A solid-state dual-pass amplifier system based on anti-resonant hollow fiber

Abstract

This invention discloses a solid-state dual-pass amplification system based on antiresonant hollow fiber, belonging to the field of laser technology. It includes at least a laser seed source, fiber pre-amplification, a pulse selector, fiber main amplification, a rod-shaped crystal amplification unit, a hollow fiber transmission unit, and a compression unit. The laser seed source, after frequency down-conversion by the pulse selector and fiber amplification, outputs a repetitive signal light. The rod-shaped crystal amplification unit provides single-pass gain to the signal light. After single-pass amplification, the pulsed light enters the antiresonant hollow fiber for fundamental mode transmission. After transmission, the pulsed light re-enters the rod-shaped crystal amplification unit by changing its polarization, achieving high-efficiency amplification and high beam quality output. This invention effectively solves the problems of beam quality degradation and poor pointing stability of regenerative amplifiers in traditional dual-pass solid-state amplifiers. It features high energy utilization, good beam quality, and strong system stability, making it a simple, efficient, and practical small-signal solid-state amplification solution.

Description

Technical Field

[0001] This invention belongs to the field of laser technology and relates to a laser system that combines solid-state amplification with hollow fiber transmission. Background Technology

[0002] High-energy, high-peak-power, and high-beam-quality ultrashort pulse lasers have significant research value in high-end manufacturing processing and cutting, scientific research, and national defense. However, due to their low nonlinearity and damage thresholds, traditional fiber amplifiers struggle to support the amplification of high-energy, high-peak-power ultrashort pulses. While using large-mode-gain fibers can improve peak power output, larger core diameters lead to beam quality degradation. Therefore, fiber amplifiers are only suitable for small-signal output in ultrafast laser front-ends.

[0003] Laser crystal materials, with their high damage threshold and high nonlinear threshold, are ideal amplification media for high-energy, high-peak-power ultrashort pulses. Crystal amplifiers can be classified into rod, slab, and disk amplifiers based on their gain medium structure. Among them, rod crystals offer advantages such as uniform heat dissipation due to their circular symmetry structure, high system stability, and low cost. Furthermore, the use of excellent vacuum reflow soldering technology and heat sink packaging structure makes them highly suitable for high-energy laser amplification at medium to low average power levels.

[0004] Crystal amplifiers can be classified into traveling-wave amplifiers and regenerative amplifiers based on their structure. While traveling-wave amplifiers are simple in design, they suffer from low single-pass small-signal amplification efficiency and low pump energy utilization. They offer no significant advantage for directly amplifying low-power signals from fiber optic front-ends, often requiring multi-stage amplification modules to achieve higher power and higher energy ultrafast laser amplification. Although traditional dual-pass solid-state amplification can effectively improve small-signal amplification efficiency, this significantly degrades beam quality. Regenerative amplifiers, on the other hand, continuously extract energy from the gain medium by repeatedly circulating the signal light within the resonant cavity, ultimately controlling the polarization output. They possess both high energy utilization and excellent beam quality. However, their high system complexity, long signal path length, and poor anti-interference capability result in poor output beam pointing stability.

[0005] Therefore, to further improve the average power of the small-signal front-end, there is an urgent need for a high-stability, low-cost, and high-efficiency amplification scheme that can maintain excellent beam quality, so as to better connect with and bring out the performance of the subsequent high-power solid-state amplifier. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a solid-state dual-pass amplification system and scheme based on antiresonant hollow-core fiber, effectively improving the small-signal amplification efficiency of solid-state traveling wave amplification. Leveraging the unique light-guiding mechanism and single-mode, low-loss, and high damage threshold characteristics of hollow-core fiber, it aims to solve the problems of beam quality degradation in traditional rod-shaped crystal dual-pass amplifiers and poor pointing stability in regenerative amplifiers. Furthermore, in femtosecond laser amplification scenarios, this invention also provides a solution to the problem of spectral narrowing associated with high-gain solid-state amplifiers by utilizing the self-phase modulation effect in gas-filled antiresonant hollow-core fiber.

