High-repetition-frequency narrow-pulse-width 1645nm non-planar laser

Abstract

The invention relates to a high-repetition-frequency narrow-pulse-width 1645nm non-planar laser, which comprises three parts, namely a pump laser injection system, a seed laser injection system and a spatial four-mirror-cavity optical parametric oscillator system. The laser has the advantages that the beam quality is high, the injection energy of the pump light is adjustable, the injection light spots and the power density of the pump light and the seed light are adjustable, the service life of the nonlinear crystal is long, the tuning range is wide, and three wavelengths are output; the high-repetition-frequency large-pulse-energy high-beam-quality laser light source can be widely applied to a plurality of applications such as laser radar systems, remote sensing, telemetering and range finders, and is an important laser light source.

Description

Technical Field

[0001] This invention relates to pulsed solid-state lasers, and more particularly to a non-planar laser with a characteristic wavelength of 1645nm. Background Technology

[0002] As is well known, methane is the second largest greenhouse gas globally after carbon dioxide, accounting for approximately one-fifth of total global greenhouse gas emissions. Although smaller in quantity than carbon dioxide, methane has a significant impact on climate change. Measuring the spatiotemporal distribution of methane using integral path differential absorption lidar is considered a promising solution for measuring methane emissions, potentially addressing key scientific questions about the carbon cycle in all critical regions of the world.

[0003] One of the most critical building blocks of a lidar system is the laser emission source, which needs to provide highly stable laser pulses in the most efficient and reliable manner. To date, only solid-state laser systems with laser diode pumps in a master oscillator power amplifier configuration have been able to generate the required laser pulses.

[0004] Because the 1645nm wavelength and wavenumber 6077 laser are located precisely at the absorption peak of methane gas, it has become the most important and optimal laser wavelength for detecting atmospheric methane. Meanwhile, lasers in the 1.5μm-1.6μm range are considered eye-safe and can be widely used in many applications besides lidar systems, including remote sensing, telemetry, and rangefinders. Summary of the Invention

[0005] The purpose of this invention is to provide a high repetition rate, narrow pulse width, 1645nm non-planar laser with good beam quality, which can provide a high-quality laser source for subsequent high repetition rates and large pulse energies.

[0006] The specific solution of this invention is as follows:

[0007] A high-repetition-rate, narrow-pulse-width 1645nm nonplanar laser comprises three parts: a pump laser injection system, a seed laser injection system, and a spatial four-mirror cavity optical parametric oscillator system.

[0008] The pump laser injection system includes: a high repetition rate, narrow pulse width 1064nm solid-state pump source, a first isolator, a first pump beam expander, a second pump beam expander, a first total reflection mirror, a first half-wave plate, and a polarizing beam splitter. The first isolator is located after the high repetition rate, narrow pulse width 1064nm solid-state pump source. The first pump beam expander is located after the first isolator. The second pump beam expander is located after the first pump beam expander. The exit directions of the first total reflection mirror and the second pump beam expander are at a 45-degree angle. The first half-wave plate is located after the first total reflection mirror. The polarizing beam splitter is located after the first half-wave plate and works in conjunction with the first half-wave plate.

[0009] The seed laser injection system includes: an optical fiber-emitting seed laser, a focusing coupling mirror, a collimating focusing mirror, a first seed beam expander, and a second seed beam expander. The optical fiber-emitting seed laser is placed in the optical path at a 45-degree angle to the beam combiner. The focusing coupling mirror is located after the optical fiber-emitting seed laser, the collimating focusing mirror is located after the focusing coupling mirror, the first seed beam expander is located after the collimating focusing mirror, and the second seed beam expander is located after the first seed beam expander and works in conjunction with the first seed beam expander.

