A high average power femtosecond laser device based on yb:calgo laser crystal

Abstract

A high-average-power femtosecond laser device based on a Yb:CALGO laser crystal is disclosed. The device, along its optical path, comprises: a seed source module, a pulse stretcher module, a regenerative amplifier module, a traveling-wave amplifier module, and a pulse compressor module. This invention, based on the aforementioned system, achieves an average power in the 200W range using a Yb:CALGO laser crystal for the first time, while maintaining a pulse width of less than 200 fs. Compared to previous laser devices constructed using this crystal, the average power is significantly improved. This system can achieve high-average-power femtosecond laser output while maintaining excellent beam quality and pulse characteristics, making it valuable for applications in precision machining, scientific research, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of femtosecond laser technology, and particularly relates to a high average power femtosecond laser device based on Yb:CALGO laser crystal. Background Technology Ultrafast lasers, especially femtosecond lasers, with their extremely short pulse widths and extremely high peak power, have demonstrated irreplaceable advantages in fields such as precision micromachining, ultrafast spectroscopy, medical surgery, and basic scientific research. Among them, high-average-power femtosecond laser sources can significantly improve processing efficiency and detection signal-to-noise ratio, and are one of the core directions of current laser technology development.

[0002] All-solid-state femtosecond lasers based on ytterbium-doped (Yb) gain media have become the mainstream technology for achieving high average power femtosecond laser output due to their emission band being located in the near-infrared region safe for the human eye, high quantum efficiency, and ease of diode pumping. A typical system architecture usually employs chirped pulse amplification (CPA) technology: first, a femtosecond seed pulse is generated by an oscillator; then, the pulse time domain is broadened by a stretcher to reduce peak power; next, the energy is boosted through multiple stages of amplification (typically including a regenerative amplifier and a subsequent traveling-wave amplifier); finally, a compressor recompresses the amplified pulse to the femtosecond level.

[0003] In this technical approach, the choice of gain medium is crucial, directly determining the system's power scaling capability, thermal management performance, and the beam quality and temporal characteristics of the final output pulse. Currently, commonly used Yb-based crystals such as Yb:YAG and Yb:KYW face bottlenecks in power enhancement. For example, while Yb:YAG crystals have high thermal conductivity, their emission bandwidth is narrow (approximately 9 nm), severely limiting the femtosecond pulse widths they can support, typically making it difficult to obtain pulses below 500 fs. Although Yb:KYW and other crystals have wider emission bandwidths, their relatively low thermal conductivity results in significant thermal lensing effects at high pump power, severely restricting further increases in average power and the maintenance of beam quality.

[0004] In recent years, ytterbium-doped calcium gallium vanadium garnet (Yb:CALGO) crystals have attracted much attention as a novel laser gain medium. Its excellent properties, combining wide emission bandwidth and high thermal conductivity, make it an ideal material for achieving high average power and short pulse width output. However, how to fully utilize the material advantages of Yb:CALGO crystals to construct stable and efficient high-power femtosecond laser amplification systems remains a pressing technical challenge for the industry. Existing reports show that the average output power of Yb:CALGO-based femtosecond laser amplifiers is mostly limited to hundreds of watts or less; for higher average powers, such as those in the 200W range, a stable and reliable solution is still lacking.

[0005] Therefore, it is necessary to develop a laser device that can fully utilize the wide bandwidth and high thermal conductivity of Yb:CALGO crystal to achieve stable output of short pulses with a high average power of over 200 watts and a range of hundreds of femtoseconds, in order to meet the urgent need for high-performance light sources in high-end industrial processing and cutting-edge scientific research. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing high-average-power femtosecond laser systems in achieving a balance between average power, pulse width, and beam quality, and to provide a high-average-power femtosecond laser device based on Yb:CALGO laser crystal. This laser, through an innovative beam-splitting pumped multi-stage amplification architecture and a specific crystal orientation design, aims to fully utilize the material advantages of Yb:CALGO crystal—its wide emission bandwidth and high thermal conductivity—to achieve stable femtosecond laser output with an average power of up to 200 watts and a pulse width below 200 fs, while maintaining excellent beam quality.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A high average power femtosecond laser device based on Yb:CALGO laser crystal is characterized in that it comprises, in sequence along the optical path: a seed source, a pulse stretcher module, a regenerative amplifier module, a traveling wave amplifier module, and a pulse compressor module; wherein the regenerative amplifier module and the traveling wave amplifier module both use Yb:CALGO crystal as the gain medium.

