WO2005088782A1 - Amplificateur optique - Google Patents

Amplificateur optique Download PDF

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Publication number
WO2005088782A1
WO2005088782A1 PCT/AU2005/000354 AU2005000354W WO2005088782A1 WO 2005088782 A1 WO2005088782 A1 WO 2005088782A1 AU 2005000354 W AU2005000354 W AU 2005000354W WO 2005088782 A1 WO2005088782 A1 WO 2005088782A1
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Prior art keywords
gain medium
composite slab
laser
cladding layers
slab gain
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PCT/AU2005/000354
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English (en)
Inventor
Damien Troy Mudge
Peter John Veitch
Jesper Munch
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Adelaide Research & Innovation Pty Ltd
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Priority claimed from AU2004901320A external-priority patent/AU2004901320A0/en
Application filed by Adelaide Research & Innovation Pty Ltd filed Critical Adelaide Research & Innovation Pty Ltd
Publication of WO2005088782A1 publication Critical patent/WO2005088782A1/fr

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    • 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
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/08—Catadioptric systems
    • G02B17/0856—Catadioptric systems comprising a refractive element with a reflective surface, the reflection taking place inside the element, e.g. Mangin mirrors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/08—Catadioptric systems
    • G02B17/0856—Catadioptric systems comprising a refractive element with a reflective surface, the reflection taking place inside the element, e.g. Mangin mirrors
    • G02B17/086—Catadioptric systems comprising a refractive element with a reflective surface, the reflection taking place inside the element, e.g. Mangin mirrors wherein the system is made of a single block of optical material, e.g. solid catadioptric systems
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
    • 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
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • 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
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/042—Arrangements for thermal management for solid state 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
    • H01S3/0612—Non-homogeneous structure
    • 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
    • H01S3/0615—Shape of end-face
    • 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
    • H01S3/08095—Zig-zag travelling beam through the active medium
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094049—Guiding of the pump light
    • H01S3/094053—Fibre coupled pump, e.g. delivering pump light using a fibre or a fibre bundle
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094049—Guiding of the pump light
    • H01S3/094057—Guiding of the pump light by tapered duct or homogenized light pipe, e.g. for concentrating pump light
    • 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
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1618—Solid materials characterised by an active (lasing) ion rare earth ytterbium
    • 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
    • H01S3/163—Solid materials characterised by a crystal matrix
    • H01S3/164—Solid materials characterised by a crystal matrix garnet
    • H01S3/1643—YAG
    • 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
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2325—Multi-pass amplifiers, e.g. regenerative amplifiers
    • H01S3/2333—Double-pass amplifiers

