Femtosecond laser chirped pulse self-similar regenerative amplification method and device

Abstract

The present invention discloses a femtosecond laser chirped pulse self-similar regenerative amplification method and device. The device includes a broadband seed source, a spectral shaping and broadening device, a self-similar regenerative amplifier, and a pulse compressor that are sequentially arranged from one side to the other side according to the optical path. The spectral shaping and broadening device includes a time-domain broadening device and a spectral shaper. The time-domain broadening device is used to broaden the seed pulse to the picosecond level or even the nanosecond level and finely regulate the pulse width. The spectral shaper is used to perform spectral shaping on the seed pulse so that the spectral intensity of the broadened seed pulse is a saddle-shaped chirped pulse with high intensity at both sides and low intensity in the center. The self-similar regenerative amplifier includes a gain crystal and a highly nonlinear crystal. After the saddle-shaped chirped pulse is injected into the self-similar regenerative amplifier, it undergoes nonlinear spectral broadening and amplification multiple times back and forth and outputs a high-energy chirped pulse to the pulse compressor.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast laser technology, and particularly to a method and device for femtosecond laser chirped pulse self-similar regenerative amplification. Background Art

[0002] Ytterbium-ion-doped solid laser amplifiers have great advantages in the generation of high-energy intense-field pulses because of their high quantum efficiency and simple pumping requirements. Based on ytterbium-ion-doped solid lasers, such as all-solid-state (crystalline gain medium), disk, slab, fiber, etc., the output energy of laser amplifiers has been pushed to the millijoule level.

[0003] In recent years, combined with chirped pulse amplification technology, solid ytterbium-doped laser amplifiers can output millijoule-level femtosecond pulses with pulse peak powers reaching the GW level. In a chirped amplification system, in order to suppress the adverse effects caused by high-peak-power pulses, such as self-focusing and device damage, the seed pulse usually needs to be broadened to the picosecond level. However, pulse broadening leads to a decrease in nonlinearity during the amplification process, and the adverse effect of gain narrowing becomes prominent, resulting in limited output pulse width, usually above 300 fs. The so-called gain narrowing stems from the inconsistency of the radiation spectrum distribution of the laser gain medium. Taking a gain medium doped with Yb ions as an example, its radiation spectrum covers a relatively wide range of 1010 - 1100, but usually has the maximum radiation intensity at 1035 nm, becoming weaker on both sides. Therefore, during the laser amplification process based on Yb-doped materials, since the 1035-nm band is easy to amplify, the pulse spectrum in this band will become prominent as the amplification factor increases, resulting in the amplification pulse spectrum being concentrated near 1035 nm, causing spectral narrowing. According to the Fourier transform limit pulse theory, to obtain a narrower output pulse, the signal light needs a wider spectral bandwidth. Therefore, effectively suppressing the gain narrowing effect during laser amplification or even achieving spectral broadening can push the output pulse width of ytterbium-doped solid laser amplifiers to the 100-fs level or even the 10-fs level.

[0004] Self-similar pulse amplification was first achieved in fiber laser amplifiers. By utilizing the nonlinear effect in the fiber gain medium, the signal light spectrum is broadened, thereby suppressing gain narrowing and achieving high-quality pulse compression, and ultrashort pulses in the sub-100-femtosecond or even few-cycle level can be obtained. The current self-similar amplification is only seen in fiber amplifiers. The characteristics of long interaction distance and high nonlinearity of the fiber medium ensure the realization of self-similar pulse evolution. However, due to the low damage threshold and strong nonlinearity of the fiber medium, the output energy is limited to the μJ level. Based on the chirped amplification system and the solid regenerative amplification system, due to the low pulse peak power and the low nonlinear coefficient of the gain crystal (3 - 4 orders of magnitude lower than that of the fiber medium), self-similar pulse evolution is difficult to achieve. Summary of the Invention

[0005] Aiming at the above deficiencies existing in the prior art, the object of the present invention is to provide a femtosecond laser chirped pulse self-similar regenerative amplification method and device, to solve the problem that it is difficult to achieve self-similar pulse evolution in solid-state laser amplifiers and chirped amplification systems, to break through the limitation of the gain narrowing effect in the generation of high-energy femtosecond lasers, to realize the self-similar pulse evolution of laser pulses in solid-state regenerative amplifiers, and the amplification process is accompanied by spectral broadening, so as to provide a new technical means for generating high-peak power pulses in the order of 10 mJ and sub-100 femtoseconds.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A femtosecond laser chirped pulse self-similar regenerative amplification method, comprising the following steps: S1, continuously injecting a seed pulse into a spectral shaping and broadening device, and broadening the injected seed pulse in the time domain through a time-domain broadening device in the spectral shaping and broadening device, and performing spectral shaping on the broadened signal light through a spectral shaper during the broadening process or after time-domain broadening, so that the seed pulse is broadened to several hundred picoseconds or nanoseconds, and the spectral intensity is a saddle-shaped chirped pulse with high sides and low center; the spectral width of the seed pulse > 7 nm, the pulse energy > 1 nJ, the spectral shape is parabolic or Gaussian, and has a linear chirp characteristic; S2, injecting the time-domain broadened and spectrally shaped saddle-shaped chirped pulse into the regenerative amplification cavity of a self-similar regenerative amplifier, and after gradually amplifying back and forth through a gain crystal and a highly nonlinear crystal in the regenerative amplification cavity for multiple times, the spectrum of the saddle-shaped chirped pulse obtains gain, and at the same time, when the spectral intensity of the saddle-shaped chirped pulse evolves from a saddle shape to a flat shape, the flat-shaped chirped pulse continues to be gradually amplified back and forth through the gain crystal in the regenerative amplification cavity for multiple times. When the pulse peak power exceeds the MW level, the flat-shaped chirped pulse obtains nonlinear spectral broadening when passing through the highly nonlinear crystal; during the regenerative amplification process, the signal light passes through the gain medium with a focused spot, avoiding nonlinear time-frequency distortion, collimated by a lens and then passes through the highly nonlinear medium with a focused spot to enhance the nonlinear spectral broadening until the chirped pulse self-similar amplification reaches gain saturation, and then outputs a high-energy chirped pulse; S3, injecting the high-energy chirped pulse after gain saturation into a pulse compressor, and compressing the high-energy chirped pulse after regenerative amplification through the pulse compressor, and then outputting the signal light. At this time, the pulse energy of the signal light > 2 mJ, the pulse width < 100 fs, the spectral width > 15 nm, and the repetition frequency can be switched in the range of 1 kHz - 200 kHz.

