A kind of narrow linewidth single frequency high energy 1064nm laser for space-based wind lidar

Abstract

A kind of narrow linewidth single frequency high energy 1064nm laser for space-based wind lidar, using seed injection-based master oscillator power amplifier (MOPA) scheme, using narrow linewidth continuous single frequency distributed feedback laser (DFB) as seed source, two-stage semiconductor optical amplifier (SOA) modulated pulse width, single-end pumped crystal as preamplifier stage, two double-end pumped Nd:YAG slab as main amplifier stage;Two DFB seed sources are used to lock the frequency difference and correct the Doppler shift;Two-stage cascaded SOA pulse modulator has the advantages of narrow linewidth, high extinction ratio and small volume. Using 885nm LD end-pumping, good thermal management performance, helps to improve beam quality;End-pumping has high optical coupling efficiency, high Stokes efficiency under 885nm LD pumping, no intermediate relaxation heat, which helps to improve optical-optical conversion efficiency and save pumping.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state laser technology, specifically relating to a narrow-linewidth single-frequency high-energy 1064nm laser for space-based wind measurement lidar, which is particularly suitable for coherent wind measurement lidar systems on spaceborne and airborne platforms with stringent requirements for size, weight, power consumption and environmental adaptability. Background Technology

[0002] Space-based wind lidar is a crucial technology for acquiring global wind profile information. However, due to performance limitations of its core component, the laser, there are currently no space-based wind lidar applications internationally. Existing spaceborne lidar systems mainly suffer from the following technical problems: First, the laser linewidth is not narrow enough, making it difficult to meet the high-precision requirements of coherent detection; second, insufficient energy output limits the detection range and accuracy; third, the narrow pulse width leads to a broadened power spectrum, limiting the accuracy of wind speed measurement; and finally, the large size and weight are unfavorable for spaceborne applications.

[0003] Currently, the common method for obtaining high-energy 1064nm single-frequency nanosecond pulsed lasers is based on a master oscillator power amplification system with seed injection. Current schemes often use NPRO seed lasers or DFB seed lasers to generate single-frequency continuous seed light, which is then shaped and chopped using active Q-switching, acousto-optic modulators, or electro-optic modulators to obtain the single-frequency pulsed seed light. However, these methods suffer from drawbacks such as the large size of NPROs, the long cavity length required for active Q-switching, the high power consumption of acousto-optic modulators, and the complex structure of electro-optic modulators, all of which are unfavorable for spaceborne applications. Furthermore, the pumping method in the amplification stage often uses 808nm LD side-pumping. In side-pumping, the close distance between the LD and the amplifying crystal hinders heat dissipation, affecting the laser beam quality. The 808nm pump also suffers from large quantum defects, low optical-to-optical conversion efficiency, and wasted pump power, further hindering spaceborne applications. Current technical solutions cannot fully meet the comprehensive requirements of space-based wind lidar for narrow linewidth, high energy, miniaturization, and high performance.

[0004] Chinese patent document CN113809620A discloses a high-energy, long-pulse 1μm single-frequency nanosecond laser for laser coherent wind measurement radar. It employs a single-frequency continuous laser seed source, which is chopped by a two-stage acousto-optic modulator to obtain a single-frequency nanosecond pulse laser. This pulse is then passed through a three-stage end-pumped single-pass pre-amplification stage before entering a side-pumped main amplification stage, resulting in a 1.0μm single-frequency pulse laser with a pulse width exceeding 100 ns. However, the dual acousto-optic modulators used in this patent have high power consumption. The three-stage pre-amplification stage all use single-pass amplification, leading to insufficient pump utilization, low optical-to-optical conversion efficiency, and wasted pump power. Furthermore, the side-pumped main amplification stage is detrimental to thermal management and further affects the beam quality of the output laser.

