A device and method for generating sub-nanosecond laser pulses and pulse trains

Abstract

The present invention relates to a device for generating sub-nanosecond laser pulses and pulse trains and a method for generating the same, comprising a semiconductor laser, a collimating and focusing system, a bonded or glued crystal, and a filter arranged in sequence along an optical path; the front and rear end face coatings of the bonded or glued crystals constitute a laser resonant cavity. The present invention achieves 1μm-band sub-nanosecond laser output by optimizing the length of the laser crystal, the small-signal transmittance T0 of the Cr:YAG crystal, and the pump light duty cycle; and then optimizes the pulse width and energy of the pump light to increase the pump intensity and achieve 1-20 pulse train modes of sub-nanosecond laser pulse output. The output sub-nanosecond laser pulses and pulse trains have high energy (>5mJ), high repetition rate (up to 1kHz), high efficiency, and high beam quality, meeting the requirements of high-efficiency and high-precision laser processing, greatly improving the efficiency and quality of laser processing.

Description

Technical Field

[0001] The present invention relates to a device and method for generating sub-nanosecond laser pulses and pulse trains, and belongs to the technical field of all-solid-state lasers. Background Art

[0002] The laser is one of the four most celebrated inventions of the 20th century. Its advantages, including excellent directionality, high brightness, and monochromaticity, have shown significant application prospects in industry, medicine, scientific research, and defense. Sub-nanosecond lasers, in particular, have a wide range of important applications in laser ranging, lidar, laser processing, biomedicine, laser induction, Raman spectroscopy, mass spectrometry, and scientific research. In industrial processing, sub-nanosecond lasers are widely used in cutting, scribing, marking, welding, and drilling.

[0003] Q-switching technology is the most important technical means to generate sub-nanosecond laser pulses. Chinese patent documents CN201726032U and CN107706733B disclose methods for generating sub-nanosecond pulsed lasers using electro-optical active Q-switching technology, which can obtain sub-nanosecond laser pulses with a repetition frequency of kHz, but the output energy of the oscillation level is low, and the electro-optical Q switch requires high-voltage drive, with a complex structure and high cost. Chinese patent documents CN202695968U, CN104701719B, CN113889829A and other patents disclose passive Q-switched lasers and methods for generating them, but the pulse width is generally in the nanosecond range, making it difficult to obtain sub-nanosecond laser pulses, and the separation of optical components poses challenges to laser installation and debugging as well as device reliability. The pulse width generated by a Q-switched laser is proportional to the cavity length, and sub-nanosecond laser pulses can be obtained by compressing the laser cavity length.

[0004] Although sub-nanosecond laser pulses can currently reach mJ or even ~10mJ levels, their repetition rate is low, less than 100Hz, limiting their application in laser processing. Furthermore, existing technologies only produce single-pulse sub-nanosecond lasers. Research has shown that burst-mode laser pulses offer higher removal efficiency, better processing quality, and greater precision when used in laser processing. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a device and method for generating sub-nanosecond laser pulses and pulse trains. The present invention adopts a pulsed semiconductor laser to pump a bonded / glued crystal, uses a high repetition rate (1-1kHz) electric drive module, optimizes the crystal coating and doping concentration, and achieves simultaneous output of high energy (>5mJ), high repetition rate (up to 1kHz), high efficiency, and high beam quality (M 2 <1.5) of sub-nanosecond laser pulses and pulse trains (1-20 pulses) to meet the needs of high-efficiency and high-precision laser processing.

[0006] Explanation of terms:

[0007] 1.Cr:YAG: chromium-doped yttrium aluminum garnet.

