto-optic modulator fabricated from a solid-state laser material
  • Figures 2,3 and 4 are examples of ring lasers which incorporate an acousto-optic modulator, where it serves as both the laser gain medium and the device for enforcing unidirectional operation.
  • the acousto-optic modulator is of the usual construction consisting of a transducer 10, bonded to the deflection (acousto-optic) medium 11, which in this case is also the solid-state laser gain medium (e.g. neodymium-doped phosphate glass). Acoustic waves are generated in the deflection medium by applying a radio-frequency (r.f.) drive signal to the transducer via electrodes located on its upper surface.
  • r.f. radio-frequency
  • acoustic waves When used as a unidirectional device in a ring laser it is desirable (though not always essential) for acoustic waves to be absorbed after propagating through the deflection medium in order to prevent a standing-acoustic wave pattern being set up which would adversely affect the performance. For this reason, and in common with many other applications (e.g. Q-switching) , an absorbing medium 15 is bonded to the lower surface of the modulator. In addition, and as an extra precaution against the occurrence of standing-waves, it is also the usual practice to angle the lower surface 16 of the deflection medium 11.
  • the cross-sectional shape of the acousto-optic modulator depends on the design of the ring resonator configuration to be used. This is illustrated in the examples shown in figures 2,3 and 4.
  • Figure 2 shows a ring laser with a triangular configuration defined by mirrors 17, 18 and 19, at least one of which must be curved for cavity stability.
  • the acousto-optic modulator 20, in this case, has a rectangular cross-section with anti-reflecting dielectric coatings on its two end faces.
  • An alternative ring resonator configuration is shown in figure 3, which consists of only two mirrors 21 and 22, and a rhomb-shaped acousto-optic modulator 23 such as is described in Clarkson, W.A., and Hanna, D.C., "Acousto-optically induced unidirectional single mode operation of a Q-switched miniature Nd:YAG ring laser," Opt. Comm, 81,375 [1991]).
  • this resonator is such that the laser beam strikes each of the four faces of the modulator at Brewster's angle in order to minimise the cavity loss.
  • Both of these lasers can be pumped longitudinally by a second laser (e.g. a diode laser).
  • Unidirectional operation can be achieved via one of two techniques, which both rely on the travelling-wave nature of the acousto-optic device.
  • the first technique makes use of an intrinsic property of all travelling-wave acousto-optic modulators, namely that the Bragg incident angle (that is, the angle that the incident laser beam makes with the acoustic wavefronts for the maximum diffracted power), is different for oppositely travelling beams.
  • the Bragg condition cannot be satisfied simultaneously for both counter-propagating beams and as a consequence they generally experience different diffraction losses. It is this difference in the diffraction losses which can be used to enforce unidirectional operation.
  • the procedure involves applying radio-frequency power to the acousto-optic modulator and tilting the modulator away slightly from the nominal Bragg angle so as to increase the loss difference.
  • the magnitude of the loss difference depends on a number of factors including; the acousto- optic modulator design, its orientation, the acousto-optic properties of the deflection medium and the radio-frequency power and drive frequency. By the appropriate choice of these parameters unidirectional operation can usually be achieved. It is the normal procedure with this technique to add an aperture in the laser cavity to prevent multiple reflections, between the cavity mirrors, of the diffracted beams. This avoids the feeding back of the diffracted beams into the acousto-optic modulator which can give rise to changes in the value of the loss difference.
  • an alternative method of enforcing unidirectional operation is the feedback technique outlined above.
  • the procedure involves feeding back the diffracted beams into the acousto-optic modulator so that they approximately re-trace their original paths. This can be done with additional mirrors or alternatively, if the appropriate laser resonator is used, by the laser mirrors themselves.
  • the resonator can be monolithic and hence fabricated entirely from the laser medium.
  • a typical example of such a ring laser is illustrated in figure 4, where the laser gain medium 25 is also the acousto-optic modulator and the mirrors 26 and 27 are coated directly on to the laser medium.
  • the ring path is completed by a total internal reflection 28 at the boundary 29 between the laser medium and air.
  • Monolithic ring resonators would offer the advantages of being extremely compact and robust, and would offer the additional advantage of very stable operation without necessitating the use of complex and expensive stabilisation electronics.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Optics & Photonics (AREA)
  • Lasers (AREA)