[0005] In summary, existing technologies cannot simultaneously meet the requirements of space-based wind lidar for laser sources with narrow linewidth (<1MHz), high energy (>100mJ), long pulse width (>100ns), and high beam quality (MJ). 2 The laser exhibits comprehensive performance requirements, including low efficiency (<1.5%), high conversion efficiency (>20%), small size, and low power consumption. Therefore, there is an urgent need to develop a new type of narrow-linewidth single-frequency high-energy 1064nm laser for space-based platforms. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of the prior art and provide a narrow-linewidth, high-energy 1064nm solid-state laser for coherent wind measurement. It utilizes two DFB seed lasers for phase locking and two cascaded SOA semiconductor optical amplifiers for modulation and chopping to obtain narrow-linewidth, high-extinction-ratio nanosecond laser pulses while minimizing size and power consumption. By employing 878nm / 885nm, end-pumping, and multi-pass amplification, it addresses the problems of severe thermal effects, limited beam quality, and low optical-to-optical conversion efficiency in existing 1064nm solid-state lasers caused by unreasonable pump wavelength selection and insufficient pump structure optimization. This results in a solid-state laser that maintains good beam quality and high conversion efficiency even under high-energy output conditions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A narrow-linewidth single-frequency high-energy laser for space-based wind measurement lidar employs a master oscillation power amplification structure, comprising a seed source module, a pre-amplification stage, and a master amplification stage arranged sequentially along the optical path.

[0009] The seed source module includes a first distributed feedback seed laser and a second distributed feedback seed laser, as well as cascaded semiconductor optical amplifiers. The first and second distributed feedback seed lasers are phase-locked via an external phase-locked loop circuit to generate dual-frequency lasers with a stable frequency difference. This frequency difference is used in the back-end system to correct for Doppler frequency shifts caused by satellite platform motion or atmospheric motion. The cascaded semiconductor optical amplifiers (preferably two cascaded stages) pulse-modulated and chop the seed lasers, outputting narrow-linewidth (<1MHz), high extinction ratio (>60dB) single-frequency nanosecond pulsed seed light, with the pulse width adjustable in the range of 100ns-500ns.

[0010] The pre-amplification stage employs an end-face-pumped solid-state amplifier to amplify the pulsed seed light twice, increasing its energy to the microjoule level. Preferably, the pump wavelength of the pre-amplification stage is 878 nm, the amplifying crystal is an Nd:YVO4 square rod, and a single-end-face-pumped method is used. The pulsed seed light passes through an isolator, a reflector, and a right-angle prism before passing through the amplifying crystal for the first time. It is then reflected by a beam splitter and passes through the amplifying crystal a second time, achieving two-way amplification.

[0011] The main amplification stage employs a slab solid-state amplifier with double-end-pumped crystals. The slab crystals have chamfered end faces to form a zigzag optical path for multi-pass amplification of the laser, increasing its energy to the level of hundreds of millijoules. Preferably, the pump wavelength of the main amplification stage is 885 nm, and the amplification crystal is an Nd:YAG double-end-bonded slab.

[0012] As a further preferred technical solution, the main amplification stage includes a first main amplification stage and a second main amplification stage arranged sequentially. The first main amplification stage is a four-pass slab solid-state amplifier, used to boost the laser energy to the tens of millijoules level; the second main amplification stage is a two-pass slab solid-state amplifier, used to boost the laser energy to the hundreds of millijoules level.

[0013] Specifically, the first main amplification stage adopts a double-ended pumped Nd:YAG slab four-pass amplification structure: the seed light enters the slab crystal in a p-polarized state, passes through the crystal four times (using a polarizing beam splitter, a quarter-wave plate, and a total reflection mirror to control the optical path direction), and each time it propagates along a zigzag path to achieve efficient energy extraction. The second main amplification stage adopts a double-ended pumped Nd:YAG slab two-pass amplification structure: after the laser light passes through the slab crystal in a p-polarized state for the first time, it is converted to an s-polarized state by a quarter-wave plate and a total reflection mirror, passes through the crystal in the reverse direction for the second time, and is finally output by a polarizing beam splitter.

[0014] Furthermore, each reflector (45° incident angle) and the total reflection mirror (0° incident angle) is coated with a 1064nm high-reflection film; the beam splitter is coated with a 1064nm high-reflection film and an 878nm anti-reflection film at a 0° incident angle; the pump incident region of the slab crystal is coated with an 885nm anti-reflection film and a 1064nm high-reflection film; and the quarter-wave plate is a standard wave plate for a wavelength of 1064nm.

[0015] Through the above technical solution, the 1064nm single-frequency nanosecond laser finally output by the present invention has the following preferred parameters: linewidth less than 1MHz, pulse width of 100ns-500ns, pulse energy greater than 100mJ, beam quality M² better than 1.5, and optical-to-optical conversion efficiency greater than 20%.

