Nonlinear cascade laser amplifier based on single crystal optical fiber

Abstract

The invention discloses a nonlinear cascade laser amplifier based on a single crystal optical fiber, which relates to the technical field of laser and comprises a seed source, a pre-chirp management module, a single crystal optical fiber cascade module and a pulse compression module which are arranged along an optical path, a pumping source is further arranged between the pre-chirp management module and the single crystal optical fiber cascade module, and the pumping source emits pumping light to a light path between the pre-chirp management module and the single crystal optical fiber cascade module; the single-crystal optical fiber cascade module comprises a plurality of cylindrical single-crystal optical fibers which are connected in series. The nonlinear phase shift and the self-focusing length in the amplification process are regulated and controlled through mixed cascade of different types of single crystal optical fibers, so that few-period pulse amplification generation with high average / peak power is realized.

Description

Technical Field

[0001] The invention relates to the field of laser technology, and more particularly to a nonlinear cascade laser amplifier based on a single crystal optical fiber. Background Art

[0002] At present, high average (~W level) / peak power (~GW) ultrafast lasers, especially pulses with few optical cycles (2-5 optical cycles), have great application prospects in basic research and large scientific facilities, micro-processing of non-metallic materials, precision medicine and national defense. Since 1965, when the first passively mode-locked ruby ​​laser outputted picosecond pulse lasers, researchers have been continuously advancing the two important indicators of short pulse width and high average power, and have carried out a large number of experimental studies.

[0003] According to the differences in ultrafast laser generation technology, the methods for generating few-cycle pulses with high average / peak power can be divided into two categories: direct generation (mode-locking technology) and indirect generation (amplification technology): The first category is based on mode-locked oscillators of activated ion-doped laser materials, mainly including solid-state mode-locked lasers, fiber mode-locked lasers, disk mode-locked lasers, etc., and its structure is mainly composed of pump sources, gain media, resonant cavities, and mode-locked elements. This type of laser is often limited by the material properties of the gain medium itself, such as spectral bandwidth, damage threshold, nonlinear effects, material dispersion, etc., and it is difficult to achieve few optical cycle pulse output. Among them, with the development of mode-locking technology and mode-locking elements, solid-state mode-locked lasers can achieve shorter pulse output (1μm~17fs, 2μm~37fs), but solid-state mode-locked lasers often require high-quality laser resonators to obtain pulses with a few optical cycles, which means that the laser output coupling is low, severely limiting the average power increase (<1W); fiber mode-locked lasers exhibit very strong nonlinear effects (stimulated Brillouin scattering, etc.) when transmitted in micron-level optical fiber cores, which causes problems such as pulse splitting, limiting their high energy and high peak power improvements; in order to reduce thermal effects, disk mode-locked lasers use very thin gain media, and weak nonlinear effects make it difficult to generate narrow pulses. In addition, due to the self-phase modulation caused by the optical nonlinear effect of air, if the dispersion compensation is not sufficient, it will lead to Q-switching or Q-switched mode-locking and other phenomena, making it difficult to obtain stable mode-locked output. At present, most of the ultrafast laser pulse widths generated by this type of oscillator are in the hundreds of femtoseconds.