[0010] The aforementioned four-mirror cavity optical parametric oscillator system includes: a beam combiner, a pinhole aperture, a second total reflection mirror, a third total reflection mirror, a fourth total reflection mirror, an M1 input mirror, an M2 total reflection mirror, an M3 total reflection mirror, an M4 output mirror, a first crystal heat sink, a first indium foil, a first potassium titanate arsenate crystal, a second crystal heat sink, a second indium foil, a second potassium titanate arsenate crystal, a second half-wave plate, a first thermistor, a second thermistor, a first temperature controller, a second temperature controller, a first beam splitter, a second beam splitter, and a third beam splitter. The pinhole aperture is located on the optical path after the pump optical path and the seed optical path are combined, and the pinhole aperture is located on another optical path of the beam combiner. The second total reflection mirror is located after the pinhole aperture, the third total reflection mirror is located after the folding optical path of the second total reflection mirror, and the fourth total reflection mirror is located after the folding optical path of the third total reflection mirror. The M1 input mirror, together with the M2 total reflection mirror, the M3 total reflection mirror, and the M4 output mirror, constitute a spatial three-dimensional laser resonant cavity. The first crystal heat sink is fitted with the first indium foil and the first potassium titanate arsenate crystal, with the inner side of the first indium foil and the outer side of the first potassium titanate arsenate crystal in close contact. Similarly, the inner side of the first crystal heat sink is fitted with the outer side of the first indium foil. The second crystal heat sink is fitted with the second indium foil and the second potassium titanate arsenate crystal, with the inner side of the second indium foil and the outer side of the second potassium titanate arsenate crystal in close contact. The outer side is tightly fitted, and the second half-wave plate is located inside the spatial three-dimensional laser resonant cavity formed by the combination of the M1 input mirror, the M2 total reflection mirror, the M3 total reflection mirror, and the M4 output mirror. The first thermistor is tightly fitted to the first crystal heat sink, and the first temperature controller is connected to the first thermistor. The second thermistor is tightly fitted to the second crystal heat sink, and the second temperature controller is connected to the second thermistor. The first beam splitter is located after the M4 output mirror, the second beam splitter is located after the first beam splitter, and the third beam splitter is located after the second beam splitter.

[0011] The repetition frequency of the high repetition rate and narrow pulse width 1064nm solid-state pump source is in kHz, including but not limited to 1-10kHz, and the pulse width of the high repetition rate and narrow pulse width 1064nm solid-state pump source includes but is not limited to 1.7ns to 5ns.

[0012] The first and second pump beam expanders work together to form a pump source beam expander group. Increasing the distance between the first and second pump beam expanders and decreasing the distance between the beam expander group and adjacent optical elements can increase the area of ​​the emitted pump light spot, which will correspondingly decrease the power density of the pump light. Conversely, decreasing the distance between the first and second pump beam expanders and increasing the distance between the beam expander group and adjacent optical elements can decrease the area of ​​the emitted pump light spot, which will correspondingly increase the power density of the pump light.

[0013] The first half-wave plate and polarizing beam splitter are placed in the pump laser injection system. By rotating the first half-wave plate, the polarization state of the P-polarized laser becomes elliptically polarized light after passing through the first half-wave plate. When it passes through the polarizing beam splitter, only the P-polarized component can pass through, while the S-polarized component is reflected. Therefore, the pump single pulse energy injected into the spatial four-mirror cavity optical parametric oscillator can be increased or decreased, thereby increasing or decreasing the pump energy.

[0014] The M1 input mirror is made of K9 glass, with dimensions of Φ20*3mm. The coating specifications are as follows: the incident angle of the incident surface is 28-38°, the reflectivity at the characteristic wavelength is 99.5%±0.2% at 1645nm, and a high transmittance film is coated at 1064nm. The incident angle of the output surface is 28-38°, a high transmittance film is coated at 1064nm, and the transmittance at 1645nm is 0.5%.

[0015] The M2 total reflection mirror is made of K9 glass, with a size of Φ20*3mm. The coating specifications are single-sided coating, incident angle of 28-38°, and a high reflectivity film at 1645nm.