[0016] The present invention also provides an aerospace-based wind-measuring lidar system, wherein the lidar system comprises a narrow-linewidth single-frequency high-energy laser as described in any of the above technical solutions as a light source.

[0017] Compared with the prior art, the present invention has the following outstanding advantages:

[0018] 1. Narrow linewidth characteristics: Through optimized narrow linewidth pulse seed source design and DFB cascaded SOA, narrow linewidth output is achieved, meeting the high precision requirements of coherent detection and providing a highly coherent light source for spaceborne wind measurement;

[0019] 2. High energy output: Achieves high energy output of hundreds of millijoules and pulse width of hundreds of nanoseconds through cascaded amplification links, covering the effective detection range requirements of spaceborne wind measurement;

[0020] 3. Miniaturized design: It selects low-power, small-volume narrow-linewidth pulse seed sources, and adopts 885nm end-face pumping and multi-pass amplification to save pump power and reduce onboard load;

[0021] 4. High beam quality: By adopting a slat structure and optimized optical path design, the beam quality is ≤1.5, ensuring the high spatial resolution and detection accuracy of the lidar;

[0022] 5. High optical efficiency: Through 885nm pump and link optimization, optical efficiency is achieved at ≥20%, significantly reducing the burden on onboard power and improving system endurance;

[0023] 6. The overall laser design is compact and can simultaneously achieve single-frequency nanosecond laser output with narrow linewidth (<1MHz), long pulse width (hundredsns), high energy (hundredsmJ), high beam quality (<1.5), and high conversion efficiency (>20%), making it suitable for spaceborne wind measurement needs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the narrow linewidth single-frequency high-energy laser of the present invention.

[0025] 1. Seed source module; 1-1. First DFB seed laser; 1-2. Second DFB seed laser; 1-3. First semiconductor optical amplifier; 1-4. Second semiconductor optical amplifier; 1-5. First reflector; 1-6. Second reflector.

[0026] 2. Pre-magnification stage; 2-1. First isolator; 2-2. First convex lens; 2-3. Third reflecting mirror; 2-4. Right-angle prism; 2-5. First magnifying crystal; 2-6. Beam splitter; 2-7. Second convex lens; 2-8. Third convex lens; 2-9. First LD.

[0027] 3. First main magnifying stage; 3-1. Fourth reflecting mirror; 3-2. Second isolator; 3-3. First polarizing beam splitter; 3-4. Fourth convex lens; 3-5. Fifth convex lens; 3-6. Sixth convex lens; 3-7. Second LD; 3-8. Second magnifying crystal; 3-9. Seventh convex lens; 3-10. Eighth convex lens; 3-11. Third LD; 3-12. Ninth convex lens; 3-13. Fifth reflecting mirror; 3-14. Sixth reflecting mirror; 3-15. Tenth convex lens; 3-16. Eleventh convex lens; 3-17. Seventh reflecting mirror; 3-18. First quarter-wave plate; 3-19. First total reflection mirror; 3-20. Third isolator;

[0028] 4. Second main magnifying stage; 4-1. Second polarizing beam splitter; 4-2. Eighth reflecting mirror; 4-3. Twelfth convex lens; 4-4. Thirteenth convex lens; 4-5. Fourth LD; 4-6. Third magnifying crystal; 4-7. Fourteenth convex lens; 4-8. Fifteenth convex lens; 4-9. Fifth LD; 4-10. Ninth reflecting mirror; 4-11. Second quarter-wave plate; 4-12. Second total reflection mirror. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, the embodiments of this invention are not limited thereto. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] Please see Figure 1 This embodiment provides a narrow-linewidth single-frequency high-energy 1064nm laser for aerospace-based wind measurement lidar. The laser adopts a master oscillator power amplifier (MOPA) structure, specifically including a seed source module 1, a pre-amplification stage 2 and a master amplification stage arranged sequentially along the seed light propagation direction.

[0031] In this embodiment, the main amplification stage preferably includes a first main amplification stage 3 and a second main amplification stage 4 arranged sequentially.

