A green fiber laser

Abstract

This application provides a green fiber laser, comprising, in sequence, a high repetition rate (PRR) polarization-maintaining fiber laser, a first Brewster window, a second half-wave plate, a first plano-convex lens, a laser crystal, a second plano-convex lens, and a first dichroic mirror. The PPR fiber laser outputs a high repetition rate polarization-maintaining fundamental frequency signal light. The first Brewster window is an optical lens placed at a Brewster angle, and the 1000-1100nm fundamental frequency signal light passing through the first Brewster window has a specific polarization state. The second half-wave plate can be rotated to adjust the polarization state rotation angle of the infrared beam after passing through the first Brewster window. By using the second half-wave plate and the first Brewster window to adjust the polarization state rotation angle to a suitable polarization state, the optical-to-optical conversion efficiency of the entire system is greatly improved, resulting in high repetition rate, high energy conversion efficiency, high power, and stable green light output.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more specifically, to a high-repetition-rate, high-stability green fiber laser. Background Technology

[0002] In recent years, with the booming demand from the new energy industry, higher requirements have been placed on front-end laser processing technology. Due to material absorption factors, traditional infrared lasers have a very low absorption rate for highly reflective materials, which can no longer meet the welding and cutting requirements of highly reflective materials such as copper in the lithium battery industry. Green lasers, with their high absorption characteristics of copper for green light beams, have become a typical light source in this industry.

[0003] Traditional green lasers are typically generated by resonating an infrared fundamental frequency light from a solid-state laser and then frequency-doubling it using a nonlinear crystal. These lasers have low repetition rate and low energy conversion efficiency, resulting in very low processing efficiency in industrial applications. Furthermore, the output power of such lasers is significantly affected by ambient temperature, leading to power instability during industrial processing. This significant power fluctuation can easily cause high-precision and expensive workpieces to be scrapped, negatively impacting processing results.

[0004] Currently, in order to improve the stability of laser output, polarizers are usually used to change the polarization state of laser transmission to meet the requirements of stable laser output. However, polarizers have a large absorption of light, resulting in significant light loss after passing through them. Furthermore, the polarizer material itself is difficult to withstand high-power lasers and is prone to material damage and failure, making it difficult to achieve high-power and stable laser output.

[0005] Therefore, it is necessary to invent a green fiber laser that can achieve high repetition rate, high energy conversion efficiency, high power, and stable green light output. Summary of the Invention

[0006] The purpose of this application is to provide a green fiber laser to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, this application provides the following technical solution: a green fiber laser, comprising, in sequence, a high repetition rate polarization-maintaining fiber laser, a first Brewster window, a second half-wave plate, a first plano-convex lens, a laser crystal, a second plano-convex lens, and a first dichroic mirror.

[0008] The specific working principle and process of this application are as follows:

[0009] The high-repetition-rate polarization-maintaining fiber laser can output linearly polarized fundamental frequency signal light of 1000-1100nm with high repetition rate. The polarization-maintaining fiber ensures that when the input laser light is linearly polarized, the output laser light remains linearly polarized after transmission through it. The first Brewster window is an optical lens placed at a Brewster angle, and the 1000-1100nm fundamental frequency signal light passing through the first Brewster window has a specific polarization state. When it passes through the second half-wave plate, the second half-wave plate adjusts the direction of the polarization state of the linearly polarized light to meet the requirements of the laser crystal for the polarization state direction of the high-power input laser light entering it, thus obtaining an ideal frequency-doubled laser. With the first plano-convex lens, the beam is focused to achieve high energy density and high power density of the beam incident on the laser crystal 7. The laser crystal uses LBO / BBO or other frequency-doubled crystals. When the 1000-1100nm fundamental frequency signal light passes through the laser crystal and the power density reaches the nonlinear threshold, a corresponding second harmonic, i.e., frequency-doubled light, is generated. The frequency of the generated frequency-doubled light is half that of the fundamental frequency light, and the resulting light is green. Since the frequency-doubled light and the fundamental frequency signal light emitted from the laser crystal are divergent, a second plano-convex lens is used to collimate them. The first and second plano-convex lenses can improve the energy density and power density of the beam, achieving high-power output. The first dichroic mirror can separate the residual fundamental frequency signal light and the frequency-doubled light.

