CN115548843A - Green fiber laser - Google Patents

Abstract

The application provides a green light fiber laser, includes high repetition frequency polarization maintaining fiber laser, first Brewster's window piece, second half-wave plate, first plano-convex lens, laser crystal, second plano-convex lens, first dichroic mirror in proper order. The high repetition frequency polarization-maintaining fiber laser can output high repetition frequency polarization-maintaining fundamental frequency signal light. The first Brewster window sheet is an optical lens placed at a Brewster angle, and 1000-1100nm fundamental frequency signal light passing through the first Brewster window sheet has a specific polarization state. The second half-wave plate can be used for adjusting the polarization state rotation angle of the infrared beam after passing through the first Brewster window plate by rotating the placement angle of the second half-wave plate. When the polarization state rotation angle is adjusted to a proper polarization state by using the second half-wave plate and the first Brewster window plate, the light-light conversion efficiency of the whole system is greatly improved, and the green light output with high repetition frequency, high energy conversion efficiency, high power and stability can be obtained.

Description

Green fiber laser

Technical Field

The invention relates to the technical field of laser, in particular to a high repetition frequency and high stability green fiber laser.

Background

With the increasing demand of new energy industries in recent years, higher requirements are put forward on front-end laser processing technology. The absorption rate of the traditional infrared laser to high-reflection materials is very low due to the factor of material absorption, the welding and cutting of the high-reflection materials such as a copper material in the lithium battery industry cannot be met, and the green laser becomes a typical light source in the industry by virtue of the high absorption characteristic of the copper material to a green light beam.

The traditional green laser is generally produced by outputting infrared fundamental frequency light through solid laser resonance and then outputting the infrared fundamental frequency light through nonlinear crystal frequency multiplication, and the laser has low repetition frequency, low energy conversion efficiency and low operation efficiency in industrial processing. In addition, the output power of the laser is obviously influenced by the ambient temperature, and the power is unstable in industrial processing, namely the power greatly fluctuates in industrial processing, so that a high-precision and expensive processed workpiece is easily scrapped, and the processing effect is influenced.

At present for the stability that improves laser output, can adopt the polaroid to change laser transmission's polarization state usually to satisfy the stable output of laser, nevertheless the polaroid is big to the absorption of light, and the light loss through the polaroid is big, and polaroid material itself is difficult to tolerate high power laser, and easy material damage loses efficacy, is difficult to realize the laser output of high power, stability.

Therefore, a green fiber laser is needed to be invented, which can obtain green output with high repetition frequency, high energy conversion efficiency, high power and stability.

Disclosure of Invention

It is an object of the present application to provide a green fiber laser to solve the problems set forth in the above background.

In order to achieve the above purpose, the present application provides the following technical solutions: a green light fiber laser sequentially comprises a high repetition frequency polarization maintaining fiber laser, a first Brewster window plate, a second half-wave plate, a first plano-convex lens, a laser crystal, a second plano-convex lens and a first dichroic mirror.

The specific working principle and process of the application are as follows:

the high-repetition-frequency polarization-maintaining fiber laser can output linear polarization fundamental frequency signal light with high repetition frequency polarization maintaining of 1000-1100nm, and when input laser light is linearly polarized light, the polarization-maintaining fiber laser still outputs linearly polarized light after the input laser light is transmitted by the polarization-maintaining fiber laser. The first Brewster window sheet is an optical lens placed at a Brewster angle, and 1000-1100nm fundamental frequency signal light passing through the first Brewster window sheet has a specific polarization state. And when the laser passes through the second half-wave plate, the second half-wave plate adjusts the direction of the polarization state of the linearly polarized light so as to meet the requirement of the laser crystal on the direction of the polarization state of the high-power input laser entering the laser crystal, and the ideal frequency doubling laser is obtained. The first plano-convex lens focuses the beam 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 doubling crystals, when 1000-1100nm fundamental frequency signal light passes through the laser crystal and the power density reaches a nonlinear threshold value, corresponding second harmonic, namely frequency doubling light, can be generated, the light frequency of the generated frequency doubling light is half of the fundamental frequency light, and the generated light is green light. Because the frequency doubling light and the fundamental frequency signal light emitted from the laser crystal are divergent light, the frequency doubling light and the fundamental frequency signal light emitted from the laser crystal are collimated by the second plano-convex lens, and the first plano-convex lens and the second plano-convex lens can improve the energy density and the power density of the light beam and realize high-power output. The first dichroic mirror may separate residual fundamental frequency signal light and frequency doubled light.

