Passive Q-switched pulse laser and laser pulse generation method thereof

Abstract

The invention discloses a passive Q-switched pulse laser and a pulse generation method thereof. The laser comprises an optical pumping device, a laser gain medium and a laser resonant cavity. The laser is characterized in that a saturated absorber crystal with an uncoated light passing surface is arranged in the resonant cavity, and the crystal is arranged in a laser light path in the resonant cavity at a Brewster angle. Through the configuration, the saturable absorber crystal serves as an intra-cavity polarization selection element while realizing a passive Q-switching function, so that the structure is simplified, and linear polarization output is realized.

Description

Technical Field

[0001] This application relates to the field of optical technology, and in particular to a passively Q-switched pulsed laser and a method for generating laser pulses thereon. Background Technology

[0002] As laser technology continues to be applied in precision manufacturing, 3D imaging radar, and medical fields, the market is placing higher demands on light source performance, especially on the control of laser polarization states. In the passive Q-switched solid-state pulsed laser technology route, outputting stable linearly polarized pulses has a significant impact on improving the precision of material processing and the signal-to-noise ratio of detection systems. Therefore, seeking a passive Q-switched laser technology solution that can efficiently generate linearly polarized pulses has significant market value and technical significance.

[0003] However, a basic passively Q-switched laser consisting only of a gain medium, a saturable absorber, and a cavity mirror, where all internal optical elements are isotropic or axisymmetric, typically exhibits no significant loss difference in the resonant cavity for light waves with different polarization directions. In this case, the polarization state of the output laser may be random or non-polarized, limiting the performance of such lasers in polarization-sensitive applications. For example, in material processing requiring precise control of polarization states, randomly polarized lasers struggle to achieve predictable and uniform results; while in lidar systems that rely on polarization information for target recognition or noise suppression, non-polarized light sources cannot provide the necessary signal dimension, potentially leading to decreased detection and anti-interference capabilities.

[0004] To address the aforementioned issues, a common approach in existing technologies is to integrate a dedicated polarization selection element, such as a thin-film polarizer (TFP) or a Glan prism, into the laser resonator. This approach enables the laser to operate in a single linear polarization mode by introducing a separate device with significantly different losses for different polarization states. However, this approach of adding a separate component also introduces new problems: the additional optical element not only complicates the laser's optical path structure, increasing assembly difficulty and potential failure points, but the insertion loss of the component itself also reduces the overall optical-to-optical conversion efficiency of the laser. Furthermore, adding components typically means increasing system size and manufacturing costs, which contradicts the current trend towards miniaturization, lightweight design, and high cost-effectiveness in laser equipment. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects existing in the prior art and to provide a passive Q-switched pulse laser and a method for generating laser pulses that can achieve polarization control without the introduction of additional independent optical components, thereby possessing high energy conversion efficiency, high operational reliability, compact structure and controllable cost.

[0006] To achieve the above objectives, a first aspect of the present invention provides a passively Q-switched pulsed laser, comprising: Optical pumping device; The laser gain medium is located in the output optical path of the optical pump device; and A laser resonant cavity containing the laser gain medium; the resonant cavity also includes a plate-shaped saturable absorber crystal, wherein the saturable absorber crystal includes two uncoated light-transmitting surfaces and is configured to intercept the laser beam path within the cavity at Brewster angle.

[0007] This application provides a passively Q-switched pulsed laser that achieves the following technical effects: 1. Polarization control is achieved through functional integration, avoiding the insertion loss of independent components: This scheme utilizes the saturable absorber crystal itself as the Brewster angle polarization selection element. According to Brewster's principle, P-polarized light and S-polarized light have different reflectivities when incident at a Brewster angle, creating a loss difference in the resonant cavity, thereby suppressing S-polarized light and causing P-polarized light to oscillate. This design achieves polarization control while avoiding the additional insertion loss caused by independent polarization elements, which helps to improve the energy conversion efficiency of the laser.

[0008] 2. Improves device reliability and damage threshold: This invention uses an uncoated saturable absorber crystal, whose light-transmitting surface is the crystal itself with high precision polishing. Its laser damage threshold is typically higher than that of optical coatings. This design removes the coating layer, a component that is easily damaged at high peak power, thus helping to enhance the long-term operational stability of the laser under high-power conditions.

