Intracavity frequency doubling passive mode-locked laser

Abstract

The utility model discloses an intracavity frequency doubling passive mode-locked laser which comprises a pumping source system, a laser crystal, a resonant cavity and a wavelength conversion structure. The pumping source system pumps the laser crystal to generate fundamental frequency laser; the resonant cavity comprises a plurality of resonant cavity mirrors, the plurality of resonant cavity mirrors are sequentially arranged in the optical path transmission direction of the fundamental frequency laser, a saturable absorber is arranged in the resonant cavity, and the saturable absorber is used for realizing passive mode locking of the fundamental frequency laser in the resonant cavity and generating short-pulse fundamental frequency laser; the wavelength conversion structure is arranged in the resonant cavity, the wavelength conversion structure is located between two adjacent resonant cavity mirrors in the multiple resonant cavity mirrors in the light path transmission direction, and the wavelength conversion structure is used for converting the short-pulse fundamental frequency laser into multi-frequency-doubling short-pulse laser with the preset wavelength. According to the scheme provided by the invention, the frequency doubling conversion efficiency of the laser can be improved, so that the laser output efficiency and power of the laser are improved.

Description

Technical Field

[0001] The present application relates to the field of laser technology, and in particular to an intracavity frequency-doubled passive mode-locked laser. Background Art

[0002] With the rise of ultrafast detection applications and the demand for high peak power, people have put forward higher requirements for the pulses of laser beams. Among them, the mode-locking technology can narrow the pulses of lasers to the picosecond or femtosecond level. Therefore, mode-locked lasers have been widely used in industrial processing, wafer detection, nonlinear frequency conversion, biomedicine, spectroscopy and other fields. Using frequency doubling technology, based on the 1064nm fundamental frequency laser, the output of doubled, tripled and quadrupled frequency light can be achieved. Among them, quadrupled frequency light has the characteristics of high photon energy and short wavelength, and is widely used in various industries. For example, in many material processing processes, multi-frequency light can be used to directly destroy the molecular bonds of the material to achieve "cold" removal and obtain good processing effects. In wafer detection equipment, the higher resolution of multi-frequency light can achieve the detection of more subtle defects.

[0003] In order to improve the applicability of the laser, the ultrashort pulse technology can be combined with the frequency doubling technology to produce ultrashort pulse multiple frequency lasers. The commonly used method for obtaining ultrashort pulse multiple frequency lasers is to use passive mode locking technology to obtain ultrashort pulse fundamental frequency lasers with sufficient energy in the optical resonant cavity. The fundamental frequency laser output by the optical resonant cavity is then converted to frequency or wavelength by a multiple frequency crystal outside the resonant cavity to obtain multiple frequency lasers. However, in the above method, since most of the fundamental frequency laser remains in the resonant cavity, only a small part of the laser output outside the resonant cavity is used for frequency doubling conversion, which makes the frequency doubling conversion efficiency low, thereby making the laser output efficiency and power of the laser low. Utility Model Content

[0004] The present application provides an intracavity frequency-doubled passive mode-locked laser, which can improve the frequency-doubled conversion efficiency of the laser, thereby improving the laser output efficiency and power of the laser. The specific scheme is as follows:

[0005] The present application provides an intracavity frequency-doubled passive mode-locked laser, comprising a pump source system, a laser crystal, a resonant cavity, and a wavelength conversion structure;

[0006] The pump source system pumps the laser crystal to generate fundamental frequency laser;

[0007] A resonant cavity, comprising a plurality of resonant cavity mirrors, which are sequentially arranged in the optical transmission direction of the fundamental frequency laser, and a saturable absorber is arranged in the resonant cavity, and the saturable absorber is used to realize passive mode locking of the fundamental frequency laser in the resonant cavity to generate a short pulse fundamental frequency laser;

[0008] The wavelength conversion structure is arranged in the resonant cavity, and the wavelength conversion structure is located between two adjacent resonant cavity mirrors along the optical path transmission direction of multiple resonant cavity mirrors. The wavelength conversion structure is used to convert short pulse fundamental frequency laser into multiple frequency short pulse laser of preset wavelength.

