A miniaturized space-based high-energy ultraviolet single-frequency laser

Abstract

This invention provides a miniaturized space-based high-energy ultraviolet single-frequency laser, comprising a single-frequency pulse seed laser module, a three-stage amplifier, and a nonlinear transformation module. The single-frequency pulse seed laser is a passively Q-switched monolithic non-planar ring cavity capable of outputting a single-frequency 1064nm pulsed laser at the level of ten microjoules. All three stages of the amplifier employ a compact side-pumped slab crystal structure, enabling 1064nm single-frequency laser output with an energy of 350mJ. By increasing the output energy of the first amplifier, high-gain amplification of small-signal incident laser pulses is achieved, reducing the burden on subsequent amplification. The nonlinear transformation module, through power density control, enables long-lifetime, high-reliability ultraviolet single-frequency pulse output at hundreds of millijoules and hundreds of hertz. It can be used in spaceborne hyperspectral lidar, spaceborne wind lidar, etc., to acquire global meteorological information. This invention primarily solves the problems of miniaturization, high frequency stability, and high reliability of high-energy space-based ultraviolet single-frequency lasers.

Description

Technical Field

[0001] This invention relates to the field of laser technology, specifically to a miniaturized spatial high-energy ultraviolet single-frequency laser. Background Technology

[0002] Spaceborne hyperspectral lidar can quantitatively acquire multi-parameter information on clouds and aerosols; spaceborne wind lidar is the only means of obtaining high-precision global wind profiles; spaceborne differential absorption lidar for greenhouse gases can effectively monitor changes in the concentrations of methane and carbon dioxide. All of these lidar systems require lasers with high energy and single-frequency pulse characteristics.

[0003] There are generally two methods to achieve high-energy single-frequency pulsed lasers: one is seed injection-locked amplification, where a continuous single-frequency seed laser is injected into a driven laser to achieve single-frequency pulsed laser output, which is then amplified through multiple stages to achieve high-energy single-frequency pulsed laser output; the other is continuous single-frequency seed laser chopping and shaping followed by amplification, where the energy is first amplified to the microjoule level by an fiber amplifier, then amplified to the millijoule level by an end-face pumped rod crystal, and finally amplified through multiple stages to achieve high-energy single-frequency pulsed laser output. The injection-locked scheme has a complex control circuit, and the uncertainty of the Q-switch turn-on time introduces frequency jitter into the single-frequency pulsed laser; the chopping amplification scheme requires two additional AOM stages, increasing system power consumption, and also requires fiber amplification and end-face rod crystal pre-amplification, resulting in high system complexity. Both schemes have high system complexity and are not advantageous in terms of miniaturization and low power consumption requirements for space applications.

[0004] Therefore, a miniaturized, highly stable, high-energy, single-frequency pulsed laser is needed. Summary of the Invention

[0005] This invention addresses the challenges of efficient amplification, stability, and miniaturization of compact single-frequency pulse lasers with a capacity of 10 microjoules. It provides a miniaturized spatial high-energy ultraviolet single-frequency laser, comprising a single-frequency pulse seed laser module, a three-stage amplifier, and a nonlinear transformation module. The single-frequency pulse seed laser is a passively Q-switched monolithic non-planar ring cavity capable of outputting a 1064nm single-frequency pulse laser with a capacity of 10 microjoules. All three stages of the amplifier employ a compact side-pumped slab crystal structure, enabling 1064nm single-frequency laser output with an energy of 350mJ. The nonlinear transformation module, through power density control, achieves long-lifetime, high-reliability ultraviolet single-frequency pulse output at hundreds of millijoules and hundreds of hertz. This laser can be used in spaceborne hyperspectral lidar, spaceborne wind lidar, and other applications to acquire global meteorological information. This invention primarily solves the problems of miniaturization, high-frequency stability, and high reliability in high-energy spatial ultraviolet single-frequency lasers.

[0006] This invention provides a miniaturized high-energy ultraviolet single-frequency laser, comprising a single-frequency pulse seed laser module, a three-stage amplifier, and a nonlinear conversion module connected in sequence.

[0007] The single-frequency pulsed laser module outputs a single-frequency pulsed laser on the order of ten microjoules and injects it into a three-stage amplifier. The three-stage amplifier amplifies the single-frequency pulsed laser and outputs it to a nonlinear transformation module, which generates an ultraviolet single-frequency pulsed laser.

