Pulse width adjustable Q-switched laser

Abstract

The utility model provides a Q-switched laser with adjustable pulse width. The Q-switched laser comprises an output coupling mirror, a laser head, a Q switch, a polarization assembly, a first plane mirror and a second plane mirror. A first included angle is formed between the first plane mirror and the central axis, a second included angle is formed between the second plane mirror and the central axis, and a third included angle is formed between the laser incident to the second plane mirror and the vertical direction of the central axis. By adjusting the first included angle, the second included angle and the third included angle, the turn-back times of laser between the first plane mirror and the second plane mirror are adjusted, so that the effective length of the laser resonant cavity is changed, the optical path is changed, the pulse width is adjustable in the Q-switched pulse laser, and the Q-switched pulse laser is more stable. The device has the characteristics of small size, low cost, convenience in operation, reliable performance and the like, and is beneficial to modularized and large-scale production.

Description

Technical Field

[0001] The utility model relates to the technical field of lasers, in particular to a Q-switched laser with adjustable pulse width. Background Art

[0002] With the rapid development of laser technology, lasers are being used more and more widely, and the requirements for peak power, beam quality and pulse width of lasers are becoming higher and higher. Among them, Q-switched lasers have shown their application characteristics in the fields of industry, medical treatment, national defense and scientific research, and have great development potential and application scenarios.

[0003] Q-switching technology, also known as Q-switching technology, is a technology that compresses the continuous laser energy outputted generally into extremely narrow pulses for emission, thereby increasing the peak power of the light source by several orders of magnitude. In order to obtain high peak power lasers while maintaining excellent beam quality, when the average power outputted by the Q-switched laser is constant, the peak power mainly depends on the repetition frequency and pulse width, which makes the adjustment of the pulse width have certain practical application value. The existing technology uses multiple Q-switched lasers in combination, which can achieve the output of multiple Q-switched lasers with discrete pulse widths. However, the use of multiple Q-switched lasers in combination is large in size, not conducive to miniaturization and practicality, and the cost of use is too high.

[0004] Therefore, how to achieve adjustable laser output pulse width has become an urgent problem to be solved. Utility Model Content

[0005] In order to solve the technical problems existing in the prior art, the utility model provides a Q-switched laser with adjustable pulse width. By adjusting the first angle, the second angle and the third angle, the number of times the laser is turned back between the first plane reflector and the second plane reflector can be adjusted, thereby increasing the effective length of the laser resonant cavity, changing the optical path, and realizing the adjustable pulse width of the Q-switched pulse laser. The utility model has the characteristics of small size, low cost, convenient operation, reliable performance, etc., and is conducive to modularization and large-scale production.

[0006] The utility model provides a Q-switched laser with adjustable pulse width, comprising an output coupling mirror, a laser head, a Q switch and a polarization component which are sequentially arranged along an optical axis; and further comprising a first plane reflector and a second plane reflector; the first plane reflector and the second plane reflector are arranged relatively to each other along a central axis, and the central axis is at a non-vertical angle to the optical axis; the first plane reflector and the central axis are at a first angle, and the second plane reflector and the central axis are at a second angle, one end of the second plane reflector is arranged along the optical axis and corresponds to a side of the polarization component away from the Q switch; the laser incident on the second plane reflector is at a third angle to the vertical direction of the central axis; the angles of the first angle, the second angle and the third angle are adjustable; and the polarization component is used for transmitting horizontally polarized light and reflecting vertically polarized light.

[0007] According to a Q-switched laser with adjustable pulse width provided by the utility model, the first angle, the second angle and the third angle satisfy a foldback formula; the foldback formula is:

[0008]

[0009] Among them, θ 1 is the first angle, θ 2 is the second angle, is the third included angle, and n is the number of times the laser is reflected between the first plane reflecting mirror and the second plane reflecting mirror.

[0010] According to a Q-switched laser with adjustable pulse width provided by the utility model, the first plane reflecting mirror and the second plane reflecting mirror are both rectangular structures.

[0011] According to a Q-switched laser with adjustable pulse width provided by the utility model, it also includes an optical rotation component, which is arranged between the polarization component and the second plane reflector along the optical axis. The optical rotation component is used to control the polarization direction of the laser so that each time the laser passes through the laser head, it passes through the first plane reflector and the second plane reflector twice.