[0009] Compared with the prior art, this application has the following advantages:

[0010] The intracavity frequency-doubling passive mode-locked laser provided by the present application includes a pump source system, a laser crystal, a resonant cavity, and a wavelength conversion structure. The pump source system can provide energy for the stimulated radiation of the laser crystal, thereby pumping the laser crystal to generate a fundamental frequency laser. The resonant cavity includes a plurality of resonant cavity mirrors, which are sequentially arranged in the optical path transmission direction of the fundamental frequency laser. A saturable absorber is arranged in the resonant cavity, and the saturable absorber is used to realize the passive mode locking of the fundamental frequency laser in the resonant cavity to generate a short pulse fundamental frequency laser. The wavelength conversion structure is arranged in the resonant cavity, and the wavelength conversion structure is located between two adjacent resonant cavity mirrors in the optical path transmission direction of the plurality of resonant cavity mirrors. Therefore, the wavelength conversion structure can convert the short pulse fundamental frequency laser in the resonant cavity into a multiple frequency-doubling short pulse laser of a preset wavelength.

[0011] The solution provided in the present application arranges a wavelength conversion structure in the resonant cavity, which can convert the short-pulse fundamental frequency laser in the resonant cavity into light of a preset wavelength in the resonant cavity. Therefore, the fundamental frequency laser in the resonant cavity can be efficiently utilized for wavelength conversion, thereby improving the frequency doubling conversion efficiency of the laser, thereby improving the laser output efficiency and power of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the structure of the intracavity frequency-doubled passive mode-locked laser provided in an embodiment of the present application.

[0013] The reference numerals in the drawings are:

[0014] 1. Pump source; 2. Pump light transmission fiber; 3. Pump light collimating lens; 4. Pump light focusing lens; 5. Dichroic mirror; 6. Laser crystal; 7. Reflector; 8. Brewster window; 9. First plano-concave reflector; 10. Double frequency crystal; 11. Quadruple frequency crystal; 12. Second plano-concave reflector; 13. Semiconductor saturable absorber; 14. Light baffle; 15. Output light shaping mirror. DETAILED DESCRIPTION

[0015] In order to enable those skilled in the art to better understand the technical solution of the present application, the present application is described clearly and completely below in conjunction with the drawings in the embodiments of the present application. However, the present application can be implemented in many other ways different from the following description. Therefore, based on the embodiments provided by the present application, all other embodiments obtained by those of ordinary skill in the art without creative work should fall within the scope of protection of the present application.

[0016] It should be noted that the terms "first", "second", "third", etc. in the claims, description and drawings of the present application are used to distinguish similar objects and are not used to describe a specific order or sequence. The data used in this way are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including", "having" and their variants are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0017] like Figure 1 As shown, the intracavity frequency-doubling passively mode-locked laser provided in the embodiment of the present application includes: a pump source system, a laser crystal, a resonant cavity and a wavelength conversion structure.

[0018] The pump source system can pump the laser crystal to generate fundamental frequency laser, and the pump source system includes a pump source 1, a pump light transmission optical fiber 2 and a pump light coupling system.