[0008] The three-stage amplifier comprises a first amplifier assembly, a second amplifier assembly, and a third amplifier assembly connected in sequence. Through polarization state control, the 10-microjoule-level single-frequency pulsed laser output from the single-frequency pulsed seed laser module undergoes two-stage double-pass amplification in the first and second amplifier assemblies. The first amplifier assembly, using a slab crystal side-pump and a Porro prism, amplifies the 10-microjoule-level single-frequency pulsed laser twice to obtain a first-stage amplified single-frequency laser with an energy of 3 mJ or higher. The second amplifier assembly, using a slab crystal side-pump and a Porro prism, amplifies the first-stage amplified single-frequency laser twice to obtain a second-stage amplified single-frequency laser. The third amplifier assembly, using a slab crystal double-side-pump, amplifies the second-stage amplified single-frequency laser once to obtain a third-stage amplified single-frequency laser, which is then output to the nonlinear transformation module.

[0009] The nonlinear transformation module outputs ultraviolet single-frequency laser with a power greater than 100 mJ.

[0010] The present invention discloses a miniaturized spatial high-energy ultraviolet single-frequency laser. In a preferred embodiment, the single-frequency pulse seed laser module includes a single-frequency pulse seed laser, a first isolator, a first half-wave plate, a first beam expander lens group, and a first polarizer connected in sequence.

[0011] A single-frequency pulsed seed laser outputs a single-frequency pulsed laser at the level of 10 microjoules. A first isolator allows the 10 microjoule-level single-frequency pulsed laser to pass through unidirectionally and prevents feedback light from damaging the single-frequency pulsed seed laser. A first half-wave plate adjusts the polarization state of the 10 microjoule-level single-frequency pulsed laser to the p-state. A first beam-expanding lens group performs beam transformation on the p-polarized 10 microjoule-level single-frequency pulsed seed light. A first polarizer directs the p-polarized 10 microjoule-level single-frequency pulse to the first amplifier assembly.

[0012] The energy of a double-amplified single-frequency laser is greater than 35 mJ, and the energy of a triple-amplified single-frequency laser is greater than 350 mJ.

[0013] The miniaturized high-energy ultraviolet single-frequency laser of this invention, as a preferred embodiment, has a single-frequency pulse seed laser operating at a frequency of 100Hz, outputting a 1064nm single-frequency pulse laser on the order of ten microjoules, with a beam quality M... 2 Less than 1.3 times the diffraction limit;

[0014] A single-frequency pulsed seed laser consists of a seed laser pump source, a pump coupling lens group, and a monolithic non-planar ring cavity. The monolithic non-planar ring cavity utilizes diffusion bonding to bond an Nd:YAG laser gain crystal to a Cr... 4+ YAG passively Q-switched saturable absorber crystal bonding, combined with active pump control, produces a single-frequency pulse laser with an output energy in the tens of microjoules and a repetition frequency adjustable from 1 Hz to 1 kHz.

[0015] The miniaturized spatial high-energy ultraviolet single-frequency laser of the present invention, in a preferred embodiment, includes a first amplifier assembly comprising a first amplifier, a first compensation waveplate, a first concave lens, and a first Porro prism located on the transmission optical path of the first polarizer and connected in sequence.

[0016] The first amplifier includes four sides, with the long side serving as the pump surface and the other three sides as cooling surfaces. The cooling surfaces are connected to the copper heat sink via indium foil or indium solder. The first concave lens compensates for the thermal lensing effect of the slab crystal. The first compensation waveplate and the first Porro prism flip the laser polarization state and spot direction by 90° to perform double-pass amplification and thermal distortion correction of the spot. The first amplifier outputs the double-pass amplified, s-polarized single-frequency laser to the first polarizer.

[0017] The present invention discloses a miniaturized spatial high-energy ultraviolet single-frequency laser. In a preferred embodiment, the second amplifier assembly includes a second isolator, a second half-wave plate, a second beam expander lens group, a second polarizer, a second amplifier, a second compensation wave plate, a second concave lens, and a second Porro prism, which are sequentially optically connected to the refracted optical path of the first polarizer.

[0018] The first amplified single-frequency laser is reflected by the first polarizer to the second isolator. The second isolator prevents the return light from the back optical path from disturbing the first amplifier assembly. The second half-wave plate adjusts the polarization state of the first amplified single-frequency laser to the p-state. The second beam expanding lens group performs beam transformation on the p-polarized single-frequency laser. The second polarizer directs the p-polarized single-frequency laser into the second amplifier. The second concave lens compensates for the thermal lensing effect of the slab crystal. The second compensation waveplate and the second Porro prism flip the laser polarization state and spot direction by 90° to perform double-pass amplification and thermal distortion correction of the spot. The second amplifier outputs the second amplified single-frequency laser to the second polarizer.

[0019] The second amplifier has four sides. The long side is the pump surface, and the other three sides are cooling surfaces. The cooling surfaces are connected to the copper heat sink by indium foil or indium solder.