[0008] Further, the spectral shaping and broadening device broadens and shapes the seed pulse in the following two ways: Way 1, the seed pulse is subjected to multiple times of time-domain broadening by a time-domain broadening device, and spectral shaping is performed by a spectral shaping device during the time-domain broadening process; Way 2, the seed pulse is subjected to one-time time-domain broadening by a time-domain broadening device, and after the time-domain broadening, the spectral shaping device performs spectral shaping on the broadened pulse signal.

[0009] Further, the gain crystal in the self-similar regenerative amplifier is a laser crystal doped with rare earth ions, and the laser crystal emits spontaneous emission laser after being excited by pump light.

[0010] Further, the rare earth ions doped in the laser crystal are neodymium ions or ytterbium ions; the spontaneous emission laser is Yb:CaF2 spontaneous emission laser or Yb:CALGO spontaneous emission laser or Yb:CALYO spontaneous emission laser or Yb:KGW / KYW spontaneous emission laser.

[0011] Further, the highly nonlinear crystal refers to a crystal material with a relatively high third-order nonlinear optical susceptibility, including silicon dioxide or calcium fluoride or aluminum oxide.

[0012] A femtosecond laser chirped pulse self-similar regenerative amplifier device, comprising a broadband seed source, a spectral shaping expander, a self-similar regenerative amplifier, and a pulse compressor arranged in sequence from one side to the other side according to the optical path; the broadband seed source is used to emit seed pulses to the spectral shaping expander; the spectral shaping expander includes a time-domain expander and a spectral shaper, the time-domain expander is used to expand the seed pulses to the picosecond order or even the nanosecond order, and finely regulate the pulse width; the spectral shaper is used to perform spectral shaping on the seed pulses, so that the spectral intensity of the expanded seed pulses is a saddle-shaped chirped pulse with high intensity at both sides and low intensity in the center; the self-similar regenerative amplifier includes a pulse input and output coupling module and a pulse regenerative amplification module, the pulse input and output coupling module is used to receive the saddle-shaped chirped pulses injected by the spectral shaping expander, and inject the received saddle-shaped chirped pulses into the pulse regenerative amplification module; the pulse regenerative amplification module can gradually amplify the injected saddle-shaped chirped pulses back and forth multiple times, including a gain crystal and a highly nonlinear crystal, the highly nonlinear crystal is located on one side of the gain crystal, in the same optical path as the gain crystal, and together with the gain crystal, gradually amplify back and forth multiple times and perform nonlinear spectral broadening back and forth multiple times until the peak power of the pulse exceeds the MW level, the signal light passes through the gain medium with a focused spot, after being collimated by a lens, and then passes through the highly nonlinear medium with a focused spot, enhancing the nonlinear spectral broadening until the chirped pulse self-similar amplification reaches gain saturation, and output high-energy chirped pulses to the pulse input and output coupling module; after receiving the high-energy chirped pulses, the pulse input and output coupling module injects the high-energy chirped pulses into the pulse compressor; the pulse compressor is used to compress the high-energy chirped pulses after regenerative amplification and then output the signal light.

[0013] Further, the time-domain expander is an Offner-type grating time-domain expander, including a thin-film polarizer, a Faraday rotator, a half-wave plate, a diffraction grating, a concave mirror, and a convex mirror arranged in sequence according to the optical path. A roof retroreflector and a plane mirror are also provided between the half-wave plate and the diffraction grating, and the roof retroreflector is arranged close to the half-wave plate; the concave mirror and the convex mirror are arranged in an up-and-down staggered manner, and the convex mirror is arranged in an up-and-down staggered manner, and the radius of curvature of the convex mirror is half of the radius of curvature of the concave mirror, and the convex mirror is located at the focal position of the concave mirror;

[0014] The spectral shaper is a mechanical spectral shaper, located between the concave mirror and the convex mirror, and the mechanical spectral shaper includes one or more opaque mechanical sheets, and there is a slit between two adjacent opaque mechanical sheets.

[0015] Furthermore, the working bands of the thin film polarizer, Faraday rotator, half-wave plate, diffraction grating, concave mirror, convex mirror, corner cube retroreflector, and plane mirror are all in the 1030 nm band; the Faraday rotator can rotate the polarization angle of the incident polarized light by 45°, and cooperate with the half-wave plate and thin film polarizer to separate and isolate the incident light and the outgoing light, and is used as an optical isolator; the diffraction grating has a grating period of 1740 line / mm, and the diffraction efficiency of the 1030 nm band laser passing through it once is >95%.

[0016] Furthermore, the time-domain stretcher is an optical fiber stretcher based on a chirped Bragg grating, and the spectral shaper is an optical interference filtering shaper based on the birefringence effect;

[0017] The time-domain stretcher includes an optical fiber circulator, a chirped fiber Bragg grating, and an optical fiber collimator arranged in sequence along the optical path. The optical fiber circulator is provided with a first port, a second port, and a third port at intervals. The incident signal light at the first port can be transmitted unidirectionally to the second port, and the incident signal light at the second port can be transmitted unidirectionally to the third port; the reflection bandwidth of the chirped fiber Bragg grating is 20 nm, the reflectivity is >50%, the dispersion coefficient is 50 ps / nm, and the fiber type is PM980;

[0018] The spectral shaper includes a third thin film polarizer, a birefringent medium, and a fourth thin film polarizer arranged in sequence along the optical path. The birefringent medium is a quartz crystal, the birefringence coefficient B = 0.0092, and the incident laser polarization angle forms an angle of 15° with the main axis angle of the birefringent medium; the optical axis of the birefringent medium forms a certain angle θ with the laser transmission polarization axis, 0° < θ < 90°.

