CN214899320U - Laser amplification system and device - Google Patents

Abstract

The application discloses a laser amplification system and equipment. The laser amplification system of the present application includes: a seed laser for providing seed light; the polarization isolator is coupled with the seed laser and is used for selectively transmitting the seed light; the laser amplifier is coupled with the polarization isolator and used for amplifying the seed light and obtaining initial laser; the polarization-changing return system is coupled with the laser amplifier and used for changing the polarization state of the initial laser to obtain first polarized light; the polarization-changing return system is further used for returning the first polarized light to the laser amplifier for secondary amplification, and obtaining second polarized light. The laser amplification system that this application provided passes through polarization control in order to increase the laser amplification number of times, promote the gain effect when enlargiing laser.

Description

Laser amplification system and device

Technical Field

The application relates to the technical field of laser amplification, in particular to a laser amplification system and equipment.

Background

In the related art, a laser amplifier is a device for amplifying energy (power) of light by stimulated radiation, and is generally classified into a regenerative amplifier and a multi-pass amplifier.

However, since the regenerative amplification system has a mode forming process, conformal transmission amplification cannot be performed on the injected light, and the structure is relatively complex, and devices such as pockels cells are required to be controlled; a plurality of reflectors are needed in a traditional dip angle multi-pass amplification system, a large amount of astigmatism and loss are introduced to the polarization of light in the process, the amplification process is limited by the size of crystals, and laser cannot be effectively amplified.

SUMMERY OF THE UTILITY MODEL

The present application is directed to solving at least one of the problems in the prior art. To this end, the present application proposes a laser amplification system. The application provides a laser amplification system, accessible polarization control is in order to laser amplification's while to increase laser amplification's number of times, promotes the gain effect.

A first aspect of an embodiment of the present application provides a laser amplification system, including: a seed laser for providing seed light; the polarization isolator is coupled with the seed laser and is used for selectively transmitting the seed light; the laser amplifier is coupled with the polarization isolator and used for amplifying the seed light and obtaining initial laser; the polarization-changing return system is coupled with the laser amplifier and used for changing the polarization state of the initial laser to obtain first polarized light; the polarization-changing return system is further used for returning the first polarized light to the laser amplifier for secondary amplification to obtain second polarized light; the polarization-changing return system is further used for returning the second polarized light to the laser amplifier for secondary amplification and polarization state conversion to obtain third polarized light; the polarization isolator is also used for carrying out polarization conversion on the third polarized light and outputting fourth polarized light; the polarization states of the initial laser light and the third polarized light are the same, and the polarization states of the first polarized light, the second polarized light and the fourth polarized light are the same. Wherein the initial laser is a high-energy high-power laser.

The laser amplification system in the embodiment of the application has the following technical effects: the polarization control is used for amplifying the laser, and the optical path distance of the laser amplification can be shortened. Further, the polarization-changing return system is coupled with the laser amplifier and used for re-coupling the light beam amplified by the laser amplifier into the laser amplifier and secondarily amplifying the light beam through the laser amplifier to increase the amplification process number, so that the light beam is subjected to high-gain conformal amplification and high-energy output is realized.

In some embodiments, the polarization isolator comprises: a first thin film polarizer for selectively transmitting the seed light or the fourth polarized light according to a polarization state; the first quarter wave plate is used for adjusting the polarization state of the seed light; a first Faraday rotator to adjust a polarization plane of the pair of input beams.

In some embodiments, the laser amplifier comprises: the laser crystal is used for amplifying the input light beam; the first reflector is arranged opposite to the laser crystal and used for reflecting the amplified initial laser; and the second reflector is arranged opposite to the first reflector and is used for transmitting the initial laser to the laser crystal again for amplification.

In some embodiments, the laser amplifier further comprises: the semiconductor laser pump is used for providing excitation laser for pumping the laser crystal; the pumping transmission optical fiber is coupled with the semiconductor laser pump and is used for pumping the excitation laser; the focusing lens group is coupled with the pumping transmission optical fiber and is used for collimating and focusing the excitation laser and obtaining a light spot approximate to flat top light; wherein the light spot of the approximately flat top light is used for carrying out high-efficiency excitation on the laser crystal.

In some embodiments, the focusing lens group further comprises: the first lens is coupled with the pumping transmission optical fiber and used for receiving the excitation laser; and the second lens is coupled with the first lens and used for collimating and focusing the excitation laser on the laser crystal.