[0008] Furthermore, the seed source is a broadband femtosecond pulse source, whose output spectrum covers the gain bandwidth of the Yb:CALGO crystal.

[0009] Furthermore, the seed source is selected from any of the following: a ytterbium-doped fiber mode-locked pulsed laser, a mode-locked solid-state laser based on a semiconductor saturable absorber mirror, or a solid-state laser based on a Kerr lens mode-locking.

[0010] Furthermore, the pulse stretcher module includes a first optical isolation system, a Martinez-type spatial stretcher, a first half-wave plate, a first mirror, a first thin-film polarizer, and a second optical isolation system arranged sequentially along the optical path; the first optical isolation system is configured to make the forward-passing beam vertically polarized; the Martinez-type spatial stretcher is used to stretch the temporal width of the seed pulse to the order of hundreds of picoseconds; the first half-wave plate is used to convert the polarization state of the stretched beam into horizontal polarization; and the second optical isolation system is configured to make the forward-passing beam horizontally polarized.

[0011] Furthermore, the regenerative amplifier module includes a regenerative cavity and a regenerative pump module; The regeneration cavity includes, in sequence along the optical path, a second thin-film polarizer, a quarter-wave plate, an electro-optic crystal, a first plane mirror, a third thin-film polarizer, a first concave mirror, a first dichroic mirror, a laser crystal, a second dichroic mirror, a second concave mirror, and a second plane mirror; The regenerative pump module includes a pump source and a beam splitter for splitting the pump beam into a first pump beam and a second pump beam, wherein the first pump beam and the second pump beam are respectively focused onto a laser crystal within the regenerative cavity.

[0012] Furthermore, the electro-optic crystal controls the introduction, amplification, and extraction of the seed pulse in the regeneration cavity by applying or removing a quarter-wave voltage.

[0013] Furthermore, the laser crystal in the regenerative amplifier module is a Yb:CALGO crystal with an a-cut shape, and its a-axis is parallel to the polarization direction of the seed light, while its c-axis is parallel to the polarization direction of the pump light.

[0014] Furthermore, the regenerative amplifier module contains two laser crystals, and the beam splitting device is a polarizing beam splitter prism.

[0015] Furthermore, the traveling-wave amplification module includes four stages of traveling-wave amplification arranged sequentially along the optical path; each stage of traveling-wave amplification includes at least two dichroic mirrors and one Yb:CALGO laser crystal; the traveling-wave amplification module also includes two pump sources, the output beam of each pump source is split into two pump beams by a corresponding beam splitter, forming a total of four pump beams, which are respectively guided and focused onto the four Yb:CALGO laser crystals corresponding to the four stages of traveling-wave amplification.

[0016] Furthermore, the Yb:CALGO laser crystal in the traveling wave amplification module has an a-cut shape, with its a-axis parallel to the polarization direction of the seed light and its c-axis parallel to the polarization direction of the pump light.

[0017] Furthermore, the beam splitting device in the traveling wave amplification module is a polarizing beam splitter prism.

[0018] Furthermore, the pulse compressor module is a pair of parallel diffraction gratings.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. Excellent pulse width and spectral fidelity: By using a broadband femtosecond seed source (such as a ytterbium-doped fiber mode-locked laser) and making full use of the emission spectral characteristics of Yb:CALGO crystals with a width of tens of nanometers, combined with fine dispersion compensation and spectral management throughout the entire chain, ultrashort pulses with a pulse width of less than 200 fs can be obtained with good spectral quality and support for high compression efficiency.

[0020] 2. Excellent beam quality and system stability: The innovative beam-splitting pump design optimizes heat distribution. Combined with the specific orientation design of the crystal tangent (a-cut, a-axis / / seed polarization, c-axis / / pump polarization) in the regenerative amplifier, the thermal lensing effect is greatly suppressed, ensuring that the laser maintains near-diffraction-limited beam quality even at high power operation. The combined architecture of regenerative pre-amplification and multi-stage traveling-wave main amplifier ensures that the system has a high amplification signal-to-noise ratio, good energy extraction efficiency, and long-term operational stability.

[0021] 3. Flexible and highly scalable architecture: The proposed technical solution provides a modular and highly scalable technical path. The selection of seed sources is flexible, and the number of stages of traveling wave amplification can be optimized and adjusted according to the target power, laying a solid technical foundation for the development of femtosecond laser sources with higher average power. It has important application value in high-end industrial precision processing (such as glass cutting and surface treatment) and ultrafast scientific research (such as attosecond physics and time-resolved spectroscopy). Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a high average power femtosecond laser device using Yb:CALGO crystal according to an embodiment of the present invention.