[0016] The M3 total reflection mirror is made of K9 glass, with a size of Φ20*3mm. The coating specifications are single-sided coating, incident angle of 28-38°, and a high reflectivity film at 1645nm.

[0017] The M4 output mirror is made of K9 glass, with a size of Φ20*3mm. The coating specifications are as follows: the incident angle of the incident surface is 28-38°, a high transmittance film is deposited at 1064nm, and the reflectivity at 1645nm is 70%. The incident angle of the output surface is 28-38°, and a high transmittance film is deposited at both 1064nm and 1645nm.

[0018] The first and second potassium titanium oxyarsenate crystals have the same specifications, with dimensions of 8mm*8mm*14mm, cutting angles of θ=65.6° and φ=0°, and incident surface coating parameters of 1064nm, 1645nm and 3015nm respectively, and exit surface coating parameters of 1064nm, 1645nm and 3015nm respectively.

[0019] The first and second potassium titanate arsenate crystals are symmetrically placed on the branch formed by the M1 input mirror and the M4 output mirror, with the inner spacing between the two crystals varying from 0.1 mm to 20 mm. Since both the first and second potassium titanate arsenate crystals have a cutting angle of θ = 65.6° and φ = 0°, their symmetrical placement at this angle can compensate for the o-ray and e-ray walk-off effects.

[0020] The second, third, and fourth total reflection mirrors are all positioned at a 45-degree angle to the incident light, and the coating parameters are all 45° incident angle, with high reflectivity films deposited at 1064nm & 1645nm. When the second total reflection mirror is tilted upwards and the third total reflection mirror is tilted downwards, the laser light, after passing through the fourth total reflection mirror, is injected into the first potassium titanate arsenate crystal in a parallel upward direction. When the second total reflection mirror is tilted downwards and the third total reflection mirror is tilted upwards, the laser light, after passing through the fourth total reflection mirror, is injected into the first potassium titanate arsenate crystal in a parallel downward direction. When the third total reflection mirror is shifted to the right, the laser light, after passing through the fourth total reflection mirror, is injected into the first potassium titanate arsenate crystal in a parallel left direction. When the third total reflection mirror is shifted to the left, the laser light, after passing through the fourth total reflection mirror, is injected into the first potassium titanate arsenate crystal in a parallel right direction. Therefore, when irreversible damage or cracks occur inside the first or second potassium titanate arsenate crystal, the laser can be transferred to a location without damage or cracks by adjusting the second, third, and fourth total reflection mirrors, thereby improving the service life and utilization rate of the first and second potassium titanate arsenate crystals.

[0021] The second half-wave plate (311) is located on any optical path of the spatial three-dimensional laser resonator, perpendicular to the direction of light propagation, and has a center wavelength of 1645 nm. The coating parameters are to deposit a high-transmittance film at 1645 nm. When located on the optical path between the M1 input mirror (31) and the M4 output mirror (34), it can only be located outside the crystal group composed of the first potassium titanate arsenate crystal (37) and the second potassium titanate arsenate crystal (310).

[0022] The beam combiner is used to combine the 1064nm pump light and the 1645nm seed light. The beam combiner is made of K9 glass, with dimensions of Φ20*3mm. The coating parameters are as follows: the incident angle of the incident surface is 45°, and the transmittance at 1064nm is greater than 99.5%; the incident angle of the exit surface is 45°, and an anti-reflection coating is applied at 1064nm, with a reflectivity greater than 95% at 1645nm.

[0023] The first beam splitter is positioned at a 45° angle to the light emitted from the M4 output mirror. It is made of K9 glass, has a size of Φ20*3mm, and has a coating parameter of 45° incident angle and a high reflectivity film at 1645nm.

[0024] The second beam splitter is positioned at a 45° angle to the light emitted from the M4 output mirror, and is located after the first beam splitter. It is made of K9 glass, has a size of Φ20*3mm, and has a coating parameter of 45° incident angle and a high reflectivity film at 1064nm.