In some embodiments, the changing polarization return system comprises: the second film polaroid is coupled with the first Faraday rotator and the laser crystal and is used for selectively transmitting light beams; the second Faraday rotator is coupled with the laser crystal and used for changing the polarization state of the initial laser to obtain first polarized light; the third reflector is coupled with the second Faraday rotator and used for reflecting the light beam passing through the second Faraday rotator into the second Faraday rotator again; and the fourth reflector is arranged opposite to the second thin film polarizer and is used for reflecting the light beam reflected by the second thin film polarizer.

In some embodiments, the polarization states of the initial laser light and the third polarized light are P-polarized, and the polarization states of the first polarized light, the second polarized light and the fourth polarized light are S-polarized.

In some embodiments, the polarization isolator is further configured to transmit a light beam having a polarization state of P polarization and reflect a light beam having a polarization state of S polarization.

In some embodiments, the second Faraday rotator adjusts the polarization state of incident light by an angle of 45 °.

A second aspect of the embodiments of the present application provides an apparatus, including the laser amplification system in any of the above embodiments.

Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description.

Drawings

The present application is further described with reference to the following figures and examples, in which:

fig. 1 is a schematic diagram of a laser amplification system according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of a laser amplification system according to an embodiment of the present application;

FIG. 3 is a schematic structural diagram of a polarization isolator according to another embodiment of the present application;

fig. 4 is a schematic structural diagram of a laser amplifier according to an embodiment of the present application;

fig. 5 is a schematic structural diagram of a system for changing polarization back according to still another embodiment of the present application.

Reference numerals: 100. a polarization isolator; 110. a first thin film polarizer; 120. a first quarter wave plate; 130. a first Faraday rotator; 200. a laser amplifier; 210. a laser crystal; 221. a first reflector; 222. a second reflector; 231. a first lens; 232. a second lens; 240. a pump transmission fiber; 250. semiconductor laser pumping; 300. changing the polarization return system; 310. a fourth mirror; 320. a second thin film polarizer; 330. a second Faraday rotator; 340. a third mirror.

Detailed Description

Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary only for the purpose of explaining the present application and are not to be construed as limiting the present application.

In the description of the present application, it is to be understood that the positional descriptions, such as the directions of up, down, front, rear, left, right, etc., referred to herein are based on the directions or positional relationships shown in the drawings, and are only for convenience of description and simplification of description, and do not indicate or imply that the referred device or element must have a specific direction, be constructed and operated in a specific direction, and thus, should not be construed as limiting the present application.

In the description of the present application, the meaning of a plurality is one or more, the meaning of a plurality is two or more, and the above, below, exceeding, etc. are understood as excluding the present number, and the above, below, within, etc. are understood as including the present number. If the first and second are described for the purpose of distinguishing technical features, they are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.

In the description of the present application, reference to the description of the terms "one embodiment," "some embodiments," "an illustrative embodiment," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

In the related art, a laser amplifier is a device for amplifying energy (power) of light by stimulated radiation, and is generally classified into a regenerative amplifier and a multi-pass amplifier.

However, since the regenerative amplifier system has a mode shaping process, it cannot perform conformal transmission amplification on the injected light, and the multi-pass amplification system cannot effectively amplify the laser light due to a large amount of astigmatism and loss introduced to the polarization of the light.

For example, regenerative amplification systems are typically resonant cavity structures, and the confinement of the mode volume limits the maximum output energy of the regenerative amplification system to millijoules. In addition, since the regenerative amplification system has a mode shaping process, the output light spot distribution is determined by its own structure, and conformal transmission amplification of the injected light cannot be performed. The traditional multi-pass amplification system is built by gain materials and a plurality of total reflection mirrors, multiple amplification is carried out on injected light through the arrangement of more total reflection mirrors, and a large amount of astigmatism and loss are introduced into the polarization of the light by the reflection mirrors, so that the multi-pass amplification system cannot effectively carry out laser amplification.

In view of the above problems, the present application provides a laser amplification system that amplifies laser light multiple times through polarization control and shortens the optical path distance of laser amplification, thereby increasing the number of amplification passes and reducing the use of a total reflection mirror to reduce astigmatism. In addition, the reflection angle of the laser amplifier and the polarization-changing return system can be adjusted to avoid the device damage caused by focusing of laser in the amplification process.