[0023] Figure 2 This is a graph showing the change in output power of the regenerative amplifier as a function of pump power in an embodiment of the present invention.

[0024] Figure 3 This is a graph showing the output power of the first two stages of the traveling wave amplifier in this embodiment of the invention as a function of pump power.

[0025] Figure 4 This is a graph showing the output power of the last two traveling wave amplifier stages as a function of pump power in an embodiment of the present invention.

[0026] Figure 5 This is a diagram showing the pulse compression result of an embodiment of the present invention.

[0027] Figure 6 The output beam quality M in this embodiment of the invention 2 Factor measurement results graph.

[0028] In the picture: Detailed Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] This embodiment provides a high average power femtosecond laser device based on a Yb:CALGO laser crystal, the schematic diagram of which is shown below. Figure 1 As shown. Along the optical path, it includes: seed source 1, pulse stretcher module (corresponding to components 2-7 in the figure), regenerative amplifier module (corresponding to components 8-29 in the figure), traveling wave amplifier module (corresponding to components 30-64 in the figure), and pulse compressor module 65.

[0030] The specific structure, connection relationship and working principle of each module are explained in detail below.

[0031] 1. Seed source and pulse stretcher module: In this embodiment, seed source 1 is a ytterbium-doped fiber mode-locked oscillator with a center wavelength of 1034.4 nm, which outputs a femtosecond seed pulse with a pulse width of 3 ps and an average power of 108 mW. This seed pulse first enters the pulse stretcher module.

[0032] Specifically, the pulse stretcher module includes, in sequence along the optical path: a first optical isolation system 2, a Martinez-type spatial stretcher 3, a first half-wave plate 4, a first reflector 5, a first thin-film polarizer 6, and a second optical isolation system 7.

[0033] The first optical isolation system 2 functions to isolate the reflected light from subsequent optical paths and protect the seed source. It is configured to vertically polarize the seed beam passing in the forward direction.

[0034] The Martinez-type spatial stretcher 3 is used to stretch the temporal width of the seed pulse to approximately 600 picoseconds to effectively reduce peak power and avoid damage to optical components during subsequent amplification.

[0035] The first half-wave plate 4 is used to rotate the polarization direction of the broadened beam. Since the output of the first isolation system is vertically polarized, the first half-wave plate 4 converts the beam polarization state to horizontal polarization.

[0036] The second optical isolation system 7 is configured to horizontally polarize the forward beam, and its output is a broadened horizontally polarized seed pulse, which is then fed into the subsequent regenerative amplifier module. The second isolation system also serves a protective function, preventing backlighting from the regenerative amplifier from affecting the front end.

[0037] 2. Regenerative Amplifier Module: Used to pre-amplify the broadened seed pulse, consisting of a regeneration chamber and a regeneration pump module.

[0038] The regenerating cavity is a linear standing wave cavity, and its closed optical path is constructed sequentially along the optical path by the following components: a second thin-film polarizer 8, a quarter-wave plate 9, a BBO electro-optic crystal 10, a first plane mirror 11, a third thin-film polarizer 12, a first concave mirror 13, a first dichroic mirror 14, two Yb:CALGO laser crystals 15, a second dichroic mirror 16, a second concave mirror 17, and a second plane mirror 18. The light beam is injected at the second thin-film polarizer 8, travels back and forth through the cavity mirror, and returns to the first thin-film polarizer 8. The pulse is extracted by controlling the electro-optic crystal.

[0039] Specifically, the seed pulse is first incident on the second thin-film polarizer 8. Initially, the combination of the quarter-wave plate 9 and the BBO electro-optic crystal 10 (without voltage) does not change the polarization state of the beam, so the horizontally polarized seed light cannot pass through the second thin-film polarizer 8 into the regeneration cavity. When a quarter-wave voltage is applied to the BBO electro-optic crystal 10, it works together with the quarter-wave plate 9, acting as a half-wave plate, rotating the incident horizontally polarized light by 90° to vertical polarization, thus allowing it to be reflected by the second thin-film polarizer 8 into the regeneration cavity. The pulse entering the cavity oscillates back and forth within the cavity composed of elements such as the first plane mirror 11 and the second plane mirror 18, gaining a gain through the Yb:CALGO laser crystal 15 with each round trip. After approximately 35 round trips of amplification, when the pulse energy reaches its maximum, the voltage on the electro-optic crystal is removed. At this point, the quarter-wave plate 9 acts alone, converting the vertically polarized light oscillating within the cavity back into horizontal polarization, which is then transmitted and extracted at the second thin-film polarizer 8, completing the regeneration amplification process.