[0025] The first thermistor, in conjunction with the first temperature controller, is used to control the temperature of the first potassium titanate oxyarsenate crystal, and the second thermistor, in conjunction with the second temperature controller, is used to control the temperature of the second potassium titanate oxyarsenate crystal.

[0026] The working principle of this invention is as follows:

[0027] By placing a nonlinear medium within a resonant cavity and incident a pump beam, when the gain of the parametric amplification exceeds the loss, the signal light can establish a sufficiently strong oscillation from the noise—this is the principle of optical parametric oscillation. The pump beam expander group and the seed beam expander group are used to achieve adjustable pump beam size and power density injected into the four-cavity oscillator. The temperature of the nonlinear crystal is controlled by a combination of a thermistor and a temperature controller. The tunability of the output wavelength is achieved by adjusting the angle between the nonlinear crystal and the optical path branch. Finally, the output laser is split and output through reflectivity achieved by coatings with different film systems.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. By utilizing a pump beam expander group and a seed beam expander group, the energy of the pump light injected into the optical parametric oscillator can be adjusted, and the injection spot and power density of the pump light and seed light can be adjusted to adapt to changes in application scenarios.

[0030] 2. The nonlinear crystal has a long working life. By adjusting the second, third, and fourth total reflection mirrors, the combined laser beam can be directed to the left end face of the first potassium titanate oxyarsenate crystal. When irreversible damage or cracks occur inside the first or second potassium titanate oxyarsenate crystal, the laser system of this invention can be restored to normal operation by adjusting the three total reflection mirrors. That is, by adjusting the second, third, and fourth total reflection mirrors, the service life and utilization rate of the first and second potassium titanate oxyarsenate crystals can be improved.

[0031] 3. By changing the spatial four-mirror cavity structure in different forms, and placing the second half-wave plate in conjunction with two crystals, the polarization direction of 1645nm polarized laser can be reproduced in the spatial four-mirror cavity, effectively improving the beam quality of the output laser, which is better than the existing 1645nm output laser beam quality.

[0032] 4. By regularly arranging the first, second, and third beam splitters, three different wavelengths of laser light can be output simultaneously. It can be widely used in many applications such as lidar systems, remote sensing, telemetry, and rangefinders, and is an important laser source. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of a high repetition rate, narrow pulse width, 1645nm non-planar laser according to the present invention.

[0034] Figure 2 This is a schematic diagram of the first scenario in a specific embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram of the second scenario in a specific embodiment of the present invention.

[0036] Figure 4 This is a schematic diagram of the third case in a specific embodiment of the present invention.

[0037] Figure 5 This is a schematic diagram of the fourth scenario in a specific embodiment of the present invention.

[0038] Figure 6 Schematic diagram for controlling the injection spot size and power density

[0039] Figure 7 Schematic diagram of the combined laser beam striking different positions on the left end face of the first potassium titanate arsenate crystal. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and should not be construed as limiting the scope of protection of the present invention.

[0041] like Figure 1 As shown, Figure 1 This is a schematic diagram of the overall structure of a high repetition rate, narrow pulse width, 1645nm non-planar laser of the present invention. The pump source is a high repetition rate, narrow pulse width, 1064nm solid-state pump source 11. The collimated laser emitted from the pump source first passes through a first isolator 12 to prevent the light reflected back from the surface of subsequent optical elements from being reflected back to the pump source at 0° and damaging the pump source.