[0007] To achieve the above objectives, the present invention adopts the following technical approach:

[0008] A solid-state dual-pass amplification system based on anti-resonant hollow fiber includes a laser seed source, a first fiber pre-amplifier, a pulse selector, a second fiber pre-amplifier, a fiber main amplifier, a rod-shaped crystal amplification unit, a hollow fiber transmission unit, and a compression unit, suitable for high peak power and high energy laser applications.

[0009] The laser seed source is a nine-cavity mode-locked seed source, which supports femtosecond output after compression. The femtosecond seed source will introduce an additional stretcher to stretch the pulse width to hundreds of picoseconds.

[0010] The laser seed source may include, but is not limited to, narrow linewidth picosecond seed sources and single-frequency nanosecond seed sources, all of which can be adapted to the entire system;

[0011] The first and second fiber pre-amplifications are used to initially increase the average laser power.

[0012] The pulse selector is used to down-frequency the laser seed source in order to increase the energy of the amplified single pulse.

[0013] In the optical fiber main amplification, in one embodiment the core-cladding ratio of the gain fiber is 20 / 130 μm. Optimizing the fiber winding method can achieve high-order mode filtering and nonlinear threshold enhancement, and the output beam quality factor is close to the diffraction limit under small-signal operating conditions. The above unit belongs to the optical fiber front end.

[0014] Furthermore, the pulse first enters the rod-shaped crystal amplification unit, and its propagation path is as follows: the optical fiber front end can output collimated linearly polarized light, which passes through an optical isolator, is polarized by the first λ / 2 waveplate, is reflected by the first thin-film polarizer, is focused by the first lens, is reflected by the first dichroic mirror and introduced into the laser gain module, is reflected by the second dichroic mirror, is polarized by the second λ / 2 waveplate, and is collimated by the second lens;

[0015] Furthermore, after a single amplification, the pulse enters the hollow fiber transmission unit. The pulse double-pass amplification propagation path is as follows: after being reflected by the second thin-film polarizer, focused by the third lens, and entering the coupling device, the pulse is transmitted in the anti-resonant hollow fiber and output by the output device. After being focused by the fourth lens, the polarization state is adjusted by the third λ / 2 waveplate, and the pulse is transmitted through the first thin-film polarizer. The pulse then enters the rod-shaped crystal amplification unit for the second time, thus forming a double-pass amplification.

[0016] Furthermore, the single pulse is transmitted and output through a second thin-film polarizer;

[0017] Furthermore, the Yb:YAG laser gain module in the rod-shaped crystal amplification unit uses a vacuum reflow welding process to tightly bond the crystal to the metal heat sink, resulting in a low void ratio and good heat dissipation performance. This allows for high beam quality to be maintained during single-pass amplification under high-power output conditions of the pump source.

[0018] Furthermore, the pump source is an optical fiber coupled output semiconductor laser, which is collimated and focused by the lens group in the sleeve and then passes through the first dichroic mirror, with the pump beam waist extending into the laser gain module.

[0019] Furthermore, the anti-resonant hollow fiber in the hollow fiber transmission unit has single-mode, low-loss, and flexible transmission characteristics. It has high loss for higher-order modes, which can suppress the generation of higher-order modes during amplification. The system improves the small-signal amplification efficiency while achieving high beam quality output.

[0020] A further technical feature of the present invention is that the anti-resonant hollow fiber is filled with argon gas, and the hollow fiber after end face cutting is placed in a ceramic ferrule. A YAG or quartz sheet coated with a signal anti-reflection film is used as an end cap for sealing. The filling of single-atom gas molecules avoids the Raman effect under high peak power conditions and can ensure transmission efficiency.

[0021] Furthermore, the hollow fiber transmission unit includes a coupling device, wherein the ceramic ferrule can be mechanically fixed on a multi-dimensional adjustment frame, which has the characteristics of high coupling stability.

[0022] A further technical feature of this invention is that, in the femtosecond seed source scenario, by controlling the length of the hollow fiber used, the laser is confined over a long distance in a fiber core with a core diameter of tens of micrometers, increasing the interaction intensity between the laser and the fiber core gas, generating a self-phase modulation effect, offsetting the gain narrowing during crystal amplification, and ensuring that the output pulse can be compressed to a narrower pulse width; in the narrow linewidth picosecond or single-frequency nanosecond seed source scenario, by controlling the length of the hollow fiber used, the laser is transmitted over a short distance to suppress nonlinearity and ensure spectral quality.