Definitions

  • the present invention relates to solid-state optical amplifiers for use in high brightness, high power optical amplifiers and lasers.
  • the invention relates to optical pumping arrangements for these devices.
  • Some examples of this approach include end-pumped Yb:YAG and Nd:YAG rod lasers.
  • Another further example that incorporates an end-pumped slab laser architecture is disclosed in US Patent 6,268,956 which describes an optical amplifier that includes an elongated slab of solid state lasing material, such as a rare earth doped Yttrium- Aluminium-Garnet (YAG) slab.
  • the optical amplifier incorporates end pumping in which the pumped light is co-aligned with the amplified light.
  • the co-aligned pumped sources are directed to lateral faces of the slab which include footprints or windows.
  • the end faces are formed at about a 45 degree angle relative to the longitudinal axis which causes the pumped light to be reflected within the slab coaxially with amplified light.
  • the slab may be formed from a composite material with the opposing end portions of the slab formed from an undoped host material while the centre portion of the slab along the longitudinal axis is forxned from a doped host material.
  • these devices also suffer beam quality defects wl en progressing to higher energies, these being due to thermally induced birefrirLgence and bi-focusing.
  • the decrease in efficiency resulting from these effects can be somewhat mitigated by the further inclusion within the optical resonators and lasers of matched pairs of rod gain media, quartz polarization rotators that rotate the polarization state by 90 degrees as it propagates from one rod to the next and furthermore carefully located image relay lenses.
  • quartz polarization rotators that rotate the polarization state by 90 degrees as it propagates from one rod to the next and furthermore carefully located image relay lenses.
  • the addition of these components adds further cost and complexity to these devices.
  • the present invention accordingly provides an elongate composite slab gain medium for producing laser radiation, said composite slab gain medium defining a longitudinal axis and including: a layer of laser-active material having first and second opposed lateral surfaces arranged substantially parallel to said longitudinal axis; and displacement means to displace by a predetermined distance successive entry points into at least one of said lateral surfaces of a light ray travelling in a zigzag path longitudinally along said composite slab gain medium.
  • said zigzag path travels substantially in a plane defined by said longitudinal axis and a normal to said lateral surfaces. This arrangement further promotes effective and uniform interaction of the light ray with the laser-active material.
  • said displacement means includes a pair of inner cladding layers hav ng a refractive index substantially matched to said laser-active layer and arranged parallel to said first and second opposed lateral surfaces to reflect said light ray into said laser-active layer.
  • This geometry allows a light ray whicl ⁇ has traversed the thickness of the laser-active layer at an angle to exit the laser-active material and to then successively re-enter the laser-active material at displaced entry points longitudinally along the laser-active material.
  • said light ray is reflected from an outer surface of said inner cladding layer.
  • said light ray is optically pumping said laser-active layer of said composite slab gain medium.
  • This arrangement is particularly suitable for optical amplifiers.
  • the present invention accordingly provides a method for controlling the trajectory of a light ray travelling in a zigzag path along an elongate composite slab gain medium, said composite slab gain medium defining a longitudinal axis and including a layer of laser-active material having first and second opposed lateral surfaces arranged substantially parallel to said longitudinal axis, said method including the step: displacing successive entry points into at least one of said first and second lateral surfaces of said laser-active medium of said light ray by a predetermined distance.
  • the present invention accordingly provides a method for optically pumping an elongate composite slab gain medium, said elongate composite slab gain medium defining a longitudinal axis and said method including the steps: injecting pump light into said elongate composite slab gain medium, said composite slab gain medium including a layer of laser-active material having first and second opposed lateral surfaces arranged substantially parallel to said longitudinal axis and a pair of inner cladding layers arranged substantially parallel to said first and second opposed lateral surfaces to clad said layer of laser-active material, wherein said pump light is injected substantially at an angle to the longitudinal axis in a plane defined by said longitudinal axis and a normal to said inner cladding layers; and reflecting said pump light from at least one of said inner cladding layers.
  • injecting pump light into said elongate composite slab gain medium said composite slab gain medium including a layer of laser-active material having first and second opposed lateral surfaces arranged substantially parallel to said longitudinal axis and a pair of inner cladding layers arranged substantially parallel to said first and second
  • FIGURE 1(a) is a side elevation view of a elongate composite slab gain medium according to an embodiment of the invention
  • FIGURE 2(a) is a side elevation view of an optical amplifier incorporating the elongate composite slab gain medium illustrated in Figure 1(a) according to an embodiment of the invention
  • FIGURE 2(b) is a top sectional view through AA of the optical amplifier illustrated in
  • FIGURE 3(a) is a side elevation view of an optical amplifier incorporating a different optical pumping means to that illustrated in Figure 2(a) according to an embodiment of the invention