[0009] 3. Improving beam quality by compensating for astigmatism through symmetrical structure: In some embodiments, two saturable absorbers are placed symmetrically at Brewster angles, and the astigmatism generated by the second element is used to compensate for the astigmatism introduced by the first element. This design can effectively correct the ellipticity of the beam, obtaining a beam with higher roundness and a better M² factor, thereby improving the focusing performance of the laser. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the structure of one of the passively Q-switched pulsed lasers provided in this application; Figure 2 This is a schematic diagram of another passively Q-switched pulsed laser provided in this application; Figure 3 This is a schematic diagram of a passively Q-switched pulsed laser provided in this application; Figure 4 This is a schematic diagram of a passively Q-switched pulsed laser provided in this application; Figure 5This is a PI curve of a passively Q-switched pulsed laser. Figure 6 This is a diagram showing the laser spot and M-squared factor of a passively Q-switched pulsed laser; Figure 7 This is a pulse waveform diagram of a passively Q-switched pulsed laser. Figure 8 This is a waveform diagram of the pulse frequency of a passively Q-switched pulsed laser.

[0011] Explanation of reference numerals in the attached figures: 10, optical pumping device; 12, pumping optical system; 20, laser resonant cavity; 21, input mirror; 22, output coupling mirror; 30, laser gain medium; 40, saturable absorber crystal; 120, fast-axis collimating lens; 122, pump focusing lens. Detailed Implementation

[0012] The following is in conjunction with the appendix Figure 1-8 The passively Q-switched pulsed laser and method provided in this application are described in further detail.

[0013] Example 1 Please see Figure 1 This embodiment discloses a passively Q-switched pulsed laser. It includes an optical pumping device 10, a laser gain medium 30, a laser resonant cavity 20, and a saturable absorber crystal 40.

[0014] In this embodiment, the optical pumping device 10 can be a high-power semiconductor laser diode (LD) or its array, whose emission wavelength matches the absorption spectrum of the laser gain medium 30. For example, the center of the emission wavelength of the optical pumping device 10 can be located in the range of 930 nm to 950 nm, which corresponds to a relatively wide absorption band of Yb:YAG. This range has relatively low requirements for the wavelength stability of the pump source, which helps to control system cost. Alternatively, the center of the emission wavelength of the optical pumping device 10 can be stabilized in the range of 969 nm ± 1 nm by active thermoelectric cooling (TEC). This wavelength corresponds to the "zero phonon line" with a strong absorption cross section of Yb:YAG, which has a higher absorption coefficient and higher quantum efficiency, and generates less heat. This helps to obtain higher gain with lower pump power, or higher output power and better beam quality at the same pump power.

[0015] To efficiently utilize pump energy, this solution may include a pump optics system 12, configured to focus the pump light and match the resulting spot within the laser gain medium 30 to the fundamental mode volume of the resonant cavity. In this embodiment, the pump optics system 12 may include a fast-axis collimating lens 120 (FAC) and a pump focusing lens 122 for shaping and focusing the highly asymmetric beam of the LD array. In other embodiments, the pump optics system 12 may also include a slow-axis collimating lens (SAC), a beam shaper, etc. The aim is to obtain a pump spot with suitable geometry and energy distribution, highly overlapping with the laser mode volume, to achieve efficient mode matching.

[0016] Furthermore, in order to optimize the size of the laser, the pump focusing lens 122 for focusing the beam can be eliminated. The pump light emitted from the optical pumping device 10 enters the laser gain medium 30 directly after passing through the fast axis collimating lens 120, and the distance between the pumping device 10 and the laser gain medium 30 is less than 1.5 mm.

[0017] In this embodiment, the laser gain medium 30 is a yttrium aluminum garnet (Yb:YAG) crystal. In other embodiments, other laser crystals or ceramics may also be used, such as neodymium aluminum garnet (Nd:YAG), neodymium yttrium vanadate (Nd:YVO4), neodymium lithium yttrium fluoride (Nd:YLF), etc., depending on the target output wavelength, power level, and availability of the pump source.

[0018] When anisotropic gain crystals such as Nd:YVO4 and Nd:YLF are selected, specific directional cutting and placement are required to achieve higher gain. If placed arbitrarily, the direction of maximum gain may not align with the intracavity P-polarization direction, potentially leading to "polarization mode competition": pump energy is used to amplify a non-P-polarized mode, but this mode, due to high reflection loss at the surface of the saturable absorber crystal 40, struggles to reach the lasing threshold, resulting in wasted pump energy and ineffective amplification of the P-polarized mode. This can ultimately lead to an increase in the laser threshold and a decrease in efficiency. Therefore, this solution precisely orients the anisotropic crystal so that the crystal axis with the maximum stimulated emission cross-section is parallel to the intracavity P-polarized light vibration direction determined by the saturable absorber crystal 40. This design helps to: 1) guide pump energy more effectively to the P-polarization channel, reducing the laser threshold; 2) improve the slope efficiency of light-to-light conversion; and 3) reduce energy competition between modes, resulting in more stable laser output.