[0032] Seed source module 1 is used to generate long-pulse single-frequency nanosecond pulsed laser with high stability, narrow linewidth, and high extinction ratio. Specifically, seed source module 1 includes a first DFB seed laser 1-1, a second DFB seed laser 1-2, a first semiconductor optical amplifier 1-3, a second semiconductor optical amplifier 1-4, a first reflector 1-5, and a second reflector 1-6. The second DFB seed laser 1-2 generates a 1064nm single-frequency continuous laser, which is modulated by the two cascaded first semiconductor optical amplifiers 1-3 and 1-4 to form a 1064nm single-frequency pulsed laser, and then reflected by the first reflector 1-5 and the second reflector 1-6 into the pre-amplification stage 2.

[0033] The pre-amplification stage 2 is used to initially amplify the weak pulsed seed light to the microjoule (μJ) level to effectively drive the subsequent main amplification stage. Specifically, it includes: a first isolator 2-1, a first convex lens 2-2, a third reflecting mirror 2-3, a right-angle prism 2-4, a first magnifying crystal 2-5, a beam splitter 2-6, a second convex lens 2-7, a third convex lens 2-8, and a first LD 2-9.

[0034] The pulsed seed light from the narrow-linewidth pulsed seed source 1 first passes through the first isolator 2-1 to prevent back-reflected light from affecting the stability of the seed source. Then, the beam is slightly focused by the first convex lens 2-2, reflected by the third reflecting mirror 2-3, and then passes through the right-angle prism 2-4 (the two right-angle faces of the right-angle prism 2-4 are coated with a 1064nm high-reflection film for refracting the optical path) before entering the first amplifying crystal 2-5. After the seed light is initially amplified by the first amplifying crystal 2-5, it illuminates the beam splitter 2-6. This beam splitter 2-6 is coated with a 0° 1064nm high-reflection film and an 878nm anti-reflection film, thus exhibiting almost total reflection of the 1064nm laser while maintaining high transmittance for the remaining 878nm pump light. The reflected seed light is then refracted back through the first amplifying crystal 2-5, achieving double-pass amplification. This double-pass amplification optical path design greatly improves the extraction efficiency of the pump light. The laser energy after double-pass amplification can reach the level of hundreds of μJ, and then returns along the original path and passes through right-angle prisms 2-4 to enter the main amplification stage 3.

[0035] The first main amplification stage 3 amplifies the laser to the tens of mJ level through four-pass amplification, and the second main amplification stage 4 amplifies the laser to the hundreds of mJ level through four-pass amplification. Finally, a 1064nm single-frequency nanosecond laser output with narrow linewidth (<1MHz), long pulse width (hundreds of ns), high energy (hundreds of mJ), high beam quality (<1.5), and high conversion efficiency (>20%) is obtained.

[0036] The main amplification stage 3 specifically comprises: a fourth reflecting mirror 3-1, a second isolator 3-2, a first polarizing beam splitter 3-3, a fourth convex lens 3-4, a fifth convex lens 3-5, a sixth convex lens 3-6, a second LD 3-7, a second magnifying crystal 3-8, a seventh convex lens 3-9, an eighth convex lens 3-10, a third LD 3-11, a ninth convex lens 3-12, a fifth reflecting mirror 3-13, a sixth reflecting mirror 3-14, a tenth convex lens 3-15, an eleventh convex lens 3-16, a seventh reflecting mirror 3-17, a first quarter-wave plate 3-18, a first total reflection mirror 3-19, and a third isolator 3-20.

[0037] The laser beam (linearly polarized light) from the pre-magnification stage 2 passes through the fourth reflecting mirror 3-1 and the second isolator 3-2, and then enters the first polarizing beam splitter 3-3. The transmission axis of the first polarizing beam splitter 3-3 is aligned with the polarization direction of the incident laser beam, ensuring high transmission. After being collimated by the fourth convex lens 3-4, the transmitted beam enters the second magnifying crystal 3-8 at a specific angle.

[0038] The second amplifying crystal, 3-8, is a double-end-bonded Nd:YAG slab with 45° chamfers at both ends, and its internal optical path is zigzag-shaped. The pump injection regions at both ends of the crystal are coated with an 885nm anti-reflection coating and a 1064nm high-reflection coating, respectively. The pump source uses two 885nm fiber-coupled LDs (second LD 3-7 and third LD 3-11), which are coupled to the slab from both ends via a coupling optical system consisting of fifth and sixth convex lenses (3-5, 3-6) and seventh and eighth convex lenses (3-9, 3-10). This double-end pumping and zigzag optical path design result in a more uniform heat distribution within the crystal, effectively suppressing thermal lensing and thermal birefringence, and ensuring high-power amplification with high beam quality.