[0023] Furthermore, the dual-pass amplifier can be extended into a multi-pass amplifier. A Pockel cell is introduced into the rod-shaped crystal amplification unit to form an optoelectronic switch. Synchronized with the trigger signal of the pulse selector, it controls whether a half-wave voltage is applied to the electro-optic crystal to control whether the polarization direction changes, thereby controlling whether a single pulse enters the hollow-core fiber transmission unit or is directly output. The anti-resonant hollow-core fiber can be used as part of the transmission and delay in the multi-pass amplifier. Most of the pulse light is transmitted in the fiber, resulting in a short spatial optical path and good beam pointing stability. Compared with the traditional regenerative amplifier spatial resonant cavity structure, it has a simpler and more stable design.

[0024] Furthermore, in the multi-pass amplifier, the anti-resonant hollow fiber has a delay effect. When the length is >3Nm, the time for one pulse cycle will be >10N ns. Therefore, the pulse timing configuration will be more flexible, and there are no strict requirements on the high voltage rise time of the Pockel cell.

[0025] Furthermore, in the femtosecond seed source scenario, the compression unit is used to compress the energy-amplified broadened chirped pulse to the femtosecond level, and the transmission diffraction grating provides negative dispersion; in the picosecond or nanosecond seed source scenario, there is no compression unit, and the system can be applied to nonlinear frequency conversion.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] On one hand, this invention provides a dual-pass amplifier that combines traveling-wave amplification with anti-resonant hollow fiber transmission. After single-pass pulse amplification, the signal is coupled into the hollow fiber for transmission. Leveraging its excellent single-mode transmission characteristics, the beam quality can be optimized. After flexible transmission, the signal re-enters the gain module for amplification, further extracting pump energy. Compared to traditional dual-pass amplifiers, this effectively improves small-signal amplification efficiency while maintaining high beam quality. Secondly, filling the hollow fiber with rare gas can also serve as a nonlinear medium. The fiber transmission length can be flexibly changed to alter the accumulation of self-phase modulation effects, achieving narrower gain suppression and ensuring a narrower pulse width in the CPA system.

[0028] On the other hand, this invention enables multi-pass amplification. Compared to traditional regenerative amplifiers, this invention simplifies the resonant cavity structure of the regenerative amplifier. Most of the pulse cycle propagates within the hollow-core fiber, eliminating the need for resonant cavity design to ensure laser mode matching. Therefore, compared to spatial resonant cavities, it improves system stability, compactness, and resistance to environmental interference. In addition to serving as a transmission fiber, the anti-resonant hollow-core fiber also provides a delay function. By controlling the fiber length, the single-pulse cycle time can be flexibly increased, thus eliminating concerns about the limitations of the Pockels cell switching speed on the regenerative amplifier. This delay characteristic also enables multi-pass amplification of pulse train modes, allowing for better compatibility with existing ultrafast laser processing technologies.

[0029] Finally, the system has a simple structure and low cost, making it an effective solution for connecting small-signal front-ends and high-power solid-state amplifiers. Attached Figure Description

[0030] Figure 1 This is a flowchart of the solid-state dual-pass amplification system based on anti-resonant hollow optical fiber of the present invention;

[0031] Figure 2 This is a schematic diagram of the structure of the rod-shaped crystal amplification unit and the hollow fiber transmission unit in the embodiment of the dual-pass amplifier of the present invention;

[0032] Figure 2 Figure label:

[0033] 1. Fiber optic front end; 2. Optical isolator; 3. First λ / 2 waveplate; 4. First thin-film polarizer; 5. First dichroic mirror; 6. Laser gain module; 7. Second dichroic mirror; 8. Second λ / 2 waveplate; 9. Second lens; 10. Second thin-film polarizer; 11. Third lens; 12. Coupling device; 13. Anti-resonant hollow fiber; 14. Output device; 15. Fourth lens; 16. Third thin-film polarizer; 17. Sleeve; 18. Pump source; 19. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] The technical means of this invention is fiber front-end + solid-state amplification, and the applicable light source types include at least femtosecond, narrow linewidth picosecond and single-frequency nanosecond lasers.