[0012] According to a pulse width adjustable Q-switched laser provided by the utility model, it also includes a total reflection mirror; the total reflection mirror is arranged along the vertical direction of the optical axis and corresponds to the position of the polarization component; the total reflection mirror is used to fully reflect the laser in the cavity.

[0013] According to a Q-switched laser with adjustable pulse width provided by the utility model, the polarization component is a thin-film polarizer.

[0014] According to a Q-switched laser with adjustable pulse width provided by the utility model, the optical rotation component is a quarter wave plate or an optical rotation crystal.

[0015] According to the Q-switched laser with adjustable pulse width provided by the utility model, the distance between the output coupling mirror and the laser head is adjustable.

[0016] According to a Q-switched laser with adjustable pulse width provided by the utility model, the distance between the first plane reflecting mirror and the second plane reflecting mirror is adjustable.

[0017] The utility model also provides a pulse width regulation method, which is beneficial for the above-mentioned pulse width adjustable Q-switched laser to regulate the laser pulse width.

[0018] The utility model provides a Q-switched laser with adjustable pulse width, which includes an output coupling mirror, a laser head, a Q switch, a polarization component, a first plane reflector and a second plane reflector. The first plane reflector forms a first angle with the central axis, the second plane reflector forms a second angle with the central axis, and the laser incident on the second plane reflector forms a third angle with the vertical direction of the central axis. The utility model adjusts the number of times the laser turns back between the first plane reflector and the second plane reflector by adjusting the first angle, the second angle and the third angle, thereby increasing the effective length of the laser resonant cavity, changing the optical path, and then realizing adjustable pulse width in the Q-switched pulse laser, which has the characteristics of small size, low cost, convenient operation, reliable performance, etc., and is conducive to modularization and large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a schematic diagram of the structure of a Q-switched laser with adjustable pulse width provided by the utility model;

[0021] Figure 2 It is a structural schematic diagram of another Q-switched laser with adjustable pulse width provided by the utility model;

[0022] Figure 3 It is a structural schematic diagram of another Q-switched laser with adjustable pulse width provided by the utility model;

[0023] Figure 4 It is a schematic diagram of the reflection path of the laser in a pair of plane reflectors provided by the utility model.

[0024] Reference numerals:

[0025] 1: Output coupling mirror; 2: Laser head; 3: Q switch; 4: Polarization component; 5: Optical rotation component; 6: First plane reflector; 7: Second plane reflector; 8: Total reflector; 9: Laser optical path. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the utility model clearer, the technical solution of the utility model will be described clearly and completely in conjunction with the drawings in the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0027] Considering that the laser processing process has a hybrid water jet process, it is necessary to adjust the pulse width of the pulsed laser in each process. In order to obtain high peak power laser while maintaining excellent beam quality, the commonly used equipment is Q-switched solid-state laser. The typical technical means of adjusting the laser pulse width is to output the pulses of multiple lasers in sequence to synthesize a large pulse, but there are problems such as large size and high cost of the laser, which makes it difficult to obtain a Q-switched laser with adjustable pulse width.

[0028] Please refer to Figure 1 , Figure 1 The utility model provides a schematic structural diagram of a Q-switched laser with adjustable pulse width.

[0029] In order to solve the technical problems existing in the prior art, the utility model provides a Q-switched laser with adjustable pulse width, comprising an output coupling mirror 1, a laser head 2, a Q switch 3 and a polarization component 4 which are sequentially arranged along an optical axis; further comprising a first plane reflector 6 and a second plane reflector 7; the first plane reflector 6 and the second plane reflector 7 are arranged relatively to each other along a central axis, and the central axis is at a non-vertical angle to the optical axis; the first plane reflector 6 and the central axis are at a first angle, the second plane reflector 7 and the central axis are at a second angle, one end of the second plane reflector 7 is arranged along the optical axis and corresponds to a side of the polarization component 4 away from the Q switch 3; the laser light incident on the second plane reflector 7 is at a third angle to the vertical direction of the central axis; the angles of the first angle, the second angle and the third angle are adjustable; the polarization component 4 is used for transmitting horizontally polarized light and reflecting vertically polarized light.