[0040] In this embodiment, the first concave mirror 13 and the second concave mirror 17 have a radius of curvature of 800 mm, which are used to form a stable Gaussian mode at the laser crystal unit with a mode radius of 250 μm, so as to achieve good matching with the pump spot.

[0041] In this embodiment, a dual-crystal design is employed to effectively manage thermal effects and improve gain. The laser crystal unit comprises two Yb:CALGO crystals 15 of identical size and doping concentration, which are sequentially placed between the first dichroic mirror 14 and the second dichroic mirror 16 along the optical path. Both crystals are a-cut, with their crystallographic a-axis parallel to the polarization direction (horizontal) of the seed light and their c-axis parallel to the polarization direction (horizontal) of the pump light. This specific orientation design maximizes the emission cross-section of the seed light at the crystal's gain peak while ensuring that the pump light pumps along the direction of strongest absorption, thereby improving optical-to-optical conversion efficiency and effectively suppressing the influence of thermally induced birefringence on beam quality.

[0042] The regenerative pump module includes a first pump source 19 and a beam-splitting pump system. The first pump source 19 is a semiconductor laser with a maximum output power of 430W, a core diameter of 200μm, and a wavelength of 981nm. Its emitted pump light is collimated by a first collimating lens 20 and then split into two beams by a first polarizing beam splitter prism 21. The first pump beam is reflected sequentially by the first pump mirror 22, and after the polarization state is adjusted to horizontal polarization by the second half-wave plate 23, it is focused by the pump focusing lens 26 and then passes through the second dichroic mirror 16, entering the Yb:CALGO laser crystal on the right side from one end face.

[0043] The transmitted second pump beam is successively deflected by the fourth pump reflector 27 and the fifth pump reflector 28, then focused by the second pump focusing lens 29, and finally passes through the first dichroic mirror 14, entering the Yb:CALGO laser crystal on the left side from the other end face. The ratio of the focusing lens to the collimating lens is 1:3.

[0044] During operation, the seed pulse is injected, amplified (approximately 35 times), and extracted within the regeneration cavity by controlling the quarter-wave voltage of the BBO electro-optic crystal 10. The repetition frequency is set to 100 kHz. The average power of the extracted amplified pulse can reach 10³ W. The Yb:CALGO laser crystal 15 has an a-cut shape, with its a-axis parallel to the polarization direction of the seed light and its c-axis parallel to the horizontal polarization direction of the pump light.

[0045] The single high-power pump light is split into two paths by a polarizing beam splitter prism 21, enabling dual-end pumping of two crystals. This distributes the total heat load across the two crystals and achieves good mode matching between the pump light and the seed light within the crystals, reducing the thermal lensing effect of a single crystal and laying the foundation for stable high-power operation.

[0046] 3. Traveling wave amplification module: The beam with an average power of approximately 100W, derived from the regenerative amplifier, is deflected by the third plane mirror at a 30° angle before entering the traveling-wave amplification module for main power amplification, achieving a final output of over 200W. This module employs a four-stage cascaded traveling-wave amplification structure and uses two independent pump sources for beam splitting pumping.

[0047] First-stage traveling wave amplification: The amplified seed beam passes sequentially through the third dichroic mirror 31, then enters the first-stage Yb:CALGO laser crystal 32, and is reflected by the fourth dichroic mirror 33, completing the first-stage single-pass amplification. The pump light path originates from the second pump source 43: the pump light emitted from the second pump source 43 is collimated by the collimating lens 44 and then incident on the polarization beam splitter prism 45. This prism splits the pump light into two beams: the third pump beam (reflection branch): is successively deflected by the eighth pump reflector 49, the ninth pump reflector 50, and the tenth pump reflector 52, and the third half-wave plate 51 converts the polarization state of the pump light to horizontal polarization. After being focused by the fourth pump focusing lens 53, it passes through the third dichroic mirror 31 and enters the first-stage laser crystal 32 from one end.