  • FIGURE 4 is a detailed view of the composite slab gain medium illustrated in the previous Figures depicting the trajectory of a pump light ray bundle;
  • FIGURE 5 is an optical amplifier incorporating close coupled fibres as the optical pumping means according to an embodiment of the invention.
  • FIGURE 6(a) is a side elevation view of the composite slab gain medium illustrated in the previous Figures with the ends clad with laser inactive material according to an embodiment of the invention
  • FIGURE 6(b) is a top sectional view through AA of the composite slab gain medium as illustrated in Figure 6(a);
  • FIGURE 7(a) is a side elevation view of an optical amplifier including an alternative arrangement for the composite slab gain medium according to an embodiment of the invention;
  • FIGURE 7(b) is a sectional view through AA of the optical amplifier illustrated in Figure 7(a);
  • FIGURE 7(c) is an end elevation view of the optical amplifier illustrated in Figure 7(a) depicting the optical pumping means;
  • FIGURE 8(a) is a detailed end elevation view of an optical amplifier having alternative optical pumping means to that illustrated in Figures 7(a) to (c) according to an embodiment of the invention
  • FIGURE 8(b) is a plan view of the optical amplifier illustrated in Figure 8(a);
  • FIGURE 9(a) is a detailed end elevation view of an optical amplifier having alternative optical pumping means to that illustrated in Figures 7(a) to (c) and 8(a) to
  • FIGURE 9(b) is a plan view of the optical amplifier illustrated in Figure 9(a);
  • FIGURE 10(a) is an elevation view of the elongate composite slab gain medium as illustrated in Figures 7(a) to (c) and 8(a) to 8(b) and 9(a) to 9(b) with the ends clad with laser-inactive material; and
  • FIGURE 10(b) is a sectional view through AA of the elongate composite slab gain medium as illustrated in Figure 10(a).
  • composite slab 1 an elongate composite slab gain medium 1 (hereinafter composite slab) according to an embodiment of the present invention.
  • composite slab 1 is arranged in a co-planar folded zigzag architecture (see for example United States Patent No. 5,651,021) in which a laser beam 2 enters and exits the slab 1 at Brewsters' angle through two windows 3 at one end of the slab, and is totally internally reflected each time it encounters lateral edges 4.
  • the laser beam is totally internally reflected at end surface 5 of slab 1.
  • a multi-layer dielectric coating is deposited on surface 5 to provide low reflectance at a pump wavelength and high reflectance at the laser wavelength.
  • Laser-active layer 6, having refractive index m is clad on opposed lateral surfaces by an inner laser-inactive cladding 7, having refractive index , and an outer laser- inactive cladding 8, having refractive index n 3 , where n ⁇ n ⁇ > ns.
  • Laser-active layer 6 and inner cladding 7 are joined using an optical or adhesive-free bond such as that described in US Patent No. 5,852,622.
  • the outer cladding 8 may similarly be bonded to inner cladding 7, or alternatively be located in close proximity to the outer surface of inner cladding.
  • the outer cladding layer 8 has a high thermal resistance to minimize heat loss in the direction perpendicular to the layers.
  • Opposing lateral surfaces 4 are coated with a dielectric layer, Si0 2 for example, having a thickness typically greater than about 2 ⁇ m. This prevents disruption of the total internal reflection of the laser beam at surfaces 4 by cooling mechanisms applied to surfaces 4.
  • FIGs 2(a) and (b) there is shown an optical amplifier incorporating the composite slab 1 illustrated in Figures 1(a) and (b) and optical pumping means which injects pump light into composite slab 1 at an angle to the longitudinal axis in the plane defined by the longitudinal axis and the normal to the cladding layers.
  • a non-imaging lens duct 9 such as for example similar to that described in U.S. Patent No. 5,307,430, funnels the pump light emitted by a 2-dimensional array of optical fibres 10, which in turn are coupled to an array of diode lasers (not shown).
  • the entrance surface 12 of duct 9 is angled relative to the exit surface 13 so as to inject the pump light into composite slab 1 at an angle to the longitudinal axis in the plane defined by the longitudinal axis and the normal to the cladding layers 7 and 8.
  • a multi-layer dielectric coating is deposited on surface 12 of duct 9 to provide low reflectance for the pump light.
  • a multi-layer dielectric coating is deposited on surface 13 of duct 9 to provide low reflectance for the pump light at the appropriate angle of incidence.
  • Opposing lateral surfaces 14 of lens duct 9 are coated with a dielectric layer, Si0 2 for example, having a thickness greater than about 2 ⁇ m, so as to prevent disruption of the total internal reflection at the surfaces 14 by the mechanism used to hold duct 9.
  • FIG. 3(a) and (b) there is shown an alternative optical pumping means wherein pump light emitted from a fast-axis collimated diode array stack 11 is injected into composite slab 1.
  • Pump rays 15, 16 and 17 indicate the trajectories of the fan of pump rays emitted by a single optical fibre 10 or single emitter in the fast-axis collimated array 11.
  • Ray 15 represents the optical axis of that fan.
  • pump rays 18, 19 and 20 indicate the trajectories of a fan of pump rays injected at a single point on end surface 5.
  • Ray 18 represents the optical axis of that fan.
  • the end surface 5, which comprises only the laser-active layer and the inner cladding layer, is densely covered with similar sets of ray fans 18, 19 and 20. Those fans that initially encounter the inner cladding are not absorbed until they traverse the laser-active layer, thereby ensuring that pump light absorption is distributed along the slab.
  • FIG. 5 there is shown another embodiment of an optical amplifier wherein the optical fibre pump sources 10 are close coupled to composite slab 1 which is suitable for those applications where reduced complexity is required as a trade-off to potentially non-uniform pumping and therefore some wavefront distortion.