[0030] The utility model provides a Q-switched laser with adjustable pulse width, comprising an output coupling mirror 1, a laser head 2 (gain medium and pump source components), a Q switch 3, a polarization component 4, a first plane reflector 6, and a second plane reflector 7. By adjusting the angles of the first angle, the second angle, and the third angle, the number of times the laser turns back between the first plane reflector 6 and the second plane reflector 7 can be adjusted, thereby changing the effective length of the resonant cavity, changing the optical path, and achieving the purpose of changing the pulse width of the Q-switched pulse laser. When the Q switch 3 is an electro-optical Q switch, the electro-optical Q switch cooperates with the polarization component 4 and the wave plate (not shown) inserted in the cavity to achieve the purpose of Q switching. Specifically, the first angle, the second angle, and the third angle satisfy the turn-back formula, which is:

[0031]

[0032] Among them, θ 1 is the first angle, θ 2 is the second angle, is the third included angle, and n is the number of times the laser is reflected between the first plane reflecting mirror 6 and the second plane reflecting mirror 7.

[0033] The relative distance between the first plane reflector 6 and the second plane reflector 7 is defined as the distance L in the X direction between the first plane reflector 6 and the second plane reflector 7 at the first incident position of the laser. 1 ,but:

[0034]

[0035]

[0036]

[0037]

[0038] l all =2(l 1 +l 2 +…)

[0039] Among them, L k is the horizontal distance between the first plane emitting mirror 6 and the second plane reflecting mirror 7 at the kth reflection, l j is the optical path of the laser during the jth reflection, l all is the total optical path traveled by the laser between the first plane emitting mirror 6 and the second plane reflecting mirror 7; is the angle between the laser light path and the horizontal direction.

[0040] The following will take the nanosecond Q-switched Nd:YAG laser as an example to further describe the pulse width changing method of the utility model from a theoretical perspective: When Nd:YAG emits 1064.2nm band laser, it is a typical four-level laser, and the rate equation is:

[0041]

[0042] Among them, n 0 is the total number of doped particles per unit volume; n 1 is the number of energy level particles per unit volume; n 2 is the number of upper energy level particles per unit volume; v is the speed of light in the gain medium; τ 21 is the spontaneous emission lifetime of the particle at the upper laser energy level; τ 10 is the particle relaxation lifetime at the lower laser energy level; W p is the pump rate, taken as a linear function of the pump power; is the photon number density; is the stimulated emission cross section; is the intracavity lifetime of the photon.

[0043] The increase in the effective length of the laser resonant cavity will prolong the intracavity lifetime of photons, which will lead to a change in the speed at which the photon number density in the cavity decreases within a single pulse, thereby affecting the pulse width broadening of a single pulse.

[0044] It should be noted that the optimization of beam quality can be understood from a theoretical level as follows: the higher the transverse mode order in the resonant cavity, the higher the diffraction loss; the change in cavity length will also change the diffraction loss of the resonant cavity. When the diffraction loss of the high-order transverse mode exceeds the gain of the laser crystal, the high-order mode cannot oscillate, and the resonant cavity can also achieve the purpose of mode selection. Only TEM 00 The fundamental mode can achieve stable operation, thereby achieving the goal of improving the laser beam quality.

[0045] In this embodiment, in the laser optical path 9, the horizontal polarized light generated by the laser head 2 will form gain in the cavity, and the vertical polarized light has no complete resonant cavity and cannot generate laser; the horizontal polarized light is transmitted by the polarization component 4 after passing through the Q switch 3, and after being turned back between the first plane reflector 6 and the second plane reflector 7, the horizontal polarized light is transmitted by the polarization component 4 to the laser head 2, the output coupling mirror 1, to form laser gain and continuously oscillate back and forth, and a pair of plane reflectors (the first plane reflector 6 and the second plane reflector 7) can adjust any one, any two or all three of the first angle, the second angle and the third angle to achieve the optical path difference between the nth turn and the n+mth (m≥1)th turn of the laser optical path 9 through the first plane reflector 6 and the second plane reflector 7. Under the condition of ensuring the output power, by adjusting the cavity length, a Q-switched pulse laser with freely adjustable pulse width and controllable beam quality is achieved, which has the characteristics of small size, low cost, convenient operation, reliable performance, etc., and is conducive to modularization and large-scale production.

[0046] Based on the above embodiments, the following embodiments are further proposed:

[0047] Please refer to Figure 2 , Figure 2 A schematic structural diagram of another Q-switched laser with adjustable pulse width provided by the utility model.