[0019] The laser resonant cavity 20 consists of an input mirror 21 and an output coupling mirror 22. The resonant cavity 20 also includes a saturable absorber crystal 40, such as chromium-doped yttrium aluminum garnet (Cr). 4⁺:YAG). In other embodiments, Co²⁺:MgAl₂O₄, V³⁺:YAG, or semiconductor saturable absorber mirrors (SESAM) may also be used.

[0020] In this embodiment, the output coupling mirror 22 has a transmittance of 15% to 60% for a wavelength of 1030nm. This transmittance range is optimized to match the high-gain system that this invention can achieve, thereby enabling efficient energy extraction. If the transmittance is below 15%, insufficient energy extraction may occur, limiting peak power; if the transmittance is above 60%, the total loss may exceed the gain that the system can provide, causing the laser to fail to oscillate. Simultaneously, the cavity length of the laser resonator 20 can be set between 10mm and 60mm, where the cavity length is the axial distance from the reflecting surface of the input mirror 21 to the reflecting surface of the output coupling mirror 22. This range is an optimized result that comprehensively considers energy storage, assembly convenience, and pulse characteristics. Experiments show that when the cavity length is less than 10mm, the effective length of the gain medium is limited, energy storage is insufficient, and component assembly is extremely difficult; while when the cavity length exceeds 60mm, due to the increase in the round-trip time within the cavity, the pulse width broadening effect becomes too significant, and the stability of the resonator decreases, leading to a significant deterioration in the laser performance parameters.

[0021] The saturable absorber crystal 40 has a pair of parallel, uncoated light-transmitting surfaces. It should be noted that, in this application, "uncoated" means that no optical thin film is deposited on the light-transmitting surface to alter its reflectivity or transmittance to the intracavity laser wavelength. This utilizes the Brewster angle between the surface and the laser to eliminate reflections of P-polarized lasers and avoids introducing films that might lower the laser damage threshold. The saturable absorber crystal 40 can be plate-shaped to save axial space within the cavity and facilitate system compactness.

[0022] It should also be noted that the term "uncoated" in this application refers to the absence of any optical thin film deposited on the light-transmitting surface to alter its reflectivity or transmittance for the intracavity laser wavelength (e.g., 1030 nm). This utilizes the Brewster angle with the laser to eliminate reflections of P-polarized lasers and avoids introducing any film layers that might lower the laser damage threshold. This does not preclude the presence of markings on the light-transmitting surface, such as for structural identification or non-optical purposes.

[0023] The initial transmittance T0 of the saturable absorber crystal 40 can be selected between 60% and 98%. Too low a T0 may result in an excessively high laser threshold; too high a T0 may lead to insufficient Q-switching modulation depth, affecting pulse quality. The saturable absorber crystal 40 is placed inside the cavity such that the laser beam is incident on its light-transmitting surface at a Brewster angle θB (θB = arctan(n), where n is the refractive index of the material). For example, Cr... 4The Brewster angle of YAG at a wavelength of 1030 nm is approximately 61.2°. In actual assembly, the angle error should be controlled within a small range (e.g., ±0.5°) to ensure sufficient reflection loss for S-polarized light while minimizing transmission loss for P-polarized light.

[0024] The light-transmitting surface of the saturable absorber crystal 40 can be 2mm × 5mm, and the thickness is preferably 1.5mm. This thickness ensures that the pump light has a sufficiently long absorption path within the crystal, thereby achieving efficient pump conversion. This is crucial for obtaining... Figure 5-8 This is one of the foundations of the high-performance output parameters shown.

[0025] This approach simplifies the structure, reduces costs, eliminates the inherent optical loss introduced by the saturable absorber by giving it dual functionality, and removes a common optical damage point, aiming to achieve a compact, efficient, and reliable linearly polarized pulsed laser.

[0026] Example 2 Please see Figure 2 Based on Example 1, this embodiment has undergone in-depth optimization of the structure and component layout of the resonant cavity.