[0019] Furthermore, the pulse input and output coupling module includes a first thin film polarizer, a first half-wave plate, and a first Faraday rotator arranged in sequence; the first Faraday rotator is arranged close to the pulse regeneration and amplification module. The first Faraday rotator is a magneto-optical crystal device, and the polarization angle rotates by 45° after passing through the polarized light; the first Faraday rotator, together with the first half-wave plate and the first thin film polarizer, constitutes an optical isolator, which can realize the coupling and separation of the incident light and the outgoing light;

[0020] The pulse regeneration and amplification module further includes a first plane mirror, a Pockels cell, a quarter-wave plate, a second thin film polarizer, and a second plane mirror arranged in sequence; the gain crystal and the high-nonlinear crystal are located between the second plane mirror and the second thin film polarizer; the second thin film polarizer is arranged opposite to the first Faraday rotator. After receiving the saddle-shaped chirped pulse from the first Faraday rotator, the second thin film polarizer can rotate the saddle-shaped chirped pulse by a set angle and then introduce it into the quarter-wave plate;

[0021] A third plano-convex lens and a fourth plano-convex lens are respectively arranged on both sides of the gain crystal, and a first plano-convex lens and a second plano-convex lens are respectively arranged on both sides of the high nonlinear crystal. The first plano-convex lens, the second plano-convex lens, the third plano-convex lens, the fourth plano-convex lens, the first plane mirror and the second plane mirror together form a stable regenerative cavity; the high nonlinear crystal is placed at the focal point of the convex lens group formed by the first plano-convex lens and the second plano-convex lens, and the gain crystal is placed at the focal point of the convex lens group formed by the third plano-convex lens and the fourth plano-convex lens;

[0022] The Pockels cell is a quarter-wave fast electro-optic device. By controlling the opening and closing of the Pockels cell, the Pockels cell and the quarter-wave plate can together form an optical regulator to adjust the polarization direction of polarized light; thereby enabling the pulsed light to be gradually amplified back and forth multiple times between the first plane mirror and the second plane mirror and the nonlinear spectral broadening back and forth multiple times.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. By combining chirped pulse amplification, self-similar pulse amplification and solid-state laser regenerative amplification, the gain narrowing effect in high-energy ultrafast laser amplification can be solved, and a millijoule-level high-peak power pulse output with <100 fs can be achieved.

[0025] 2. By inserting a nonlinear medium into the solid-state laser regenerative amplifier, self-similar regenerative amplification is realized, solving the problem that it is difficult to achieve self-similar pulse evolution in a low-nonlinear solid gain medium, and providing a new method for suppressing gain narrowing in multi-pass regenerative amplification. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the femtosecond laser chirped pulse self-similar regenerative amplification device in Embodiment 1 and Embodiment 2;

[0027] Figure 2 It is a structural diagram of the spectral shaping and broadening device in Embodiment 1;

[0028] Figure 3 It is a structural diagram of the spectral shaping and broadening device in Embodiment 2;

[0029] Figure 4 It is a structural diagram of the self-similar regenerative amplifier in Embodiment 1 and Embodiment 2;

[0030] Figure 5 It is a schematic diagram of the saddle-shaped spectrum output after the spectral shaping and broadening of the spectral shaping and broadening device in the embodiment;

[0031] Figure 6Schematic diagram of the amplification vertical simulation results of Gaussian and saddle-shaped spectra with the same parameters in the embodiment after being injected into a self-similar regenerative amplifier; among them, (a) is the energy evolution of the two spectra, and (b) is the evolution of the amplified spectral width of the two spectra;

[0032] Figure 7 Diagram of the self-similar regenerative amplification pulse evolution process of Gaussian and saddle-shaped spectra in the embodiment; among them, (a) and (c) are diagrams of the evolution process of Gaussian incident pulses; (b) and (d) are diagrams of the evolution process of saddle-shaped incident pulses;

[0033] Figure 8 Diagram of the amplification evolution simulation of a narrowband signal light pulse in a femtosecond laser chirped pulse self-similar regenerative amplification device; among them, (a) is the pulse evolution; (b) is the spectral evolution; (c) is the pulse curve at a specific number of turns; (d) is the spectral curve at a specific number of turns;

[0034] Figure 9 Diagram of the change process of the pulse width and spectral width of a broadband signal light pulse in a femtosecond laser chirped pulse self-similar regenerative amplification device. Detailed implementation manners

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and illustrated herein generally can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0036] It should be noted that like reference numerals and letters denote like items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, terms such as "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance. In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging vertically, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined. In the description of the present invention, it should also be noted that unless otherwise clearly specified and limited, the terms "arranged", "installed", "connected", "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] Example 1:

[0038] The method for self-similar regenerative amplification of femtosecond laser chirped pulses provided by this embodiment includes the following steps: S1, continuously injecting the seed pulse δ1 (the spectral width of the seed pulse > 7 nm, the pulse energy > 1 nJ, the spectral shape is parabolic or Gaussian, and has a linear chirp characteristic) into the spectral shaping expander 200. The injected seed pulse δ1 is subjected to two-time time-domain broadening by the time-domain expander of the spectral shaping expander 200, and during the broadening process or after the time-domain broadening, the broadened signal light is subjected to two-time spectral shaping by the spectral shaper, so that the seed pulse is broadened to several hundred picoseconds or nanoseconds, and the spectral intensity is a saddle-shaped chirped pulse δ2 with high sides and low center; S2, injecting the time-domain broadened and spectrally shaped saddle-shaped chirped pulse δ2 into the regenerative amplification cavity of the self-similar regenerative amplifier 300. After gradually amplifying back and forth multiple times through the gain crystal and the highly nonlinear crystal in the regenerative amplification cavity, the role of the gain crystal makes the middle part of the seed pulse spectrum gradually prominent, and the spectra on both sides become weaker. The initial saddle-shaped spectrum cancels out the gain narrowing effect, so that the spectral intensity of the saddle-shaped chirped pulse evolves from a saddle shape to a flat shape. Then, the flat-shaped chirped pulse continues to be gradually amplified back and forth multiple times through the gain crystal in the regenerative amplification cavity. When the pulse peak power exceeds the MW level, the flat-shaped chirped pulse is subjected to multiple-time nonlinear spectral broadening through the highly nonlinear crystal. The signal light passes through the gain medium with a focused spot, avoiding nonlinear time-frequency distortion. After being collimated by a lens, it then passes through the highly nonlinear medium with a focused spot to enhance the nonlinear spectral broadening until the chirped pulse self-similar amplification reaches gain saturation, and then a high-energy chirped pulse δ3 is output; S3, injecting the high-energy chirped pulse δ3 after gain saturation into the pulse compressor 400. After the pulse compressor 400 compresses the high-energy chirped pulse δ3 after regenerative amplification, the signal light δ4 is output. At this time, the pulse energy of this signal light δ4 > 2 mJ, the pulse width < 100 fs, the spectral width > 15 nm, and the repeat frequency can be switched in the range of 1 kHz - 200 kHz.