[0036] Please see Figure 1 , Figure 1 This is a flowchart of the solid-state dual-pass amplification system based on anti-resonant hollow fiber of the present invention, including a laser seed source, a first fiber pre-amplifier, a pulse selector, a second fiber pre-amplifier, a fiber main amplifier, a rod-shaped crystal amplification unit, a hollow fiber transmission unit, and a compression unit. A dual-pass amplifier embodiment is defined as the pulse cycling once between the rod-shaped crystal amplification unit and the hollow fiber transmission unit; a multi-pass amplifier embodiment is defined as the pulse cycling multiple times between the rod-shaped crystal amplification unit and the hollow fiber transmission unit.

[0037] Please see Figure 2 , Figure 2The fiber optic front-end 1 includes a laser seed source, a first fiber pre-amplifier, a pulse selector, a second fiber pre-amplifier, and a fiber main amplifier. The repetition frequency is adjusted via the pulse selector to meet different repetition frequencies ranging from tens to hundreds of kHz. Taking a 20 / 130 μm gain fiber as an example in the fiber main amplifier, the peak power nonlinear threshold for maintaining signal spectral fidelity is at most twenty kilowatts, corresponding to an average output signal power of at most hundreds of milliwatts, and the output pulse is a small signal. By applying the dual-pass amplifier embodiment or multi-pass amplifier embodiment of this invention, signal light with an average power of at most fifty watts and a beam quality factor of less than 1.1 can be obtained.

[0038] In the dual-pass amplifier embodiment:

[0039] Please refer to the main text. Figure 2 , Figure 2 This is a diagram of the rod-shaped crystal amplification unit and the hollow-core fiber transmission unit in the embodiment of the dual-pass amplifier of the present invention. According to the signal light transmission path, it includes, in sequence, an optical fiber front end 1, an optical isolator 2, a first λ / 2 waveplate 3, a first thin-film polarizer 4, a first lens 5, a first dichroic mirror 6, a laser gain module 7, a second dichroic mirror 8, a second λ / 2 waveplate 9, a second lens 10, a second thin-film polarizer 11, a third lens 12, a coupling device 13, an anti-resonant hollow-core fiber 14, an output device 15, a fourth lens 16, and a third thin-film polarizer 17; according to the pump light transmission path, it includes, in sequence, a pump source 19 and a sleeve 18.

[0040] The collimated linearly polarized laser emitted from the fiber front end 1 first passes through the optical isolator 2, which reflects the light back to avoid damage to the main amplification end face and gain fiber of the fiber.

[0041] Rotating the angle of the first λ / 2 waveplate 3 adjusts the polarization state of the signal to s-polarization. The first pulse is reflected at the first thin-film polarizer 4, and the first lens 5 focuses the signal and then diverges it. The first dichroic mirror 6 is coated with high reflectivity for the signal light band and high transmittance for the pump light band, which can combine the signal light and the pump light. After being reflected by the first dichroic mirror 6, the signal light enters the laser gain module 7. The focal point of the signal is located in front of the crystal end face, and the signal spot enters the crystal in a divergent state to match the magnified focusing thermal lens and avoid spot mismatch under high-power pumping conditions. The signal beam quality factor is close to 1.0, which can maintain a relatively long Rayleigh distance. The signal spot size is controlled at around 400 μm, and the divergence variation within the crystal is at most 50 μm.

[0042] The laser gain module 7 uses a Yb:YAG rod-shaped crystal as an example, with a size of 1×40mm and a doping concentration of 1 at.%. The thin rod is beneficial for improving small-signal amplification efficiency, and the low doping concentration reduces thermal load. A metallized film is deposited on the crystal side to provide a waveguide for pumping. The pump source 19 uses a 940nm fiber-optic semiconductor laser as an example, with a maximum output power of 200W, an output core diameter of 135μm, and an NA of 0.22. The output pump light is directly focused by a lens in the sleeve 18, passes through the first dichroic mirror 6, and enters the laser gain module 7. The pump focus enters the interior of the crystal, and the spot size at the pump focus is controlled to be around 500μm. High pump brightness can improve gain. The pump beam has a large quality factor; unabsorbed pump light diverges rapidly within the crystal, reaches the crystal sidewalls, and is reflected by the side metal film, forming a waveguide structure.