[0048] To achieve higher power extraction efficiency based on the single-pass configuration, multi-pass structures such as double-pass and four-pass can be introduced into any stage or all traveling-wave amplification stages. Taking the first stage as an example, a double-pass structure 66, consisting of an optical isolation system, a collimating lens, and a plane mirror, can be added to the single-pass structure (crystal 32, dichroic mirrors 31 and 33). Specifically, the beam output from the fourth dichroic mirror 33 can be guided through the double-pass structure 66. This structure causes the beam to bend in space and collimate again before passing through the first-stage laser crystal 32 a second time along the original path or a parallel optical path, thereby achieving double extraction of energy stored in the crystal and significantly improving the amplification gain and total output power of this stage. Similar double-pass designs can be used in other stages as well. When all four stages adopt optimized double-pass structures, the final average output power of the system can be further improved.

[0049] The fourth pump beam (transmitted light) is successively deflected by the sixth pump mirror 46 and the seventh pump mirror 47, focused by the third pump focusing lens 48, and incident on the second-stage laser crystal 35 from the direction of the fifth dichroic mirror 34 (the output mirror of this stage), providing pump for the next stage. A single pump source is used to simultaneously provide pump light for two consecutive amplifier stages.

[0050] Second-stage traveling wave amplification: The beam output from the first stage is reflected by the fifth dichroic mirror 34, enters the second-stage Yb:CALGO laser crystal 35, gains gain, and is then output through the sixth dichroic mirror 36. Its pump light is the aforementioned fourth pump beam.

[0051] Third-order traveling wave amplification: The beam output from the second stage is reflected by the seventh dichroic mirror 37 and enters the third-stage Yb:CALGO laser crystal 38, then exits through the eighth dichroic mirror 39. The pump light path originates from the third pump source 54: the pump light emitted from the third pump source 54 is collimated by the collimating lens 55 and then incident on the polarization beam splitter prism 56. This prism splits the pump light into two beams: the fifth pump beam in the reflection branch: it is successively deflected by pump reflectors 60, 61, and 63, and the fourth half-wave plate 62 converts the polarization state of the pump light to horizontal polarization. After being focused by the pump focusing lens 64, it passes through the seventh dichroic mirror 37 and enters the third-stage laser crystal 38.

[0052] Fourth-stage traveling wave amplification: The beam output from the third stage is reflected by the ninth dichroic mirror 40 and enters the fourth-stage Yb:CALGO laser crystal 41, then exits through the tenth dichroic mirror 42. The pump for this stage is provided by the sixth pump beam in the transmission branch after the third-stage pump source is split. The beam is then deflected by the pump reflector 57 and the pump reflector 58, focused by the pump focusing lens 59, and enters the fourth-stage laser crystal 41 through the ninth dichroic mirror 40.

[0053] All traveling-wave amplification stages use Yb:CALGO laser crystals (32, 35, 38, 41) with an a-cut shape, where the a-axis is parallel to the polarization direction of the seed light and the c-axis is parallel to the horizontal polarization direction of the pump light.

[0054] The second pump source 43 and the third pump source 54 are semiconductor lasers with a maximum output power of 430W, a core diameter of 200μm, and a wavelength of 981nm. The seed beam spot radius at the fourth-order laser crystal (32, 35, 38, 41) is 250μm. The focusing lens to collimating lens ratio used in both the second pump source 43 and the third pump source 54 is 1:3.

[0055] After this four-stage beam-pumped traveling-wave amplification, the average power of the pulse is amplified to over 200 watts. The entire amplification chain has high energy conversion efficiency, and due to the effective management of thermal load by beam-pumping, the output beam quality remains good.

[0056] 4. Pulse compressor module: The amplified beam is a time-domain broadened chirped pulse, which eventually enters the pulse compressor module 65. In this embodiment, a pair of parallel transmission gratings are used as compressors to compress the pulse width back to the femtosecond level. After compression, the final output laser pulse width is 196 fs, the average power exceeds 200 W, and the beam quality M² factor is better than 1.3.

[0057] The laser device built in this embodiment was tested, and the results are as follows: Figures 2 to 6 As shown.

[0058] Figure 2 The diagram shows the output power of the regenerative amplifier, indicating that its stable output power is approximately 103 W.

[0059] Figure 3 This is a schematic diagram of the output power of the first two stages of the traveling wave amplifier (the first and second stages), showing that the power has been further increased.

[0060] Figure 4 The diagram shows the output power of the last two traveling wave amplifier stages (the third and fourth stages), indicating that the average power after final amplification exceeds 200 W.

[0061] Figure 5 This is a schematic diagram of the pulse compression results and beam quality. The left side shows the compressed autocorrelation trace, indicating a pulse width of 196 fs; the right side shows the output spectrum, with a center wavelength of approximately 1034 nm. The spectral shape is smooth, indicating that the amplification process did not introduce severe gain narrowing or spectral distortion.