[0010] The laser in this application is achieved by extracavity frequency doubling of a high-repetition-rate polarization-maintaining fiber laser. The high-repetition-rate polarization-maintaining fiber laser outputs high-repetition-rate polarization-maintaining 1000–1100 nm infrared light. After reaching the first Brewster window, due to the angle between the first Brewster window and the optical path, the backlight caused by incomplete transmission or other reasons is minimal, and the first Brewster window allows for good transmittance of linearly polarized light. Furthermore, the beam after passing through the first Brewster window, i.e., the 1000–1100 nm fundamental frequency signal light, has a specific polarization state. However, a three-dimensional coordinate relationship is formed between the optical path direction and the polarization direction. Simply adjusting the first Brewster window alone is insufficient to fully meet the laser crystal's requirement for the polarization state of the incident laser. In other words, simply adjusting the first Brewster window generally only controls one or two dimensions of the direction, making it difficult to stably output the laser light required by the laser crystal.

[0011] A second half-wave plate is placed behind the first Brewster window. The main function of this half-wave plate is to adjust the polarization direction of the beam in another dimension after the lens so that it rotates with the previous polarization direction. The purpose of this is to further improve the laser beam that meets the requirements of the laser crystal, reduce backlight, and improve the overall stability of the device.

[0012] When the half-wave plate adjusts the lens, the polarization state of the light beam is perpendicular to the previous polarization direction. The reflected light generated from behind the lens due to incomplete transmission or other reasons is polarized perpendicular to the first Brewster window after passing through the half-wave plate. Thus, it is almost impossible to return along the original path.

[0013] This application can protect the front-end high repetition rate polarization-maintaining fiber laser (high repetition rate polarization-maintaining fiber laser is very sensitive to the returned light, and the fiber is prone to spotting or device damage when the returned light is strong). On the other hand, this design can greatly improve the power stability of the system because the light returned from the original optical path and the light transmitted in the forward direction have the same phase, frequency, period and other parameters, which are prone to interference and interfere with the original optical path transmission.

[0014] After the second half-wave plate, the first plano-convex lens is placed. At this time, the beam will be focused and enter the laser crystal placed behind the first plano-convex lens, which meets the conditions for the laser crystal to generate frequency doubling. Frequency doubling is generated in the laser crystal, and the frequency doubling crystal outputs the newly generated 500-550nm green light and the unconverted 1000-1100nm fundamental frequency light.

[0015] A second plano-convex lens is placed behind the laser crystal to collimate the diverging beam. The first and second plano-convex lenses can improve the energy density and power density of the beam, thereby achieving high power output.

[0016] The green fiber laser provided in this application can significantly improve the stability of the green fiber laser system. The green fiber laser includes at least a first Brewster window and a second half-wave plate. Since the Brewster window and half-wave plate absorb light much less than conventional polarizers, and the materials have stronger tolerance to high-power lasers, stable high-power output can be achieved. At the same time, based on the characteristics of the Brewster angle, the polarization state is cleverly adjusted by using the half-wave plate, thereby achieving laser optical path stability and output power stability, and greatly reducing the device damage rate of the green fiber laser. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A first structural schematic diagram of the green fiber laser provided in this application;

[0019] Figure 2A schematic diagram of the second structure of the green fiber laser provided in this application;

[0020] Figure 3 This application provides a schematic diagram of the third structure of a green fiber laser;

[0021] Figure 4 A fourth structural schematic diagram of a green fiber laser provided in this application;

[0022] Figure 5 The fifth structural schematic diagram of a green fiber laser provided in this application.

[0023] Figure reference numerals: 1. High repetition rate polarization-maintaining fiber laser; 2. First half-wave plate; 3. First Brewster window; 4. Second half-wave plate; 5. First plano-convex lens; 6. Crystal temperature control system; 7. Laser crystal; 8. Second plano-convex lens; 9. Third half-wave plate; 10. Second Brewster window; 11. First dichroic mirror; 12. Second dichroic mirror; 13. Pinhole aperture; 14. Third Brewster window; 15. Mirror; 16. Idle light collector. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present application and are not intended to limit the scope of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort are within the scope of protection of the present application.