[0039] In this embodiment, a four-pass amplification optical path is implemented in the first main amplification stage 3:

[0040] First stage (single-stage amplification): The laser enters the second amplifying crystal 3-8 in a p-polarized state and propagates along a zigzag path to achieve the first amplification.

[0041] The second stage (double-pass amplification): The laser emitted from the crystal passes through the ninth convex lens 3-12, the fifth reflecting mirror 3-13, the sixth reflecting mirror 3-14, and the tenth convex lens 3-15, and is then reguided and enters the second amplifying crystal 3-8 from the other end, achieving a second amplification.

[0042] The third stage (triple-stage amplification): The laser beam, amplified by the double-stage process, passes through the eleventh convex lens 3-16 and the seventh reflecting mirror 3-17, then through the first quarter-wave plate 3-18 (the fast axis is at 45° to the polarization direction), becoming circularly polarized light. After being reflected by the first total reflection mirror 3-19, it passes through the first quarter-wave plate 3-18 again, this time becoming s-polarized light. This s-polarized light returns along the original path and enters the second amplifying crystal 3-8 for a third time for amplification.

[0043] Fourth stage (fourth stage amplification): The s-polarized light, after being amplified three times, exits from the other end of the crystal and passes sequentially through the tenth convex lens 3-15, the sixth reflecting mirror 3-14, the fifth reflecting mirror 3-13, and the ninth convex lens 3-12 before entering the second amplifying crystal 3-8 for the fourth time, thus obtaining the final amplification.

[0044] The s-polarized laser, amplified four times, is output from the original input end of the crystal (on the side of the fourth convex lens 3-4) and is incident again on the first polarization beam splitter 3-3. Since the laser is now s-polarized, it is reflected by the first polarization beam splitter 3-3 and enters the main amplification stage 4 after passing through the third isolator 3-20. After this stage of amplification, the laser energy can be increased to the tens of mJ level.

[0045] The second main amplification stage 4 is used to increase the energy from tens of mJ to the final millijoules (above 100 mJ) level. It includes: the second polarizing beam splitter 4-1, the eighth reflecting mirror 4-2, the twelfth convex lens 4-3, the thirteenth convex lens 4-4, the fourth LD 4-5, the third magnifying crystal 4-6, the fourteenth convex lens 4-7, the fifteenth convex lens 4-8, the fifth LD 4-9, the ninth reflecting mirror 4-10, the second quarter-wave plate 4-11, and the second total reflection mirror 4-12.

[0046] The laser (s-polarized light) from the first main amplification stage 3 first enters the second polarization beam splitter 4-1. Since its polarization state is s-polarized, it is reflected. After being deflected by the eighth reflecting mirror 4-2, the reflected light spot size is adjusted by the coupling system composed of the twelfth convex lens 4-3 and the thirteenth convex lens 4-4. Then, it enters the third amplification crystal 4-6 with a p-polarized state (the polarization can be changed by appropriately adjusting the waveplate; here it is designed to enter with p-polarization, or it can be adjusted by a half-wave plate; in this embodiment, it is optimized to enter with p-polarization to reduce reflection loss).

[0047] The third amplifying crystal 4-6 has the same structure as the second amplifying crystal 3-8, both being double-ended bonded Nd:YAG strips with a 45° chamfer, and are double-ended end-face pumped by two 885nm fiber-coupled LDs (fourth LD 4-5 and fifth LD 4-9). The pump coupling method is the same as the previous stage.

[0048] In this embodiment, double-pass amplification is achieved in the second main amplification stage 4:

[0049] First stage (single-pass amplification): The p-polarized laser passes through the third amplifying crystal 4-6 for the first time and is amplified.

[0050] The second stage (double-pass amplification): The emitted laser is reflected by the ninth mirror 4-10, passes through the second quarter-wave plate 4-11 and becomes circularly polarized light. After being reflected by the second total reflection mirror 4-12, it passes through the second quarter-wave plate 4-11 again and becomes s-polarized light. This s-polarized light is reflected by the ninth mirror 4-10 and then passes in the opposite direction a second time through the third amplifying crystal 4-6, where energy is extracted again.