  • FIG. 6(a) and (b) there is shown another embodiment of the composite slab gain medium 21, wherein one or both of the end surfaces of the composite slab 21 are clad with a laser-inactive material 22, using an optical or adhesive-free bond such as that described in US Patent No. 5,852,622.
  • the laser-inactive end caps 22 ensure that the heat deposited within the composite slab 21 by the optical pumping is separated from the end surfaces that may otherwise warp, thereby causing wavefront distortion.
  • FIG. 7(a), (b) and (c) there is shown another embodiment of an optical amplifier, wherein composite slab 23 is essentially the same as that shown in Figures 1(a) and (b).
  • laser beam 24 enters composite slab 23 via a suitably coated window 25 at one end, is totally internally reflected each time it encounters the lateral surfaces 26, and then exits the composite slab through a suitably coated window 27.
  • Pump light is injected into composite slab 23 through one or more windows 28 onto which may be deposited dielectric coating(s) to form an anti-reflection coating at the pump wavelength.
  • Remaining lateral surfaces 26 are coated with a low thermal resistance, dielectric coating having a thickness sufficient to prevent disruption of the total internal reflection of the laser beam by cooling mechanisms applied to these surfaces.
  • the pump light is injected into slab 23 such that it propagates at an angle to the longitudinal axis in the plane defined by the longitudinal axis and the normal to the cladding layers.
  • One or both of the end surfaces of composite slab 23 are orientated at an angle a of approximately 45 degrees to the longitudinal axis to direct the pump light in the longitudinal direction but at an angle to the longitudinal axis as described above.
  • the end surfaces are coated with multi-layer dielectric coatings such that the reflectance of the pump light is maximal while the reflectance of the laser beam is minimal.
  • Optical pumping means including a 2-dimensional array of optical fibres 10 that are coupled to diode lasers (not shown) directly injects pump light through the windows 28 of composite slab 23.
  • Composite slab 23 provides more spatial separation between the input and output laser beams 24 compared to the input and output beams 2 in composite slab 1, which can be convenient for some amplifier or laser resonator designs. Further, composite slab 23 may be optically pumped from both ends, which could be useful for quasi-3- level gain media such as Yb:YAG, where it is important that a population inversion is created in all of the gain medium through which the laser beam passes. However, composite slab 23 may have a smaller gain-length product than composite slab 1, which may be an important consideration for some amplifier or laser resonator designs.
  • optical pumping means that includes a non-imaging lens duct 29 that funnels pump light emitted by a 2- dimensional array of optical fibres 10 that are coupled to an array of diode lasers through windows 28 of composite slab 23 illustrated in Figures 7(a) and (b).
  • optical pumping means that includes a non-imaging lens duct 29 that instead funnels pump light emitted by a fast-axis collimated diode array stack 11 to the composite slab 23.
  • the entrance surface 30 of duct 29 is angled relative to exit surface 31 so as to inject the pump light into composite slab 23 at an angle to the longitudinal axis in the plane defined by the longitudinal axis and the normal to the cladding layers 7 and 8.
  • a multi-layer dielectric coating is deposited on the surface 30 of duct 29 to provide low reflectance for the pump light.
  • a multi-layer dielectric coating is deposited on surface 31 of duct 29 to provide low reflectance for the pump light at the appropriate angle of incidence.
  • Opposing lateral surfaces 32 of the lens duct 29 are coated with a dielectric layer, having a thickness greater than about 2 ⁇ m, so as to prevent disruption of the total internal reflection of the pump light at the surfaces 32 by the mechanism used to hold duct 29.
  • FIG. 10(a) and (b) there is shown an elongate composite slab gain medium 33 of the type illustrated in Figures 7(a) to (c) and 8(a) to 8(b) and 9(a) to (9b), further incorporating one or both of the end surfaces of the composite slab 33 being clad with a laser-inactive material 34 to further reduce wavefront distortion.
  • the thickness and doping concentration of the laser-active layer and the thickness of the inner cladding layers of the composite slab are determined by a multi-parameter optimisation procedure.
  • This optimisation procedure is described here but as would be apparent to those skilled in the art different optimisation approaches may be used.
  • a particular application will necessarily determine the length and width of the composite slab and the absorbed pump power required.
  • the thickness of the laser- active layer is also determined by considering the thermally induced stresses and the fracture strength of the material selected for the laser-active layer.
  • the critical angle for total internal reflection at the outer surfaces of the inner cladding is used to determine the smallest allowed angle of incidence of the steepest pump ray 20 (see Figure 4), which determines the maximum angle between the injected pump light and the longitudinal axis. Initially, as an example, an injection- angle about 4 degrees less than the maximum angle is chosen. Then, for rays 18-20 within ray fans injected into the composite slab, the path lengths through the laser- active layer as they propagate longitudinally are calculated for various thicknesses of the inner cladding layers. From the calculated path lengths and the required pump absorption, the doping concentrations are then calculated. This process is then repeated for various angles of injection of the pump light. In general, decreasing the angle of injection would require the doping concentration to be increased, which may not be possible in all circumstances.
  • the laser-active medium 6 is an approximately 2 mm thick layer of 0.6% Nd:YAG.
