Method and apparatus for efficient operation of an optically pumped laser

Abstract

An optically pumped single mode laser, e.g. Nd:YAG crystal (20) with planoconcave mirrors is increased in efficiency by an order of magnitude to about 8% by optics (25, 27) for focusing the high power multimode output of laser diode arrays (21, 22) into the mode volume (20') of the laser medium (20). A plurality of these optically pumped single mode lasers (1-4) may be cascaded in a ring with dichroci mirrors (M 1 -M 4 ) at the corners for coupling in the laser diode arrays, each having its own means for spatially tailoring its beam to concentrate pump distribution inside the lasing mode volume of the medium. An InGaAlAs pump diode (30) with its wavelength of the same as a lasing medium makes the ring unidirectional. The questions raised in reexamination request No. 90/002,473, filed Oct. 10, 1991, have been considered and the results thereof are reflected in this reissue patent which constitutes the reexamination certificate required by 35 U.S.C. 307 as provided in 37 CFR 1,570(e).

What is claimed is: 
     
       1. .[.An optically.]. .Iadd.A Laser diode pumped .Iadd.single mode .Iaddend.laser comprising an optical resonator cavity, a laser medium in said resonator cavity, said laser medium having an optical axis and two ends, one end at each of two opposite sides of said medium intersected by said optical axis, an array of laser diodes positioned for pumping said laser medium in the direction of the axis of said resonator cavity, .Iadd.said laser diode array being a source of light of poor spatial and spectral qualities .Iaddend.and means for causing .[.the pump.]. distribution .Iadd.of the light .Iaddend.from .[.said.]. .Iadd.the .Iaddend.array of laser diodes to be concentrated inside .[.the.]. .Iadd.a .Iaddend.lasing mode volume of said medium .Iadd.at an imput pump power of at least 100 milliwatts.Iaddend.. .[. 
     
     
       2.  An optically pumped laser as defined in claim 1 wherein an array of laser diodes and said means for concentration is provided at both ends of said medium, and including a mirror for separating the output of said medium as an output beam from the pump distribution at one end of said medium..]. .[. 
     
     
       3.  An optically pumped laser as defined in claim 2 including a second array of laser diodes at one end of said medium, and means for combining at said one end the output of the second array of laser diodes with the output of the first array of laser diodes for a combined pumping beam into said lasing mode volume through separate means for each array of laser diodes for concentration of the pump distribution form each of said array of laser diodes inside the lasing mode volume of said medium..]. .[.4. An optically pumped laser as defined in claim 2 including a plurality of cascaded laser mediums arranged with separate mirrors to form a closed optical polygon for each laser medium, each laser medium having at least one laser diode array and means for concentration of pump distribution of light from the laser diode array into the lasing mode volume of the laser medium through one of said separate mirrors coupling said laser mediums in said polygon, an injection locking laser diode operating at the wavelength of said medium, and means for combining the output of said injection locking laser diode with the output of one array of laser diodes for pumping one of said mediums in a predetermined direction around said closed optical polygon, and means for extracting from said closed optical polygon output laser beam emanating from one medium in said predetermined direction..]. .[.5. An optically pumped laser as defined in claim 2 including a plurality of cascaded laser mode volumes arranged in a zig-zag pattem with the optical axis of adjacent optical mode volumes intersecting at a corner of said zig-zag pattern, a mirror at each corner, each mode volume having at each end a laser diode array and means for concentration of light from said laser diode array into the mode volume for pumping and means at one end of said zig-zag pattern for extracting an output laser 
     
     
        beam emanating from one laser mode volume..]. 6. .[.An optically.]. .Iadd.A laser diode .Iaddend.pumped single mode laser comprising an optical resonator cavity, a laser medium in said resonator cavity, said laser medium having an optical axis and two ends .Iadd.and being selected from the group (Nd:YAG, ND:GGG and Nd:YLF), .Iaddend.one end at each of two opposite sides of said laser medium intersected by said optical axis, an array of .[.multimode.]. laser diodes .Iadd.that provides multimode light .Iaddend.positioned for pumping said laser medium in the direction of the axis of said resonator cavity, and means for concentration of .[.the pump.]. .Iadd.a .Iaddend.distribution .Iadd.of the multimode light .Iaddend.from said .[.multimode.]. laser diodes inside .[.the.]. .Iadd.a 
     