The laser is realized by carrying out frequency doubling outside a cavity on a high repetition frequency polarization-maintaining optical fiber laser, and after the high repetition frequency polarization-maintaining optical fiber laser outputs 1000-1100nm infrared light with high repetition frequency polarization maintaining to a first Brewster window sheet, because a certain included angle is formed between the first Brewster window sheet and an optical path, light beams have little return light due to incomplete transmission or other reasons, and the first Brewster window sheet can enable linear polarization to have better transmittance. Secondly, the light beam passing through the first brewster window plate, that is, the 1000-1100nm fundamental frequency signal light has a specific polarization state, but a three-dimensional coordinate relationship is formed between the light path direction and the polarization direction, and the independent regulation and control of the first brewster window plate is difficult to completely meet the requirement of the laser crystal on the direction of the incident laser polarization state, or the independent regulation and control of the first brewster window plate is generally only capable of regulating and controlling the direction of 1-2 dimensions, and is difficult to stably output the laser required by the laser crystal.

The second half-wave plate is arranged behind the first Brewster window plate, and the half-wave plate is mainly used for adjusting the polarization direction of the light beam behind the lens to rotate with the polarization direction of the light beam in the other dimension.

When the half-wave plate adjusts the polarization state of the light beam behind the lens to be perpendicular to the previous polarization direction, the polarization state of the return light generated by incomplete transmission or other reasons behind the lens is perpendicular to that of the first Brewster window plate after passing through the half-wave plate, and thus, an almost-impossible path is returned.

This application can protect the high repetition frequency polarization maintaining fiber laser of front end on the one hand (high repetition frequency polarization maintaining fiber laser is very sensitive to the returning light, easily takes place during the returning light intensity that optic fibre is got a little or the device damage), and on the other hand this design can greatly improve the power stability of system, because the light that the former light path route returned and forward transmission have same phase place, frequency, cycle isoparametric, easily takes place to interfere, disturbs former light path transmission.

And a first plano-convex lens is arranged behind the second half-wave plate, light beams enter a laser crystal arranged behind the first plano-convex lens after being focused, the frequency doubling generation condition of the laser crystal is achieved, frequency doubling is performed in the laser crystal, and newly generated green light of 500-550 nm and unconverted fundamental frequency light of 1000-1100nm are output by the frequency doubling crystal.

And a second plano-convex lens is arranged behind the laser crystal to collimate the divergent light beam, and the first plano-convex lens and the second plano-convex lens can improve the energy density and the power density of the light beam and realize high-power output.

The application provides a green glow fiber laser can improve green glow fiber laser system stability by a wide margin, this green glow fiber laser includes first brewster window piece at least, the second half wave plate, because brewster window piece, the half wave plate is less than the absorption of conventional polaroid to light far away to the absorption of light, and the material has stronger tolerance to high power laser, can realize the stable output of high power then, and simultaneously, based on the characteristic of brewster angle, the ingenious half wave plate that utilizes is adjusted the polarization state, and then can realize laser light path stability, output power stability, and greatly reduced the device damage rate to green glow fiber laser.

Drawings

In order to clearly illustrate the embodiments or technical solutions of the present application, the drawings used in the embodiments or technical solutions of the present application will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic diagram of a first structure of a green fiber laser provided in the present application;

fig. 2 is a schematic diagram of a second structure of a green fiber laser provided in the present application;

fig. 3 is a schematic diagram of a third structure of a green fiber laser provided in the present application;

fig. 4 is a schematic diagram of a fourth structure of a green fiber laser provided in the present application;

fig. 5 is a schematic diagram of a fifth structure of a green fiber laser provided in the present application.

Reference numerals are as follows: 1. the device comprises a high-repetition-frequency polarization-maintaining fiber laser, 2, a first half-wave plate, 3, a first Brewster window plate, 4, a second half-wave plate, 5, a first plano-convex lens, 6, a crystal temperature control system, 7, a laser crystal, 8, a second plano-convex lens, 9, a third half-wave plate, 10, a second Brewster window plate, 11, a first dichroic mirror, 12, a second dichroic mirror, 13, an aperture diaphragm, 14, a third Brewster window plate, 15, a reflector, 16 and an idle-frequency light collector.