[0027] The laser resonator 20 is designed as a plano-concave cavity. The spatial arrangement of the components within the cavity utilizes the non-uniformity of the optical field distribution within the plano-concave cavity. In a stable plano-concave cavity, the beam waist (the point of minimum beam size) is typically located near the plane mirror 22. In this embodiment, the saturable absorber crystal 40 is placed in the beam waist region. This arrangement utilizes the higher intracavity power density in this region, allowing it to be saturated more quickly and deeply, which helps to compress the Q-switching settling time and is one of the key factors in obtaining narrow pulses. Simultaneously, the laser gain medium 30 is placed in a region far from the beam waist with a larger beam diameter (such as near the concave input mirror 21).

[0028] The advantage of this layout is that: 1. A larger mode volume enables better mode matching with the pump spot, improving energy storage levels; 2) Reducing the power density acting on the gain medium helps alleviate thermal effects and increase the damage threshold, supporting stable operation of the laser at high average power.

[0029] Those skilled in the art will understand that this idea of ​​optimizing component layout by utilizing differences in intracavity light spot size is also applicable to other stable resonant cavity configurations. Furthermore, regarding the implementation of the input mirror 21, there are several equivalent solutions: Option A (Integrated): A dual-color dielectric film is directly deposited on the pump input surface of the laser gain medium 30. This film layer must meet the requirements of high transmittance (T>99.5%) for the pump wavelength (e.g., 969nm) and high reflectance (R>99.8%) for the laser wavelength (e.g., 1030nm). The advantage of this option is its extremely compact structure and minimal number of components, making it very suitable for applications that pursue miniaturization and low cost.

[0030] Option B (Discrete): A separate mirror with a specific curvature is used as the input mirror 21, coated with the same dichroic film as in Option A. In this case, both light-transmitting end faces of the laser gain medium 30 need to be coated with an AR film (R<0.2%) that inhibits both pump light and laser wavelength. The advantage of this option is its high flexibility; engineers can easily replace the input mirror 21 with different radii of curvature to fine-tune the cavity mode parameters, or replace the gain crystal with different lengths and doping concentrations, without needing to customize expensive coated crystals, greatly facilitating laser research and development and debugging.

[0031] In another embodiment of the invention, the laser resonator 20 can also be designed as a planar cavity, i.e., both the input mirror 21 and the output coupling mirror 22 are planar mirrors. In particular, when using the aforementioned integrated scheme (Scheme A), the planar cavity configuration has a significant manufacturing cost advantage. This is because, when the input mirror is directly integrated onto the end face of the laser gain medium 30, if the end face of the gain medium is planar, its processing and coating costs are far lower than processing it into a curved surface. Therefore, the combination of a planar cavity and an integrated input mirror provides a very attractive technical path for achieving an extremely compact and low-cost laser.

[0032] To verify the technical effects of this invention, we built a prototype of a passively Q-switched pulsed laser based on a plano-concave cavity structure as described in Example 1, and conducted tests. The main configuration parameters are as follows: Laser gain medium (30): Yttrium aluminum garnet (Yb:YAG) doped with yttrium, 5 mm thick.

[0033] Saturated absorber crystal (40): Chromium-doped yttrium aluminum garnet (Cr 4 ⁺:YAG), initial transmittance T0=95%, thickness 1.5mm, placed at Brewster angle.

[0034] Laser resonator (20): plano-concave cavity, with a physical cavity length set to L = 20mm. Input mirror 21 is a concave mirror with a radius of curvature R = 100mm, integrated on the end face of the gain medium; output coupling mirror 22 is a planar mirror with a transmittance of T = 40% for 1030nm laser.

[0035] Pump device 10: Employs TEC active temperature control to stabilize the emitted wavelength at 969nm.

[0036] Figure 5 , Figure 6 , Figure 7 and Figure 8 These are performance curves and waveforms of the laser described in Embodiment 2 of this application, measured under specific parameter configurations. Figure 5 This is a PI curve graph; Figure 6 The diagram shows the laser spot size and the M-squared factor. Figure 7 This is a pulse waveform diagram; Figure 8 Pulse frequency waveform diagram Under this configuration, the following was obtained: Figure 5-8 The experimental results shown are as follows: Figure 5 The PI (output power - pump current) curve of the laser is shown. At a maximum pump power of 17W, an average output power of over 8W was achieved, and the calculated slope efficiency was as high as 60.63%, which strongly demonstrates the low loss and high efficiency advantages brought by the functional integration scheme of this invention (saturable absorber also serving as polarizer).

[0037] Figure 6 The beam morphology and M² factor measurements at maximum output power are shown. The output beam has a near-ideal Gaussian distribution, and the measured M² factor is better than 1.5 in both directions, indicating that even with the saturable absorber placed at a large angle, this scheme can still achieve excellent beam quality and is suitable for high-end applications such as precision machining.