[0051] The s-polarized laser, amplified twice, is output from the original input of the crystal. After being reflected by the eighth mirror 4-2, it is again incident on the second polarization beam splitter 4-1. At this point, the laser is s-polarized and reflected by the second polarization beam splitter 4-1, becoming the final high-energy laser output. This amplification stage ultimately yields an energy greater than 100 mJ, a pulse width adjustable from 100-500 ns, a linewidth less than 1 MHz, and a beam quality M... 2 A 1064nm single-frequency nanosecond pulsed laser with a light-to-light conversion efficiency of over 20%, superior to 1.5.

[0052] In this embodiment, the narrow linewidth pulse seed source includes two DFB seed lasers for phase locking and two SOA semiconductor optical amplifiers cascaded for modulation chopping to obtain a high extinction ratio long pulse single-frequency nanosecond pulse laser.

[0053] The pre-amplification stage 2 is pumped by an 878nm LD single-end pump. The pump source, the first LD2-9, is output through fiber coupling, collimated by the second convex lens 2-7, and focused by the third convex lens 2-8 before entering the first amplifying crystal. The pump light and seed light have good coupling effect. The first main amplification stage 3 and the second main amplification stage 4 are pumped by an 885nm LD double-end pump. Similarly, the pump source is output through fiber coupling, collimated and focused by a convex lens before entering the amplifying crystal. The pump light and seed light have good coupling effect, and the 885nm pump has a small quantum defect, which improves the optical-to-optical conversion efficiency.

[0054] The seed light is transmitted through a zigzag optical path in the first main amplification stage 3 and the second main amplification stage 4, which reduces the optical path difference and thermal lensing effect and improves the beam quality.

[0055] The first, second, third, fourth, fifth, sixth, seventh, eighth, and ninth reflecting mirrors are all coated with a 45° 1064nm high-reflection film. The beam splitter is coated with a 0° 1064nm high-reflection film and an 878nm anti-reflection film. The right-angle prism is coated with a 1064nm high-reflection film. The first and second total reflection mirrors are both coated with a 0° 1064nm high-reflection film.

[0056] Both the first and second quarter-wave plates are 1064nm quarter-wave plates.

[0057] The first magnifying crystal is The square rod, the second amplifying crystal, and the third amplifying crystal are Nd:YAG double-end bonded strips with a 45° chamfer. The strips are coated with an 885nm antireflection film and a 1064nm high reflectivity film in the pump incident region.

[0058] This embodiment constructs a high-performance, compact, narrow-linewidth, single-frequency, high-energy 1064nm laser suitable for aerospace platforms by employing a dual DFB phase-locked seed source, cascaded SOA modulation, a MOPA structure combining Nd:YVO4 two-way pre-amplification and Nd:YAG slab multi-way main amplification, and fully utilizing low quantum defect 878 / 885nm end-face pumping technology.

[0059] The examples described above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited thereto. Any simple variations or equivalent transformations of the technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, or various other corresponding changes and modifications made according to the technical concept of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A narrow-linewidth single-frequency high-energy laser for space-based wind lidar, characterized in that, The main oscillator power amplifier structure includes: The seed source module includes a first DFB seed laser and a second DFB seed laser, as well as a cascaded semiconductor optical amplifier. The first and second DFB seed lasers are phase-locked through an external phase-locked circuit to generate dual-frequency lasers with a stable frequency difference to correct the Doppler frequency shift. The cascaded semiconductor optical amplifier is used to pulse-modulate and chop the seed lasers to output a single-frequency nanosecond pulse seed light with a narrow linewidth and a high extinction ratio. The pre-amplification stage employs an end-pumped solid-state amplifier to amplify the pulsed seed light twice, raising its energy to the first energy level. The main amplification stage employs a slab solid-state amplifier with dual-end-face pumping. Its slab crystal has chamfered end faces to form a zigzag optical path, which is used to amplify the laser through multiple passes, raise its energy to the second energy level, and output a narrow-linewidth, high-energy single-frequency nanosecond laser.

2. The narrow-linewidth single-frequency high-energy laser for space-based wind lidar according to claim 1, characterized in that, The main amplification stage includes a first main amplification stage and a second main amplification stage arranged sequentially; the first main amplification stage is used to increase the laser energy to the tens of millijoules level, and the second main amplification stage is used to increase the laser energy to the hundreds of millijoules level.