Detailed Description

In order that those skilled in the art will better understand the disclosure, the following detailed description will be given with reference to the accompanying drawings. It should be apparent that the described embodiments are only some of the embodiments of the present application, and do not limit the scope of the claims of the present application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.

Referring to fig. 1, fig. 1 is a schematic diagram of a first structure of a green fiber laser provided in the present application, the green fiber laser includes, in order, a high repetition frequency polarization maintaining fiber laser 1, a first brewster window plate 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 frequency polarization-maintaining fiber laser 1 can output the linear polarization type fundamental frequency signal light with the high repetition frequency polarization-maintaining wavelength of 1000-1100 nm. The first Brewster window piece 3 is an optical lens placed at a Brewster angle, and 1000-1100nm fundamental frequency signal light passing through the first Brewster window piece 3 has a specific polarization state. The second half-wave plate 4 can be used to adjust the polarization state rotation angle of the linearly polarized infrared light after passing through the first brewster window plate 3 by rotating the placement angle of the second half-wave plate 4. Because the requirement of the laser crystal 7 on the polarization state of the incident light entering the laser crystal is very strict, when the input laser is high-power laser, the requirement of the laser crystal 7 on the polarization state of the incident light entering the laser crystal is more strict, the difficulty of meeting the polarization state of the incident light by adjusting the setting of the laser crystal 7 is higher, the effect is not ideal, the direction requirement of the laser crystal 7 on the direction polarization state of the incident light is difficult to meet by independently setting the first Brewster window plate 3, and when the polarization state rotation angle is adjusted to a proper polarization state by using the second half-wave plate 4 and the first Brewster window plate 3, the light-light conversion efficiency of the whole system is greatly improved, the cost is greatly saved, and the power consumption is reduced. When the light beam passes through the first plano-convex lens 5, the light beam is focused, so that the energy density and the power density of the light beam are improved. The laser crystal 7 uses LBO/BBO or other frequency doubling crystals, when 1000-1100nm fundamental frequency signal light passes through the crystal and the power density reaches a nonlinear threshold value, corresponding second harmonic, namely frequency doubling light, can be generated, the light frequency of the generated frequency doubling light is half of the fundamental frequency light, and the generated light is green light. Because the frequency doubling light and the fundamental frequency signal light emitted from the laser crystal 7 are divergent light, the frequency doubling light and the fundamental frequency signal light emitted from the laser crystal 7 are collimated by the second plano-convex lens 8. The first dichroic mirror 11 is present to separate the residual fundamental frequency signal light and the frequency doubled light.

Further, in order to substantially eliminate the reflected light from the end face of the optical component returning along the original path and further affecting the stability of the system light beam, when the polarization state of the light beam is adjusted by using the second half-wave plate 4, the polarization direction of the adjusted light beam should be perpendicular to that before the adjustment.

Furthermore, in order to reduce the loss of the fundamental frequency light, the front and back light receiving surfaces of the second half-wave plate 4 are plated with 1000-1100nm antireflection films, so that the transmittance of the fundamental frequency light passing through the component is improved.

Further, the first brewster window piece 3 can be placed at the most appropriate angle according to the refractive index of the material corresponding to the wavelength of 1000-1100nm, so that the loss of the first brewster window piece 3 to the fundamental frequency light in the system is reduced, and further, the transmittance of the fundamental frequency light when the fundamental frequency light passes through the first brewster window piece 3 is greatly improved.

Further, the first brewster window 3 can greatly reduce the influence of light returned along the original path on the stability and safety of the front-end frequency optical path due to incomplete transmission on all the lens end surfaces after passing through the lens, the design can greatly protect the high-repetition-frequency polarization-maintaining optical fiber laser 1 at the front end, and meanwhile, the existence of the lens can greatly improve the stability of the output optical path of the whole system.

Further, in order to improve the transmittance of fundamental frequency light when passing through the member, the light-receiving end face of the first brewster window sheet 3 is subjected to high polishing treatment.

Further, in order to improve the damage threshold of the first brewster window piece 3, the two end faces of the first brewster window piece 3 are not coated with a film.

Further, the first dichroic mirror is arranged at an angle of 45 degrees with respect to the main light path, and is a double-end plane dichroic mirror.

Furthermore, in order to improve the overall output power of the system, the light receiving end face of the first dichroic mirror is plated with a high reflection film of 500-550 nm.