[0048] Please refer to Figure 3 , Figure 3 A schematic structural diagram of another Q-switched laser with adjustable pulse width provided by the utility model.

[0049] Please refer to Figure 4 , Figure 4 This is a schematic diagram of the reflection path of the laser provided by the utility model in a pair of plane reflectors.

[0050] As a preferred embodiment, the first angle, the second angle and the third angle satisfy a fold-back formula; the fold-back formula is:

[0051]

[0052] Among them, θ 1 is the first angle, θ 2 is the second angle, is the third included angle, and n is the number of times the laser is reflected between the first plane reflecting mirror 6 and the second plane reflecting mirror 7.

[0053] In this embodiment, the first angle, the second angle and the third angle also satisfy the return formula. For ease of understanding, the utility model defines the direction of the central axis as the Y-axis direction of the coordinate axis, and the perpendicular direction to the central axis as the X-axis direction of the coordinate axis. The component of the propagation direction of the laser on the Y-axis is along the positive direction of the Y-axis, and the component of the propagation direction of the laser on the Y-axis after the n-th reflection between the first plane reflector 6 and the second plane reflector 7 is along the negative direction of the Y-axis.

[0054] For example, the first plane reflector 6 forms a first angle θ with the Y axis. 1 =4°, the second plane reflector 7 forms a second angle θ with the Y axis 2 =4°, the outgoing light path forms a third angle with the X-axis within the spatial range of the plane reflector pair Using the return formula, under this angle parameter, the light begins to return toward the negative direction of the Y axis after being reflected 7 times, and finally returns to the laser resonant cavity.

[0055] exist Figure 2 In the corresponding embodiment, only the first plane reflector 6 is adjustable in angle, and the adjustment angle is dθ 1 By adjusting dθ 1 is -1.143°, the first plane reflector 6 is at a first angle θ with the Y axis 1 =2.857°, the light begins to turn back toward the negative direction of the Y axis after 8 reflections, and finally returns to the laser resonant cavity. Since the process after each reflection is basically unchanged, but the number of reflections increases, the cavity length of the laser resonant cavity is at a first angle θ with the Y axis compared to the first plane reflector 6 1 =4°, the second plane reflector 7 forms a second angle θ with the Y axis 2 =4°, only 7 reflections increase.

[0056] In order to further make the effect of adjusting the pulse width more obvious and allow the cavity length to be adjusted more times, Figure 3 In the corresponding embodiment, the first plane reflector 6 and the second plane reflector 7 are both adjustable in angle, and the adjustment angle is dθ 1 , dθ 2 Adjust dθ 2 The first plane reflector 6 is at a first angle θ with the Y axis. 2 =3°; adjust dθ 1 is -1.5556°, and the first plane reflector 6 is at a first angle θ with the Y axis. 1 =2.4444°, after 10 reflections, the light begins to turn back toward the negative direction of the Y axis and finally returns to the laser resonant cavity. The cavity length of the laser resonant cavity is further compared with the first plane reflector 6 and the Y axis to form a first angle θ 1 =3°, the second plane reflector 7 forms a second angle θ with the Y axis 2=4°, only 8 reflections increase.

[0057] The effect of adjusting the pulse width can be further made more obvious, and the first angle, the second angle and the third angle can be set to be adjustable. In order to make the adjustment of the mechanical structure more concise, any one or two of the first angle, the second angle and the third angle can be set to be adjustable. By adjusting the first plane reflector 6 to form a first angle θ with the Y axis 1 , the number of reflections in the first plane reflector 6 and the second plane reflector 7 is adjusted, and the optical path can be adjusted, thereby adjusting the effective length of the laser resonant cavity, thereby achieving the purpose of changing the pulse width of the Q-switched pulse laser. At the same time, the increase in cavity length also increases the optical path traveled by the laser, that is, increases the loss of the resonant cavity. Since the beam quality of high-order mode lasers is poorer than that of fundamental mode lasers and the threshold is higher, when the loss increases, the high-order mode lasers are less likely to form lasers than fundamental mode lasers when the single-pass gain of the gain medium is the same, thus achieving the purpose of improving the laser beam quality.

[0058] As a preferred embodiment, the first plane reflector 6 and the second plane reflector 7 are both rectangular structures.