[0043] The position of the signal light is adjusted by adjusting the first thin-film polarizer 4 and the first dichroic mirror 6; the sleeve 18 is fixed on the four-dimensional adjustment frame, and the position of the pump light is adjusted by adjusting the four-dimensional adjustment frame. The signal light and the pump light are adjusted to the center of the rod crystal and are concentric. The two light spots are observed to be concentric at the front end of the laser gain module 7 and at the rear end of the laser gain module 7. At this time, the signal and pump light spots are concentric.

[0044] The second dichroic mirror 8 splits the signal light and pump light beams, reflecting the signal light and transmitting the pump light.

[0045] After the linearly polarized signal light passes through the crystal in the pump state, its polarization direction will change. Rotating the angle of the second λ / 2 waveplate 9 will adjust the polarization state of the signal to s-polarization. The signal will be reflected at the second thin-film polarizer 11. At this time, the first pulse after single-pass amplification enters the hollow fiber transmission unit.

[0046] Before a single pulse enters the coupling device 13, the beam needs to be matched with the anti-resonant hollow fiber mode field and NA, which can be achieved by only the second lens 10 and the third lens 12, according to the relationship... The size of the collimated beam and the focal length of the focusing lens can be determined, where f is the focal length of the third lens 12, d is the collimated beam size, MFD is the fiber mode field diameter, and λ is the signal wavelength. When the signal beam passes through a crystal with an equivalent thermal lens, it is first focused and then diverged. Subsequently, by flexibly changing the focal length and position of the second lens 10 (collimating lens), the signal beam can be collimated to any preset size d, and then focused again by the third lens 12 with a preset focal length before entering the coupling device 13, achieving high-efficiency coupling. The single pulse is transmitted in the anti-resonant hollow fiber 14. Unlike conventional coupling systems, this invention does not require additional beam expanders or shrinkers for matching the hollow fiber mode field and NA.

[0047] The anti-resonant hollow fiber 14 is filled with argon gas using an air pump. The hollow fiber, after being cut at the end face, is placed inside a ceramic ferrule and sealed with a YAG or quartz sheet coated with a signal anti-reflection film as an end cap. The filling with single-atom gas molecules avoids the Raman effect under high peak power conditions, ensuring transmission efficiency. The ceramic ferrule is fixed by a V-shaped clamp and then fixed on a multi-dimensional adjustment frame to achieve the fixation and precise adjustment of the coupling end and output end of the hollow fiber, which has the characteristics of high coupling stability.

[0048] In femtosecond seed source scenarios, controlling the length of the hollow fiber allows for long-distance confinement of the laser within a core with a diameter of tens of micrometers. This increases the interaction intensity between the laser and the core gas, generating a self-phase modulation effect that counteracts the gain narrowing during crystal amplification, ensuring that the output pulse can be compressed to a narrower pulse width. In narrow-linewidth picosecond or single-frequency nanosecond seed source scenarios, controlling the length of the hollow fiber allows for short-distance laser transmission to suppress nonlinearity and ensure spectral quality.

[0049] After single-pulse transmission, the signal is output by output device 15. The fourth lens 16 collimates the signal spot, and the size of the collimated spot is the same as the size of the collimated spot emitted by the fiber front end 1. The polarization direction of the transmitted signal will change. Rotating the angle of the third λ / 2 waveplate 17 adjusts the polarization state of the transmitted signal to p-polarization (perpendicular to the polarization direction of the first pass amplification). At this time, the signal will pass through the first thin-film polarizer 4, and the first pulse re-enters the rod crystal amplification unit. The single pulse after the second amplification passes through the second λ / 2 waveplate 9, which adjusts the polarization direction to p-polarization. The pulse will pass through the second thin-film polarizer 11 and be output, realizing dual-pass amplification.

[0050] Anti-resonant hollow fiber has a delay effect, which can increase the time interval between two amplifications of a pulse. Before the second amplification, the inverted particle number of the crystal gain medium can be recovered, which is different from the traditional double-pass amplifier and has a higher energy extraction efficiency.