Furthermore, in order to reduce the stability and the heat influence of residual fundamental frequency signal light on the light path of the whole green light system, the two end faces of the first dichroic mirror receiving light and emitting light are respectively plated with an anti-reflection film of 1000-1100 nm.

Furthermore, in order to reduce the influence of secondary light spots in the system, the light-emitting end face of the first dichroic mirror is not plated with a 500-550 nm high-reflection film.

Furthermore, in order to reduce the loss of light transmitted by the first brewster window sheet 3, the front and rear light-receiving end faces of the first plano-convex lens 5 are plated with anti-reflection films of 1000-1100 nm. More specifically, the first plano-convex lens 5 will eventually focus the beam into the laser crystal 7. Meanwhile, the first plano-convex lens 5 is arranged in a manner that the convex end receives light and the plane end faces to one side of the laser crystal 7, so that the influence of aberration on the system can be reduced.

Furthermore, in order to improve the power of the fundamental frequency light which is subjected to nonlinear conversion in the laser crystal 7 and further improve the frequency doubling efficiency, the light receiving end face of the laser crystal is plated with an anti-reflection film of 1000-1100 nm.

Furthermore, after nonlinear conversion, in order to reduce the influence of residual signal light on the laser crystal and to improve the power of the emitted frequency doubling light, a 1000-1100nm antireflection film and a 500-550 n antireflection film are simultaneously plated on the light emitting surface of the laser crystal.

Further, to reduce the effect of aberration on the system, the second plano-convex lens 8 is placed such that the flat end receives light and the convex end emits light.

Further, in order to improve the power value output by the whole green light system and the power stability of the system, and reduce the proportion of frequency doubling light and fundamental frequency signal light emitted from the laser crystal 7 and reflected back to the laser crystal 7 through the second plano-convex lens 8, and further reduce the damage to the laser crystal 7, the light receiving surface and the light emitting surface of the second plano-convex lens 8 are both plated with antireflection films of 1000-1100nm and 500-550 nm.

Referring to fig. 2, fig. 2 is a schematic diagram of a second structure of the green fiber laser provided in the present application, the green fiber laser further includes a first half-wave plate 2 on the basis of the green fiber laser shown in fig. 1, the first half-wave plate 2 is located between the high repetition frequency polarization maintaining fiber laser 1 and the first brewster window plate 3, and similarly, a three-dimensional coordinate relationship is formed between the optical path direction and the polarization direction, and by rotating the placing angle of the first half-wave plate 2, the polarization state direction of the signal light transmitted through the component can be adjusted, so as to meet the polarization state requirement of the incident light of the first brewster window plate 3, so that the fundamental frequency of the light transmitted through the first brewster window plate 3 is greatly improved, and the output is stable, and even the light output by the high repetition frequency polarization maintaining fiber laser can completely transmit through the first brewster window plate.

Referring to fig. 3, fig. 3 is a schematic diagram of a third structure of a green fiber laser provided in the present application, which may further include a crystal temperature control system 6 on the basis of the green fiber laser shown in fig. 2, wherein the crystal temperature control system surrounds the laser crystal 7, and is configured to provide a constant temperature working environment for the laser crystal 7 and provide a fixed setting condition for the laser crystal 7.

Furthermore, the system comprises a temperature rising/reducing component and a temperature feedback adjusting system, and can automatically adjust according to real-time temperature feedback under the influence of ambient temperature or other factors, so that the laser crystal always works at a specific temperature, and the power stability of the system is greatly improved.

Referring to fig. 4, fig. 4 is a schematic diagram of a fourth structure of a green fiber laser provided in the present application, and the green fiber laser may further include a third half-wave plate 9 and a second brewster window plate 10 on the basis of the green fiber laser shown in fig. 3.

The third half-wave plate 9 and the second brewster window plate 10 are sequentially located between the second plano-convex lens 8 and the first dichroic mirror 11. Likewise, the third half-wave plate can adjust the polarization state of the light beam passing through the component by adjusting the placement angle of the component, and the second brewster window plate 10 is also an optical lens placed at the brewster angle. The third half-wave plate 9 can adjust the polarization direction of the beam of light that the component passes through the component 10, greatly increasing the transmittance of the second brewster window plate 10.

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

Further, to improve the stability of the system, the third half-wave plate 9 should be placed so that the polarization directions of the light beams before and after passing through the component are exactly perpendicular.