[0008] The technical solution of the present invention is:

[0009] A device for generating sub-nanosecond laser pulses and pulse trains, comprising a semiconductor laser, a collimating and focusing system, a bonded or glued crystal, and a filter arranged in sequence along an optical path;

[0010] The bonded or glued crystal includes an Nd or Yb-doped laser crystal and a Cr:YAG crystal, and the rear end face of the Nd or Yb-doped laser crystal is bonded or glued to the front end face of the Cr:YAG crystal; the front end face coating of the Nd or Yb-doped laser crystal and the rear end face coating of the Cr:YAG crystal form a resonant cavity;

[0011] The operating wavelength of the semiconductor laser is 808nm, 880nm, 940nm, and 976nm, and the duty cycle of the electric drive module of the semiconductor laser is adjustable;

[0012] After being collimated by the collimation and focusing system, the pulsed pump light output by the semiconductor laser is incident on the laser crystal for pumping, forming optical oscillation in the resonant cavity. The Cr:YAG crystal acts as a saturated absorber and passively Q-switches the laser oscillation. When the gain of the Cr:YAG crystal is greater than the loss, sub-nanosecond laser pulses and pulse trains are generated and output through the coating coupling of the rear end face of the Cr:YAG crystal. The filter filters out the remaining pump laser light and outputs laser light in the 1μm band.

[0013] The sub-nanosecond laser provided by the present invention has the following working principle: pulse-modulated pump light is incident into the interior of the laser crystal, and then laser oscillation is generated in the laser resonant cavity. When the oscillating light passes through the Cr:YAG crystal, due to its saturation absorption effect, the loss is large, and the gain is less than the loss, and it is in the energy storage stage. As the intensity of the oscillating light beam in the laser resonant cavity increases, the absorption of the oscillating light beam by the Cr:YAG decreases. When the intensity of the oscillating light beam reaches a certain level, it causes the Cr:YAG crystal to bleach, that is, the Cr:YAG crystal no longer absorbs the oscillating light beam. At this time, the gain is greater than the loss, and sub-nanosecond laser pulse output is generated. By further optimizing parameters such as the pump light spot, duty cycle, and pump intensity, the output of a sub-nanosecond laser pulse train with an adjustable pulse number can be achieved.

[0014] Preferably, according to the present invention, the front end face and the rear end face of the Cr:YAG crystal are both planes, the front end face of the Nd or Yb-doped laser crystal is a plane, a convex surface or a concave surface, and the rear end face of the Nd or Yb-doped laser crystal is a plane, thereby forming a flat-flat resonant cavity, a concave-flat resonant cavity or a convex-flat resonant cavity, respectively.

[0015] The front and rear facets of the laser crystal can be bonded or glued to an undoped matrix crystal, improving heat dissipation efficiency and ensuring good beam quality at high energy output. The front facet of the laser crystal is machined into a convex surface, forming a concave-flat unstable resonant cavity, which increases the mode volume and helps improve pulse output energy and beam quality. The front facet of the laser crystal is machined into a concave surface, forming a convex-flat stable resonant cavity, which helps improve pulsed laser stability.

[0016] Preferably, according to the present invention, the laser crystal in the Nd or Yb doped laser crystal is any one of yttrium aluminum garnet YAG, yttrium vanadate YVO4, gadolinium gallium garnet GGG, lutetium oxide Lu2O3, yttrium aluminate YAP, lithium yttrium fluoride YLF, and gadolinium vanadate GdVO4.

[0017] Preferably, according to the present invention, the semiconductor laser uses an electric drive module with an operating repetition frequency of 1 Hz-1 kHz, which can achieve high repetition rate pumping.

[0018] According to a preferred embodiment of the present invention, the duty cycle of the semiconductor laser's electric drive module is adjustable, with the duty cycle adjustable range being 1%-80%. The adjustable duty cycle output of the electric drive module, i.e., the adjustable pulse width of the pump light, can be optimized based on the upper energy level lifetime of the laser crystal and the number of desired pulse trains.

[0019] Preferably, according to the present invention, the small signal transmittance of the Cr:YAG crystal is less than or equal to 60%, and the sum of the small signal transmittance of the Cr:YAG crystal and the transmittance of the rear end face coating of the laser crystal is 100%, thereby controlling the width of the output laser pulse.