[0059] In this embodiment, the specific geometric structure of the first plane reflector 6 and the second plane reflector 7 can be a rectangular structure to ensure that the laser light path 9 repeatedly passes through the two plane reflectors without overflowing the light path.

[0060] Of course, the geometric structures of the first plane reflector 6 and the second plane reflector 7 may also be elliptical, triangular or other polygonal or irregular shapes, and the present invention does not make any special limitation thereto.

[0061] As a preferred embodiment, it also includes an optical rotation component 5, which is arranged along the optical axis between the polarization component 4 and the second plane reflector 7. The optical rotation component 5 is used to control the polarization direction of the laser so that each time the laser passes through the laser head 2, it passes through the first plane reflector 6 and the second plane reflector 7 for two rounds.

[0062] As a preferred embodiment, it further comprises a total reflection mirror 8 ; the total reflection mirror 8 is arranged along the vertical direction of the optical axis and corresponds to the position of the polarization component 4 ; the total reflection mirror 8 is used for total reflection of the laser in the cavity.

[0063] As a preferred embodiment, the polarization component 4 is a thin film polarizer.

[0064] Thin-film polarizers are a type of optical polarizer that utilizes the interference effect of a multilayer dielectric coating. The coating is usually placed on a glass sheet. At certain incident angles, a reflectivity that varies with polarization can be obtained. When used in lasers, it can transmit horizontally polarized light and reflect vertically polarized light.

[0065] As a preferred embodiment, the optical rotation component 5 is a quarter wave plate or an optical rotation crystal.

[0066] In this embodiment, the pulse width adjustable Q-switched laser may further include an optical rotation component 5 and a total reflection mirror 8. Taking the polarization component 4 as a thin film polarizer and the optical rotation component 5 as a quarter wave plate or an optical rotation crystal as an example, the operation process of this optical path will be further described in detail below:

[0067] The thin film polarizer is used to transmit horizontal polarized light and reflect vertical polarized light. The fast axis of the optical rotation component 5 is 45° to the horizontal polarization direction. After the linear polarized laser passes through twice, the polarization direction rotates 90°. In the laser optical path 9, when the optical rotation component 5 is not withdrawn and plays an optical rotation role, the optical rotation component 5 doubles the effect of a pair of plane mirrors on increasing the optical path of the laser; the horizontal polarized light generated by the laser head 2 is transmitted by the polarization component 4 after passing through the Q switch 3, and passes through the optical rotation component 5, the first plane mirror 6 and the second plane mirror 7, and then rotated to become vertical polarized light after the optical rotation component 5. The vertical polarized light is reflected by the polarization component 4 to the total reflection mirror 8, and then reflected by the total reflection mirror 8 and the polarization component 4 again, and passes through the optical rotation component 5, the first plane mirror 6 and the second plane mirror 7, and then rotated to become horizontal polarized light after the optical rotation component 5, and then transmitted by the polarization component 4 to the laser head 2, the output coupling mirror 1, part of the horizontal polarized light is transmitted by the output coupling mirror 1 to output the laser, and part of the horizontal polarized light is reflected back to the cavity by the output coupling mirror 1 to form laser gain and continuously oscillate back and forth.

[0068] When linearly polarized light passes through certain substances, its vibration plane will rotate around the direction of light propagation, which is called optical rotation.

[0069] As a preferred embodiment, the distance between the output coupling mirror 1 and the laser head 2 is adjustable.

[0070] In this embodiment, by adjusting the front and rear positions of the output coupling mirror 1 in the direction of the laser optical path 9, the effective cavity length of the resonant cavity can be further fine-tuned, so that the cavity length of the resonant cavity is changed from being intermittently adjustable by only adjusting the first angle, the second angle and the third angle to being continuously adjustable by adjusting the first angle, the second angle, the third angle and the front and rear distance of the output coupling mirror 1, thereby further fine-tuning the pulse width and controlling the beam quality, and ultimately achieving continuous adjustment of the pulse width.

[0071] As a preferred embodiment, the distance between the first plane reflector 6 and the second plane reflector 7 is adjustable.