Referring to fig. 1 to 2, the present application provides a laser amplification system, including: a seed laser 400 for providing seed light; the polarization isolator 100 is coupled with the seed laser 400 and is used for selectively transmitting the seed light; the laser amplifier 200 is coupled to the polarization isolator 100, and is configured to amplify the seed light and obtain initial laser light; the polarization-changing return system 300 is coupled with the laser amplifier 200 and is used for changing the polarization state of the initial laser to obtain first polarized light; the polarization-changing returning system 300 is further configured to return the first polarized light to the laser amplifier 200 for secondary amplification, and obtain a second polarized light; the polarization-changing returning system 300 is further configured to return the second polarized light to the laser amplifier 200 for secondary amplification and polarization state conversion, so as to obtain third polarized light; the polarization isolator 100 is further configured to perform polarization conversion on the third polarized light and output fourth polarized light; the polarization states of the initial laser light and the third polarized light are the same, and the polarization states of the first polarized light, the second polarized light and the fourth polarized light are the same. Wherein the initial laser is a high-energy high-power laser.

Seed light is provided by a seed laser 400 and injected into the polarization isolator 100. The polarization isolator 100 selectively transmits the seed light or the output light beam according to the polarization state, so as to prevent the final output light beam from returning to the laser amplifier 200 and causing damage to the laser amplifier 200.

The laser amplifier 200 is coupled to the polarization isolator 100, and amplifies the seed light output from the polarization isolator 100 to obtain the initial laser light. The polarization-changing return system 300 is coupled with the laser amplifier 200, and is configured to re-couple the light beam amplified by the laser amplifier 200 into the laser amplifier 200, and amplify the light beam twice through the laser amplifier 200 to increase the amplification degree, so as to perform high-gain conformal amplification on the light beam and achieve high energy output.

For example, the laser amplifier 200 is used to amplify the seed light and obtain the initial laser light, which is twice passed through the faraday rotator in the polarization-changing return system 300 to perform polarization state conversion and obtain the second polarized light.

The second polarized light passes through the laser crystal 210 in the laser amplifier 200 again for secondary amplification, and the polarization-changing returning system 300 reflects the amplified second polarized light back to the laser amplifier 200, and the laser amplifier 200 continuously amplifies the second polarized light.

The resulting second polarized light is polarization-switched again by the faraday rotator in the polarization-altered return system 300 to obtain third polarized light. The third polarized light is transmitted to the polarization isolator 100, and polarization conversion is performed to obtain fourth polarized light. Since the polarization state of the fourth polarized light is not identical to the polarization state of the light beam passing through the polarization isolator 100, the fourth polarized light is reflected by the thin film polarizer in the polarization isolator 100 and output.

In some embodiments, the polarization state of the initial laser light and the third polarized light is P polarization, and the polarization state of the first polarized light, the second polarized light and the fourth polarized light is S polarization. The polarization state of the light beam is selectively transmitted through the polarization isolator 100 to confine the light beam in the laser amplifier 200 in a polarization-controlled manner, and to achieve multiple laser amplifications.

Referring also to FIG. 3, in some embodiments, the polarization isolator 100 includes: a first thin film polarizer 110 for selectively transmitting the seed light or the fourth polarized light according to a polarization state; a first quarter-wave plate 120 for adjusting the polarization state of the input light beam; a first Faraday rotator 130 to adjust a polarization plane of an input beam.

As shown, the first thin film polarizer 110 exhibits a pass characteristic for a P-polarized light beam, and the first thin film polarizer 110 exhibits a reflection characteristic for an S-polarized light beam, i.e., selective transmission or reflection according to a polarization state of light.

In addition, the P-polarized seed light passes through the first thin film polarizer 110 and is transmitted to the first half wave plate 120. The first one-half wave plate 120 is used to adjust the polarization state of the seed light. For example, when the input beam passes through the first half wave plate 120, the polarization state of the input beam changes by 2 times the angle formed with the fast axis. It will be appreciated that the input beam is at an angle α to the fast axis, and that the output beam is at an angle 2 α to the fast axis after the input beam passes through the first half wave plate 120.

When the seed light with the polarization state of P polarization is input into the polarization isolator 100 from one end of the first thin film polarizer 110, the polarization state of the output light is still P polarization; when the third polarized light with the polarization state of P polarization is inputted into the polarization isolator 100 from one end of the first faraday rotator 130, the third polarized light sequentially passes through the first faraday rotator 130 and the first quarter-wave plate 120, and is converted into the fourth polarized light with the polarization state of S polarization. The fourth polarized light is reflected at the surface of the first thin film polarizer 110 as the final output beam.