[0039] As Figure 1 shown, the chirped pulse self-similar regenerative amplification device adopted in the method for self-similar regenerative amplification of femtosecond laser chirped pulses in this embodiment includes: a broadband seed source 100, a spectral shaping expander 200, a self-similar regenerative amplifier 300, and a pulse compressor 400 sequentially arranged from one side to the other side according to the optical path; the broadband seed source 100 is used to send a seed pulse to the spectral shaping expander 200.

[0040] The spectral shaping and broadening device 200 includes a time-domain broadening device 210 and a spectral shaping device 220. The time-domain broadening device 210 is used to broaden the seed pulse δ1 to the picosecond level or even the nanosecond level and finely regulate the pulse width. The spectral shaping device 220 is used to perform spectral shaping on the seed pulse δ1 so that the spectral intensity of the broadened seed pulse is in the shape of a saddle-shaped chirped pulse δ2 with high sides and low center.

[0041] As Figure 2 shown, the time-domain broadening device 210 in this embodiment is an Offner-type broadening device based on a diffraction grating, including a thin-film polarizer 211, a Faraday rotator 212, a half-wave plate 213, a diffraction grating 214, a concave mirror 215, and a convex mirror 216 arranged in sequence along the optical path. A roof retroreflector 217 and a plane mirror 218 are also provided between the half-wave plate 213 and the diffraction grating 214, and the roof retroreflector 218 is arranged close to the half-wave plate 213. The concave mirror 215 and the convex mirror 216 are arranged in an up-and-down staggered manner, and the radius of curvature of the convex mirror 216 is half of the radius of curvature of the concave mirror 215, and the convex mirror 216 is located at the focal position of the concave mirror 215.

[0042] The spectral shaping device 220 is a mechanical spectral shaping device and is located between the concave mirror 215 and the convex mirror 216. The mechanical spectral shaping device includes one or more opaque mechanical thin sheets, and there are slits between two adjacent opaque mechanical thin sheets. The mechanical spectral shaping device mechanically blocks the long-strip diffraction beam to achieve spectral shaping of the laser output by the broadening device. The principle is as follows: In the Offner-type time-domain broadening device, the broadband seed pulse is diffracted by the grating and collimated by the lens, and there is a collimated long-strip diffraction spot. The spectral components in the spot are linearly related to their relative positions. Using a single or multiple opaque thin sheets of different thicknesses to locally or entirely block the long-strip diffraction spot can achieve shaping of the spectral distribution and shape of the broadened pulse. Among them, in the narrow thin-sheet spectral shaping, optical diffraction is beneficial for achieving the saddle-shaped shaped spectrum.

[0043] The above-mentioned Faraday rotator 212 can rotate the polarization angle of the incident polarized light by 45°. Cooperating with the half-wave plate 213 and the thin-film polarizer 211 can achieve separation and isolation of the incident light and the outgoing light, and can be used as an optical isolator.

[0044] The diffraction grating 214 has a light-transmitting size of 65 * 25 mm2, a grating period of 1740 line / mm, and a single-pass diffraction efficiency of >95% for the 1030 nm band laser. The diffraction grating 214 is placed at a distance s from the concave mirror (s = 500 mm, R1 < s < R2).

[0045] The above s is the distance value between the diffraction grating and the concave mirror, R represents the curvature of the concave mirror or convex mirror. The curvature of the convex mirror is set as R1, and the curvature of the concave mirror is set as R2. Specifically, in this embodiment, the radius of curvature of the convex mirror 216 (R1 = 400 mm) is half of the radius of curvature of the concave mirror 215 (R2 = 800 mm), and the convex mirror is located at the focal position (R / 2) of the concave mirror. The grating 214 is placed at a distance s from the concave mirror (s = 500 mm, R1 < s < R2). The concave mirror and the convex mirror form a telescopic system.

[0046] Specifically, in this embodiment, the spectral shaping and broadening device 200 broadens the broadband seed light in the time domain and shapes the spectrum, successively obtaining the signal light δ2’ and δ2. The typical feature is that the pulse width is broadened to 400 ps, carrying positive linear chirp, and the pulse shape is close to a parabolic shape. Compared with δ1, the energy is reduced by about half, and other parameters remain unchanged. The energy of δ2 is further lost compared with δ2’, and the spectral shape is modulated by the spectral shaper into a saddle shape as shown in the appendix Figure 5 as shown.

[0047] The broadening process of the time-domain broadening device 210 is as follows: The seed pulse δ1 passes through the thin-film polarizer 211, the Faraday rotator 212, and the half-wave plate 213 and then is incident on the diffraction grating 214. After the incident light is diffracted by the diffraction grating 214 of the diffraction grating, lasers in different bands respectively reach the concave mirror 215. Among them, the laser in the short-wave direction is incident on the upper side of the concave mirror 215, and the laser in the long-wave direction reaches the lower side of the concave mirror 215. The above-mentioned long wave and short wave are respectively reflected by the concave mirror 215 and reach the convex mirror 216, and then are reflected by the concave mirror 215 and the convex mirror 216 again and re-incident on the diffraction grating 214 (in this process, when the long wave and short wave pass through the spectral shaper 220, the incident light will be spectrally shaped). After being diffracted by the diffraction grating 214 of the diffraction grating, the laser pulse frequency is linearly distributed in space (spatial chirp), the light spot is in the shape of a horizontal long strip and is incident on the roof mirror 217 and then returns to the diffraction grating 214, and then exits through the concave mirror 215, the spectral shaper 220, the convex mirror 216, and the diffraction grating 214 to the rear plane mirror 218, restoring the shape of the incident light spot and eliminating the spatial chirp. This is a process of one-time broadening and shaping.