Abstract

Un modulateur acousto-optique dans un laser en anneau comprend un transducteur (10) collé à un milieu de déflexion (11). Le milieu de déflexion est un milieu activé par laser qui, lors de l'utilisation, agit comme le milieu de gain du laser. Des ondes acoustiques sont induites dans le milieu de déflexion (11) de manière à effectuer la déflexion de la lumière transmise à travers ce milieu. Le modulateur peut ainsi être formé en un seul bloc, le milieu de gain du laser en anneau produisant un dispositif robuste et stable.
PCT/GB1994/000371 1993-03-01 1994-02-24 Dispositif acousto-optique WO1994021012A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9304077.2 1993-03-01
GB939304077A GB9304077D0 (en) 1993-03-01 1993-03-01 Acousto-optic device

Publications (1)

Publication Number Publication Date
WO1994021012A1 true WO1994021012A1 (fr) 1994-09-15

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Family Applications (1)

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PCT/GB1994/000371 WO1994021012A1 (fr) 1993-03-01 1994-02-24 Dispositif acousto-optique

Country Status (2)

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GB (1) GB9304077D0 (fr)
WO (1) WO1994021012A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996024971A1 (fr) * 1995-02-10 1996-08-15 Thorsteinn Halldorsson Gyroscope a laser annulaire a solide et pompage par diodes
FR2854947A1 (fr) * 2003-05-16 2004-11-19 Thales Sa Gyrolaser a etat solide stabilise par des dispositifs acousto-optiques

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0354985A2 (fr) * 1988-08-19 1990-02-21 Hewlett-Packard Company Laser annulaire unidirectionnel en deux blocs
US4955034A (en) * 1989-03-01 1990-09-04 Electro-Optics Technology, Inc. Planar solid state laser resonator
WO1990012435A1 (fr) * 1989-04-12 1990-10-18 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Laser a anneau

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0354985A2 (fr) * 1988-08-19 1990-02-21 Hewlett-Packard Company Laser annulaire unidirectionnel en deux blocs
US4955034A (en) * 1989-03-01 1990-09-04 Electro-Optics Technology, Inc. Planar solid state laser resonator
WO1990012435A1 (fr) * 1989-04-12 1990-10-18 The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Laser a anneau

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
A.R. CLOBES ET AL,: "Single-frequency traveling-wave Nd: YAG laser", APPL. PHYS. LETT., vol. 21, no. 6, September 1972 (1972-09-01) *
THOMAS J. KANE ET AL,: "Monolithic, unidirectional single-mode Nd:YAG ring laser", OPTICS LETTERS, vol. 10, no. 2, February 1985 (1985-02-01), XP000567906 *
W.A. CLARKSON ET AL,: "Explanation of the mechanism for acousto-optically induced unidirectional operation of a ring laser", OPTICS LETTERS, vol. 17, no. 8, April 1992 (1992-04-01) *
W.A. CLARKSON ET AL: "Acousto-optically induced unidirectional operation of a ring laser: a feedback mechanism", OPTICS COMMUNICATIONS, vol. 91, 1992, pages 365 - 370, XP024490737, DOI: doi:10.1016/0030-4018(92)90361-T *
W.A. CLARKSON ET AL: "Acousto-optically induced unidirectional single mode operation of a Q-switched miniature Nd:YAG ring laser", OPTICS COMMUNICATIONS, vol. 81, no. 6, March 1991 (1991-03-01), XP025849746, DOI: doi:10.1016/0030-4018(91)90601-9 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996024971A1 (fr) * 1995-02-10 1996-08-15 Thorsteinn Halldorsson Gyroscope a laser annulaire a solide et pompage par diodes
US5960022A (en) * 1995-02-10 1999-09-28 Daimler-Benz Aerospace Ag Diode-pumped solid-state ring laser gyroscope
FR2854947A1 (fr) * 2003-05-16 2004-11-19 Thales Sa Gyrolaser a etat solide stabilise par des dispositifs acousto-optiques
WO2004102120A1 (fr) * 2003-05-16 2004-11-25 Thales Gyrolaser a etat solide stabilise par des dispositifs acousto-optiques
US7446879B2 (en) 2003-05-16 2008-11-04 Thales Solid-state gyrolaser stabilised by acousto-optic devices

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GB9304077D0 (en) 1993-04-14

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