  • the optical axis of the injected pump light 18 is at an angle of about 25 degrees to the longitudinal axis.
  • the inner cladding 7 is fabricated from ndoped YAG, with each layer having a thickness of approximately 2 mm.
  • the outer cladding 8 is fabricated from BK1 glass with a thickness that is determined by thermal lensing considerations but is typically greater than 0.5 mm.
  • the invention can be applied to composite slabs using other suitable laser- active materials which include but are not limited to Nd:YAG, Nd:YV0 , Nd:YALO, Yb:YAG, Tm:YAG, Er:YAG, Tm:YAG and Tm:Ho:YAG.
  • the invention may be applied to composite slabs in which lateral surfaces 4 and 26 are coated with a highly reflective coating at the laser wavelength for those instances where relying on total internal reflection to reflect the laser light within the slab is not suitable.
  • reflection at the inner cladding could be provided by a highly reflective coating at the pump wavelength rather than relying on total internal reflection at the outer surface of the inner cladding layer as contemplated in the embodiments described herein.
  • the optical amplifier according to the present invention provides numerous significant advantages over prior-art end-pumped slab and waveguide type optical amplifiers and lasers. Due to the pump light successively crossing the laser-active layer as it travels longitudinally down the composite slab the pump light is more uniformly absorbed throughout the laser-active medium. This then reduces wavefront distortion and minimizes birefringence and bi-focussing in the laser-active region, which improves overall efficiency and brightness.
  • this feature also allows the use of more extended pump sources than in waveguide optical amplifiers and lasers, as the zigzag of the pump light ensures that light injected into the cladding will propagate through and be absorbed by the laser- active material without requiring propagation distances that are much longer than typical slab lengths. This will significantly simplify pump architectures and reduce costs.
  • an advantage of the present invention is that heat may be removed through the lateral edges perpendicular to the cladding and laser-active layers. Heat removal may be effected using either contact gas or liquid forced- convection cooling, or conduction cooling.
  • gas or liquid cooling gaskets are used to control the flow of the coolant.
  • a dielectric coating applied to the cooled lateral edges prevents degradation of the total internal reflection of the laser beam from these lateral edges.
  • conduction cooling a soft metal, such as indium or gold, is used to ensure good thermal contact between metallic conduction cooling fingers and the lateral edges of the composite slab.
  • the metallic cooling fingers can themselves be cooled using, for example, either forced-convention or heat-pipes or thermo-electric or Peltier cells. Generally the cooling fingers contact the lateral edges only at the laser-active layer so as to minimize the resultant thermal gradient in the direction perpendicular to the layers. Again the dielectric coating on the cooled lateral edges will prevent degradation of the total internal reflection of the laser beam.
  • the thickness of the laser-active layer in the composite slab of the present invention is much greater than that in waveguide optical amplifiers and lasers, in which it is typically 10 ⁇ m.
  • waveguide optical amplifiers the heat is removed in the direction perpendicular to the layers and there is minimal thermal lensing in the direction perpendicular to the layers.
  • the thickness of the laser- active layer must be increased, leading to formation of a strong thermal lens, which would reduce the efficiency of the waveguide optical amplifier.
  • the significantly thicker laser-active layer in the present invention allows cooling via the lateral edges perpendicular to the layers. The resulting thermal lens is mitigated by the zigzag path of the laser beam.
  • the present invention facilitates the production of optical amplifiers and resonators that can provide high output powers as the thickness of the laser-active layer may be increased as the pump power is increased, thereby preventing the degradation of the thermal gradients and stresses within the laser-active laser and thus maintaining good beam quality.
  • the cladding of the laser-active layer with laser-inactive layers increases the aspect ratio of the slab compared to that of an unclad slab. It is well known to those skilled in the art that uniformly pumped slabs with large lateral aspect ratios have lower thermally induced stresses and are therefore less likely to fracture than those with aspect ratios of order unity. This rule also applies to non-uniformly pumped slabs.
  • the increased aspect ratio of the composite slab in the present invention compared with that of prior-art end-pumped slabs, enables more intense pumping without fracture, which will increase the gain of the amplifier and thus improve the efficiency.
  • the present invention also provides for the removal of hard-edged apertures on the laser-active region in the direction perpendicular to the layers. This feature allows good overlap of the lowest-order optical mode with the laser-active region, compared with prior-art end-pumped lasers, which will significantly improve efficiency.
  • the optical amplifier may be used to amplify a laser beam.
  • a laser beam 2 from a master oscillator is directed through the pumped composite slab 1 as shown (see Figures 1(a) and (b)) and described above, thereby forming a master- oscillator-power-amplifier (MOP A) system.
  • MOP A master- oscillator-power-amplifier
  • the optical amplifier in the present invention may also be used to form an optical oscillator by using mirrors to partially reflect the laser beams back into the amplifier. The oscillator may then be employed to produce a continuous laser beam, or a pulsed beam if a Q-switch is incorporated in the resonator.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Lasers (AREA)