Further, in order to reduce the loss of the second brewster window piece 10 to the frequency doubling light in the system, the second brewster window piece 10 is placed at an optimal angle calculated according to the refractive index of the material corresponding to the wavelength of 500-550 nm, so that the transmittance of the frequency doubling light when the lens is transmitted is greatly improved.

Further, the second brewster window sheet 10 can greatly reduce the influence of light returning along the original path on the stability and safety of the front optical path caused by incomplete transmission of all lens end surfaces behind the second brewster window sheet 10, the existence of the design can greatly protect the optical elements in front of the second brewster window sheet 10, and meanwhile, the second brewster window sheet 10 can greatly improve the stability of the output optical path of the whole system.

Further, in order to improve the transmittance of the doubled frequency light when the doubled frequency light passes through the second brewster window sheet 10, the light receiving end face of the second brewster window sheet 10 is subjected to high polishing treatment.

Further, in order to improve the damage threshold of the second brewster window piece 10, the two end faces of the second brewster window piece 10 are not coated with a film.

Referring to fig. 5, fig. 5 is a schematic diagram of a fifth structure of a green fiber laser provided in the present application, and the green fiber laser may further include one or more components of a second dichroic mirror 12, an aperture stop 13, a third brewster window sheet 14, a reflecting mirror 15, and an idle frequency light collector 16, which are located behind the first dichroic mirror 11, on the basis of the green fiber laser shown in fig. 4.

The second dichroic mirror 12 is positioned on one side of the light receiving end face of the first dichroic mirror 11, is placed at an angle of 45 degrees with respect to the main light path, and is a double-end plane dichroic mirror. The second dichroic mirror 12 exists to completely separate the residual fundamental frequency signal light and the main frequency doubled light reflected by the first dichroic mirror 11. Generally, no matter the film coating process is a high-reflection film or a high-transmission film, the theoretical value of the film coating process cannot be 100%, and always, idle frequency light within 1% can be reflected, for the component, the idle frequency light is residual fundamental frequency signal light within 1% and 1000-1100nm within 1% reflected by the first dichroic mirror 11, and the light beam subjected to color separation by the first dichroic mirror 11 is subjected to supplementary color separation again through the second dichroic mirror 12, so that the monochromaticity of green light output by the system is better.

Furthermore, in order to improve the overall output power of the system, the light receiving end surface of the second dichroic mirror 12 is plated with a high reflection film of 500-550 nm.

Furthermore, in order to reduce the influence of residual fundamental frequency signal light on the stability and the heat of the light path of the whole green light system, 1000-1100nm antireflection films are plated on two end faces of the second dichroic mirror 12 for receiving and emitting light.

Further, in order to reduce the influence of the secondary light spots in the system, the light-emitting end face of the second dichroic mirror 12 is not plated with a 500-550 nm high-reflection film.

The aperture stop 13 is located behind the second dichroic mirror 12, the aperture stop 13 can largely block the influence of the non-axial light beams reflected by other devices behind the component on the stability of the light path of the whole system, and meanwhile, the aperture stop 13 can block stray light possibly generated in front of the component from exiting from the system and also has the effect of a finite mode.

Further, the aperture stop 13 can limit the outgoing light of the green light system to be consistent with the design when the outgoing light is transmitted in the outer light path, namely, the debugging deviation is reduced.

Further, in order to improve the stability of the light path, the bottom of the aperture stop 13 should be subjected to corresponding heat dissipation treatment.

The third brewster window plate 14 is located behind the aperture stop 13, and is an optical lens placed at the brewster angle.

Further, in order to reduce the loss of the third brewster window piece 14 to the frequency doubling light in the system, the third brewster window piece 14 is placed at an optimal angle calculated according to the refractive index of the material corresponding to the wavelength of 500-550 nm, so as to greatly improve the transmittance of the frequency doubling light when the frequency doubling light penetrates through the third brewster window piece 14.

Further, the third brewster window sheet 14 can greatly reduce the influence of light returning along the original path on the stability and safety of the front-end optical path caused by other reasons in the application process of the external optical path of the green light system, and can greatly protect the optical elements in front of the lens, and meanwhile, the existence of the lens can greatly improve the stability of the output optical path of the whole system.

Further, to improve the transmittance of green light through the third brewster window piece 14, the light-receiving end faces of the members are each subjected to a high polishing treatment.

Further, in order to improve the damage threshold of the third brewster window piece 14, the two end faces of the third brewster window piece 14 are not coated with a film.