[0025] Please see Figure 1 , Figure 1This is a schematic diagram of the first structure of the green fiber laser provided in this application. The green fiber laser sequentially includes a high-repetition-rate polarization-maintaining fiber laser 1, a first Brewster window 3, a second half-wave plate 4, a first plano-convex lens 5, a laser crystal 7, a second plano-convex lens 8, and a first dichroic mirror 11. The high-repetition-rate polarization-maintaining fiber laser 1 can output linearly polarized fundamental frequency signal light with a high repetition-rate of 1000–1100 nm. The first Brewster window 3 is an optical lens placed at a Brewster angle, and the 1000–1100 nm fundamental frequency signal light passing through the first Brewster window 3 has a specific polarization state. The second half-wave plate 4 can be rotated to adjust the polarization state rotation angle of the linearly polarized infrared light after passing through the first Brewster window 3. Because the laser crystal 7 has extremely strict requirements on the polarization state of the incident light entering it, when the input laser is a high-power laser, the requirements for the polarization state of the incident light entering it are even more stringent. Furthermore, adjusting the settings of the laser crystal 7 to achieve the required polarization state of the incident light is difficult and ineffective. Even with the first Brewster window 3 alone, it is difficult to meet the directional polarization state requirements of the laser crystal 7. By using the second half-wave plate 4 and the first Brewster window 3 to adjust the polarization state rotation angle to a suitable polarization state, the optical-to-optical conversion efficiency of the entire system will be greatly improved, significantly saving costs and reducing power consumption. When the beam passes through the first plano-convex lens 5, the beam is focused, thereby increasing the energy density and power density of the beam. The laser crystal 7 uses LBO / BBO or other frequency-doubled crystals. When the 1000-1100nm fundamental frequency signal light passes through the crystal and the power density reaches the nonlinear threshold, a corresponding second harmonic, i.e., frequency-doubled light, is generated. The frequency of the generated frequency-doubled light is half that of the fundamental frequency light, and this results in green light. Since the frequency-doubled light and fundamental frequency signal light emitted from the laser crystal 7 are divergent, a second plano-convex lens 8 is used to collimate the frequency-doubled light and fundamental frequency signal light emitted from the laser crystal 7. The first dichroic mirror 11 exists to separate the residual fundamental frequency signal light and frequency-doubled light.

[0026] Furthermore, in order to fundamentally eliminate the return of reflected light from the end face of the optical components along the original path, thereby affecting the stability of the system beam, when using the second half-wave plate 4 to adjust the polarization state of the beam, the polarization direction of the adjusted beam should be perpendicular to that before adjustment.

[0027] Furthermore, to reduce the loss of fundamental frequency light, the front and rear light-receiving surfaces of the second half-wave plate 4 are coated with an anti-reflection film of 1000-1100 nm, thereby improving the transmittance of fundamental frequency light when passing through the component.

[0028] Furthermore, the most suitable angle for placing the first Brewster window 3 can be calculated according to the refractive index of the material corresponding to wavelengths of 1000-1100nm, so as to reduce the loss of the fundamental frequency light in the system by the first Brewster window 3, thereby greatly improving the transmittance of the fundamental frequency light when passing through the first Brewster window 3.

[0029] Furthermore, the first Brewster window 3 can greatly reduce the impact of light returning along the original path due to incomplete transmission from all lens end faces after passing through the lens on the stability and safety of the front-end fundamental frequency optical path. This design can greatly protect the high repetition rate polarization-maintaining fiber laser 1 at the front end. At the same time, the presence of this lens can greatly improve the output optical path stability of the entire system.

[0030] Furthermore, in order to improve the transmittance of fundamental frequency light when it passes through the component, the light-receiving end face of the first Brewster window 3 is treated with high polishing.

[0031] Furthermore, in order to improve the damage threshold of the first Brewster window 3, the two ends of the first Brewster window 3 are not coated.

[0032] Furthermore, the first dichroic mirror is placed at a 45° angle to the main optical path and is a dichroic mirror with a double-ended plane.

[0033] Furthermore, to improve the overall output power of the system, the light-receiving end face of the first dichroic mirror is coated with a 500-550nm high-reflectivity film.

[0034] Furthermore, to reduce the impact of residual fundamental frequency signal light on the optical path stability and thermal effects of the entire green light system, both the light-receiving and light-emitting end faces of the first dichroic mirror are coated with an anti-reflection film of 1000-1100 nm.

[0035] Furthermore, to reduce the influence of secondary light spots in the system, the light-emitting end face of the first dichroic mirror is not coated with a 500-550nm high-reflectivity film.