[0020] According to a preferred embodiment of the present invention, the A operating wavelength of the semiconductor laser is 808nm. The front facet of the laser crystal is coated with a film system with high transmittance at 808nm and high reflection at 1064nm, while the rear facet of the laser crystal is coated with a film system with a transmittance of 40% at 1064nm. The small signal transmittance of the Cr:YAG crystal is 60%. This ensures both high pump light power and low quantum loss and thermal effects in the laser. By jointly regulating the pump wavelength, pump light duty cycle, and pump intensity, 1064nm sub-nanosecond laser pulses and pulse trains can be output.

[0021] Preferably, according to the present invention, the angle a between the filter and the optical path satisfies: 10°<a<45°.

[0022] According to the present invention, preferably, the output mode of the semiconductor laser is one of free space direct output, fiber coupled output, stack array output and linear array output.

[0023] A method for generating sub-nanosecond laser pulses and pulse trains, based on the above-mentioned device for generating sub-nanosecond laser pulses and pulse trains, comprises the following steps:

[0024] According to the first pulse establishment time t1 during pulse laser pumping and the pulse width t of the sub-nanosecond laser output by the device p , as shown in formula (I) and formula (II):

[0025]

[0026]

[0027] In formula (I), σ is the stimulated emission cross section of the laser, ω p is the pumping rate, l1 is the length of the laser crystal, τ is the lifetime of the upper energy level of the laser crystal, T0 is the small signal transmittance of the Cr:YAG crystal, R is the reflectivity of the coating on the rear end face of the laser crystal, and L is the loss in the laser resonant cavity;

[0028] In formula (II), c is the speed of light in vacuum, N0 is the initial inversion particle density when the pulse starts to build, N th is the threshold inversion particle number density, N f is the residual inversion particle number density, l c represents the length of Cr:YAG crystal, E represents the single pulse energy, and P represents the average power;

[0029] Sub-nanosecond laser output is achieved by optimizing the length of the laser crystal, the small signal transmittance T0 of the Cr:YAG crystal, and the duty cycle of the pump light. Then, by optimizing the pulse width and energy of the pump light and increasing the pump intensity, sub-nanosecond laser pulse output in a pulse train mode of 1-20 is achieved.

[0030] The beneficial effects of the present invention are:

[0031] 1. The present invention uses pulsed semiconductor laser to pump bonded or glued crystals to achieve miniaturized, high-energy sub-nanosecond laser pulse and pulse train output with high efficiency and good beam quality.

[0032] 2. The present invention can output sub-nanosecond laser in high-energy, high-repetition-rate pulse train mode, which can greatly improve the efficiency and quality of light-adding processing.

[0033] 3. Currently, there is no report on sub-nanosecond lasers that can output pulse trains with a repetition rate of 100Hz-1kHz and millijoules. By optimizing the duty cycle of the pump light, the intensity of the pump light, and the bonding or gluing crystal parameters (including crystal length, small signal transmittance, and coating transmittance), high energy (>5mJ), high repetition rate (up to 1kHz), high efficiency, and high beam quality (M 2<1.5) of sub-nanosecond laser pulses and pulse trains (1-20 pulses) to meet the needs of high-efficiency and high-precision laser processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the flat-flat structure of bonded / glued crystals;

[0035] Figure 2 Schematic diagram of the convex-flat structure of bonded / glued crystals;

[0036] Figure 3 Schematic diagram of the concave-flat structure of bonded / glued crystals;

[0037] Figure 4 A schematic structural diagram of a device for generating sub-nanosecond laser pulses and pulse train pulses provided in Example 2 of the present invention;

[0038] Figure 5 is the pump light pulse duration;

[0039] Figure 6 is the pump sequence of pump light pulses;

[0040] Figure 7 To output sub-nanosecond laser pulse waveform;

[0041] Figure 8 is the overall output laser energy and light conversion rate corresponding to different pump energies;