[0051] In a specific implementation case, the experiment shows that when the fiber front end 1 is an injection signal with an average power of 1W and a repetition frequency of 100kHz, the double-pass amplifier of the present invention can output an average power of 18W when the pump power is 180W, and an average power of 45W when the double-pass amplifier can output, while keeping the beam quality factor within 1.1.

[0052] In a multi-pass amplifier embodiment:

[0053] To accommodate lower injection energy and repetition frequency front-ends, multi-pass amplifiers have been extended.

[0054] Please refer to the main text. Figure 2The pulse cyclic amplification process is consistent with that of a two-pass amplifier, and the two-pass amplifier embodiment can be referred to. A Pockel cell is inserted between the first thin-film polarizer 4 and the first dichroic mirror 6, and is triggered synchronously with the signal of the pulse selector. When the single pulse first enters the rod crystal amplification unit, no half-wave voltage is applied to the Pockel cell, and the signal polarization state is s-polarized. After passing through the hollow fiber transmission unit, it passes through the first thin-film polarizer 4, and the signal polarization state is p-polarized. After the pulse passes through the Pockel cell for the first time and before it passes through the Pockel cell for the second time, a half-wave voltage is applied to change the signal polarization state from p-polarized to s-polarized. The s-polarized single pulse is amplified for the second time and is reflected at the second thin-film polarizer 11 before entering the hollow fiber transmission unit for the second time. When the single pulse is amplified for the Nth time, the half-wave voltage is removed after the pulse passes through the Pockel cell for the Nth time and before it passes through the Pockel cell for the N+1th time. The signal light will continue to maintain the p-polarized state after the N+1th amplification. Finally, the pulse will be transmitted and output at the second thin-film polarizer 11, realizing multi-pass amplification.

[0055] Due to the delay effect of the anti-resonant hollow fiber, the time between two passes of a single pulse through the Pockel cell can be increased, and there are no strict requirements on the high voltage rise time of the Pockel cell. Furthermore, the pulse cycling system of this invention is not a traditional resonant cavity, eliminating the need for cavity mode design to ensure laser mode matching. The fundamental mode transmission advantage based on the hollow fiber also maintains high beam quality. This invention differs from traditional regenerative amplifiers with spatial resonant cavities, featuring a simple system structure, flexible pulse cycling timing settings, and strong beam pointing stability.

Claims

1. A solid-state dual-pass amplifier system based on anti-resonant hollow fiber, characterized in that, include: Laser seed source, first fiber pre-amplifier, pulse selector, second fiber pre-amplifier, fiber main amplifier, rod crystal amplifier unit, hollow fiber transmission unit and compression unit; The laser seed source is a nine-cavity mode-locked seed source, which supports femtosecond output after compression. The femtosecond seed source will introduce an additional stretcher to stretch the pulse width to hundreds of picoseconds. The laser seed source includes a narrow linewidth picosecond seed source and a single-frequency nanosecond seed source, which can be adapted to the entire system; The first and second fiber pre-amplifications are used to initially increase the average laser power. The pulse selector is used to down-frequency the laser seed source in order to increase the energy of the amplified single pulse. The fiber main amplification optimizes the gain fiber winding method to achieve high-order mode filtering and nonlinear threshold enhancement, and the output beam quality factor is close to the diffraction limit under small signal operating conditions. The rod-shaped crystal amplification unit includes at least an optical isolator, a λ / 2 waveplate, a thin-film polarizer, a lens, a sleeve, a dichroic mirror, a laser gain module, and a pump source. The hollow-core optical fiber transmission unit includes a highly stable coupling device and an output device, wherein the anti-resonant hollow-core optical fiber has the characteristics of single-mode, low loss, and flexible transmission, and serves as both a transmission and a delay device. The compression unit is used to compress the energy-amplified broadened chirped pulse to the femtosecond level, and the transmission diffraction grating provides negative dispersion.