[0048] After the first broadening is completed, the plane mirror 218 reflects the pulse to the diffraction grating 214 for grating diffraction. Then, it passes through the concave mirror 215, the spectral shaper 220, the convex mirror 216, the diffraction grating 214, the roof retroreflector 217, the diffraction grating 214, the concave mirror 215, the spectral shaper 220, the convex mirror 216, and the diffraction grating 214 and exits to the plane mirror 218, achieving secondary broadening and shaping, broadening the seed pulse to several hundred picoseconds or nanoseconds, and making the spectral intensity in a saddle-shaped chirped pulse δ2 with high sides and low center. Finally, the saddle-shaped chirped pulse δ2 exits through the path of the half-wave plate 213, the Faraday rotator 212, and the thin-film polarizer 211.

[0049] As Figure 3 shown, the self-similar regenerative amplifier 300 in this embodiment includes a pulse input and output coupling module and a pulse regenerative amplification module. The pulse input and output coupling module includes a first thin-film polarizer 301, a first half-wave plate 302, and a first Faraday rotator 303, which are used to receive the saddle-shaped chirped pulse injected by the spectral shaping and broadening device and inject the received saddle-shaped chirped pulse into the pulse regenerative amplification module. The first Faraday rotator 303 is arranged close to the pulse regenerative amplification module. The first Faraday rotator 303 is a magneto-optical crystal device, and the polarization angle of the polarized light rotates by 45° after passing through it. The first Faraday rotator 303, together with the first half-wave plate 302 and the first thin-film polarizer 301, constitutes an optical isolator, which can realize the coupling and separation of incident light and outgoing light.

[0050] The pulse regenerative amplification module can gradually amplify the injected saddle-shaped chirped pulse back and forth multiple times, including a first plane mirror 307, a Pockels cell 306, a quarter-wave plate 305, a second thin-film polarizer 304, a highly nonlinear crystal 309, a gain crystal 312, and a second plane mirror 314 arranged in sequence. The second thin-film polarizer 304 is arranged opposite to the first Faraday rotator 303. After receiving the saddle-shaped chirped pulse from the first Faraday rotator 303, the second thin-film polarizer 304 can rotate the saddle-shaped chirped pulse by a set angle and then introduce it into the quarter-wave plate 305.

[0051] A third plano-convex lens 311 and a fourth plano-convex lens 313 are respectively arranged on both sides of the gain crystal 312, and a first plano-convex lens 308 and a second plano-convex lens 310 are respectively arranged on both sides of the high nonlinearity crystal 309. The first plano-convex lens 308, the second plano-convex lens 310, the third plano-convex lens 311, the fourth plano-convex lens 313, the first plane mirror 307 and the second plane mirror 314 together form a stable regenerative cavity; the high nonlinearity crystal 309 is placed at the focal point of the convex lens group formed by the first plano-convex lens 308 and the second plano-convex lens 310, and the gain crystal 312 is placed at the focal point of the convex lens group formed by the third plano-convex lens 311 and the fourth plano-convex lens 313;

[0052] The Pockels cell 306 is a quarter-wave fast electro-optic device, which behaves as a quarter-wave plate under high voltage (>2 kV) operation. The rise and fall edges of the response time (high voltage signal) of the Pockels cell are both <10 ns. By controlling the opening and closing of the Pockels cell 306, the Pockels cell and the quarter-wave plate can together form an optical regulator to adjust the polarization direction of polarized light; thus enabling the pulsed light to be gradually amplified back and forth multiple times and the nonlinear spectral broadening to occur back and forth multiple times between the first plane mirror and the second plane mirror.

[0053] All the optical elements in the self-similar regenerative amplifier 300 operate in the 1030 nm band and are coated with antireflection or high reflection films. The overall cavity length of the regenerative cavity is 2.2 m. The gain crystal 312 is preferably a Yb:CaF2 crystal, with dimensions of 3 mm×10 mm×10 mm. The crystal is cut at the Brewster angle, which can increase the crystal loss threshold. The ytterbium ion doping concentration is 3.at%. Under 976 nm LD pumping, the 1030 nm signal light can obtain effective gain, realizing the power amplification and energy enhancement of the signal light.

[0054] The nonlinear crystal 309 is selected as a silica wafer with dimensions of 20 mm*20 mm*1.5 mm, and its nonlinear refractive index is n2 = 3.0x10-20 m2W-1. When a laser pulse with a peak power reaching the MW level is incident, the self-phase modulation effect is excited to realize the spectral broadening of the signal light. The nonlinear crystal 309 realizes self-similar regenerative amplification, solves the problem that it is difficult to realize self-similar pulse evolution in a low-nonlinear solid gain medium, and provides a new method for suppressing gain narrowing in multi-pass regenerative amplification.

[0055] The regenerative amplification circuit after the saddle-shaped chirped pulse δ2 is injected into the self-similar regenerative amplifier 300 is as follows: The saddle-shaped chirped pulse δ2 passes through the first thin-film polarizer 301, the first half-wave plate 302, and the first Faraday rotator 303 in sequence, and then is incident on the second thin-film polarizer 304. After the polarization of the second thin-film polarizer 304 is rotated by a certain angle, it is incident on the quarter-wave plate 305, passes through the Pockels cell 306 (the Pockels cell is in the off state) and shoots towards the first plane mirror 307. After being reflected by the first plane mirror 307, it passes through the quarter-wave plate 305 again and then transmits through the second thin-film polarizer 304, and then is incident on the first plano-convex lens 308, the high-nonlinearity crystal 309, the second plano-convex lens 310, the third plano-convex lens 311, the gain crystal 312, and the fourth plano-convex lens 313 in sequence, and then reaches the second plane mirror 314; at this time, the Pockels cell 306 is turned on, and the second plane mirror 314 returns the pulse along the original path to the second thin-film polarizer 304, then transmits through the second thin-film polarizer 304, and reaches the first plane mirror 307 through the quarter-wave plate 305 and the Pockels cell 306; then, the amplification and the nonlinear spectral broadening are repeated multiple times back and forth between the first plane mirror 307 and the second plane mirror 314 until the peak power of the pulse exceeds the MW level. The signal light passes through the gain medium with a spot, and then passes through the high-nonlinearity medium with a focused spot to enhance the nonlinear spectral broadening until the self-similar amplification of the chirped pulse reaches gain saturation, and then outputs a high-energy chirped pulse to the pulse input and output coupling module; after receiving the high-energy chirped pulse, the pulse input and output coupling module injects the high-energy chirped pulse into the pulse compressor; the pulse compressor is used to compress the high-energy chirped pulse after regenerative amplification and then output the signal light.