[0019] Specifically, the pump source 1 can be an LD pump source, which is an 880nm fiber-coupled semiconductor laser module, or other laser modules that can be used as pump sources. The output power of the pump source 1 is 0-60W, and the output end of the pump source 1 is an SMA905 optical fiber interface. The entire module of the pump source 1 is placed on a temperature electric controller (Thermoelectric Cooler, TEC for short) and a heat sink, so that the temperature of the pump source 1 shell is controlled by the temperature electric controller, and the temperature control accuracy is 0.01°C. Both ends of the pump light transmission optical fiber 2 are SMA905 connectors, which are respectively connected to the pump source 1 and the pump light coupling system. The core diameter of the pump light transmission optical fiber 2 is 800um, and the NA value is 0.22. Figure 1As shown, the pump light coupling system includes a pump light collimating lens 3 and a pump light focusing lens 4 which are sequentially arranged along the optical path. The pump light collimating lens 3 and the pump light focusing lens 4 can both be plano-convex lenses, and the convex surfaces of the pump light collimating lens 3 and the pump light focusing lens 4 are placed opposite to each other. The pump light collimating lens 3 and the pump light focusing lens 4 are coated with 880nm anti-reflection film on both sides, and the focal length range of the lens is between 20 and 50mm. The end face of the pump light transmission optical fiber 2 is located at the focus of the pump light collimating lens 3, and the front end face of the laser crystal 6 is located at the focus of the pump light focusing lens 4. The laser crystal 6 outputs 1064nm fundamental frequency laser under the pumping of the 880nm laser emitted by the pump source 1.

[0020] Exemplarily, the laser crystal 6 is neodymium-doped yttrium vanadate Nd:YVO4 or neodymium-doped yttrium aluminum garnet Nd:YAG, or other laser crystals 6. The specifications of the laser crystal 6 are 3mm×3mm×10mm, or other specifications. The molecular percentage of Nd ions doped in the laser crystal 6 is 0.4% to 0.6%. Both ends of the laser crystal 6 are coated with 880nm and 1064nm anti-reflection films. The laser crystal 6 adopts TEC temperature control, and the temperature is adjustable between 15 and 25°C, with a temperature control accuracy of 0.01°C.

[0021] The resonant cavity includes a plurality of resonant cavity mirrors, which are sequentially arranged in the optical path transmission direction of the fundamental frequency laser. A saturable absorber is arranged in the resonant cavity, and the saturable absorber is used to realize passive mode locking of the fundamental frequency laser in the resonant cavity to generate short pulse fundamental frequency laser.

[0022] The resonant cavity of the present application adopts a compact folded cavity, that is, the multiple resonant cavity mirrors of the resonant cavity are arranged in a folded manner, and the wavelength conversion structure is arranged in the resonant cavity. The wavelength conversion structure is arranged in the resonant cavity, and the wavelength conversion structure is located between two adjacent resonant cavity mirrors along the optical path transmission direction among the multiple resonant cavity mirrors. The wavelength conversion structure is used to convert a short-pulse fundamental frequency laser into a multiple frequency short-pulse laser of a preset wavelength.

[0023] The solution provided in the present application arranges a wavelength conversion structure in the resonant cavity, which can convert the short-pulse fundamental frequency laser in the resonant cavity into light of a preset wavelength in the resonant cavity. Therefore, the fundamental frequency laser in the resonant cavity can be efficiently utilized for wavelength conversion, thereby improving the frequency doubling conversion efficiency of the laser, thereby improving the laser output efficiency and power of the laser.

[0024] In a specific embodiment, Figure 1As shown, one end mirror of the resonant cavity is a dichroic mirror 5, which is located on the optical path between the pump source system and the laser crystal 6. The dichroic mirror 5 is used to transmit the pump light emitted by the pump source system and reflect the fundamental frequency laser emitted by the laser crystal 6, so that the fundamental frequency laser in the resonant cavity is reflected by the dichroic mirror 5 and will not be emitted from the direction of the pump source system, thereby increasing the retention amount of the fundamental frequency laser in the resonant cavity and further improving the utilization rate of the fundamental frequency laser by the laser.

[0025] The dichroic mirror 5 can be coated with an 880nm (i.e., the wavelength of the light emitted by the pump source 1) anti-reflection film on both sides, and the inner side of the cavity of the dichroic mirror 5 (i.e., the side facing the laser crystal 6) can be coated with a 1064nm high-reflection film on one side. The dichroic mirror 5 can be a 0° plane reflector, and the dichroic mirror 5 can be placed at 90° to the incident light.

[0026] The plurality of resonant cavity mirrors further include a first plano-concave reflecting mirror 9, a second plano-concave reflecting mirror 12 and a semiconductor saturable absorption mirror 13 which are sequentially arranged along the optical transmission direction of the fundamental frequency laser in the resonant cavity.