[0038] Figure 7 The output laser pulse waveform is shown. A stable pulse sequence with a pulse width as narrow as 6.22 ns was obtained at a repetition frequency of 28.6 kHz. This was achieved by placing the saturable absorber in the beam waist region and by using a synergistic design of short cavity length and high output coupling, thus realizing high energy storage and fast energy extraction.

[0039] Figure 8 The stability of the pulse repetition frequency of the laser when operating in the frequency range of 20kHz to 150kHz is demonstrated. It can be seen that the frequency jitter is extremely small, indicating that the passive Q-switching mechanism of this invention operates stably and reliably.

[0040] Example 3 Please see Figure 3-4This embodiment provides a compensation scheme to address the astigmatism problem that may be introduced by a single tilted element. Placing a single element tilted at a large angle (such as the saturable absorber crystal 40 of this invention) within the cavity may introduce astigmatism, causing different focusing characteristics of the beam in the tangential plane and the sagittal plane, resulting in an elliptical output spot and thus affecting beam quality. To solve this problem, this embodiment proposes a symmetrical design. Two saturable absorber crystals 40 with uncoated light-transmitting surfaces are placed within the laser resonant cavity 20. These two saturable absorber crystals 40 are symmetrically tilted relative to the optical axis and are also placed in the optical path within the cavity at Brewster's angle.

[0041] In addition, in this embodiment, the input mirror 21 is integrated on the end face of the laser gain medium 30 to further optimize the overall size of the laser and improve the integration.

[0042] The beneficial technical effect of this symmetrical arrangement of the two saturable absorber crystals 40 is that the astigmatism introduced by the second tilting element is similar in magnitude and opposite in direction to that introduced by the first tilting element, and the two compensate for each other during the round-trip propagation of the beam. This design helps to achieve automatic astigmatism compensation, restoring better circular symmetry of the resonant cavity mode. For example, the low beam roundness caused by astigmatism (e.g., below 0.7) can be corrected to a higher level (e.g., above 0.95), and the M² factor can be optimized from greater than 2.0 to within 1.2, close to the diffraction limit, thereby improving the focusing characteristics and far-field energy concentration of the beam.

[0043] Of course, it is not limited to using only two saturable absorber crystals 40; the number of saturable absorber crystals 40 can be selected according to actual needs. In short, when saturable absorber crystals 40 are included, the latter saturable absorber crystal 40 is arranged in a figure-eight shape with the former saturable absorber crystal 40. Alternatively, any two adjacent saturable absorber crystals 40 are arranged symmetrically in a figure-eight shape with respect to the laser beam path to mutually compensate for astigmatism introduced by tilted placement.

[0044] Example 4 This application also provides a method for generating Q-switched laser pulses, which can be implemented using the laser of any of the foregoing embodiments. The method includes: Step 1: Pumping the gain medium. Start the optical pumping device 10 to pump the Yb:YAG laser gain medium 30 to establish population inversion.

[0045] Step Two: Energy Accumulation and Mode Selection. Under pumping action, the energy accumulated in the laser gain medium 30 increases the number of photons within the cavity. The beam oscillates within the laser resonant cavity 20. When it passes through the saturable absorber crystal 40 placed at Brewster's angle, P-polarized light passes with lower loss, while S-polarized light is suppressed, achieving polarization selection. Simultaneously, the saturable absorber exhibits high absorption for low-power light, preventing premature laser oscillation and allowing more energy to be stored in the gain medium.

[0046] Step 3: Pulse Generation and Extraction. When the optical power density inside the cavity accumulates to a level sufficient to instantaneously saturate the saturable absorber crystal 40, the Q value of the laser resonant cavity 20 changes abruptly, forming a giant pulse. This pulse is extracted from the resonant cavity 20, which has a specific cavity length (e.g., 10-60 mm), through the output coupling mirror 22 with a specific transmittance (e.g., 15%-60%).

[0047] In high-gain systems (such as 969nm pumped Yb:YAG), high gain can easily lead to spontaneous emission amplification (ASE) and premature oscillation. The design of placing the saturable absorber at the Brewster angle in this scheme demonstrates its synergistic value here: on the one hand, it achieves low-loss polarization selection, improving the net gain within the cavity; on the other hand, the large tilt angle increases the spot area, objectively raising the saturation threshold of the saturable absorber. This characteristic helps suppress premature oscillation in high-gain systems, allowing more energy to be stored in the gain medium. When the energy accumulated within the cavity is sufficient to overcome this higher saturation threshold, the energy is released rapidly. To match this process, a combination of "short cavity length + high output coupling ratio" is an effective energy extraction strategy. The short cavity length helps to obtain a narrow pulse width; while the high output coupling ratio plays the role of an efficient energy extraction channel in high-gain systems, enabling the output of most of the energy within the cavity in the form of a strong pulse within a short time.