[0020] The miniaturized spatial high-energy ultraviolet single-frequency laser of the present invention, in a preferred embodiment, includes a third amplifier assembly comprising a third half-wave plate, a third beam expander lens group, a third amplifier, a cylindrical lens group, and a fourth half-wave plate that are sequentially optically connected to the reflected optical path of the second polarizer.

[0021] The third half-wave plate adjusts the polarization state of the second-amplified single-frequency laser to the p-state. The third beam expanding lens group performs beam transformation on the p-polarized second-amplified single-frequency laser. The third amplifier makes the p-polarized second-amplified single-frequency laser advance in a zigzag pattern. The cylindrical lens group performs thermal distortion correction on the beam spot of the third amplifier and outputs the third-amplified single-frequency laser. The fourth half-wave plate adjusts the polarization state of the third-amplified single-frequency laser to the s-state.

[0022] The third amplifier is dual-pumped and dual-cooled, with the cooling surface connected to the copper heat sink via indium foil or indium solder.

[0023] In a preferred embodiment of the miniaturized spatial high-energy ultraviolet single-frequency laser described in this invention, both the first amplifier and the second amplifier are Nd:YAG lath crystals with a doping concentration of 1% and a length of 56 mm.

[0024] The pump sources for the first amplifier and the second amplifier are three 808nm LD arrays located at the laser footprint on one side. Each LD array contains six bars, and the peak power of a single bar is 100W.

[0025] Both end faces of the Nd:YAG slab crystals of the first and second amplifiers are coated with 1064nm horizontal and vertical polarization 45° antireflection coatings.

[0026] The third amplifier is a 0.8% doped Nd:YAG lath crystal with a length of 160 mm;

[0027] The pump source for the third amplifier is nine 808nm LD arrays located at the laser footprints on both sides. Each LD array contains 10 bars, and the peak power of a single bar is 100W.

[0028] The LD arrays of the first, second, and third amplifiers are all 1 mm away from the Nd:YAG lath crystal.

[0029] The present invention discloses a miniaturized spatial high-energy ultraviolet single-frequency laser. In a preferred embodiment, the nonlinear transformation module includes a first LBO crystal, a second LBO crystal, a dichroic mirror, and an optical trash can, which are sequentially optically connected to the output of a three-stage amplifier. The refractive output of the dichroic mirror outputs an ultraviolet single-frequency laser with a power greater than 100 mJ.

[0030] The first LBO crystal performs frequency doubling, the second LBO crystal performs sum-frequency doubling, the dichroic mirror emits single-frequency laser light, and the optical bin receives laser light of other wavelengths.

[0031] The present invention discloses a miniaturized spatial high-energy ultraviolet single-frequency laser. In a preferred embodiment, a first LBO crystal is used to perform frequency doubling of 1064nm to obtain 532nm laser output, and a second LBO crystal is used to perform sum-frequency generation of 1064nm and 532nm lasers to obtain 355nm laser output. A dichroic mirror has high transmittance for 1064nm and 532nm lasers and high reflectivity for 355nm laser to emit 355nm laser. An optical bin receives 1064nm and 532nm lasers.

[0032] In a preferred embodiment of the miniaturized spatial high-energy ultraviolet single-frequency laser described in this invention, the temperature control accuracy of both the first LBO crystal and the second LBO crystal is 0.01 degrees Celsius.

[0033] The first LBO crystal uses type I phase matching to control the maximum peak power of the incident laser to 100 MW / cm². 2 The maximum value for controlling the second harmonic efficiency is 50%;

[0034] The second LBO crystal uses type II phase matching to control the maximum peak power of the incident laser to 100 MW / cm². 2 The maximum value for controlling the third harmonic efficiency is 30%.

[0035] In this invention, the first concave lens and the second concave lens are used to adjust the divergence angle so that the divergence angle of the outgoing light spot is basically consistent with the divergence angle of the incident light spot, thus ensuring that the return laser and the pump light also have good mode matching.

[0036] This invention provides a miniaturized space-based high-energy ultraviolet single-frequency laser, comprising a single-frequency pulsed seed laser, a three-stage amplifier, and a nonlinear conversion module. The single-frequency pulsed seed laser is a passively Q-switched monolithic non-planar ring cavity capable of outputting a single-frequency 1064nm pulsed laser at the level of ten microjoules. All three stages of the amplifier employ a compact side-pumped slab crystal structure, enabling 1064nm single-frequency laser output with an energy of 350mJ. The nonlinear conversion module, through power density control, achieves long-lifetime, high-reliability ultraviolet single-frequency pulsed output at hundreds of millijoules and hundreds of hertz. It can be used in spaceborne hyperspectral lidar, spaceborne wind lidar, etc., to acquire global meteorological information. This invention primarily solves the problems of miniaturization, high frequency stability, and high reliability of high-energy space-based ultraviolet single-frequency lasers.