[0027] Along the optical transmission direction of the fundamental frequency laser, a reflector 7 may be provided between the laser crystal 6 and the first plano-concave reflector 9 , and the reflector 7 is used to reflect the fundamental frequency laser emitted by the laser crystal and then emit it into the first plano-concave reflector 9 .

[0028] The concave surfaces of the first plano-concave reflector 9 and the second plano-concave reflector 12 are arranged opposite to each other, and the wavelength conversion structure is located between the first plano-concave reflector 9 and the second plano-concave reflector 12 along the optical path transmission direction of the fundamental frequency laser; the first plano-concave reflector 9 is used for receiving the fundamental frequency laser from the laser crystal 6 and then reflecting it to the double frequency crystal 10, and the second plano-concave reflector 12 is used for receiving the fundamental frequency laser from the quadruple frequency crystal 11 and then reflecting it to the semiconductor saturable absorber 13, and the semiconductor saturable absorber 13 is used for realizing passive mode locking in the resonant cavity.

[0029] The semiconductor saturable absorber mirror 13 may also be replaced by other saturable absorbers and a total reflection end mirror, and the saturable absorber may be disposed close to the inner side surface of the total reflection end mirror.

[0030] The first plano-concave reflector 9, the second plano-concave reflector 12, and the reflector 7 can be total reflectors of 5-15°. The first plano-concave reflector 9, the second plano-concave reflector 12 and the incident light can be placed at a certain acute angle, and the specific angle of the certain acute angle can be 30, 40, 60, etc., which is not specifically limited in this application. The inner single surface (i.e., concave surface) of the first plano-concave reflector 9 and the second plano-concave reflector 12 can be plated with a 1064nm high-reflection film, and the concave curvature radius of the first plano-concave reflector 9 and the second plano-concave reflector 12 can be the same, for example, both can be 300mm, or other curvature radii, and those skilled in the art can set the specific structure and placement of the two plano-concave reflectors according to actual needs.

[0031] The central wavelength of the semiconductor saturable absorber mirror 13 can be 1064nm to achieve passive mode locking to obtain ultrashort pulse fundamental frequency laser. The semiconductor saturable absorber mirror 13 is placed at 90° to the incident light. The semiconductor saturable absorber mirror 13 can be welded on a copper heat sink to facilitate heat dissipation of the semiconductor saturable absorber mirror 13. The working wavelength of the semiconductor saturable absorber mirror 13 can be 1064nm, the modulation depth is 3%, the non-saturated loss is 1%, and the saturation flux is 70μJ / cm 2 The semiconductor saturable absorber mirror 13 can utilize its unique saturable absorption characteristics to achieve passive mode locking of the 1064nm fundamental frequency laser in the resonant cavity and obtain an ideal ultrashort pulse laser. Those skilled in the art can set the specific structural parameters of the semiconductor saturable absorber mirror 13 according to actual needs, and this application does not specifically limit it.

[0032] The wavelength conversion structure is used to convert the fundamental frequency laser into a multiple frequency laser, and the wavelength conversion structure may include at least one of a double frequency crystal 10, a triple frequency crystal, and a quadruple frequency crystal 11, and may also include other multiple frequency crystals. Those skilled in the art may select a phase-matched multiple frequency crystal according to the wavelength of the fundamental frequency laser and the laser of the preset wavelength to be obtained, and the present application does not specifically limit this.

[0033] In this embodiment, the wavelength conversion structure is arranged between the first plano-concave reflector 9 and the second plano-concave reflector 12. Since the energy of the short pulse fundamental frequency laser between the first plano-concave reflector 9 and the second plano-concave reflector 12 is better, the power of the overall output of the laser multiplied short pulse laser can be increased.