[0048] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A passively Q-switched pulsed laser, characterized in that, The application relates to a laser device, comprising: an optical pumping device (10); a laser gain medium (30) located in the light path of the optical pumping device (10); and a laser resonant cavity (20) containing the laser gain medium (30); one or more saturable absorber crystals (40) are further arranged in the laser resonant cavity (20), and each of the saturable absorber crystals (40) has a pair of mutually parallel uncoated light transmission surfaces and is configured to intercept the laser beam light path of the laser resonant cavity (20) at the Brewster angle. The laser resonant cavity (20) is a plano-concave cavity, the laser resonant cavity (20) comprises an input mirror (21) and an output coupling mirror (22), the input mirror (21) is a concave mirror, and the output coupling mirror (22) is a plane mirror; further, 2. The passively Q-switched pulsed laser of claim 1, wherein, the input mirror (21) is composed of a double-color medium film directly coated on the input end surface of the laser gain medium (30); or the input mirror (21) is an independent double-color mirror, and the pump input end surface of the laser gain medium (30) is coated with a film layer which has a high transmittance for both pump light and laser oscillation wavelength. The optical pumping device (10) and the laser gain medium (30) are further provided with a pump optical system (12) for shaping and focusing pump light, the optical pumping device (10) is a semiconductor laser chip array, the pump optical system (12) comprises a fast-axis collimating lens (120) for collimating the light beam in the fast-axis direction of the semiconductor laser chip array and a pump focusing lens (122) for focusing the light beam, and the pump optical system (12) is configured to focus the pump light into a spot which matches the cavity mode volume.

3. The passively Q-switched pulsed laser of claim 1, wherein: The saturable absorber crystal (40) is arranged in the beam waist region of the laser resonant cavity (20), and the laser gain medium (30) is arranged in the region of the laser resonant cavity (20) where the spot diameter is larger than the beam waist diameter.

4. The passively Q-switched pulsed laser of claim 2, wherein, There are two uncoated saturable absorber crystals (40) in the laser resonant cavity (20), the two saturable absorber crystals (40) are arranged in an eight-shaped symmetry, and each of the saturable absorber crystals (40) is configured to intercept the laser beam light path in the cavity at the Brewster angle.

5. The passively Q-switched pulsed laser of claim 1, wherein: The laser gain medium (30) is an anisotropic crystal which has a crystal axis direction with the maximum stimulated emission cross section and is arranged to be parallel to the vibration direction of the P-polarized laser light in the cavity which is determined by the Brewster angle of the saturable absorber crystal (40).

6. The passively Q-switched pulsed laser of claim 1, wherein: The laser resonant cavity (20) is a short resonant cavity with a physical cavity length of 10mm to 60mm, the saturable absorption crystal (40) is a Cr:YAG crystal with an initial transmittance higher than 60%, and the output coupling mirror (22) has a transmittance of 15% to 60% for the laser wavelength.

7. The passively Q-switched pulsed laser of claim 1, wherein: The laser gain medium (30) is a Yb:YAG crystal, and the output coupling mirror (22) has a transmittance of 15% to 60% for the 1030nm wavelength.

8. The passively Q-switched pulsed laser of claim 1, wherein: ​ 9. The passively Q-switched pulsed laser of claim 8, wherein: the optical pumping device (10) has an emission wavelength centered in the range of 930 nm to 950 nm; or the optical pumping device (10) has an emission wavelength centered in the range of 969 nm ± 1 nm.

10. A method of generating a laser pulse, characterized by, The method comprises the following steps: a) providing a passively Q-switched pulsed laser as claimed in any of claims 1 to 9; b) pumping the laser gain medium (30) using the optical pumping device (10) to establish population inversion; c) accumulating energy within the laser resonator (20), wherein the saturable absorber crystal (40) placed at the Brewster angle simultaneously performs Q-switching modulation and polarization selection; d) when the intracavity optical power reaches the saturation threshold of the saturable absorber crystal (40), a Q-switched pulse is formed and extracted from the laser resonator (20) through the output coupler.

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