Referring to fig. 2 to 4, in some embodiments, the laser amplifier 200 includes: a laser crystal 210 for amplifying an input beam; a first reflecting mirror 221, disposed opposite to the laser crystal 210, for reflecting the amplified initial laser light; and a second mirror 222 disposed opposite to the first mirror 221 for transmitting the initial laser light again into the laser crystal 210 for amplification.

The laser crystal 210 can convert externally supplied energy into spatially and temporally coherent laser light having a high degree of parallelism and monochromaticity through an optical resonator. As can be appreciated, the laser crystal 210 is used to amplify the incoming beam. The laser crystal 210 may be a Yb: YAG crystal.

As shown, the first mirror 221 is disposed opposite to the laser crystal 210 to reflect the output beam amplified by the laser crystal 210 to the surface of the second mirror 222. Since the laser crystal 210, the first reflector 221, and the second reflector 222 are disposed in an isosceles triangle, the second reflector 222 receives the output beam from the first reflector 221 and reflects the output beam to the laser crystal 210 for secondary amplification. In addition, if the input beam is incident on the surface of the second reflector 222 and reflected to the surface of the first reflector 221, the first reflector 221 re-reflects the input beam into the laser crystal 210 for secondary amplification.

By setting the included angle between the first mirror 221 and the second mirror 222 and the axial direction of the laser crystal 210, the input light beam can be re-coupled into the laser crystal 210 for multiple times of amplification processing.

In some embodiments, the laser amplifier 200 further comprises: a semiconductor laser pump 250 for providing excitation laser for pumping the laser crystal 210; the pumping transmission optical fiber 240 is coupled with the semiconductor laser pump 250 and used for transmitting the excitation laser; the focusing lens group is coupled with the pumping transmission optical fiber 240 and is used for collimating and focusing the excitation laser and obtaining a light spot approximate to flat top light; wherein a near-flat-top light spot is used to excite the laser crystal 210. For example, the wavelength of the excitation laser generated by the semiconductor laser pump 250 is 940 nm.

The semiconductor laser pump 250 provides excitation laser for pumping the laser crystal 210, and the excitation laser is transmitted to the focusing lens group surface via the pump transmission fiber 240. The laser crystal 210 is excited by a spot of approximately flat top light to achieve population inversion inside the laser crystal 210.

When the input beam passes through the laser crystal 210, atoms inside the laser crystal 210 are excited and radiated, and a beam having the same frequency, propagation direction, polarization state and phase as the input beam is generated, thereby realizing amplification of the input beam.

It will be appreciated that the input beam is amplified multiple times by having the input beam input into the laser crystal 210 in different input directions.

In some embodiments, the focusing lens group further comprises: a first lens 231 coupled to the pump transmission fiber 240 for receiving the excitation laser; and a second lens 232 coupled to the first lens 231 for collimating and focusing the excitation laser onto the laser crystal 210.

The excitation laser is focused by arranging the first lens 231 and the second lens 232, and is focused on the surface of the laser crystal 210. For example, the excitation laser is transmitted to the first lens 231 via the pump transmission fiber 240 to perform the initial excitation laser collimation adjustment, and transmitted to the second lens 232. The conditioned excitation laser light is transmitted to the surface of the laser crystal 210.

Referring also to FIG. 5, in some embodiments, a modified polarization return system 300 includes: a second thin film polarizer 320 coupled to the first faraday rotator 130 and the laser crystal 210 for selectively transmitting the light beam; the second Faraday rotator 330, coupled to the laser crystal 210, for changing the polarization state of the initial laser to obtain a first polarized light; a third mirror 340 coupled to the second faraday rotator 330 for reflecting the light beam passing through the second faraday rotator 330 to the second faraday rotator 330; and a fourth reflecting mirror 310 disposed opposite to the second thin film polarizer 320, for reflecting the light beam reflected by the second thin film polarizer 320. The second faraday rotator 330 adjusts the polarization state of incident light by an angle of 45 °.

The second thin film polarizer 320 is provided to separate the light beams in polarization, so as to prevent the first polarized light and the second polarized light from exiting. For example, the second thin film polarizer 320 allows only a light beam having a polarization state of P polarization to pass through, and reflects a light beam having a polarization state of S polarization.

The rotation angle of the second faraday rotator 330 with respect to the light beam in a single pass is 45 °, and the rotation angle of the light beam is 90 ° when the light beam passes back and forth through the second faraday rotator 330. For example, after the light beam having the polarization state of P polarization passes through the second faraday rotator 330 twice, the polarization state of the light beam is changed to S polarization. After the light beam having the polarization state of S polarization passes through the second faraday rotator 330 twice, the polarization state of the light beam is changed to P polarization.