[0037] The present invention has the following advantages:

[0038] (1) This invention innovatively combines a 10 microjoule-level single-frequency pulsed seed laser with a side-pumped slab crystal first-level dual-pass amplifier, avoiding the complex structure of fiber amplification and end-pumped rod crystal heterogeneous hybrid amplification after continuous seed source AOM chopping, greatly simplifying the complex control circuit and complex optical path of the traditional implementation method, and reducing the size of the laser.

[0039] (2) The present invention improves the output energy of the first amplifier, realizes high-gain amplification of small-signal incident laser pulses, and reduces the pressure of subsequent amplification; the first and second amplifiers use a compensating waveplate and a concave lens combined with a Porro prism for double-pass amplification, realize thermal lensing effect compensation of the slab crystal and correction of thermal distortion of the spot; a suitable beam expansion factor is selected before the multi-stage amplifier for beam transformation, and a suitable distance is selected between the amplifier LD and the slab crystal to optimize the laser mode matching and improve amplification efficiency.

[0040] (3) The present invention can output a single-frequency ultraviolet laser of 100 Hz and 100 millijoules through conduction cooling, which can simultaneously meet the requirements of spaceborne lidar for high energy, single frequency, miniaturization and high reliability of laser. Attached Figure Description

[0041] Figure 1 A system block diagram of a miniaturized, high-energy, single-frequency ultraviolet laser.

[0042] Figure 2 This is a schematic diagram of a miniaturized, high-energy, single-frequency ultraviolet laser.

[0043] Figure 3 This is a graph showing the output energy of a miniaturized, high-energy, ultraviolet single-frequency laser as a function of pump energy, specifically the first-stage and second-stage amplification output energies.

[0044] Figure 4 This is a graph showing the variation of the output energy of a miniaturized, high-energy ultraviolet single-frequency laser with pump energy, based on the principle of a three-stage amplification.

[0045] Figure label:

[0046] 1. Single-frequency pulsed seed laser module; 11. Single-frequency pulsed seed laser; 12. First isolator; 13. First half-wave plate; 14. First beam expanding lens group; 15. First polarizer; 2. Three-stage amplifier; 21. First amplifier assembly; 211. First amplifier; 212. First compensation wave plate; 213. First concave lens; 214. First Porro prism; 22. Second amplifier assembly; 221. Second isolator; 222. Second half-wave plate; 223. Second beam expander 224. Lens group; 225. Second polarizer; 226. Second amplifier; 227. Second compensating waveplate; 228. Second concave lens; 229. Second Porro prism; 2003. Third amplifier assembly; 230. Third half-wave plate; 231. Third beam expander lens group; 232. Third amplifier; 233. Cylindrical lens group; 234. Fourth half-wave plate; 3003. Nonlinear transformation module; 31. First LBO crystal; 32. Second LBO crystal; 33. Dichroic mirror; 34. Optical trash can. Detailed Implementation

[0047] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0048] Example 1

[0049] like Figure 1 , 2 As shown, a miniaturized spatial high-energy ultraviolet single-frequency laser includes a single-frequency pulse seed laser module 1, a three-stage amplifier 2, and a nonlinear transformation module 3.

[0050] The single-frequency pulsed seed laser module 1 outputs a single-frequency pulsed laser on the order of ten microjoules, which is then injected into a three-stage amplifier 2. The multi-stage amplifier 2 amplifies the single-frequency pulsed laser and then sends it to the nonlinear transformation module 3. The nonlinear transformation module 3 generates an ultraviolet single-frequency pulsed laser.

[0051] Single-frequency pulsed seed laser 1 is a passively Q-switched monolithic non-planar ring cavity laser, which combines an Nd:YAG laser gain crystal with a Cr... 4+ YAG passively Q-switched saturable absorber crystals are bonded together and processed into a single non-planar ring cavity. Combined with active pump control, it can output a 1064nm single-frequency pulse laser with energy in the order of ten microjoules and a repetition frequency adjustable from 1Hz to 1kHz.

[0052] The single-frequency pulsed seed laser module 11 includes a seed laser pump source, a pump coupling lens group, and a single non-planar ring cavity. The single non-planar ring cavity utilizes diffusion bonding technology to bond an Nd:YAG laser gain crystal to a Cr... 4+YAG passively Q-switched saturable absorber crystals are bonded together and processed. Combined with active pump control, it can output a single-frequency pulse laser with energy in the order of ten microjoules and a repetition frequency adjustable from 1Hz to 1kHz.

[0053] The single-frequency pulsed seed laser 11 operates at 100Hz.

[0054] The three-stage amplifier includes a first amplifier 21, a second amplifier 22, and a third amplifier 23; polarization state control enables two-stage double-pass amplification in the first amplifier 21 and the second amplifier 22, while the third amplifier 23 enables single-pass amplification.