Further, in order to ensure the internal air pressure stability, the environmental dryness and the environmental cleanliness of the product of the whole green laser, attention should be paid to sealing treatment when the third brewster window sheet 14 is installed, and the third brewster window sheet 14 also has an effect of isolating the green laser system from the external environment.

The total reflection mirror 15 is located behind the first dichroic mirror 11, and the mirror can perform total reflection on the residual fundamental frequency signal light and the incompletely reflected frequency doubled light.

Further, in order to improve the reflectivity, the light receiving end face of the lens is plated with 1000-1100nm and 500-550 nm high-reflection films, and residual fundamental frequency signal light transmitted by the component 11 and incompletely reflected frequency doubling light are reflected to the heat dissipation light absorption plate of the idler frequency light collector 16 by the component.

The idler frequency light collector 16 is located behind the total reflection mirror 15, and the component is mainly used for absorption and heat dissipation of residual fundamental frequency signal light, and both the residual fundamental frequency signal light reflected by the total reflection mirror 15 and incompletely reflected frequency doubling light can be annihilated in the collector.

Further, in order to reduce the influence of heat energy caused by annihilation of idler frequency light on the stability of the system, the collector is subjected to strong heat dissipation treatment.

Further, in order to reduce the influence of the specular reflection of the inner wall material of the collecting box on the stability of the light path, the light receiving area of the collecting box is roughened, so that the influence of the idle-frequency collector 16 on the system is minimized.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Furthermore, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include the inherent elements. Without further limitation, an element defined by the phrases "comprising a," "8230," "8230," or "comprising" does not exclude the presence of other like elements in a process, method, article, or device comprising the element. In addition, parts of the above technical solutions provided in the embodiments of the present application, which are consistent with the implementation principles of corresponding technical solutions in the prior art, are not described in detail so as to avoid redundant description.

The principles and embodiments of the present application are described herein using specific examples, which are only used to help understand the method and its core idea of the present application. It should be noted that, for a person skilled in the art, several modifications and adaptations can be made to the present application and combinations of the various embodiments described in the present application without departing from the principle of the present application, and such modifications, adaptations and combinations also fall within the scope of the claims of the present application.

Claims (10)

1. A green light fiber laser is characterized by sequentially comprising a high repetition frequency polarization-maintaining fiber laser (1), a first Brewster window plate (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), wherein the high repetition frequency polarization-maintaining fiber laser (1) outputs linear polarization type fundamental frequency signal light with high repetition frequency polarization maintaining range of 1000-1100nm, the first Brewster window plate (3) is an optical lens placed at a Brewster angle, when the light beam passes through the first plano-convex lens (5), the light beam can be focused, the laser crystal (7) is a frequency doubling crystal, the second plano-convex lens (8) collimates the fundamental frequency signal light and the frequency doubling signal light emitted from the laser crystal (7), and the first dichroic mirror (11) separates the residual fundamental frequency signal light and the frequency doubling light.

2. The green fiber laser of claim 1, further comprising a first half-wave plate (2), the first half-wave plate (2) being located between the high repetition frequency polarization-maintaining fiber laser (1) and the first brewster window plate (3).

3. The green fiber laser of claim 1, further comprising a crystal temperature control system (6), the crystal temperature control system (6) surrounding the laser crystal (7).

4. The green fiber laser of claim 1, further comprising a third half-wave plate (9), a second brewster window plate (10), the third half-wave plate (9), the second brewster window plate (10) being located between the second plano-convex lens (8), the first dichroic mirror (11) in that order.

5. The green fiber laser of claim 1, further comprising one or more of a second dichroic mirror (12), an aperture stop (13), a third brewster window plate (14), a mirror (15), an idler collector (16), which are located behind the first dichroic mirror (11).

6. The green fiber laser of claim 1, wherein the second half-wave plate (4) adjusts the polarization state of the beam such that the adjusted polarization direction of the beam is perpendicular to the polarization direction before the adjustment.

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

8. The green fiber laser of claim 1, wherein the light-receiving end faces of the first brewster window plate (3) are each treated with a high polish.

9. The green fibre laser of claim 1 wherein the first dichroic mirror (11) is a double-ended planar dichroic mirror, positioned at 45 ° to the main optical path.

10. The green fiber laser of claim 4, wherein the second Brewster's window plate (10) is positioned at an angle calculated to be most appropriate for the refractive index of the material corresponding to a wavelength of 500-550 nm.

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