[0042] The laser emitted from the first isolator 12 travels a distance L1 to the first pump beam expander 13, then travels a distance L2 to the second pump beam expander 14, and finally travels a distance L3 to the first total reflection mirror 15. The incident angle of the first total reflection mirror 15 is 45° with the laser beam, and its surface is coated with a high-reflectivity film of 1064 nm. The function of the first total reflection mirror 15 is to deflect the optical path, compressing the volume of the laser beam path as much as possible, making the entire laser system smaller and easier to move and place. The laser emitted from the first total reflection mirror 15 passes through the first half-wave plate 16, which is placed vertically in the laser beam path with a center wavelength of 1064 nm. It is used to change the polarization state of the incident laser, thus changing the polarization state of the output laser. It works in conjunction with the polarization beam splitter prism 17 to dynamically adjust the pump energy injected into the optical parametric oscillator.

[0043] like Figure 1 As shown, since the laser emitted from the seed laser 21 from the fiber has a certain divergence angle, it must pass through the focusing coupling mirror 22 and the collimating focusing mirror 23 to adjust the divergent beam output from the fiber into a collimated beam. The laser output from the collimating focusing mirror 23 reaches the first seed beam expander 24 after traveling a distance of L4. After exiting the first seed beam expander 24, the seed laser reaches the second seed beam expander 25 after traveling a distance of L5. The laser emitted from the second seed beam expander 25 reaches the beam combiner 319 after traveling a distance of L6. It is then combined with the pump light emitted from the polarizing beam splitter 17 at the beam combiner 319 to form a combined laser beam with a concentric cross-section.

[0044] like Figure 6 As shown, by changing L1, L2, and L3, the spot size and power density of the pump light injected into the spatial four-cavity optical parametric oscillator can be reduced or increased. By changing L4, L5, and L6, the spot size and power density of the seed light injected into the spatial four-cavity optical parametric oscillator can be reduced or increased, thereby achieving a more flexible control of the spot size matching mode of the pump light and the seed light.

[0045] The combined laser beam emitted from the beam combiner 319 passes through the pinhole aperture 26, which filters out stray light generated in the actual laser system, resulting in better beam quality when it enters the subsequent four-mirror cavity optical parametric oscillator 3, which is more conducive to obtaining the final high beam quality laser.

[0046] like Figure 1 As shown, the laser emitted from the aperture 26 passes through the second total reflection mirror 321, the third total reflection mirror 322, and the fourth total reflection mirror 323. The incident angle of the laser with the second total reflection mirror 321, the third total reflection mirror 322, and the fourth total reflection mirror 323 is 45°. These three mirrors are used to adjust the initial position of the combined laser beam injected into the spatial four-mirror cavity optical parametric oscillator 3, that is, the specific position injected into the left end face of the first potassium titanate arsenate crystal 37.

[0047] like Figure 7 As shown, the laser beam may strike the left end face of the first potassium titanate oxy-acetate crystal 37. When an irreversible crack appears inside the first potassium titanate oxy-acetate crystal 37, the laser system of the present invention can be restored to normal operation by adjusting the second total reflection mirror 321, the third total reflection mirror 322, and the fourth total reflection mirror 323. That is, by adjusting the second total reflection mirror 321, the third total reflection mirror 322, and the fourth total reflection mirror 323, the service life and utilization rate of the first potassium titanate oxy-acetate crystal 37 can be improved.

[0048] like Figure 1 As shown, the combined laser beam emitted from the fourth total reflection mirror 29 is injected into the first potassium titanate arsenate crystal 37 through the M1 input mirror 31. After exiting the first potassium titanate arsenate crystal 37, it travels 5 mm before being injected into the second potassium titanate arsenate crystal 310. The laser beam emitted from the second potassium titanate arsenate crystal 310 reaches the M4 output mirror 34. Part of the signal light is reflected from the M4 output mirror 34 to the M2 total reflection mirror 32, and the other part is output through the M4 output mirror 34. The M2 total reflection mirror 32 has a reflectivity of over 99.5% for the signal light, with a reflection working angle of 28° to 38°. After reflection, it reaches the second half-wave plate 311. The laser beam emitted from the second half-wave plate 311 reaches the M3 total reflection mirror 33. After being reflected by the M3 total reflection mirror 33, it reaches the M1 input mirror 31. At this time, the signal light has completed one full cycle of the four-mirror cavity. The second half-wave plate 311 in the optical path is a zero-order wave plate with a center wavelength of 1645nm. It is used to adjust the polarization state caused by spatial reflection, so that the signal light can achieve parametric oscillation in the four mirror cavities in space, and finally achieve high-quality laser output.