[0034] In a specific embodiment, the doubled frequency crystal 10 can be located at the waist spot of the fundamental frequency laser between the first plano-concave reflector 9 and the second plano-concave reflector 12, so as to greatly improve the nonlinear frequency conversion efficiency of the doubled frequency crystal 10 and the quadruple frequency crystal 11 by utilizing the high energy density at the waist spot, thereby obtaining a deep ultraviolet 266nm laser output with higher conversion efficiency, and effectively improving the frequency doubling conversion efficiency from 1064nm to 532nm. The quadruple frequency crystal 11 and the doubled frequency crystal 10 can be arranged close to each other to further improve the quadruple frequency conversion efficiency.

[0035] The reflector 7 is a total reflector, and the reflective surface inside the reflector 7 can be coated with a 1064nm high-reflection film on one side. The reflector 7 can be placed at an acute angle to the incident light to reflect the incident fundamental frequency laser with a folding effect, thereby reducing the distribution and occupation volume of each resonant cavity mirror in the resonant cavity, making the laser structure more compact. The reflector 7 can be a plane reflector.

[0036] Specifically, the reflection angle range of the reflector 7, the first plano-concave reflector 9 and the second plano-concave reflector 12 may be 5° to 15° to increase the reflection range.

[0037] In a specific embodiment, a Brewster window 8 is provided between the reflector 7 and the first plano-concave reflector 9 along the transmission direction of the optical path, and the fundamental frequency laser reflected by the reflector 7 can reach the first plano-concave reflector 9 after passing through the Brewster window 8, so as to improve the polarization extinction ratio of the fundamental frequency laser. Specifically, the Brewster window 8 is two quartz lenses of the same thickness, and the two quartz lenses are placed in two Brewster angle directions. The thickness of the two quartz lenses can be 3 mm or other thicknesses. The polarization extinction ratio of the fundamental frequency laser in the resonant cavity can be further improved by the Brewster window 8, and a linearly polarized fundamental frequency laser with a sufficiently high polarization extinction ratio is provided for the nonlinear frequency doubling conversion of the doubled frequency crystal 10 and the quadrupled frequency crystal 11.

[0038] In a specific embodiment, the laser may further include a light shielding plate 14, which is disposed on the optical path of the 532nm laser separated and output by the quadruple frequency crystal 11 and is located outside the resonant cavity to shield the 532nm double frequency laser separated by the quadruple frequency crystal 11.

[0039] like Figure 1 As shown, the wavelength conversion structure includes a frequency doubling crystal 10 and a frequency quadrupling crystal 11 which are sequentially arranged along the optical transmission direction. The frequency doubling crystal 10 is used to convert the 1064nm fundamental frequency laser in the resonant cavity into a 532nm laser and transmit it to the frequency quadrupling crystal 11. The frequency quadrupling crystal 11 is used to convert the 532nm laser converted by the frequency doubling crystal 10 into a 266nm deep ultraviolet laser. The frequency doubling crystal 10 and the frequency quadrupling crystal 11 can be arranged close to each other to improve the conversion efficiency.

[0040] In actual application, limited by the conversion efficiency of the quadruple frequency crystal 11 and other factors, the light emitted from the quadruple frequency crystal 11 may simultaneously contain the fundamental frequency laser in the resonant cavity, the doubled frequency output 532nm laser and the 266nm laser. In this case, the laser also includes a beam splitter, which is a beam splitter prism or a dichroic beam splitter. The beam splitter is arranged in the optical path transmission direction of the quadruple frequency crystal 11, and is used to split the laser emitted by the quadruple frequency crystal 11 to obtain a 1064nm fundamental frequency laser, a 532nm laser, and a 266nm laser.

[0041] In order to make the structure of the laser more compact and simple, the output end of the quadruple frequency crystal 11 (the end away from the double frequency crystal 10) is set to the Brewster angle. In this way, the 1064nm fundamental frequency laser, the 532nm laser and the 266nm deep ultraviolet laser are separated by the output end of the quadruple crystal Brewster angle, so there is no need to set up an additional spectroscope to split the light emitted by the quadruple frequency crystal 11. At the same time, the polarization extinction ratio of the fundamental frequency laser in the resonant cavity can be improved. Since there is no need to use a spectroscopic prism, the problems of unreliable spectroscopic coating, complex extracavity frequency doubling structure and spectroscopic structure with many adjustment links can be avoided, so that the structure of the laser is more reliable and the overall stability of the laser is significantly improved.