[0042] Figure 9 The pulse train output within a single pump pulse envelope at different pump energies;

[0043] Figure 10 To output sub-nanosecond laser beam quality;

[0044] Figure 11 is the output sub-nanosecond laser stability curve;

[0045] Figure 12 The pulse train output within a single pump pulse envelope at different pump pulse widths;

[0046] Figure 13 A schematic structural diagram of a device for generating sub-nanosecond laser pulses and pulse train pulses provided in Example 5 of the present invention;

[0047] Figure 14 A schematic structural diagram of a device for generating sub-nanosecond laser pulses and pulse train pulses provided in Example 6 of the present invention;

[0048] 1. Semiconductor laser, 2. Collimation and focusing system, 3. Bonded or glued crystal, 4. Filter. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to the embodiments and the accompanying drawings, but is not limited thereto.

[0050] Example 1

[0051] A device for generating sub-nanosecond laser pulses and pulse trains, comprising a semiconductor laser 1, a collimating and focusing system 2, a bonded or glued crystal 3, and a filter 4, which are sequentially arranged along an optical path;

[0052] The bonded or glued crystal 3 includes an Nd or Yb-doped laser crystal and a Cr:YAG crystal, and the rear end face of the Nd or Yb-doped laser crystal is bonded or glued to the front end face of the Cr:YAG crystal; the front end face coating of the Nd or Yb-doped laser crystal and the rear end face coating of the Cr:YAG crystal form a resonant cavity;

[0053] The operating wavelengths of the semiconductor laser 1 are 808 nm, 880 nm, 940 nm, and 976 nm, and the duty cycle of the electric drive module of the semiconductor laser 1 is adjustable;

[0054] After being collimated by the collimating and focusing system 2, the pulsed pump light output by the semiconductor laser 1 is incident on the laser crystal for pumping, forming optical oscillations in the resonant cavity. The Cr:YAG crystal acts as a saturated absorber and passively Q-switches the laser oscillations. When the gain of the Cr:YAG crystal is greater than the loss, sub-nanosecond laser pulses and pulse trains are generated and output through the coating coupling of the rear end face of the Cr:YAG crystal. The filter 4 filters out the remaining pump laser light and outputs laser light in the 1μm band.

[0055] The sub-nanosecond laser provided by the present invention has the following working principle: pulse-modulated pump light is incident into the interior of the laser crystal, and then laser oscillation is generated in the laser resonant cavity. When the oscillating light passes through the Cr:YAG crystal, due to its saturation absorption effect, the loss is large, and the gain is less than the loss, and it is in the energy storage stage. As the intensity of the oscillating light beam in the laser resonant cavity increases, the absorption of the oscillating light beam by the Cr:YAG decreases. When the intensity of the oscillating light beam reaches a certain level, it causes the Cr:YAG crystal to bleach, that is, the Cr:YAG crystal no longer absorbs the oscillating light beam. At this time, the gain is greater than the loss, and sub-nanosecond laser pulse output is generated. By further optimizing parameters such as the pump light spot, duty cycle, and pump intensity, the output of a sub-nanosecond laser pulse train with an adjustable pulse number can be achieved.

[0056] Example 2

[0057] The device for generating sub-nanosecond laser pulses and pulse trains provided in Example 1 has the following differences:

[0058] In this embodiment, the bonding or gluing crystal 3 is Nd:YAG / Cr:YAG, such as Figure 1 and Figure 4 As shown, the bonded or glued crystal 3 has a flat-flat structure. The front and rear faces of the Cr:YAG crystal are both flat, and the rear and front faces of the Nd:YAG crystal are both flat. That is, the front and rear faces of the bonded or glued crystal 3 are both flat.