[0049] like Figure 2The diagram shown is a schematic of the first embodiment of the spatial four-mirror cavity optical parametric oscillator 3 in this invention. Two potassium titanate oxyarsenate crystals are located between the M1 input mirror 31 and the M4 output mirror 34. The second half-wave plate 311 is located between the second potassium titanate oxyarsenate crystal 310 and the M4 output mirror 34. The spatial four-mirror cavity structure composed of the M1 input mirror 31, the M2 total reflection mirror 32, the M3 total reflection mirror 33 and the M4 output mirror 34 is one of many cases.

[0050] like Figure 3 The diagram shown is a schematic of the second embodiment of the spatial four-mirror cavity optical parametric oscillator 3 in this invention. Two potassium titanate oxyarsenate crystals are located between the M1 input mirror 31 and the M4 output mirror 34. The second half-wave plate 311 is located between the M4 output mirror 34 and the M2 total reflection mirror 32. The spatial four-mirror cavity structure composed of the M1 input mirror 31, the M2 total reflection mirror 32, the M3 total reflection mirror 33, and the M4 output mirror 34 is one of many cases.

[0051] like Figure 4 The diagram shown is a schematic of the third embodiment of the spatial four-mirror cavity optical parametric oscillator 3 in this invention. Two potassium arsenate oxy-acetate crystals are located between the M1 input mirror 31 and the M4 output mirror 34. The second half-wave plate 311 is located between the M2 total reflection mirror 32 and the M3 total reflection mirror 33. The spatial four-mirror cavity structure composed of the M1 input mirror 31, the M2 total reflection mirror 32, the M3 total reflection mirror 33 and the M4 output mirror 34 is one of many cases.

[0052] like Figure 5 The diagram shown is a schematic of the fourth embodiment of the spatial four-mirror cavity optical parametric oscillator 3 in this invention. Two potassium titanate arsenate crystals are located between the M1 input mirror 31 and the M4 output mirror 34. The second half-wave plate 311 is located between the M3 total reflection mirror 33 and the M1 output mirror 31. The spatial four-mirror cavity structure composed of the M1 input mirror 31, the M2 total reflection mirror 32, the M3 total reflection mirror 33 and the M4 output mirror 34 is one of many cases.

[0053] like Figure 1 As shown, the signal light transmittance of the fourth total reflection mirror 29 is 30%. The light emitted from the fourth total reflection mirror 29 includes the remaining pump light, the generated signal light, and the idler light. The three light waves pass through the same spatial optical path and are concentric beams. After reaching the first beam splitter 316, the signal light is reflected and split by the first beam splitter 316, which is placed at 45°. After the remaining pump light and idler light reach the second beam splitter 317, the remaining pump light is reflected and split by the second beam splitter 317, which is placed at 45°. At this time, the only idler light in the optical path reaches the third beam splitter 318 and is reflected and split by the third beam splitter 318, which is placed at 45°, thus completing the high beam quality output of three wavelengths.

[0054] like Figure 1 As shown, under normal light output conditions, rotating the first potassium titanate oxyarsenate crystal 37 and the second potassium titanate oxyarsenate crystal 310 within a range of 5 degrees clockwise and 5 degrees counterclockwise within the horizontal plane of the optical path can achieve a continuously tunable output laser wavelength from 1645.1 nm to 1645.9 nm.