[0056] As the number of circulating amplification cycles increases, the pulse energy continuously increases, and the peak power of the pulse also increases accordingly. When the peak power of the pulse reaches the MW level, when the laser is incident on the highly nonlinear Kerr medium, nonlinear effects such as self-phase modulation and four-wave mixing will be induced, resulting in the broadening of the pulse spectrum. The seed light pulse is injected into the self-similar regenerative amplifier 300 after passing through the time-domain stretcher 210 and the spectral shaper 220. The broadened pulse spectrum can effectively suppress the gain narrowing in the high-energy regenerative amplification process, which is convenient for subsequent realization of higher-quality pulse compression to obtain femtosecond pulses below a hundred femtoseconds or even in the few-cycle range.

[0057] During the above amplification process, in the self-similar regenerative amplification process, when the number of amplification cycles < 50 cycles (one cycle is defined as the signal light traveling back and forth between the first plane mirror 307 and the second plane mirror 314), the signal light obtains an increase in pulse energy after passing through the gain crystal. The gain effect gradually modulates the saddle-shaped spectrum into a flat spectrum, effectively suppressing gain narrowing. However, the peak power is still lower than the MW level. When the signal light passes through the highly nonlinear medium, the nonlinear spectral broadening is not obvious. After the number of amplification cycles > 50, the peak power of the signal light pulse reaches the MW level. It passes through the gain medium with a relatively large spot, avoiding nonlinear time-frequency distortion, and passes through the highly nonlinear medium with a converging beam to obtain nonlinear spectral broadening, realizing self-similar pulse evolution.

[0058] The broadened pulse spectrum can effectively suppress gain narrowing in the high-energy regenerative amplification process, facilitating subsequent realization of higher-quality pulse compression to obtain femtosecond pulses below a few hundred femtoseconds or even few-cycle femtosecond pulses. Attached Figure 6 The changes in pulse energy and spectral width with the number of amplification cycles of different-shaped incident pulses in the self-similar regenerative amplifier were compared. First, for two different-shaped incident pulses, with other initial parameters being the same, after 70 cycles of regenerative amplification, the pulse energy can be increased to nearly 4 mJ, and the amplification efficiency > 60 dB. During the amplification process, the pulse energy increases exponentially with the number of amplification cycles. Near the 70th cycle, an energy saturation trend appears. Comparatively speaking, the energy finally obtained by the saddle-shaped pulse is slightly higher, showing more amplification advantages.

[0059] Secondly, for the suppression of gain narrowing and self-similar spectral broadening during the amplification process, the saddle-shaped incident spectrum proposed in this invention document has obvious advantages [(see Figure 6 (b)]. When the incident spectral width is the same (7 nm), when the incident spectrum is Gaussian, in the first 57 cycles of the amplification process, the gain narrowing effect is significant, and the spectral width narrows by nearly 1 nm (narrowed by about 14%). Subsequently, with the increase in the amplified pulse energy, spectral broadening caused by the nonlinear effect occurs. After 70 cycles of amplification, the Gaussian signal spectral width returns to 6.5 nm. Comparatively speaking, when the incident spectral shape is saddle-shaped, in the first 50 cycles, the gain narrowing effect is significantly suppressed, and the spectral width narrows from 7 nm to about 6.8 nm (only narrowed by about 3%). Moreover, with the increase in energy, the nonlinear spectral broadening caused by the saddle-shaped incident spectrum is more significant. After 70 cycles of pulse amplification, the spectral width broadens to nearly 7.8 nm (spectral broadening of about 11%). Attached Figure 7 shows the detailed pulse evolution processes of Gaussian incident pulses [(a) and (c)] and saddle-shaped incident pulses [(b) and (d)] in the self-similar regenerative amplifier, where Figure 7(c) For the 1st - 80th pulse curves, the outermost one is the 1st, and from the outside to the inside are the 1st, 40th, 60th, 65th, and 67th in sequence; Figure 7 (d) For the 1st - 80th pulse curves, the innermost one is the 1st, and from the inside to the outside are the 1st, 40th, 60th, 65th, and 67th in sequence.

[0060] Appendix Figure 8 and 9 The figure shows the pulse evolution process when a narrow - band signal optical pulse is incident on the self - similar regenerative amplifier device of the present invention. Among them, Figure 8 For the 1 - 80 loop pulse curves in (C), the innermost one is the 1st, and the number of loops increases from the inside to the outside in sequence; Figure 8 For the 1st - 80th spectral curves in (d), the innermost one is also the 1st, and the number of loops increases from the inside to the outside in sequence. The width of the incident signal optical pulse is 10 ps, the spectral width is < 0.5 nm, the pulse energy is 1 nJ, and the central wavelength is 1030 nm. As Figure 8 shown in (a) and (b), during the pulse regeneration amplification process, as the number of amplification loops increases, the pulse energy increases accordingly. When the number of amplification loops exceeds 60 loops, the high - peak - power pulse induces the signal optical pulse to achieve self - similar amplification evolution in the self - similar regenerative amplifier device, and the pulse width and spectral width accelerate to broaden as the number of amplification loops and energy increase. The pulse shape gradually evolves from a Gaussian type to a parabolic type [see Appendix Figure 8 (c)], which conforms to the law of self - similar pulse evolution. After 80 loops of amplification, the pulse width broadens to 18 ps (1.8 times), and the spectral width broadens to nearly 30 nm (see Appendix Figure 9 ).