[0036] Furthermore, to reduce light loss transmitted from the first Brewster window 3, the front and rear light-receiving surfaces of the first plano-convex lens 5 are coated with an anti-reflection film of 1000-1100 nm. More specifically, the first plano-convex lens 5 ultimately focuses the light beam into the laser crystal 7. Simultaneously, the arrangement of the first plano-convex lens 5 with its convex end receiving light and its flat end facing the laser crystal 7 reduces the impact of aberrations on the system.

[0037] Furthermore, in order to increase the power of the fundamental frequency light undergoing nonlinear transformation inside the laser crystal 7 and further improve the frequency doubling efficiency, a 1000-1100nm antireflection coating is deposited on the light-receiving end face of the laser crystal.

[0038] Furthermore, after the nonlinear transformation, in order to reduce the influence of residual signal light on the laser crystal and to increase the power of the emitted frequency-doubled light, a 1000-1100 nm antireflection coating and a 500-550 nm antireflection coating are simultaneously deposited on the light-emitting surface of the laser crystal.

[0039] Furthermore, to reduce the impact of aberrations on the system, the second plano-convex lens 8 is also positioned such that the planar end receives light and the convex end emits light.

[0040] Furthermore, in order to improve the output power value and power stability of the entire green light system, reduce the proportion of frequency-doubled light and fundamental frequency signal light emitted from the laser crystal 7 reflected back to the laser crystal 7 through the second plano-convex lens 8, and thus reduce damage to the laser crystal 7, the light-receiving surface and the light-emitting surface of the second plano-convex lens 8 are coated with anti-reflection films of 1000-1100nm and 500-550nm respectively.

[0041] Please see Figure 2 , Figure 2 This is a schematic diagram of the second structure of the green fiber laser provided in this application. The green fiber laser, in... Figure 1 Based on the green fiber laser shown, a first half-wave plate 2 is also included. The first half-wave plate 2 is located between the high repetition rate polarization-maintaining fiber laser 1 and the first Brewster window 3. Similarly, a three-dimensional coordinate relationship is formed between the optical path direction and the polarization direction. By rotating the placement angle of the first half-wave plate 2, the polarization state direction of the signal light passing through the component can be adjusted, thereby meeting the polarization state requirements of the incident light of the first Brewster window 3. This greatly increases the fundamental frequency light passing through the first Brewster window 3 and stabilizes the output. It can even allow the light output by the high repetition rate polarization-maintaining fiber laser to completely pass through the first Brewster window.

[0042] Please see Figure 3 , Figure 3 This application provides a third structural schematic diagram of a green fiber laser, which, in... Figure 2 Based on the green fiber laser shown, a crystal temperature control system 6 may also be included, which surrounds the laser crystal 7. This system is used to provide a constant temperature working environment for the laser crystal 7 and to provide fixation conditions for the laser crystal 7.

[0043] Furthermore, the system includes heating / cooling components and a temperature feedback regulation system, which can autonomously adjust based on real-time temperature feedback under the influence of ambient temperature or other factors, ensuring that the laser crystal always operates at a specific temperature, greatly improving the power stability of the system.

[0044] Please see Figure 4 , Figure 4This application provides a fourth structural schematic diagram of a green fiber laser, which, in... Figure 3 Based on the green fiber laser shown, it may also include a third half-wave plate 9 and a second Brewster window 10.

[0045] The third half-wave plate 9 and the second Brewster window 10 are sequentially located between the second plano-convex lens 8 and the first dichroic mirror 11. Similarly, the third half-wave plate can adjust the polarization state of the light beam passing through this component, which can be achieved by adjusting the placement angle of the component. The second Brewster window 10 is also an optical lens placed at a Brewster angle. The third half-wave plate 9 can adjust the polarization direction of the light beam passing through component 10, greatly improving the transmittance of the second Brewster window 10.

[0046] Furthermore, in order to improve the output power and power stability of the system, both end faces of the third half-wave plate 9 are coated with anti-reflection films of 1000-1100 nm and 500-550 nm respectively.

[0047] Furthermore, to improve the stability of the system, the third half-wave plate 9 should be adjusted so that the polarization direction of the light beams passing through the component is exactly perpendicular.

[0048] Furthermore, in order to reduce the loss of frequency-doubled light in the system by the second Brewster window 10, the second Brewster window 10 is placed at the most suitable angle calculated according to the material refractive index corresponding to the wavelength of 500-550nm, thereby greatly improving the transmittance of frequency-doubled light when passing through the lens.