[0042] The frequency doubling crystal 10 is a lithium triborate LBO crystal or a potassium titanyl phosphate KTP crystal, or a frequency doubling crystal 10 made of other materials. The frequency doubling crystal 10 can be coated with a 1064nm anti-reflection film on both sides to improve the transmittance of the fundamental frequency laser. The side of the frequency doubling crystal 10 close to the first plano-concave reflector 9 can be coated with a 532nm high-reflection film to prevent the 532nm laser from being emitted from the front end, thereby increasing the energy of the laser injected into the quadruple frequency crystal 11 and improving the conversion efficiency. The side of the frequency doubling crystal 10 close to the quadruple frequency crystal 11 can be coated with a 5 A 32nm anti-reflection film is used to increase the energy of the 532nm laser transmitted to the quadrupled frequency crystal 11. The doubled frequency crystal 10 can be set in a non-critical phase matching manner (θ=90°, φ=0°), θ represents the angle between the polarization direction of the doubled frequency crystal 10 and the pump light wave vector, φ represents the angle between the input and output wave vectors, when θ=90°, φ=0°, the non-critical phase matching condition is met, at this time the pump light wave vector is perpendicular to the polarization direction of the doubled frequency crystal 10, and the wave vector direction of the second harmonic is parallel to the wave vector direction of the pump light.

[0043] The quadrupled frequency crystal 11 may be cesium lithium hexaborate CLBO or barium metaborate BBO crystal. The quadrupled frequency crystal 11 may be coated with 1064nm and 532nm anti-reflection films on both sides, the side of the quadrupled frequency crystal 11 close to the double frequency crystal 10 may be coated with a 266nm high-reflection film, and the Brewster angle cut surface of the quadrupled frequency crystal 11 may be coated with a 266nm anti-reflection film. The quadrupled frequency crystal 11 may be set in an angle phase matching manner (θ=62°, φ=45°), θ=62° indicates that the angle between the polarization direction of the quadrupled frequency crystal 11 and the pump light wave vector is 62°, and φ=45° indicates that the angle between the input and output wave vectors of the quadrupled frequency crystal 11 is 45°. This angle phase matching manner can realize efficient multi-frequency laser generation and improve the efficiency and stability of multi-frequency laser generation.

[0044] In the specific application process, the doubled frequency crystal 10 and the quadrupled frequency crystal 11 can be placed in a constant temperature sealed heating furnace for precise temperature control. The temperatures are set to 149°C and 150°C respectively. Dry air is continuously passed through the sealed furnace to prevent the crystal from deliquescing and extend its service life.

[0045] In a specific embodiment, the laser may further include an output light shaping mirror 15, which is arranged on the output optical path of the quadrupled frequency laser. Specifically, the output light shaping mirror 15 is arranged on the optical path of the 266nm laser separated and output from the quadrupled frequency crystal 11, and is used to collimate the 266nm laser and output it in parallel. The output light shaping mirror 15 may be a plano-convex lens or a biconvex lens, or may be other lenses with a collimating function. For example, the output light shaping mirror 15 may be a biconvex lens made of calcium fluoride CaF2. The focal length range of the output light shaping mirror 15 is between 30mm and 100mm. The output light shaping mirror 15 may be coated with a 266nm anti-reflection film on both sides. The output light shaping mirror 15 can improve the beam quality of the 266nm deep ultraviolet laser output.

[0046] In addition, although the components and the installation methods of the components or devices in the present application are described in a specific order in the drawings, this does not require or imply that the components or devices must be designed according to the specific components or the installation methods of the components, or that all the components shown must be included to achieve the desired results. Additionally or alternatively, some components can be omitted, multiple components can be combined into one component to achieve corresponding functions, and / or one component can be decomposed into multiple components to achieve corresponding functions, etc.