3. The narrow-linewidth single-frequency high-energy laser for space-based wind lidar according to claim 2, characterized in that, The first main amplification stage is a four-pass slab solid-state amplifier, and the second main amplification stage is a two-pass slab solid-state amplifier.

4. The narrow-linewidth single-frequency high-energy laser of claim 1, wherein, The pump wavelength of the pre-amplification stage is 878 nm; the pump wavelength of the main amplification stage is 885 nm.

5. The narrow-linewidth single-frequency high-energy laser of claim 1, wherein, The amplifying crystal of the pre-amplification stage is an Nd:YVO4 crystal, and the amplifying crystal of the main amplification stage is an Nd:YAG lath crystal.

6. The narrow-linewidth single-frequency high-energy laser according to claim 1, characterized in that, The cascaded semiconductor optical amplifier includes a first semiconductor optical amplifier and a second semiconductor optical amplifier, which are cascaded together to perform pulse chopping on the continuous seed laser to obtain a single-frequency nanosecond pulse seed light with an extinction ratio greater than 60dB.

7. The narrow-linewidth single-frequency high-energy laser according to claim 1, c h a r a c t e r i z e d i n t h a t The pre-magnification stage includes: a first isolator, a first convex lens, a third reflecting mirror, a right-angle prism, a first magnifying crystal, a beam splitter, a second convex lens, a third convex lens, and a first LD; The first LD is a fiber-coupled laser diode, whose output pump light is focused by the second and third convex lenses and injected from the end face of the first magnifying crystal. The pulsed seed light passes through the first isolator, the first convex lens, the third reflecting mirror, and the right-angle prism. It is amplified by the first magnifying crystal for the first time, then reflected by the beam splitter, and then amplified twice in the opposite direction by passing through the first magnifying crystal.

8. The narrow-linewidth single-frequency high-energy laser of claim 2, wherein, The first main amplification stage includes: a fourth reflecting mirror, a second isolator, a first polarizing beam splitter, a fourth convex lens, a second magnifying crystal, a second LD, a third LD, a ninth convex lens, a fifth reflecting mirror, a sixth reflecting mirror, a tenth convex lens, an eleventh convex lens, a seventh reflecting mirror, a first quarter-wave plate, a first total reflection mirror, and a third isolator. The second amplifying crystal is a double-ended bonded Nd:YAG strip with two end faces cut at 45°; the second LD and the third LD are both 885nm fiber-coupled laser diodes, which are pumped from both ends of the second amplifying crystal. Through the cooperation of the first polarizing beam splitter, the first quarter-wave plate, the first total reflection mirror, and multiple reflecting mirrors and lenses, the laser light passes through the second amplifying crystal four times, achieving four-stage amplification.

9. The narrow-linewidth single-frequency high-energy laser of claim 8, wherein, The second main amplification stage includes: a second polarizing beam splitter, an eighth reflecting mirror, a twelfth convex lens, a thirteenth convex lens, a fourth LD, a third amplifying crystal, a fourteenth convex lens, a fifteenth convex lens, a fifth LD, a ninth reflecting mirror, a second quarter-wave plate, and a second total reflection mirror; the third amplifying crystal is a double-ended bonded Nd:YAG slab, and its structure and pumping method are the same as those of the second amplifying crystal. The laser from the first main amplification stage is amplified for the first time by the third amplification crystal after passing through the second polarization beam splitter and the eighth reflector. Then, after passing through the ninth reflector, the second quarter-wave plate and the second total reflection mirror, it is amplified twice in reverse by passing through the third amplification crystal. Finally, it is output through the eighth reflector and the second polarization beam splitter.

10. The narrow-linewidth single-frequency high-energy laser of any of claims 1-9, wherein, The single-frequency nanosecond laser output by the laser has at least one of the following parameters: linewidth less than 1 MHz, pulse width of 100 ns-500 ns, pulse energy greater than 100 mJ, beam quality M² better than 1.5, and optical-to-optical conversion efficiency greater than 20%.

11. A space-based wind-profiling lidar system, characterized by, The light source includes the narrow linewidth single-frequency high-energy laser as described in any one of claims 1-10.

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