[0061] Embodiment 2:

[0062] The femtosecond laser chirped - pulse self - similar regenerative amplification method provided in this embodiment is the same as that in Embodiment 1, except that the structure of the spectral shaping expander 200 and the number of broadening times are different. The femtosecond laser chirped - pulse self - similar regenerative amplification device in this embodiment includes: a broadband seed source 100, a spectral shaping expander 200, a self - similar regenerative amplifier 300, and a pulse compressor 400, which are arranged in sequence from one side to the other side according to the optical path. Specifically, the broadband seed source 100, the self - similar regenerative amplifier 300, and the pulse compressor 400 in this embodiment are all the same as those in Embodiment 1, except that the structure of the spectral shaping expander 200 is different.

[0063] Specifically, the time - domain expander 210 of the spectral shaping expander 200 provided in this embodiment is an optical - fiber expander based on a chirped Bragg grating, and the spectral shaper 220 is an optical interference - type filtering shaper based on the birefringence effect;

[0064] AsFigure 4 As shown in the figure, the time-domain stretcher 210 in this embodiment includes an optical fiber circulator 201, a chirped fiber Bragg grating 202, and an optical fiber collimator 203 that are sequentially arranged in the optical path sequence. The optical fiber circulator 201 is provided with a first port, a second port, and a third port at intervals. The incident signal light of the first port can be unidirectionally transmitted to the second port, and the incident signal light of the second port can be unidirectionally transmitted to the third port. The reflection bandwidth of the chirped fiber Bragg grating 202 is 20 nm, the reflectivity > 50%, the dispersion coefficient is 50 ps / nm, and the fiber type is PM980. The typical feature of the optical fiber collimator 203 is that the working distance is 1 m, and it can collimate the incident laser to free space output.

[0065] The spectrum shaper 220 includes a third thin-film polarizer 204, a birefringent medium 205, and a fourth thin-film polarizer 206 that are sequentially arranged in the optical path sequence. The birefringent medium 205 is a quartz crystal, the birefringence coefficient B = 0.0092, and the incident laser polarization angle forms a 15° angle with the birefringent medium principal axis angle. The optical axis of the birefringent medium 205 forms a certain angle θ with the laser transmission polarization axis, 0° < θ < 90°, and the transmission function of the Lyot filter formed by the birefringent medium 205 is as shown in the attached Figure 5 dotted line.

[0066] As Figure 5 shown, assume that the central wavelength of the seed light is 1030 nm and the full width at half maximum of the spectrum is 15 nm. After spectrum shaping, its output spectrum has a saddle shape with prominent edges and a sunken center.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and do not limit the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solution should be covered within the scope of the claims of the present invention.

Claims

1. A method for self-similar regenerative amplification of femtosecond laser chirped pulses, characterized in that It includes the following steps: S1, continuously inject the seed pulse into the spectral shaping and broadening device. The spectral shaping and broadening device broadens the injected seed pulse in the time domain through the time domain broadening device and performs spectral shaping on the broadened signal light through the spectral shaper during or after the broadening process in the time domain, so that the seed pulse is broadened and the spectral intensity is a saddle-shaped chirped pulse with high intensity at both sides and low intensity in the center; S2, inject the saddle-shaped chirped pulse after time domain broadening and spectral shaping into the regeneration amplification cavity of the self-similar regeneration amplifier. After gradually amplifying back and forth multiple times through the gain crystal and the highly nonlinear crystal in the regeneration amplification cavity, the spectrum of the saddle-shaped chirped pulse obtains gain. At the same time, when the spectral intensity of the saddle-shaped chirped pulse evolves from the saddle shape to the flat shape, the flat-shaped chirped pulse continues to be gradually amplified back and forth multiple times through the gain crystal in the regeneration amplification cavity. When the peak power of the pulse exceeds the MW level, the flat-shaped chirped pulse obtains nonlinear spectral broadening when passing through the highly nonlinear crystal; during the regeneration amplification process, the signal light passes through the gain medium with a focused spot, is collimated by the lens and then passes through the highly nonlinear medium with a focused spot to enhance the nonlinear spectral broadening until the chirped pulse is self-similarly amplified to reach gain saturation, and then a high-energy chirped pulse is output; S3, inject the high-energy chirped pulse after gain saturation into the pulse compressor. After the pulse compressor compresses the high-energy chirped pulse after regeneration amplification, the signal light is output.

2. The method for femtosecond laser chirped pulse self-similar regenerative amplification according to claim 1, wherein The spectral shaping and broadening device broadens and shapes the seed pulse in the following two ways: Method 1, the seed pulse is broadened in the time domain multiple times through the time domain broadening device, and spectral shaping is performed through the spectral shaper during the time domain broadening process; Method 2, the seed pulse is broadened in the time domain once through the time domain broadening device, and the spectral shaper performs spectral shaping on the broadened pulse signal after the time domain broadening.

3. The femtosecond laser chirped pulse self-similar regenerative amplification method according to claim 1 or 2, characterized in that, The gain crystal in the self-similar regeneration amplifier is a laser crystal doped with rare earth ions. The laser crystal emits spontaneous emission laser after being excited by the pump light.

4. The method for femtosecond laser chirped pulse self-similar regenerative amplification according to claim 3, wherein The rare earth ions doped in the laser crystal are neodymium ions or ytterbium ions; the spontaneous emission laser is Yb:CaF2 spontaneous emission laser or Yb:CALGO spontaneous emission laser or Yb:CALYO spontaneous emission laser or Yb:KGW / KYW spontaneous emission laser.

5. The method for femtosecond laser chirped pulse self-similar regenerative amplification according to claim 1 or 2 or 4, characterized in that, The highly nonlinear crystal refers to a crystal material with a high third-order nonlinear optical susceptibility, including silicon dioxide or calcium fluoride or aluminum oxide.