     
        .Iaddend.lasing mode volume of said laser medium. .[.7.  An optically pumped singlemode laser as defined in claim 6 wherein an array of multimode laser diode and concentration means is provided at both ends of said laser medium, and including a mirror at one end of said laser medium for separating the singlemode output of said laser medium as an output beam..]. .[.8. An optically pumped singlemode laser as defined in claim 7 including a second array of multimode laser diodes at one end of said medium, and means for combining the output of said second array with the output of said first array of multimode laser diodes at said one end for a combined pumping beam directed into said means for concentration of the 
     
     
        pump distribution from said laser diodes..]. .[.9.  An optically pumped singlemode laser as defined in claim 6 including a plurality of cascaded single-mode laser mediums arranged in a closed optical polygon with a separate mirror between each pair of cascaded laser mediums, each medium having at each end a multimode laser diode array and concentration means for pumping through said separate mirrors between cascaded laser mediums into the mode volume of said laser medium between said separate mirrors, an injection locking laser diode operating at the wavelength of said medium, and means for combining the output of said injection locking laser diode with the output of one laser medium in a predetermined direction, and means for extracting from said closed optical polygon an output laser 
     
     
        beam emanating from one medium in said desired direction..]. .Iadd.10.  A laser diode pumped laser comprising an optical resonator cavity, a laser medium in said resonator cavity, the laser medium having an optical axis and two ends, one end at each of two opposite sides of the laser medium intersected by the optical axis, and array of laser diodes positioned for pumping the laser medium in the direction of the axis of the resonator cavity, the laser diode array being a source of light having poor spatial and spectral qualities, and means for concentrating a distribution of the light from the laser diodes inside a lasing mode volume of the laser medium such that the laser exhibits an overall electrical-to-optical efficiency of approximately five (5) percent or more. .Iaddend. .Iadd.11. A laser diode pumped laser comprising an optical resonator cavity, a laser medium in the resonator cavity, the laser medium having an optical axis and two ends, one end at each of two opposite sides of the medium intersected by the optical axis, first and second arrays of laser diodes, wherein one of said arrays is positioned at each of the two ends of said laser medium for pumping the medium at each end in the direction of the axis of the resonator cavity, each of the laser diode arrays being a source of light of poor spatial and spectral qualitites and means for causing a distribution of the light from each array of laser diodes to be concentrated inside a lasing mode volume of the medium. .Iaddend. 
     
     
        .Iadd.     A laser diode pumped laser comprising an optical resonator cavity, a laser medium in the resonator cavity, the laser medium having an optical axis and two ends, one end at each of two opposite sides of the medium intersected by the optical axis, first and second arrays of laser diodes positioned at one end of the medium for pumping the laser medium in the direction of the axis of the resonator cavity, the laser diode arrays each being a source of light of poor spatial and spectral qualities and a focusing subsystem including a coupling between the arrays of the laser medium other than a fiberoptical coupling for combining the light from the arrays to provide a distribution of the light concentrated inside a lasing mode volume of the medium. .Iadd.13. A laser diode pumped laser comprising a plurality of cascaded laser mediums forming a closed optical polygon in an optical resonator cavity, each laser medium having an optical axis and two ends, one end at each of two opposite sides of the medium intersected by the optical axis, each of the laser mediums being associated with an array of laser diodes positioned for pumping the laser medium in the direction of the optical axis, each of the laser diode arrays being a source of light of poor spatial and spectral qualities, means for causing a distribution of the light from each array of laser diodes to be concentrated inside a lasing mode volume of the associated laser medium, and means for extracting from the closed optical polygon an output laser 
     
     
        beam. .Iaddend. .Iadd.14.  A laser diode pumped laser as defined in claim 13 including a separate mirror between each pair of cascaded laser mediums. .Iaddend. .Iadd.15. A laser diode pumped laser as defined in claim 13 including an injection locking laser operating at the wavelength of the laser mediums and means for combining an output of the injection locking laser with the output of one array of laser diodes for pumping one of the laser mediums in a predetermined direction around the closed 
     
     
        optical polygon. .Iaddend. .Iadd.16.  A laser diode pumped laser comprising an optical resonator cavity, a laser medium in the cavity, a plurality of cascaded laser mode volumes in the laser medium each having first and second ends and collectively arranged in a zig-zag pattern, each laser mode volume having an optical axis such that the optical axes of adjacent optical mode volumes intersect at a corner of the zig-zag pattern, a mirror at each corner, a plurality of said mode volumes having a laser diode at one or both of said first and second ends for pumping the mode volume and means for concentration of light from each of the laser diodes into the mode volume being pumped and means at one end of the zig-zag pattern for extracting an output laser beam emanating from one of 
     
     
        the laser mode volumes. .Iaddend. .Iadd.17.  A laser diode pumped laser as defined in claim 16 wherein each mode volume has at each of its first and 
     
     
        second ends a laser diode array. .Iaddend. .Iadd.18.  A laser diode pumped laser comprising an optical resonator cavity, a laser medium in said resonator cavity, the laser medium having an optical axis and two ends, one end at each of two opposite sides of the laser medium intersected by the optical axis, an array of laser diodes positioned for pumping the laser medium in the direction of the axis of the resonator cavity, the laser diode array being a source of light having poor spatial and spectral qualities, and means for concentrating a distribution of the light from the laser diodes inside a lasing mode volume of the laser medium such that the laser medium exhibits an operating efficiency (η o ) of approximately 90 percent or more. .Iadd.19. A laser diode pumped laser comprising an optical resonator cavity, a laser medium in said resonator cavity, said laser medium having an optical axis and two ends and being selected from the group (Nd:YAG, Nd:GGG and Nd:YLF), one end at each of two opposite sides of said medium intersected by said optical axis, an array of laser diodes positioned for pumping said laser medium in the direction of the axis of said resonator cavity, the laser diode array being a source of light of poor spatial and spectral qualities and means for causing a distribution of the light from the array of laser diodes to be concentrated inside a lasing mode volume of said medium. .Iaddend. .Iadd.20. A laser diode pumped laser comprising an optical resonator cavity, a laser medium in said resonator cavity, said laser medium having an optical axis and two ends, one end at each of two opposite sides of said medium intersected by said optical axis, an array of laser diodes positioned for pumping said laser medium in the direction of the axis of said resonator cavity, the laser diode array being a source of light of poor spatial and spectral qualities and a focusing subsystem including a coupling between the array of laser diodes and the laser medium other than a fiberoptical coupling for concentrating a distribution of the light from the array of laser diodes inside a lasing mode volume of said medium. 
     