2. The solid-state dual-pass amplification system based on anti-resonant hollow fiber according to claim 1, characterized in that, The pulse first enters the rod crystal amplification unit, and its propagation path is as follows: the fiber front end (1) can output collimated linearly polarized light, which passes through the optical isolator (2), the polarization state is adjusted by the first λ / 2 waveplate (3), is reflected by the first thin film polarizer (4), is focused by the first lens (5), is reflected by the first dichroic mirror (6) and introduced into the laser gain module (7), is reflected by the second dichroic mirror (8), the polarization state is adjusted by the second λ / 2 waveplate (9), and is collimated by the second lens (10); The pump source (19) is a fiber-coupled output semiconductor laser. It is collimated and focused by the lens group in the sleeve (18), and passes through the first dichroic mirror (6). The pump beam waist is located deep into the laser gain module (7). After a single amplification, the pulse enters the hollow fiber transmission unit. The pulse double-pass amplification propagation path is as follows: after being reflected by the second thin-film polarizer (11), it is focused by the third lens (12) and enters the coupling device (13). The pulse is transmitted in the anti-resonant hollow fiber (14) and output by the output device (15). After being focused by the fourth lens (16), the polarization state is adjusted by the third λ / 2 waveplate (17). After being transmitted through the first thin-film polarizer (4), the pulse enters the rod crystal amplification unit for the second time, thus forming a double-pass amplification. In the dual-pass amplification system, the pulse is transmitted into the first thin-film polarizer (4) and transmitted out through the second thin-film polarizer (11).

3. The solid-state dual-pass amplification system based on anti-resonant hollow fiber according to claim 1, characterized in that, The rod-shaped crystal amplification unit includes a Yb:YAG laser gain module (7), which uses, but is not limited to, a Yb:YAG crystal; the crystal is tightly bonded to the metal heat sink using a vacuum reflow soldering process.

4. The solid-state dual-pass amplification system based on anti-resonant hollow fiber according to claim 1, characterized in that, The anti-resonant hollow fiber (14) in the hollow fiber transmission unit has single-mode transmission characteristics and high loss for higher-order modes, suppressing the generation of higher-order modes during amplification; the selected single pulse is confined in the rod crystal amplification unit and the hollow transmission unit to realize single-pulse dual-pass amplification or forward cyclic multi-pass amplification; while improving the small signal amplification efficiency, high beam quality output is achieved.

5. The solid-state dual-pass amplification system based on anti-resonant hollow fiber according to claim 1, characterized in that, The anti-resonant hollow fiber (14) is filled with argon gas. The hollow fiber after end face cutting is placed in a ceramic ferrule and sealed with YAG or quartz sheet coated with signal anti-reflection film as end cap. The filling of single-atom gas molecules avoids the Raman effect under high peak power conditions and ensures transmission efficiency. The hollow fiber transmission unit includes a coupling device (13), wherein the ceramic ferrule is mechanically fixed on a multi-dimensional adjustment frame, which has the characteristics of high coupling stability.

6. The solid-state dual-pass amplification system based on anti-resonant hollow fiber according to claim 1, characterized in that, In femtosecond seed source scenarios, controlling the length of the hollow fiber increases the interaction intensity between the laser and the fiber core gas by confining the laser over a long distance in a fiber core with a core diameter of tens of micrometers. This generates a self-phase modulation effect, which counteracts the gain narrowing during crystal amplification and ensures that the output pulse is compressed to a narrower pulse width. In narrow-linewidth picosecond or single-frequency nanosecond seed source scenarios, controlling the length of the hollow fiber allows for short-distance laser transmission to suppress nonlinearity and ensure spectral quality.

7. The solid-state dual-pass amplification system based on anti-resonant hollow fiber according to claim 1, characterized in that, The dual-pass amplifier can be extended into a multi-pass amplifier. A Pockel cell is introduced into the rod crystal amplification unit to form an optoelectronic switch. It is synchronized with the trigger signal of the pulse selector and controls whether the electro-optic crystal applies a half-wave voltage to control whether the polarization direction changes, thereby controlling whether a single pulse enters the hollow fiber transmission unit or is directly output. Among them, the anti-resonant hollow fiber (14) is part of the transmission and delay in the multi-pass amplifier, and most of the pulse light is transmitted in the fiber.

8. The multi-pass amplifier according to claim 7, characterized in that, The anti-resonant hollow fiber (14) has a delay effect. When the length is >3N m, the time for one pulse cycle will be >10N ns.

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