[0055] Beam transformation is performed before the first amplifier 21, the second amplifier 22, and the third amplifier 23 to ensure high amplification efficiency of the three-stage amplifier.

[0056] The three-stage amplifiers 21, 22, and 23 use Nd:YAG slab crystals. The laser advances in a zigzag pattern in the slab crystals, and laser diodes (LDs) are placed at the laser footprints for side pumping.

[0057] The four sides of the Nd:YAG slab crystal of the first amplifier 21 and the second amplifier 22 are as follows: the long side is the pump surface, and the other three sides are the cooling surfaces. The cooling surfaces are connected to the copper heat sink by indium foil or indium solder.

[0058] Both end faces of the Nd:YAG slab crystals of the first amplifier 21 and the second amplifier 22 are coated with 1064nm horizontal and vertical polarization 45° antireflection coatings.

[0059] The third amplifier 23 has four sides of the Nd:YAG slab crystal, with dual-sided pumping and dual-sided cooling. The cooling surfaces are connected to the copper heat sink by indium foil or indium solder.

[0060] All three amplifiers employ conductive cooling for thermal control.

[0061] The first amplifier 21 and the second amplifier 22 compensate for the thermal lensing effect through concave lenses.

[0062] The first amplifier 21 and the second amplifier 22 correct the thermal distortion of the light spot by flipping the direction of the light spot by 90° through the Porro prisms 214 and 228. The third amplifier 23 corrects the thermal distortion of the light spot through the cylindrical mirror 234.

[0063] The nonlinear transformation module 3 uses a high-precision temperature-controlled LBO crystal, and controls the third harmonic efficiency to ~30% by reducing the laser power density.

[0064] The nonlinear transformation module 3 includes a first LBO crystal 31, a second LBO crystal 32, a dichroic mirror 33, and an optical waste bin 34. The 1064nm single-frequency pulsed laser emitted from the three-stage amplifier 2 enters the first LBO crystal 31 for frequency doubling and then emits 1064nm and 532nm single-frequency pulsed lasers. The frequency-doubled 1064nm and 532nm single-frequency pulsed lasers enter the second LBO crystal 32 for frequency summing and then emit 1064nm, 532nm, and 355nm single-frequency pulsed lasers. After being split by the dichroic mirror 33, a 355nm single-frequency pulsed laser is emitted. The remaining 1064nm and 532nm single-frequency pulsed lasers enter the optical waste bin 34.

[0065] The temperature control accuracy of the first LBO crystal 31 and the second LBO crystal 32 in the nonlinear transformation module 3 is 0.01 degrees Celsius.

[0066] The single-frequency pulsed seed laser 1 outputs a 1064nm single-frequency pulsed laser with a beam quality of M on the order of ten microjoules. 2 Less than 1.3 times the diffraction limit.

[0067] Specifically:

[0068] Figure 1 This is a block diagram of the miniaturized spatial high-energy ultraviolet single-frequency pulsed laser system of the present invention. The single-frequency pulsed seed laser 1 outputs a 1064nm single-frequency pulsed laser at the level of ten microjoules; the first amplifier 21 amplifies the single-frequency pulse energy to 3mJ through double-pass amplification; the second amplifier 22 amplifies the single-frequency pulse energy to 35mJ through double-pass amplification; the third amplifier 23 amplifies the single-frequency pulse energy to 350mJ through single-pass amplification; and the nonlinear conversion module achieves a 355nm wavelength laser output of greater than 100mJ.