Further, by disposing the third reflecting mirror 340 coupled to the second faraday rotator 330 to re-reflect the light beam outputted via the second faraday rotator 330 into the second faraday rotator 330, it is ensured that the P-polarized light beam is converted into the S-polarized light beam or the S-polarized light beam is converted into the P-polarized light beam.

Further, a fourth mirror 310 disposed opposite to the second thin film polarizer 320 is provided to re-couple the S-polarized beam reflected by the second thin film polarizer 320 into the laser amplifier 200, thereby achieving re-amplification of the beam.

In some embodiments, the polarization isolator 100 is further configured to transmit light having a polarization state of P-polarization and reflect light having a polarization state of S-polarization.

The seed laser 400 is damaged by disposing the polarization isolator 100 to selectively transmit the seed light and the beam amplified by the laser amplifier 200, so that the amplified third polarized light or the amplified fourth polarized light is focused on the surface of the seed laser 400.

The optical path of the above embodiment is further described below with reference to specific embodiments.

The seed laser 400 generates seed light, and the polarization isolator 100 selectively transmits the seed light having the polarization state of P polarization. The seed light is transmitted to the laser crystal 210 in which population inversion has been achieved in the laser amplifier 200, and laser amplification is performed.

After the seed light is projected through the laser crystal 210, the seed light is reflected by the surfaces of the first and second reflection mirrors 221 and 222 and transmitted into the laser crystal 210 again. The seed light passing through the laser crystal 210 twice is transmitted to the second faraday rotator 330, and the polarization angle is rotated by 45 ° with respect to before incidence. The seed light with the polarization angle rotated by 45 ° is transmitted to the surface of the third reflector 340 to be reflected and returned in the original path to pass through the laser crystal 210 again, and the polarization angle is rotated by 45 ° again. I.e. the polarization angle is rotated by 90 deg. with respect to the polarization angle before incidence, the originally P-polarized seed light is converted into S-polarized first polarized light.

The first polarized light passes through the laser crystal 210, the second reflecting mirror 222, and the first reflecting mirror 221 in sequence, and amplified second polarized light is obtained, and the second polarized light is transmitted to the surface of the second thin-film polarizer 320.

Since the second thin film polarizer 320 exhibits a reflective state for the S-polarized light beam, the second thin film polarizer 320 reflects the second polarized light to the fourth mirror 310. The fourth mirror 310 reflects the second polarized light and returns the second polarized light as it is.

The second polarized light sequentially passes through the laser crystal 210, the first reflector 221, the second reflector 222, the laser crystal 210, the second faraday rotator 330, the third reflector 340, the second faraday rotator 330, the laser crystal 210, the second reflector 222, the first reflector 221, and the laser crystal 210 to obtain third polarized light. Since the polarization state of the second polarized light passes through the second faraday rotator 330 twice and the second polarized light passes through the second faraday rotator 330 every time, the polarization state of the second polarized light is increased by 45 °, when the polarization state of the second polarized light is S-polarized, the polarization state of the third polarized light is P-polarized.

The second thin film polarizer 320 allows the P-polarized light beam to pass through, and the third polarized light with the polarization state of P passes through the first faraday rotator 130 and the first half wave plate 120 in sequence. Since the finally outputted fourth polarized light passes through the first faraday rotator 130 twice, the polarization state of the fourth polarized light becomes S-polarized and is reflected by the first thin film polarizer 110 to be emitted.

It is understood that P-polarization and S-polarization are relative to the optical axis of the thin film polarizer itself, i.e., P-polarization and S-polarization correspond to the optical axis of the second thin film polarizer 320 in the laser amplifier 200; the P-polarization and S-polarization within the polarization isolator 100 correspond to the optical axis of the first thin film polarizer 110. For example, the optical axes of the first thin-film polarizer 110 and the second thin-film polarizer 320 are arranged to form an included angle of 45 ° to ensure that the seed light passes through the second thin-film polarizer 320 after passing through the first faraday rotator 130, and the fourth polarized light obtained after the third polarized light passes through the first faraday rotator 130 for the second time is S-polarized with respect to the polarization state of the first thin-film polarizer 110, and then cannot pass through the first thin-film polarizer 110. And since the transmission optical axis of the seed light is obliquely arranged, the first thin-film polarizer 110 and the second thin-film polarizer 320 reflect the fourth polarized light, and the fourth polarized light is used as the final output light of the laser amplification system.