[0049] Furthermore, the second Brewster window 10 can greatly reduce the impact of light returning along the original path due to incomplete transmission from all lens end faces after the second Brewster window 10 on the stability and safety of the front-end optical path. The existence of this design can greatly protect the optical components before the second Brewster window 10. At the same time, the second Brewster window 10 can greatly improve the output optical path stability of the entire system.

[0050] Furthermore, in order to improve the transmittance of the frequency-doubled light when it passes through the second Brewster window 10, the light-receiving end face of the second Brewster window 10 is treated with high polishing.

[0051] Furthermore, in order to improve the damage threshold of the second Brewster window 10, the two ends of the second Brewster window 10 are not coated.

[0052] Please see Figure 5 , Figure 5This is a fifth structural schematic diagram of a green fiber laser provided in this application. The green fiber laser, in... Figure 4 Based on the green fiber laser shown, it may also include one or more of the following components: a second dichroic mirror 12, a pinhole aperture 13, a third Brewster window 14, a reflector 15, and an idler light collector 16. These components are located behind the first dichroic mirror 11.

[0053] The second dichroic mirror 12 is located on one side of the light-receiving end face of the first dichroic mirror 11, positioned at 45° to the main optical path, and is a double-ended planar dichroic mirror. The second dichroic mirror 12 exists to completely separate the residual fundamental frequency signal light and the dominant harmonic light reflected by the first dichroic mirror 11. Generally, current coating processes, whether high-reflection or high-transmittance coatings, cannot achieve 100% of the theoretical value; there will always be less than 1% of idler frequency light reflected. For this component, the idler frequency light refers to the less than 1% of residual fundamental frequency signal light (1000-1100nm) reflected by the first dichroic mirror 11. The second dichroic mirror 12 further supplements the color separation of the beam after it has been separated by the first dichroic mirror 11, resulting in better monochromaticity of the green light output by the system.

[0054] Furthermore, to improve the overall output power of the system, the light-receiving end face of the second dichroic mirror 12 is coated with a 500-550nm high-reflectivity film.

[0055] Furthermore, in order to reduce the impact of residual fundamental frequency signal light on the optical path stability and thermal effects of the entire green light system, both the light-receiving and light-emitting end faces of the second dichroic mirror 12 are coated with an anti-reflection film of 1000-1100 nm.

[0056] Furthermore, to reduce the influence of secondary light spots in the system, the light-emitting end face of the second dichroic mirror 12 is not coated with a 500-550nm high-reflectivity film.

[0057] The pinhole aperture 13 is located behind the second dichroic mirror 12. The pinhole aperture 13 can greatly block the influence of off-axis light beams reflected back from other devices after this component on the stability of the entire system's optical path. At the same time, the pinhole aperture 13 can block stray light that may be generated before this component from escaping from the system, and also has a mode-limiting function.

[0058] Furthermore, the pinhole aperture 13 can limit the outgoing light of the green light system to be consistent with the design when it is transmitted through the external optical path, thereby reducing debugging deviations.

[0059] Furthermore, to improve the stability of the optical path, the bottom of the pinhole aperture 13 should be subjected to appropriate heat dissipation treatment.

[0060] The third Brewster window 14 is located behind the pinhole aperture 13, and this component is an optical lens placed at a Brewster angle.

[0061] Furthermore, in order to reduce the loss of frequency-doubled light in the system by the third Brewster window 14, the third Brewster window 14 is placed at the most suitable angle calculated according to the material refractive index corresponding to the wavelength of 500-550nm, thereby greatly improving the transmittance of frequency-doubled light when it passes through the third Brewster window 14.

[0062] Furthermore, the third Brewster window 14 can greatly reduce the impact of light returning along the original path due to other reasons on the stability and safety of the front-end optical path during the application of the green light system in the external optical path. It can greatly protect the optical components before the lens. At the same time, the presence of the lens can greatly improve the stability of the output optical path of the entire system.

[0063] Furthermore, to improve the transmittance of green light when it passes through the third Brewster window 14, the light-receiving end face of this component is treated with high polishing.

[0064] Furthermore, in order to improve the damage threshold of the third Brewster window 14, the two end faces of the third Brewster window 14 are not coated.

[0065] Furthermore, to ensure the stability of the internal air pressure, the dryness of the environment, and the cleanliness of the environment of the entire green fiber laser, the third Brewster window 14 should be sealed during installation. The third Brewster window 14 also serves to isolate the green fiber laser system from the external environment.