[0062] Figure 6 This is a schematic diagram of beam quality, with M measured. 2 The factor is better than 1.3 in both the X and Y directions, indicating that the device maintains excellent beam quality close to the diffraction limit even at a high power output of 200W.

[0063] Those skilled in the art will readily understand that the above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high average power femtosecond laser device based on Yb:CALGO laser crystal, characterized in that, The optical path includes, in sequence: a seed source, a pulse stretcher module, a regenerative amplifier module, a traveling-wave amplification module, and a pulse compressor module; wherein, both the regenerative amplifier module and the traveling-wave amplification module use Yb:CALGO crystal as the gain medium, and the Yb:CALGO crystal is cut in an a-cut shape, with its a-axis parallel to the polarization direction of the seed light and its c-axis parallel to the polarization direction of the pump light.

2. The high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 1, characterized in that: The seed source is a broadband femtosecond pulse source whose output spectrum covers the gain bandwidth of the Yb:CALGO crystal; the seed source is selected from any of the following: a ytterbium-doped fiber mode-locked pulsed laser, a mode-locked solid-state laser based on a semiconductor saturable absorber mirror, or a mode-locked solid-state laser based on a Kerr lens.

3. The high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 1, characterized in that: The pulse stretcher module includes a first optical isolation system, a Martinez-type spatial stretcher, a first half-wave plate, a first reflector, a first thin-film polarizer, and a second optical isolation system arranged sequentially along the optical path. The first optical isolation system is configured to make the forward-passing beam vertically polarized. The Martinez-type spatial stretcher is used to stretch the time domain width of the seed pulse to the order of hundreds of picoseconds. The first half-wave plate is used to change the polarization state of the stretched beam to horizontal polarization. The second optical isolation system is configured to make the forward-passing beam horizontally polarized to match the injection polarization state of the regenerative amplifier module and to guide the stretched beam into the regenerative amplifier module.

4. A high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 1, characterized in that: The regenerative amplifier module includes a regenerative cavity and a regenerative pump module; The regeneration cavity includes, in sequence along the optical path, a second thin-film polarizer, a quarter-wave plate, an electro-optic crystal, a first plane mirror, a third thin-film polarizer, a first concave mirror, a first dichroic mirror, a laser crystal, a second dichroic mirror, a second concave mirror, and a second plane mirror; The regenerative pump module includes a first pump source and a beam splitting device for splitting the pump beam into a first pump beam and a second pump beam. The first pump beam and the second pump beam are respectively focused to the two ends of the laser crystal in the regenerative cavity to form a dual-end pumping structure.

5. A high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 4, characterized in that: The electro-optic crystal controls the introduction, amplification, and extraction of seed pulses by applying and removing a quarter-wave voltage.

6. A high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 4, characterized in that: The laser crystal (15) is a Yb:CALGO crystal, and there are two laser crystals (15) placed sequentially along the optical path, namely the first laser crystal and the second laser crystal, forming a dual-crystal regeneration amplification structure; the first beam splitting device is a first polarization beam splitter prism, which is used to split the pump light into two beams according to the polarization state, and pump the two laser crystals respectively.

7. A high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 1, characterized in that: The traveling-wave amplification module includes four stages of traveling-wave amplification arranged sequentially along the optical path; each stage includes at least two dichroic mirrors and one Yb:CALGO laser crystal; the traveling-wave amplification range of each stage can be set to single-pass or multi-pass; the traveling-wave amplification module also includes at least two pump sources, the output beam of each pump source is split into two pump beams by a corresponding beam splitter, forming four pump beams, which are respectively guided and focused onto the four Yb:CALGO laser crystals corresponding to the four stages of traveling-wave amplification.

8. A high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 7, characterized in that: At least one of the traveling wave amplification stages is a multi-pass traveling wave amplification structure, which includes a dual-pass structure. The dual-pass structure consists of an optical isolation system, a collimating lens, and a plane mirror, and is used to allow the seed beam to pass through the same Yb:CALGO laser crystal a second time along the original path or a parallel optical path, thereby realizing the dual extraction of energy stored in the crystal.

9. A high average power femtosecond laser device based on Yb:CALGO laser crystal according to claim 7, characterized in that: The pulse compressor module (65) is a pair of parallel diffraction gratings used to recompress the time domain width of the amplified chirped pulse to the femtosecond level.

Images