[0047] The above description is only a specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any modification, equivalent substitution and improvement made by any technician familiar with the technical field within the technical scope disclosed in the present application and within the spirit and principle of the present application shall be covered by the protection scope of the present application.

Claims

1. An intracavity frequency-doubled passive mode-locked laser, characterized in that: Including pump source system, laser crystal, resonant cavity and wavelength conversion structure; The pump source system pumps the laser crystal to generate fundamental frequency laser; The resonant cavity comprises a plurality of resonant cavity mirrors, which are sequentially arranged in the optical path transmission direction of the fundamental frequency laser, and a saturable absorber is arranged in the resonant cavity, and the saturable absorber is used to realize passive mode locking of the fundamental frequency laser in the resonant cavity to generate short pulse fundamental frequency laser; The wavelength conversion structure is arranged in the resonant cavity, and the wavelength conversion structure is located between two adjacent resonant cavity mirrors along the optical path transmission direction among the multiple resonant cavity mirrors. The wavelength conversion structure is used to convert the short pulse fundamental frequency laser into a multiple frequency short pulse laser with a preset wavelength.

2. The laser according to claim 1, characterized in that The multiple resonant cavity mirrors include a dichroic mirror, a first plano-concave reflector, a second plano-concave reflector and a total reflection end mirror which are sequentially arranged along the light path transmission direction; The laser crystal is arranged between the dichroic mirror and the first plano-concave reflecting mirror; The dichroic mirror is used to transmit the pump light emitted by the pump source system and reflect the fundamental frequency laser emitted by the laser crystal; The concave surfaces of the first plano-concave reflector and the second plano-concave reflector are arranged opposite to each other; The saturable absorber is arranged closely to the inner side of the total reflection end mirror or the two are arranged integrally.

3. The laser according to claim 2, characterized in that The wavelength conversion structure is located between the first plano-concave reflecting mirror and the second plano-concave reflecting mirror.

4. The laser according to claim 3, characterized in that The wavelength conversion structure comprises a frequency doubling crystal and a frequency quadrupling crystal which are sequentially arranged along the transmission direction of the optical path.

5. The laser according to claim 4, characterized in that The output end of the quadruple frequency crystal is set to the Brewster angle, so as to separate the fundamental frequency laser, the double frequency laser and the quadruple frequency laser through the output end of the quadruple frequency crystal.

6. The laser according to claim 3, characterized in that The frequency doubling crystal is located at the waist spot of the fundamental frequency laser between the first plano-concave reflecting mirror and the second plano-concave reflecting mirror, and the frequency quadrupling crystal is arranged next to the frequency doubling crystal.

7. The laser according to claim 4, characterized in that The laser also includes an output light shaping mirror, which is arranged on the output light path of the quadruple frequency laser and has a focal length range of 30 mm to 100 mm; The frequency doubling crystal was set up using a noncritical phase matching method (θ = 90°, φ = 0°); The quadruple frequency crystal is set using an angular phase matching method (θ = 62°, φ = 45°).

8. The laser according to claim 2, characterized in that The multiple resonant cavity mirrors also include a reflecting mirror located between the laser crystal and the first plano-concave reflecting mirror, and the reflecting mirror, the first plano-concave reflecting mirror and the second plano-concave reflecting mirror are all reflecting mirrors with an angle of 5-15°.

9. The laser according to claim 8, characterized in that Along the transmission direction of the optical path, a Brewster window is provided between the reflector and the first plano-concave reflector to improve the polarization extinction ratio of the fundamental frequency laser.

10. The laser according to claim 1, characterized in that The pump source is an 880nm fiber-coupled semiconductor laser; The laser crystal is neodymium-doped yttrium vanadate Nd:YVO4 or neodymium-doped yttrium aluminum garnet Nd:YAG; The laser crystal adopts TEC temperature control method with a temperature control accuracy of 0.01°C; The central wavelength of the saturable absorber is 1064 nm.

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