[0066] The total reflection mirror 15 is located behind the first dichroic mirror 11. This mirror can perform total reflection of the residual fundamental frequency signal light and the incompletely reflected frequency-doubled light.

[0067] Furthermore, in order to improve reflectivity, the light-receiving end face of the lens is coated with high-reflectivity films of 1000-1100nm and 500-550nm. The residual fundamental frequency signal light transmitted through component 11 and the incompletely reflected second-order light will be reflected by the component to the heat dissipation light absorption plate of the idler frequency light collector 16. This design can greatly reduce the amount of light returning along the original optical path, thereby greatly improving the stability of the system and the safety of the components.

[0068] The idler frequency light collector 16 is located behind the total reflection mirror 15. This component is mainly used for the absorption and heat dissipation of residual fundamental frequency signal light. The residual fundamental frequency signal light reflected by the total reflection mirror 15 and the incompletely reflected frequency harmonic light will be annihilated in the collector.

[0069] Furthermore, in order to reduce the impact of heat generated during idler frequency annihilation on system stability, the collector has been equipped with strong heat dissipation measures.

[0070] Furthermore, in order to reduce the impact of specular reflection from the inner wall material of the collection box on the stability of the optical path, the light-receiving area of ​​the collection box is roughened to minimize the impact of the idler frequency optical collector 16 on the system.

[0071] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that the elements inherent in a process, method, article, or apparatus that includes a list of elements are included. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Additionally, portions of the technical solutions provided in the embodiments of this application that are consistent with the implementation principles of corresponding technical solutions in the prior art have not been described in detail to avoid excessive elaboration.

[0072] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made to this application, as well as combinations of the various embodiments in this application, without departing from the principles of this application. These improvements, modifications, and combinations also fall within the protection scope of the claims of this application.

Claims

1. A green fiber laser, characterized in that... The assembly includes, in sequence, a high repetition rate polarization-maintaining fiber laser (1), a first Brewster window (3), a second half-wave plate (4), a first plano-convex lens (5), a laser crystal (7), a second plano-convex lens (8), and a first dichroic mirror (11). The high repetition rate polarization-maintaining fiber laser (1) outputs a linearly polarized fundamental frequency signal light with a high repetition rate polarization of 1000-1100nm. The first Brewster window (3) is an optical lens placed at a Brewster angle. When the beam passes through the first plano-convex lens (5), the beam will be focused. The laser crystal (7) is a frequency doubling crystal. The second plano-convex lens (8) collimates the frequency doubling light and fundamental frequency signal light emitted from the laser crystal (7). The first dichroic mirror (11) separates the residual fundamental frequency signal light and frequency doubling light. The green fiber laser also includes a first half-wave plate (2), which is located between the high repetition rate polarization-maintaining fiber laser (1) and the first Brewster window (3). The green fiber laser also includes a third half-wave plate (9) and a second Brewster window (10), which are located between the second plano-convex lens (8) and the first dichroic mirror (11). The green fiber laser also includes one or more of the following components: a second dichroic mirror (12), a pinhole aperture (13), a third Brewster window (14), a reflector (15), and an idler light collector (16). The second dichroic mirror (12), the pinhole aperture (13), the third Brewster window (14), the reflector (15), and the idler light collector (16) are all located behind the first dichroic mirror (11).

2. The green fiber laser according to claim 1, characterized in that... It also includes a crystal temperature control system (6) surrounding the laser crystal (7).

3. The green fiber laser according to claim 1, characterized in that... When adjusting the polarization state of the beam using the second half-wave plate (4), the polarization direction of the adjusted beam should be perpendicular to that before adjustment.

4. The green fiber laser according to claim 1, characterized in that... The first Brewster window (3) is placed at the most suitable angle according to the material refractive index corresponding to wavelengths of 1000-1100nm.

5. The green fiber laser according to claim 1, characterized in that, The light-receiving end face of the first Brewster window (3) is treated with high polishing.

6. The green fiber laser according to claim 1, characterized in that, The first dichroic mirror (11) is placed at 45° to the main optical path and is a dichroic mirror with a double-ended plane.

7. The green fiber laser according to claim 1, characterized in that, The second Brewster window (10) is placed at the most suitable angle according to the material refractive index corresponding to wavelengths of 500-550nm.

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