As can be seen from the above, in the process of amplifying the seed light into the third polarized light or the fourth polarized light, the light beam passes through the laser crystal 210 eight times in total, and undergoes eight times of gain amplification. The laser amplification system circularly amplifies the light beam in the laser amplifier 200 to a preset amplification degree by changing the polarization state of the light beam, and has the advantages of simple structure and high feasibility.

In some embodiments, multiple sets of mirrors are arranged to make the light beam travel back and forth in the laser crystal 210 multiple times, thereby increasing the number of amplification steps of the laser amplification system. For example, if the laser amplifier 200 has a four-pass structure, the actual number of amplification steps of the laser amplification system is 16.

The present application also provides an apparatus comprising the laser amplification system of any of the embodiments.

The embodiments of the present application have been described in detail with reference to the drawings, but the present application is not limited to the embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present application. Furthermore, the embodiments and features of the embodiments of the present application may be combined with each other without conflict.

Claims (10)

1. A laser amplification system, comprising:

a seed laser for providing seed light;

the polarization isolator is coupled with the seed laser and is used for selectively transmitting the seed light;

the laser amplifier is coupled with the polarization isolator and used for amplifying the seed light and obtaining initial laser;

the polarization-changing return system is coupled with the laser amplifier and used for changing the polarization state of the initial laser to obtain first polarized light; the polarization-changing return system is further used for returning the first polarized light to the laser amplifier for secondary amplification to obtain second polarized light;

the polarization-changing return system is further used for returning the second polarized light to the laser amplifier for secondary amplification and polarization state conversion to obtain third polarized light; the polarization isolator is also used for carrying out polarization conversion on the third polarized light and outputting fourth polarized light; the polarization states of the initial laser light and the third polarized light are the same, and the polarization states of the first polarized light, the second polarized light and the fourth polarized light are the same.

2. The laser amplification system of claim 1, wherein the polarization isolator comprises:

a first thin film polarizer for selectively transmitting the seed light or the fourth polarized light according to a polarization state;

the first quarter wave plate is used for adjusting the polarization state of the input light beam;

a first Faraday rotator to adjust a polarization plane of the input beam.

3. The laser amplification system of claim 2, wherein the laser amplifier comprises:

the laser crystal is used for amplifying the input light beam;

the first reflector is arranged opposite to the laser crystal and is used for reflecting the amplified initial laser;

and the second reflector is arranged opposite to the first reflector and is used for transmitting the initial laser to the laser crystal again for amplification.

4. The laser amplification system of claim 3, further comprising:

the semiconductor laser pump is used for providing excitation laser for pumping the laser crystal;

the pumping transmission optical fiber is coupled with the semiconductor laser pump and is used for transmitting the excitation laser;

the focusing lens group is coupled with the pumping transmission optical fiber and is used for collimating and focusing the excitation laser and obtaining a light spot approximate to flat top light;

wherein the light spot of the approximately flat top light is used for carrying out high-efficiency excitation on the laser crystal.

5. The laser magnification system of claim 4, wherein the focusing lens group further comprises:

the first lens is coupled with the pumping transmission optical fiber and used for receiving the excitation laser;

and the second lens is coupled with the first lens and used for collimating and focusing the excitation laser on the laser crystal.

6. The laser amplification system of claim 5, wherein the altered polarization return system comprises:

the second film polaroid is coupled with the first Faraday rotator and the laser crystal and is used for selectively transmitting light beams;

the second Faraday rotator is coupled with the laser crystal and used for changing the polarization state of the initial laser to obtain first polarized light;

the third reflector is coupled with the second Faraday rotator and used for reflecting the light beam passing through the second Faraday rotator into the second Faraday rotator again;

and the fourth reflector is arranged opposite to the second thin film polarizer and is used for reflecting the light beam reflected by the second thin film polarizer.

7. The laser amplification system of claim 6, wherein the polarization state of the initial laser light and the third polarized light is P-polarized, and the polarization state of the first polarized light, the second polarized light and the fourth polarized light is S-polarized.

8. The laser amplification system of claim 1 wherein the polarization isolator is further configured to transmit a P-polarized light beam and reflect an S-polarized light beam.

9. The laser amplification system of claim 6, wherein the second Faraday rotator adjusts the polarization state of incident light by an angle of 45 °.

10. Apparatus comprising a laser amplification system as claimed in any one of claims 1 to 9.

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