Abstract

L'invention porte sur un barreau composite allongé servant de milieu (1) de gain en vue de la production de rayons laser. La longueur du barreau composite servant de milieu (1) de gain définit un axe longitudinal (A-A), ledit barreau (1) comportant une couche de matériau actif (6) pour laser et une première et une deuxième surfaces latérales opposées sensiblement parallèles audit axe longitudinal, et un moyen de déplacement (9) déplaçant d'une distance prédéterminée les points d'entrée successifs, dans l'une au moins des surfaces latérales, du rayon lumineux (10) progressant longitudinalement en zigzag le long du barreau composite.
PCT/AU2005/000354 2004-03-15 2005-03-15 Amplificateur optique WO2005088782A1 (fr)

Applications Claiming Priority (2)

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AU2004901320A AU2004901320A0 (en) 2004-03-15 Optical amplifier
AU2004901320 2004-03-15

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WO2005088782A1 true WO2005088782A1 (fr) 2005-09-22

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100399652C (zh) * 2006-07-28 2008-07-02 中国科学院上海光学精密机械研究所 包层掺杂的平板波导激光放大器
US7756167B2 (en) 2005-12-05 2010-07-13 Adelaide Research & Innovation Pty Ltd. Q-switched laser
US11289872B2 (en) * 2017-12-28 2022-03-29 Mitsubishi Electric Corporation Planar waveguide and laser amplifier
CN114824998A (zh) * 2022-06-30 2022-07-29 中国工程物理研究院应用电子学研究所 一种高交叠效率分布反射式直接液冷激光增益装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5729375A (en) * 1996-03-01 1998-03-17 Hughes Electronics Optical amplification system with non-orthogonal signal and distributed multi-pump beams and photorefractive cleanup
EP1063743A1 (fr) * 1998-03-12 2000-12-27 Vasily Ivanovich Shveikin Amplificateur optique a semi-conducteur
EP0973236B1 (fr) * 1998-07-07 2004-09-08 Northrop Grumman Corporation Matériau actif pour laser en plaque "zig-zag" pompée à une extrémité

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5729375A (en) * 1996-03-01 1998-03-17 Hughes Electronics Optical amplification system with non-orthogonal signal and distributed multi-pump beams and photorefractive cleanup
EP1063743A1 (fr) * 1998-03-12 2000-12-27 Vasily Ivanovich Shveikin Amplificateur optique a semi-conducteur
EP0973236B1 (fr) * 1998-07-07 2004-09-08 Northrop Grumman Corporation Matériau actif pour laser en plaque "zig-zag" pompée à une extrémité

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7756167B2 (en) 2005-12-05 2010-07-13 Adelaide Research & Innovation Pty Ltd. Q-switched laser
CN100399652C (zh) * 2006-07-28 2008-07-02 中国科学院上海光学精密机械研究所 包层掺杂的平板波导激光放大器
US11289872B2 (en) * 2017-12-28 2022-03-29 Mitsubishi Electric Corporation Planar waveguide and laser amplifier
CN114824998A (zh) * 2022-06-30 2022-07-29 中国工程物理研究院应用电子学研究所 一种高交叠效率分布反射式直接液冷激光增益装置

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