[0059] The semiconductor laser 1 utilizes an electric drive module with an operating repetition rate of 1Hz-1kHz, enabling high-repetition-rate pumping. It also features adjustable duty cycle pulse output, with an adjustable duty cycle range of 1%-80%. This adjustable duty cycle, i.e., the pulse width of the pump light, can be adjusted, which can be optimized based on the upper energy level lifetime of the laser crystal and the number of desired pulse trains.

[0060] like Figure 5 As shown in Figure 2, the width of the pump light pulse is 300 μs, and the pump sequence of the pump light pulse is as follows: Figure 6 shown.

[0061] The A operating wavelength of semiconductor laser 1 is 808nm. The front end of the laser crystal is coated with a film system with high transmittance at 808nm and high reflection at 1064nm, and the rear end of the laser crystal is coated with a film system with a transmittance of 40% at 1064nm; the small signal transmittance of the Cr:YAG crystal is 60%.

[0062] After the pump light output by the semiconductor laser 1 is collimated by the collimating and focusing system 2, the pulsed pump light is incident on the Nd:YAG laser crystal for pumping, forming optical oscillations in the resonant cavity. The Cr:YAG crystal acts as a saturated absorber and passively Q-switches the laser oscillations. When the oscillation conditions are met, sub-nanosecond laser pulses and pulse trains are generated and output by coupling through the rear facet coating of the bonded or glued crystal 3. The filter 4 filters out the remaining pump laser light and outputs a laser with a wavelength of 1064nm.

[0063] The bonded or glued crystal 3 is placed in a heat sink, which is a device used to control / regulate the temperature of the bonded or glued crystal 3 in the present invention. Cooling and temperature control are performed by controlling the TEC current or water speed. The heat sink is not shown in the figure.

[0064] The angle a between the filter 4 and the optical path is 15°-45°.

[0065] The output mode of the semiconductor laser 1 is free space direct output.

[0066] The sub-nanosecond laser pulse and pulse train generating device provided in this embodiment outputs a sub-nanosecond laser pulse waveform as follows: Figure 7 As shown in Figure 2, the full width at half maximum of the laser pulse is 574 ps, which indicates that a sub-nanosecond laser pulse has been generated. Figure 8 As shown, the overall output laser energy and light conversion rate corresponding to different pump energies.

[0067] like Figure 10 As shown in the figure, the two fitting curves respectively represent the beam quality in the x / y axis direction and the beam quality in the x axis direction of the sub-nanosecond laser beam obtained by the device under the focus of the lens. Beam quality in the y-axis direction It can be seen that the obtained sub-nanosecond laser beam has high beam quality. Figure 10 The left illustration is a top view of the energy distribution of the sub-nanosecond laser, and the right illustration is a three-dimensional schematic diagram of the energy distribution of the sub-nanosecond laser.

[0068] like Figure 11 As shown, within 90 minutes, the power stability of the output sub-nanosecond laser is RMS=1.08%, which shows that the sub-nanosecond laser output by the device has good stability.

[0069] Example 3

[0070] The device for generating sub-nanosecond laser pulses and pulse trains provided in Example 1 has the following differences:

[0071] In this example, the operating wavelength of the semiconductor laser 1 is 808 nm, the output mode of the semiconductor laser 1 is fiber-coupled output, and the pump pulse width is 400 μs.

[0072] The small signal transmittance of Cr:YAG is 50%, and the rear end face is plated with a film system with a transmittance of 50% at 1064nm.

[0073] Example 4

[0074] The device for generating sub-nanosecond laser pulses and pulse trains provided in Example 1 has the following differences:

[0075] The bonded or glued crystal 3 is Yb:YAG / Cr:YAG; the operating wavelength of the pump light is 940 nm or 976 nm, and the central wavelength of the output laser is 1030 nm.

[0076] Example 5

[0077] The device for generating sub-nanosecond laser pulses and pulse trains provided in Example 1 has the following differences:

[0078] like Figure 2 and 13 As shown, the front end face of the laser crystal is processed into a convex surface to form a concave-flat laser resonant cavity. This cavity is stable and strong, which reduces the oscillation threshold and improves the sub-nanosecond laser output energy.