[0055] like Figure 1 As shown, a first thermistor 312 is attached to the surface of the first potassium titanate oxyarsenate crystal 37 and connected to a first temperature controller 314. The first temperature controller 314 monitors the temperature of the first potassium titanate oxyarsenate crystal 37 in real time and can change the temperature of the first potassium titanate oxyarsenate crystal 37 to achieve temperature tuning. A second thermistor 313 is attached to the surface of the second potassium titanate oxyarsenate crystal 310 and connected to a second temperature controller 315. The second temperature controller 315 monitors the temperature of the second potassium titanate oxyarsenate crystal 310 in real time and can change the temperature of the second potassium titanate oxyarsenate crystal 310 to achieve temperature tuning.

Claims

1. A high-repetition-rate, narrow-pulse-width 1645nm non-planar laser, characterized in that, include: The system consists of three parts: a pump laser injection system (1), a seed laser injection system (2), and a spatial four-mirror cavity optical parametric oscillator system (3). The pump laser injection system (1) includes a high repetition rate and narrow pulse width 1064nm solid-state pump source (11), and a first isolator (12), a first pump beam expander (13), a second pump beam expander (14), a first total reflection mirror (15), a first half-wave plate (16), and a polarization beam splitter (17) arranged sequentially along the collimated laser emitted from the high repetition rate and narrow pulse width 1064nm solid-state pump source (11). The seed laser injection system (2) includes an optical fiber seed laser (21), and a focusing coupling mirror (22), a collimating focusing mirror (23), a first seed beam expander (24), and a second seed beam expander (25) arranged sequentially along the seed laser emitted from the optical fiber seed laser (21). The spatial four-mirror cavity optical parametric oscillator system (3) consists of a laser emitted from the pump laser injection system (1) and a laser emitted from the seed laser injection system (2) that are combined by a beam combiner (319) and then pass sequentially through a pinhole aperture (320), a second total reflection mirror (321), a third total reflection mirror (322), a fourth total reflection mirror (323), a spatial three-dimensional laser resonator assembly, a first beam splitter (316), a second beam splitter (317), and a third beam splitter (318). The spatial three-dimensional laser resonator assembly includes a second half-wave plate (311), a spatial three-dimensional laser resonator composed of an M1 input mirror (31), an M2 total reflection mirror (32), an M3 total reflection mirror (33), and an M4 output mirror (34), as well as a first potassium titanate oxyarsenate crystal (37) and a second potassium titanate oxyarsenate crystal (310). After the laser reflected by the fourth total reflection mirror (323) enters the spatial three-dimensional laser resonator through the M1 input mirror (31), part of the laser is output to the first beam splitter (316) through the M4 output mirror (34), and the other part of the laser is reflected to the M1 input mirror (31) after passing through the M2 total reflection mirror (32) and the M3 total reflection mirror (33) in sequence. The end faces of the first potassium titanate oxyarsenate crystal (37) and the second potassium titanate oxyarsenate crystal (310) are symmetrically placed on the optical path between the M1 input mirror (31) and the M4 output mirror (34). The second half-wave plate (311) is located on any optical path of the spatial three-dimensional laser resonator, and when it is located on the optical path between the M1 input mirror (31) and the M4 output mirror (34), it can only be located outside the crystal group composed of the first potassium titanate oxyarsenate crystal (37) and the second potassium titanate oxyarsenate crystal (310).

2. The high repetition rate, narrow pulse width 1645nm non-planar laser as described in claim 1, characterized in that, The first potassium titanate oxygenate crystal (37) is wrapped in a first indium foil (36) and placed in a first crystal heat sink (35). A first thermistor (312) is provided on the first crystal heat sink (35), and the first thermistor (312) is connected to a first temperature controller (314) for real-time monitoring of the temperature of the first potassium titanate oxygenate crystal (37). The second potassium titanate oxygenate crystal (310) is wrapped in a second indium foil (39) and placed in a second crystal heat sink (38). A second thermistor (313) is provided on the second crystal heat sink (38), and the second thermistor (313) is connected to a second temperature controller (315) for real-time monitoring of the temperature of the second potassium titanate oxygenate crystal (310).