     
        .Iaddend. .Iadd.21.  An optically pumped laser comprising an optical resonator cavity, a laser medium in said resonator cavity, said laser medium having an optical axis and two ends, one end at each of two opposite sides of said laser medium intersected by said optical axis, an array of laser diodes positioned for pumping said laser medium in the direction of the axis of said resonator cavity, and means for causing the pump distribution from said array of laser diodes to be concentrated inside a lasing mode volume of said medium at an input pump power of at least 100 milliwatts. .Iaddend. .Iadd.22. An optically pumped laser comprising an optical resonator cavity, a laser medium in said resonator cavity, said laser medium having an optical axis and two ends, one end at each of two opposite sides of said laser medium intersected by said optical axis, an array of laser diodes positioned for pumping said laser medium in the direction of the axis of said resonator cavity, and means for causing the pump distribution from said array of laser diodes to be concentrated inside a lasing mode volume of said medium to provide an 
     
     
        output power of at least 80 milliwatts. .Iaddend. .Iadd.23.  A laser as defined in any one of claims 1, 6, 10, 11, 12, 13, 16, 18, 19, 20, 21 having an output power of at least 80 milliwatts. .Iaddend. .Iadd.24. A laser as defined in any one of claims 1, 6, 10, 18, 19, 20, 21 or 22 wherein the light from the array of laser diodes has more than one lobe and all of the lobes are directed into the lasing volume by the means for concentrating the distribution of the light. .Iaddend. .Iadd.25. A laser as defined in claim 24 wherein the means for concentrating the distribution of the light from the array of laser diodes is a focusing subsystem having a coupling efficiency (η o ) of approximately 90 percent or more. .Iaddend. .Iadd.26. A laser as defined in any one of claims 1, 10, 11, 12, 16, 18, 20, 21 or 22 wherein the laser medium is selected from the group (Nd:YAG,Nd:GGG and Nd:YLF). .Iaddend. .Iadd.27. A laser as defined in any one of claims 1, 6, 10, 11, 12, 13, 16, 19, 20, 21 or 22 having an operating efficiency (η o ) of approximately 90 percent or more. .Iaddend. .Iadd.28. A laser as defined in any one of claims 1, 6, 10, 11, 12, 13, 16, 18, 19, 20, 21 or 22 having a total optical conversion efficiency (η opt ) and a quantum efficiency (η q ) whose ratio (η opt  /η q ) is approximately 
     
     
        0.65. .Iaddend. .Iadd.29.  A laser as defined in any one of claims 1 or 21 wherein the input pump power is at least 200 milliwatts. .Iaddend. .Iadd.30. A laser as defined in any one of claims 1, 6, 10, 18, 19, 20, 21 or 22 wherein the concentration of the distribution from the array of laser diodes provides an input intensity of approximately 100 w/cm 2   
     
     
        or more. .Iadd.31.  A laser as defined in any one of claims 1, 6, 10, 18, 19, 21 or 22 wherein the means for concentrating the distribution from the array is a focusing subsystem that includes a coupling between the array of laser diodes and the laser medium other than a fiberoptical coupling. .Iaddend. .Iadd.32. A laser as defined in either claim 11 or 13 wherein the means for concentrating the distribution of the light from at least one of the arrays is a focusing subsystem that includes a coupling between the array of laser diodes and the laser medium other than a fiberoptical coupling. .Iaddend. .Iadd.33. A laser as defined in any one of claims 1, 6, 10, 18, 19, 20, 21 or 22 wherein the axis of said resonator cavity forms a closed polygon. .Iaddend. .Iadd.34. A laser as defined in any one of claims 1, 6, 10, 18, 19, 20, 21 or 22 wherein said optical resonator cavity is a ring cavity, and said laser additionally comprises means for insuring unidirectional power flow within the cavity. .Iaddend. .Iadd.35. A laser as defined in any one of claims 1, 6, 10, 18, 19, 20, 21 or 22 wherein said laser medium comprises a single crystal, and the axis of said resonator cavity in the crystal is a zig-zag path. .Iaddend. .Iadd.36. A laser as defined in claim 35 which comprises a plurality of pump volumes along said zig-zag path, wherein each pump volume is pumped by at least one laser diode of the array. .Iaddend.