[0079] Example 6

[0080] The device for generating sub-nanosecond laser pulses and pulse trains provided in Example 1 has the following differences:

[0081] like Figure 3 and Figure 14 As shown, the front end face of the laser crystal is processed into a concave surface to form a convex-flat laser resonant cavity. This cavity is highly unstable, has a large mode volume, and a strong cavity mode selection ability, achieving sub-nanosecond laser output with high energy and high beam quality.

[0082] Example 7

[0083] The device for generating sub-nanosecond laser pulses and pulse trains provided in Example 1 has the following differences:

[0084] The laser crystal in the Nd or Yb doped laser crystal is any one of yttrium vanadate YVO4, gadolinium gallium garnet GGG, lutetium oxide Lu2O3, yttrium aluminate YAP, yttrium lithium fluoride YLF, and gadolinium vanadate GdVO4.

[0085] Example 8

[0086] A method for generating sub-nanosecond laser pulses and pulse trains, based on a device for generating sub-nanosecond laser pulses and pulse trains provided in any one of Examples 1-7, comprises the steps of:

[0087] According to the first pulse establishment time t1 during pulse laser pumping and the pulse width t of the sub-nanosecond laser output by the device p , as shown in formula (I) and formula (II):

[0088]

[0089]

[0090] In formula (I), σ is the stimulated emission cross section of the laser, ω p is the pumping rate, l1 is the length of the laser crystal, τ is the lifetime of the upper energy level of the laser crystal, T0 is the small signal transmittance of the Cr:YAG crystal, R is the reflectivity of the coating on the rear end face of the laser crystal, and L is the loss in the laser resonant cavity;

[0091] In formula (II), c is the speed of light in vacuum, N0 is the initial inversion particle density when the pulse starts to build, N th is the threshold inversion particle number density, N f is the residual inversion particle number density, l c represents the length of Cr:YAG crystal, E represents the single pulse energy, and P represents the average power;

[0092] Sub-nanosecond laser output is achieved by optimizing the length of the laser crystal, the small signal transmittance T0 of the Cr:YAG crystal, and the pump light duty cycle; the smaller the length of the laser crystal, the easier it is to generate sub-nanosecond laser pulses;

[0093] Under different pump energies, the sub-nanosecond laser pulse train output within a single pump pulse envelope is as follows: Figure 9 As shown, when the pump energy is 20mJ, the device outputs one sub-nanosecond laser pulse train under a single pump pulse envelope; when the pump energy is 27mJ, the device outputs two sub-nanosecond laser pulse trains under a single pump pulse envelope; when the pump energy is 33mJ, the device outputs three sub-nanosecond laser pulse trains under a single pump pulse envelope.

[0094] Under different pump pulse widths, the sub-nanosecond laser pulse train output within a single pump pulse envelope is as follows: Figure 12 As shown, when the pump pulse width is 200μs, under a single pump pulse envelope, the device outputs one sub-nanosecond laser pulse train; when the pump pulse width is 250μs, under a single pump pulse envelope, the device outputs two sub-nanosecond laser pulse trains; when the pump pulse width is 450μs, under a single pump pulse envelope, the device outputs three sub-nanosecond laser pulse trains.

[0095] That is, by optimizing the pulse width and energy of the pump light and increasing the pump intensity, it is possible to achieve sub-nanosecond laser pulse output in a pulse train mode of 1-20.