[0069] Figure 2This is a schematic diagram of the miniaturized spatial high-energy ultraviolet single-frequency pulsed laser of this embodiment. The single-frequency pulsed seed laser 11 outputs a single-frequency pulsed laser at the level of ten microjoules. The first isolator 12 ensures unidirectional passage of the 1064nm wavelength, preventing damage to the seed laser caused by feedback light. The first half-wave plate 13 adjusts the polarization state of the 1064nm single-frequency pulsed laser to p-polarization. The first beam-expanding lens group 14 performs beam transformation on the single-frequency pulsed seed light, enabling the first amplifier to have high amplification efficiency. The seed pulsed laser is incident on the first amplifier 211 via the first polarizer 15. The first concave lens 213 optimizes the laser mode matching to compensate for the thermal lensing effect of the slab crystal. The first compensation waveplate 212... The first Porro prism 214 flips the laser polarization state and spot direction by 90° to achieve double-pass amplification and thermal distortion correction of the spot. The laser amplified by the first amplifier 211 is reflected by the first polarizer 15 and incident on the second isolator 221. The second isolator 221 prevents the return light from the back path from disturbing the first amplifier 211, achieving high-energy stable pulsed laser amplification. The second half-wave plate 222 adjusts the polarization state of the laser to p-beam. The second beam expander lens group 223 performs beam transformation on the laser to give the second amplifier high amplification efficiency. The laser output from the first amplifier 211 is then... The second polarizer 224 is incident on the second amplifier 225. The second concave lens 227 optimizes the mode matching of the laser to compensate for the thermal lensing effect of the slab crystal. The second compensating waveplate 226 and the second Porro prism 228 flip the laser polarization state and spot direction by 90° to achieve double-pass amplification and thermal distortion correction of the spot. The laser amplified by the second amplifier assembly 22 is reflected by the second polarizer 224 and incident on the third half-wave plate 231. The third half-wave plate 231 adjusts the polarization state of the laser to p-beam. The third beam expanding lens group 232 performs beam transformation on the laser to enable the third amplifier 233. With high amplification efficiency, the cylindrical lens group 234 is used to correct the thermal distortion of the light spot of the third amplifier 233; the fourth half-wave plate 235 adjusts the polarization state of the laser to make its polarization state s-light; the first LBO crystal 31 achieves frequency doubling of 1064nm to obtain 532nm laser output; the second LBO crystal 32 achieves sum-frequency of 1064nm and 532nm to obtain 355nm laser output; the dichroic mirror 33 has high transmittance for 1064nm and 532nm and high reflectivity for 355nm, realizing the emission of 355nm laser; the optical trash can 34 receives 1064nm and 532nm lasers.

[0070] Preferably, the Nd:YAG crystal of the single-frequency pulsed seed laser 11 has a doping concentration of 1% and a repetition frequency of 100Hz.

[0071] Preferably, the Nd:YAG slab crystals of the first amplifier 211 and the second amplifier 225 have a doping concentration of 1% and a length of 56 mm.

[0072] Preferably, the pump source of the first amplifier 211 and the second amplifier 225 adopts three groups of 808nm LD arrays, each group of arrays contains 6 bars, and the peak power of a single bar is 100W.

[0073] Preferably, the Nd:YAG slab crystal of the third amplifier 225 has a doping concentration of 0.8% and a length of 160 mm.

[0074] Preferably, the pump source of the third amplifier 225 adopts 9 groups of 808nm LD arrays, each group of arrays contains 10 bars, and the peak power of a single bar is 100W.

[0075] Preferably, the distance between the LD and the Nd:YAG slab crystal in the multi-stage amplifier 2 is 1 mm.

[0076] Preferably, the first LBO crystal 31 employs type I phase matching to control the peak power of the incident laser to ~100MW / cm². 2 The second harmonic efficiency is controlled to be ~50%;

[0077] Preferably, the second LBO crystal 32 employs type II phase matching to control the peak power of the incident laser to ~100MW / cm². 2 By controlling the third harmonic efficiency to ~30%, the lifespan of high-energy ultraviolet single-frequency lasers can be improved.

[0078] This invention employs a compact, high-efficiency slab crystal amplification module to amplify a single-frequency pulsed, single-block non-planar ring cavity seed laser to obtain a high-energy single-frequency 1064nm laser, avoiding frequency jitter caused by injection-locked schemes and improving frequency stability. Combining a 10-microjoule-level single-frequency pulsed seed laser 11 with a side-pumped slab crystal first-stage dual-pass amplifier not only avoids the complex structure of fiber amplification and end-face-pumped rod-shaped crystal heterogeneous hybrid amplification after continuous seed source AOM chopping, greatly simplifying the complex control circuitry and optical path of traditional implementations and reducing laser size; it also increases the output energy of the first amplifier 211, achieving high-gain amplification of small-signal incident laser pulses and reducing the pressure on subsequent amplification. The first amplifier 211 and the second amplifier 225 use a compensating waveplate and a Pohr prism combined with a concave lens for double-pass amplification, achieving thermal lensing effect compensation and beam thermal distortion correction of the slab crystal. Appropriate beam expansion factors are selected before the multi-stage amplifiers for beam transformation, and an appropriate distance is chosen between the amplifier LD and the slab crystal to optimize laser mode matching and improve amplification efficiency. By controlling the peak power density of the laser, the third-harmonic efficiency is kept at approximately 30%, thus improving the lifespan and reliability of the high-energy ultraviolet single-frequency laser. In summary, this invention achieves high-energy single-frequency laser output with high frequency stability, high reliability, and long lifespan, and also offers the advantage of miniaturization, making it a preferred light source for space-based lidar.