6. A femtosecond laser chirped pulse self-similar regenerative amplification device, characterized in that, It includes a broadband seed source, a spectral shaping and broadening device, a self-similar regenerative amplifier, and a pulse compressor, which are sequentially arranged from one side to the other side in the optical path order; the broadband seed source is used to emit seed pulses to the spectral shaping and broadening device; the spectral shaping and broadening device includes a time-domain broadening device and a spectral shaper; the time-domain broadening device is used to broaden the seed pulses to the picosecond level or even the nanosecond level and finely regulate the pulse width; the spectral shaper is used to perform spectral shaping on the seed pulses so that the spectral intensity of the broadened seed pulses is a saddle-shaped chirped pulse with high intensity at both sides and low intensity in the center; the self-similar regenerative amplifier includes a pulse input and output coupling module and a pulse regenerative amplification module. The pulse input and output coupling module is used to receive the saddle-shaped chirped pulses injected by the spectral shaping and broadening device and inject the received saddle-shaped chirped pulses into the pulse regenerative amplification module; the pulse regenerative amplification module can gradually amplify the injected saddle-shaped chirped pulses back and forth multiple times, including a gain crystal and a highly nonlinear crystal. The highly nonlinear crystal is located on one side of the gain crystal, in the same optical path as the gain crystal, and together with the gain crystal, it gradually amplifies back and forth multiple times and nonlinearly broadens the spectrum back and forth multiple times until the peak power of the pulse exceeds the MW level. The signal light passes through the gain medium with a focused spot, is collimated by a lens, and then passes through the highly nonlinear medium with a focused spot to enhance the nonlinear spectral broadening until the chirped pulse self-similar amplification reaches gain saturation, and then outputs high-energy chirped pulses to the pulse input and output coupling module; after receiving the high-energy chirped pulses, the pulse input and output coupling module injects the high-energy chirped pulses into the pulse compressor; The pulse compressor is used to compress the high-energy chirped pulses after regenerative amplification and then output the signal light.

7. The femtosecond laser chirped pulse self-similar regenerative amplification device according to claim 6, characterized in that, The time-domain broadening device is an Offner-type grating time-domain broadening device, which includes a thin-film polarizer, a Faraday rotator, a half-wave plate, a diffraction grating, a concave mirror, and a convex mirror arranged in sequence in the optical path order. A roof retroreflector and a plane mirror are also provided between the half-wave plate and the diffraction grating, and the roof retroreflector is arranged close to the half-wave plate; the concave mirror and the convex mirror, and the roof retroreflector and the plane mirror are arranged in a vertically staggered manner. The radius of curvature of the convex mirror is half of the radius of curvature of the concave mirror, and the convex mirror is located at the focal position of the concave mirror; The spectral shaper is a mechanical spectral shaper, which is located between the concave mirror and the convex mirror. The mechanical spectral shaper includes one or more opaque mechanical thin sheets, and there is a slit between two adjacent opaque mechanical thin sheets.

8. The femtosecond laser chirped pulse self-similar regenerative amplification device according to claim 7, characterized in that The working bands of the thin-film polarizer, the Faraday rotator, the half-wave plate, the diffraction grating, the concave mirror, the convex mirror, the roof retroreflector, and the plane mirror are all in the 1030 nm band; the Faraday rotator can rotate the polarization angle of the incident polarized light by 45°, and cooperate with the half-wave plate and the thin-film polarizer to separate and isolate the incident light and the outgoing light and be used as an optical isolator; the grating period of the diffraction grating is 1740 line / mm, and the diffraction efficiency of the 1030 nm band laser passing through it once is >95%.

9. The femtosecond laser chirped pulse self-similar regenerative amplification device according to claim 6, characterized in that, The time-domain stretcher is an optical fiber stretcher based on a chirped Bragg grating, and the spectral shaper is an optical interference filtering shaper based on the birefringence effect; The time-domain stretcher includes an optical fiber circulator, a chirped fiber Bragg grating, and an optical fiber collimator arranged in sequence along the optical path. The optical fiber circulator is provided with a first port, a second port, and a third port at intervals. The incident signal light at the first port can be unidirectionally transmitted to the second port, and the incident signal light at the second port can be unidirectionally transmitted to the third port; the reflection bandwidth of the chirped fiber Bragg grating is 20 nm, the reflectivity > 50%, the dispersion coefficient is 50 ps / nm, and the fiber type is PM980; The spectral shaper includes a third thin-film polarizer, a birefringent medium, and a fourth thin-film polarizer arranged in sequence along the optical path. The birefringent medium is a quartz crystal, the birefringence coefficient B = 0.0092, and the incident laser polarization angle forms an angle of 15° with the main axis angle of the birefringent medium; the optical axis of the birefringent medium forms an angle θ with the laser transmission polarization axis, 0° < θ < 90°.

10. The femtosecond laser chirped pulse self-similar regenerative amplification device according to claim 6 or 7 or 8 or 9, characterized in that, The pulse input and output coupling module includes a first thin-film polarizer, a first half-wave plate, and a first Faraday rotator arranged in sequence; the first Faraday rotator is arranged close to the pulse regeneration and amplification module. The first Faraday rotator is a magneto-optical crystal device, and the polarization angle rotates by 45° after passing through the polarized light; the first Faraday rotator, together with the first half-wave plate and the first thin-film polarizer, forms an optical isolator, which can realize the coupling and separation of the incident light and the outgoing light; The pulse regeneration and amplification module further includes a first plane mirror, a Pockels cell, a quarter-wave plate, a second thin-film polarizer, and a second plane mirror arranged in sequence; the gain crystal and the high-nonlinearity crystal are located between the second plane mirror and the second thin-film polarizer; the second thin-film polarizer is arranged opposite to the first Faraday rotator. After receiving the saddle-shaped chirped pulse from the first Faraday rotator, the second thin-film polarizer can rotate the saddle-shaped chirped pulse by a set angle and then introduce it into the quarter-wave plate; A third plano-convex lens and a fourth plano-convex lens are respectively arranged on both sides of the gain crystal, and a first plano-convex lens and a second plano-convex lens are respectively arranged on both sides of the high-nonlinearity crystal. The first plano-convex lens, the second plano-convex lens, the third plano-convex lens, the fourth plano-convex lens, the first plane mirror, and the second plane mirror together form a stable regeneration cavity; The high-nonlinearity crystal is placed at the focus of the convex lens group formed by the first plano-convex lens and the second plano-convex lens, and the gain crystal is placed at the focus of the convex lens group formed by the third plano-convex lens and the fourth plano-convex lens; The Pockels cell is a quarter-wave fast electro-optical device. By controlling the opening and closing of the Pockels cell, the Pockels cell and the quarter-wave plate can together form an optical regulator to adjust the polarization direction of the polarized light; thereby enabling the pulsed light to be gradually amplified back and forth multiple times between the first plane mirror and the second plane mirror and the non-linear spectral broadening back and forth multiple times.

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