Claims

1. A device for generating sub-nanosecond laser pulses and pulse trains, characterized in that: It includes a semiconductor laser, a collimating and focusing system, a bonded or glued crystal and a filter arranged in sequence along the optical path; The bonded or glued crystal includes an Nd or Yb-doped laser crystal and a Cr:YAG crystal, and the rear end face of the Nd or Yb-doped laser crystal is bonded or glued to the front end face of the Cr:YAG crystal; the front end face coating of the Nd or Yb-doped laser crystal and the rear end face coating of the Cr:YAG crystal form a resonant cavity; The operating wavelength of the semiconductor laser is 808nm, 880nm, 940nm, and 976nm, and the duty cycle of the electric drive module of the semiconductor laser is adjustable; After the pulsed pump light output by the semiconductor laser is collimated by the collimation and focusing system, it is incident on the laser crystal for pumping, forming optical oscillation in the resonant cavity. The Cr:YAG crystal acts as a saturated absorber and passively Q-switches the laser oscillation. When the gain of the Cr:YAG crystal is greater than the loss, sub-nanosecond laser pulses and pulse trains are generated and output through the coating coupling of the rear end face of the Cr:YAG crystal. The filter filters out the remaining pump laser light and outputs laser light in the 1μm band. The method for producing the generating device comprises the steps of: According to the first pulse establishment time t1 during pulse laser pumping and the pulse width t of the sub-nanosecond laser output by the device p , as shown in formula (I) and formula (II): In formula (I), σ is the stimulated emission cross section of the laser, ω p is the pumping rate, l1 is the length of the laser crystal, τ is the lifetime of the upper energy level of the laser crystal, T0 is the small signal transmittance of the Cr:YAG crystal, R is the reflectivity of the coating on the rear end face of the laser crystal, and L is the loss in the laser resonant cavity; In formula (II), c is the speed of light in vacuum, N0 is the initial inversion particle density when the pulse starts to build, N th is the threshold inversion particle number density, N f is the residual inversion particle number density, l c represents the length of Cr:YAG crystal, E represents the single pulse energy, and P represents the average power; Sub-nanosecond laser output is achieved by optimizing the length of the laser crystal, the small signal transmittance T0 of the Cr:YAG crystal, and the duty cycle of the pump light. Then, by optimizing the pulse width and energy of the pump light and increasing the pump intensity, sub-nanosecond laser pulse output in a pulse train mode of 1-20 is achieved.

2. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 1, characterized in that: The front and rear facets of the Cr:YAG crystal are both planes, the front facet of the Nd or Yb-doped laser crystal is a plane, a convex surface or a concave surface, and the rear facet of the Nd or Yb-doped laser crystal is a plane, thereby forming a flat-flat resonant cavity, a concave-flat resonant cavity or a convex-flat resonant cavity respectively.

3. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 1, characterized in that: The laser crystal in the Nd or Yb doped laser crystal is any one of yttrium aluminum garnet YAG, yttrium vanadate YVO4, gadolinium gallium garnet GGG, lutetium oxide Lu2O3, yttrium aluminate YAP, yttrium lithium fluoride YLF, and gadolinium vanadate GdVO4.

4. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 1, characterized in that: The semiconductor laser adopts an electric drive module with a working repetition frequency of 1 Hz-1 kHz.

5. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 1, characterized in that: The duty cycle of the electric drive module of the semiconductor laser is adjustable, and the adjustment range of the duty cycle is 1%-80%.

6. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 1, characterized in that: The small signal transmittance of the Cr:YAG crystal is less than or equal to 60%, and the sum of the small signal transmittance of the Cr:YAG crystal and the transmittance of the rear end coating of the laser crystal is 100%, thereby controlling the width of the output laser pulse.

7. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 6, characterized in that: The A operating wavelength of the semiconductor laser is 808nm. The front end of the laser crystal is plated with a high transmittance of 808nm and a high reflection mode of 1064nm. The rear end of the laser crystal is plated with a film system with a transmittance of 40% at 1064nm. The small signal transmittance of the Cr:YAG crystal is 60%.

8. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 1, characterized in that: An angle a between the filter and the optical path satisfies the following: 10°<a<45°.

9. The device for generating sub-nanosecond laser pulses and pulse trains according to claim 1, characterized in that: The output mode of the semiconductor laser is one of free space direct output, fiber coupled output, stack array output and linear array output.

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