[0079] Implementation Results: This invention was applied to a spaceborne high-energy 355nm single-frequency pulsed laser. A single-frequency pulsed seed laser with a repetition frequency of 100Hz outputs 20μJ of 1064nm single-frequency pulsed laser. The first amplifier 211 amplifies the single-frequency pulse energy to 3.1mJ through double-pass amplification; the second amplifier 225 amplifies the single-frequency pulse energy to 35.6mJ through double-pass amplification; and the third amplifier 233 amplifies the single-frequency pulse energy to 350.3mJ through single-pass amplification. The nonlinear transformation module 3 achieves 112mJ of 355nm wavelength laser output. The curves showing the variation of the three-stage amplification output energy with pump energy are shown below. Figure 3 and Figure 4 .

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A miniaturized spatial high-energy ultraviolet single-frequency laser, characterized in that: It includes a single-frequency pulse seed laser module (1), a three-stage amplifier (2), and a nonlinear transformation module (3) that are connected in sequence by optical connection; The single-frequency pulse seed laser module (1) outputs a single-frequency pulse laser of the order of ten microjoules and injects it into the three-stage amplifier (2). The three-stage amplifier (2) amplifies the single-frequency pulse laser and outputs it to the nonlinear transformation module (3). The nonlinear transformation module (3) generates an ultraviolet single-frequency pulse laser. The three-stage amplifier (2) includes a first amplifier assembly (21), a second amplifier assembly (22), and a third amplifier assembly (23) connected in sequence. By controlling the polarization state, the single-frequency pulse laser with a magnitude of 10 microjoules output by the single-frequency pulse seed laser module (1) is amplified in two stages by the first amplifier assembly (21) and the second amplifier assembly (22). The first amplifier assembly (21) amplifies the single-frequency pulse laser with a magnitude of 10 microjoules by side pumping of a slab crystal and a Porro prism to obtain a first-stage amplified single-frequency laser with an energy of 3 mJ or more. The second amplifier assembly (22) amplifies the first-stage amplified single-frequency laser by side pumping of a slab crystal and a Porro prism to obtain a second-stage amplified single-frequency laser. The third amplifier assembly (23) amplifies the second-stage amplified single-frequency laser by side pumping of a slab crystal to obtain a third-stage amplified single-frequency laser, which is then output to the nonlinear transformation module (3). The nonlinear transformation module (3) outputs ultraviolet single-frequency laser with a power greater than 100 mJ.

2. The miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 1, characterized in that: The single-frequency pulse seed laser module (1) includes a single-frequency pulse seed laser (11), a first isolator (12), a first half-wave plate (13), a first beam expander lens group (14), and a first polarizer (15) connected in sequence. The single-frequency pulse seed laser (11) outputs the 10 microjoule-level single-frequency pulse laser. The first isolator (12) allows the 10 microjoule-level single-frequency pulse laser to pass through unidirectionally and prevents feedback light from damaging the single-frequency pulse seed laser (11). The first half-wave plate (13) adjusts the polarization state of the 10 microjoule-level single-frequency pulse laser to the p state. The first beam expanding lens group (14) performs beam transformation and amplification on the p-polarized 10 microjoule-level single-frequency pulse seed light. The first polarizer (15) incident the p-polarized 10 microjoule-level single-frequency pulse onto the first amplifier assembly (21). The energy of the secondary amplified single-frequency laser is greater than 35mJ, and the energy of the tertiary amplified single-frequency laser is greater than 350mJ.

3. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 2, characterized in that: The single-frequency pulsed seed laser (11) operates at a frequency of 100Hz and outputs a 1064nm single-frequency pulsed laser with a beam quality M on the order of ten microjoules. 2 Less than 1.3 times the diffraction limit; The single-frequency pulsed seed laser (11) includes a seed laser pump source, a pump coupling lens group, and a single non-planar ring cavity. The single non-planar ring cavity utilizes diffusion bonding to bond the Nd:YAG laser gain crystal to a Cr... 4+ YAG passively Q-switched saturable absorber crystal bonding, combined with active pump control, produces a single-frequency pulse laser with an output energy in the tens of microjoules and a repetition frequency adjustable from 1 Hz to 1 kHz.

4. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 2, characterized in that: The first amplifier assembly (21) includes a first amplifier (211), a first compensation waveplate (212), a first concave lens (213), and a first Porro prism (214) located on the transmission optical path of the first polarizer (15) and connected in sequence. The first amplifier (211) includes four sides, with the long side being the pump surface and the other three sides being cooling surfaces. The cooling surfaces are connected to the copper heat sink via indium foil or indium solder. The first concave lens (213) compensates for the thermal lensing effect of the slab crystal. The first compensation waveplate (212) and the first Porro prism (214) flip the laser polarization state and spot direction by 90° to perform double-pass amplification and thermal distortion correction of the spot. The first amplifier (211) outputs the double-pass amplified, s-polarized single-frequency laser to the first polarizer (15).

5. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 4, characterized in that: The second amplifier assembly (22) includes a second isolator (221), a second half-wave plate (222), a second beam expander lens group (223), a second polarizer (224), a second amplifier (225), a second compensation wave plate (226), a second concave lens (227), and a second Porro prism (228) that are sequentially optically connected to the refracted optical path of the first polarizer (15). The first amplified single-frequency laser is reflected by the first polarizer (15) to the second isolator (221). The second isolator (221) prevents the back light from disturbing the first amplifier assembly (21). The second half-wave plate (222) adjusts the polarization state of the first amplified single-frequency laser to the p-state. The second beam expanding lens group (223) performs beam transformation on the p-polarized single-frequency laser. The second polarizer (224) incident the p-polarized single-frequency laser onto the second amplifier (225). The second concave lens (227) compensates for the thermal lensing effect of the lath crystal. The second compensation waveplate (226) and the second Porro prism (228) flip the laser polarization state and spot direction by 90° to perform double-pass amplification and thermal distortion correction of the spot. The second amplifier (225) outputs the second amplified single-frequency laser to the second polarizer (224). The second amplifier (225) includes four sides, with the long side being the pump surface and the other three sides being cooling surfaces. The cooling surfaces are connected to the copper heat sink via indium foil or indium solder.

6. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 5, characterized in that: The third amplifier assembly (23) includes a third half-wave plate (231), a third beam expander lens group (232), a third amplifier (233), a cylindrical lens group (234), and a fourth half-wave plate (235) that are sequentially optically connected to the reflected light path of the second polarizer (224); The third half-wave plate (231) adjusts the polarization state of the secondary amplified single-frequency laser to the p-state; the third beam expanding lens group (232) performs beam transformation on the p-polarized secondary amplified single-frequency laser; the third amplifier (233) makes the p-polarized secondary amplified single-frequency laser advance in a zigzag pattern; the cylindrical lens group (234) performs thermal distortion correction on the spot of the third amplifier (233) and outputs the tertiary amplified single-frequency laser; and the fourth half-wave plate (235) adjusts the polarization state of the tertiary amplified single-frequency laser to the s-state. The third amplifier (233) is dual-pumped and dual-cooled, and the cooling surface is connected to the copper heat sink by indium foil or indium solder.

7. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 6, characterized in that: The first amplifier (211) and the second amplifier (225) are both Nd:YAG lath crystals with a doping concentration of 1% and a length of 56 mm. The pump sources of the first amplifier (211) and the second amplifier (225) are three groups of 808nm LD arrays located at the laser footprint on one side. Each LD array contains six bars, and the peak power of a single bar is 100W. The two end faces of the Nd:YAG slab crystals of the first amplifier (211) and the second amplifier (225) are coated with 1064nm horizontal and vertical polarization 45° anti-reflection coatings. The third amplifier (233) is a 0.8% doped Nd:YAG lath crystal with a length of 160 mm; The pump source of the third amplifier (233) is 9 groups of 808nm LD arrays located at the laser footprints on both sides. Each LD array contains 10 bars, and the peak power of a single bar is 100W. The LD arrays of the first amplifier (211), the second amplifier (225), and the third amplifier (233) are all 1 mm away from the Nd:YAG slab crystal.

8. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 3, characterized in that: The nonlinear transformation module (3) includes a first LBO crystal (31), a second LBO crystal (32), a dichroic mirror (33), and an optical trash can (34) that are sequentially optically connected to the output end of the three-stage amplifier (2). The dichroic mirror (33) outputs ultraviolet single-frequency laser with a refraction output of more than 100mJ. The first LBO crystal (31) performs frequency doubling, the second LBO crystal (32) performs sum-frequency doubling, the dichroic mirror (33) emits single-frequency laser light, and the optical trash can (34) receives laser light of other wavelengths.

9. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 8, characterized in that: The first LBO crystal (31) performs frequency doubling of 1064nm to obtain 532nm laser output, the second LBO crystal (32) performs sum-frequency mixing of 1064nm laser and 532nm laser to obtain 355nm laser output, the dichroic mirror (33) has high transmittance for 1064nm laser and 532nm laser and high reflectivity for 355nm laser to emit 355nm laser, and the optical trash can (34) receives 1064nm laser and 532nm laser.

10. A miniaturized spatial high-energy ultraviolet single-frequency laser according to claim 8, characterized in that: The temperature control accuracy of both the first LBO crystal (31) and the second LBO crystal (32) is 0.01 degrees Celsius; The first LBO crystal (31) uses type I phase matching to control the maximum peak power of the incident laser to be 100 MW / cm². 2 The maximum value for controlling the second harmonic efficiency is 50%. The second LBO crystal (32) uses type II phase matching to control the maximum peak power of the incident laser to 100 MW / cm². 2 The maximum value for controlling the third harmonic efficiency is 30%.

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