3. A high-repetition-rate, narrow-pulse-width 1645nm non-planar laser as described in claim 1, characterized in that, The coating parameters of the M1 input mirror (31) are as follows: the incident angle of the incident surface is 28-38°, the reflectivity at 1645nm is 99.5% ± 0.2%, and the high transmittance film is deposited at 1064nm; the incident angle of the exit surface is 28-38°, the high transmittance film is deposited at 1064nm, and the transmittance at 1645nm is 0.5%. The coating specifications of the M2 total reflection mirror (32) are single-sided coating, incident angle of 28-38°, and high reflectivity film at 1645nm. The coating specifications of the M3 total reflection mirror (33) are single-sided coating, incident angle of 28-38°, and high reflectivity film at 1645nm. The coating specifications of the M4 output mirror (34) are as follows: the incident angle of the incident surface is 28-38°, a high transmittance film is deposited at 1064nm, the reflectance at 1645nm is 70%, the incident angle of the output surface is 28-38°, and a high transmittance film is deposited at both 1064nm and 1645nm.

4. A high repetition rate, narrow pulse width, 1645nm non-planar laser as described in claim 1, characterized in that, The first potassium titanate oxyarsenate crystal (37) and the second potassium titanate oxyarsenate crystal (310) are both 8mm*8mm*14mm in size, with cutting angles of θ=65.6° and φ=0°. The incident surface coating parameters are both: high transmittance film is deposited at 1064nm&1645nm&3015nm, and the exit surface coating parameters are both: high transmittance film is deposited at 1064nm&1645nm&3015nm.

5. A high-repetition-rate, narrow-pulse-width 1645nm non-planar laser as described in claim 1, characterized in that, The distance between the first potassium titanate oxygenate crystal (37) and the second potassium titanate oxygenate crystal (310) is 0.1 mm to 20 mm.

6. A high-repetition-rate, narrow-pulse-width 1645nm non-planar laser as described in claim 1, characterized in that, The laser is incident perpendicularly onto the second half-wave plate (311), and the center wavelength of the second half-wave plate (311) is 1645nm. The coating parameters are to deposit a high transmittance film at 1645nm.

7. A high repetition rate, narrow pulse width, 1645nm non-planar laser as described in claim 1, characterized in that, The first beam splitter (316) and the second beam splitter (317) are positioned at 45° to the light emitted from the M4 output mirror (34), and the coating parameter is an incident angle of 45°.

8. A high-repetition-rate, narrow-pulse-width 1645nm non-planar laser as described in claim 7, characterized in that, The first beam splitter (316) is coated with a high reflectivity film at 1645nm, and the second beam splitter (317) is coated with a high reflectivity film at 1064nm.

9. A high-repetition-rate, narrow-pulse-width 1645nm non-planar laser as described in claim 1, characterized in that, Adjusting the distances between the first pump beam expander (13), the second pump beam expander (14) and adjacent optical elements, as well as the distance between the first pump beam expander (13) and the second pump beam expander (14), can change the spot size and power density of the pump light injected into the spatial four-cavity optical parametric oscillator system. Adjusting the distances between the first seed beam expander (24), the second seed beam expander (25) and adjacent optical elements, as well as the distance between the first seed beam expander (24) and the second seed beam expander (25), can change the spot size and power density of the seed light injected into the spatial four-cavity optical parametric oscillator system, thereby achieving a mode for controlling the spot size matching of the pump light and the seed light.

10. A high-repetition-rate, narrow-pulse-width 1645nm non-planar laser as described in claim 1, characterized in that, Adjust the second total reflection mirror (321), the third total reflection mirror (322), and the fourth total reflection mirror (323) to avoid the locally damaged areas of the first potassium titanate arsenate crystal (37) and the second potassium titanate arsenate crystal (310) until the crystals are in normal working condition.

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