[0072] In this embodiment, in order to increase the adjustable range of the number of laser round trips, the relative distance between the first plane reflector 6 and the second plane reflector 7 can also be adjusted. The relative distance between the first plane reflector 6 and the second plane reflector 7 is defined as the distance between the first plane reflector 6 and the second plane reflector 7 in the X direction at the first incident position of the laser as L. 1 Then L 1 , the first angle θ 1 , the second angle θ 2 , the third angle With optical path l all The relationship can be expressed as follows:

[0073]

[0074]

[0075]

[0076]

[0077] l all =2(l 1 +l 2 +…)

[0078] Among them, L k is the horizontal distance between the first plane emitting mirror 6 and the second plane reflecting mirror 7 at the kth reflection, l j is the optical path of the laser during the jth reflection, l all It is the total optical path that the laser travels between the first plane emitting mirror 6 and the second plane reflecting mirror 7.

[0079] In the simulation experiment, when other parameters remain unchanged, only by adjusting the second plane reflector 7 to form a second angle θ with the Y axis 1 , adjust the front and rear position of the output coupling mirror 1 in the direction of the laser optical path 9, and then adjust the cavity length of the nanosecond Q-switched Nd:YAG laser, and adjust the cavity length to 1m, 1.5m, and 2m respectively, and the changes in the laser pulse width are 44ns, 56ns, and 66ns respectively. It should be pointed out that in some embodiments of the utility model, the cavity length is not intermittently adjustable, but continuously adjustable, so the pulse width can also be continuously adjustable.

[0080] In summary, the utility model introduces a pair of plane total reflection mirrors with adjustable angles and an output coupling mirror 1 whose position can be finely adjusted forward and backward into the laser resonant cavity, thereby making the resonant cavity length continuously adjustable, thereby achieving a Q-switched pulse laser in which the pulse width of the nanosecond pulse can be freely adjusted and the beam quality can be controlled.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the utility model.

Claims

1. A Q-switched laser with adjustable pulse width, characterized in that: It includes an output coupling mirror, a laser head, a Q switch and a polarization component which are sequentially arranged along the optical axis; it also includes a first plane reflecting mirror and a second plane reflecting mirror; The first plane reflector and the second plane reflector are arranged opposite to each other along a central axis, and the central axis is at a non-perpendicular angle to the optical axis; the first plane reflector and the central axis are at a first angle, and the second plane reflector and the central axis are at a second angle, and one end of the second plane reflector is arranged along the optical axis and corresponds to a side of the polarization component away from the Q switch; the laser light incident on the second plane reflector and the vertical direction of the central axis are at a third angle; the first angle, the second angle and the third angle are adjustable; The polarization component is used for transmitting horizontally polarized light and reflecting vertically polarized light.

2. The Q-switched laser with adjustable pulse width according to claim 1, characterized in that: The first angle, the second angle and the third angle satisfy a foldback formula; The foldback formula is: φ+θ1=n(θ2+θ1) Wherein, θ1 is the first angle, θ2 is the second angle, φ is the third angle, and n is the number of times the laser is reflected between the first plane reflector and the second plane reflector.

3. The Q-switched laser with adjustable pulse width according to claim 1, characterized in that: The first plane reflector and the second plane reflector are both rectangular structures.

4. The Q-switched laser with adjustable pulse width according to claim 1, characterized in that: It also includes an optical rotation component, which is arranged between the polarization component and the second plane reflector along the optical axis. The optical rotation component is used to control the polarization direction of the laser so that each time the laser passes through the laser head, it passes through the first plane reflector and the second plane reflector for two rounds.

5. The Q-switched laser with adjustable pulse width according to claim 4, characterized in that: It also includes a total reflection mirror; the total reflection mirror is arranged along the vertical direction of the optical axis and corresponds to the position of the polarization component; the total reflection mirror is used for total reflection of the laser in the cavity.

6. The Q-switched laser with adjustable pulse width according to claim 1, characterized in that: The polarization component is a thin film polarizer.

7. The Q-switched laser with adjustable pulse width according to claim 4, characterized in that: The optical rotation component is a quarter wave plate or an optical rotation crystal.

8. The Q-switched laser with adjustable pulse width according to claim 1, characterized in that: The distance between the output coupling mirror and the laser head is adjustable.

9. The Q-switched laser with adjustable pulse width according to any one of claims 1 to 8, characterized in that: The distance between the first plane reflecting mirror and the second plane reflecting mirror is adjustable.

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