[0004] The second category is to generate a few-cycle pulses with high average / peak power by means of amplification technology, mainly including chirped pulse amplification technology (OPCPA) based on optical parametric process, chirped pulse amplification (CPA) combined with nonlinear post-compression technology, and nonlinear amplification technology based on optical fiber. OPCPA combines optical parametric amplification (OPA) and chirped pulse amplification (CPA). OPA technology is based on the second-order nonlinear effect of the nonlinear effect of parametric crystals. There is no heat accumulation during the amplification process. It can maintain broadband laser amplification through non-collinear phase matching and support the generation of mid-infrared pulses of the order of period. However, due to the small pulse width, the output pulse energy is limited by the damage threshold and nonlinear effects of optical components, making it difficult to further improve the amplification efficiency. The OPCPA technology uses the optical parametric process in nonlinear crystals to amplify chirped pulses. There is no gain bandwidth limitation and no energy is stored inside the crystal, which greatly reduces the limitations of the OPA technology. However, because the signal light and idler light are involved in the amplification process at the same time, the efficiency is low, and the thermal effect is serious at high repetition rate (>100KHz), making it difficult to increase the average power. In addition, the system requires a high-energy picosecond laser for synchronous pumping, which inevitably increases the complexity and is extremely costly. The amplification medium in CPA amplification combined with nonlinear post-compression technology mainly includes bulk materials and fiber materials. The CPA system based on fiber materials can achieve high average power due to its high gain and strong heat dissipation ability, but is limited by severe nonlinear effects and low laser damage threshold, and the pulse energy and peak power are low. In particular, the preparation of high-optical quality mid-infrared microstructure gain fiber and high nonlinear microstructure fiber is complex and has extremely high process requirements. Only a few teams in the world can provide them. In the amplification process of bulk material CPA system, due to the gain narrowing effect and severe thermal effect caused by the material bandwidth, it is difficult to amplify the pulse energy to a very high level and compress the pulse width to a very short level. In addition, the pre-pulse that is also amplified will seriously affect the interaction between the main pulse and the material in practical applications. Although the fiber-based nonlinear amplification technology can directly realize the generation of broadband few-cycle pulses, it is difficult to achieve high average / high peak power compatible amplification because the fiber length is much longer than the self-focusing length, which leads to pulse splitting and even fiber damage at high peak power.

[0005] Therefore, how to achieve the compatibility of peak power, high average power and high peak power of short-cycle pulses at high repetition frequency in the laser and simplify the laser structure while ensuring the output effect is an urgent problem to be solved by technical personnel in this field. Summary of the invention

[0006] In view of this, the present invention provides a single crystal fiber nonlinear cascade laser amplifier, which relates to a few-cycle, high-power pulse laser. An amplification technology based on single crystal fiber nonlinear cascade is proposed to solve the above-mentioned problem. The nonlinear phase shift and self-focusing length in the amplification process are regulated by hybrid cascading of different types of single crystal fibers, thereby achieving high average / peak power few-cycle pulse amplification generation.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A single crystal fiber nonlinear cascade laser amplifier comprises a seed source, a pre-chirp management module, a single crystal fiber cascade module and a pulse compression module arranged along an optical path; a pump source is also arranged between the pre-chirp management module and the single crystal fiber cascade module, and the pump source emits pump light to the optical path between the pre-chirp management module and the single crystal fiber cascade module; the single crystal fiber cascade module comprises a plurality of cylindrical single crystal fibers connected in series.

[0009] Preferably, the seed source is a femtosecond laser with adjustable wavelength and repetition rate, including a solid laser, a fiber laser or a laser based on frequency conversion technology.

[0010] Preferably, the pre-chirp management module uses a chirped mirror pair or ZnSe material with positive or negative group delay dispersion to achieve dispersion control and regulate the chirp amount of the seed source pulse.

[0011] Preferably, the pump source is a continuous laser, including a semiconductor laser or a fiber laser.

[0012] Preferably, the doping ions of the single crystal optical fiber include Nd 3+ , Yb 3+ , Er 3+ 、Tm 3+ 、Ho 3+ The matrix materials of single crystal optical fiber include garnet and aluminate. The spectral bandwidth and output power obtained by the single crystal optical fiber cascade module are jointly determined by nonlinear accumulation, self-focusing length and dispersion management.

[0013] Preferably, the pulse compression module uses a chirped mirror combination, including several groups of chirped mirror pairs, to provide accurate control and compensation of second-order and high-order dispersion, and achieve high-quality and low-cycle pulse compression. The number of chirped mirror pairs is determined by adding according to the actual dispersion demand.

[0014] Preferably, the chirped mirror pair includes two chirped mirrors that are offset and arranged in parallel. The input light is irradiated by the second chirped mirror and then reflected to the first chirped mirror. After multiple reflections between the two chirped mirrors, it is emitted from the first chirped mirror along the transmission path of the input light.

[0015] Preferably, the self-focusing length in the process of nonlinear accumulation and amplification is regulated by the size of the single crystal fiber and the number of cascade stages in the single crystal fiber cascade module to generate a pulsed laser with a broadband spectrum and high peak power.

[0016] Preferably, the arrangement method of the single crystal optical fiber cascade module is:

[0017] Step 1: Collect the seed light spectrum width of the seed source, set the target spectrum width of the amplified laser, and calculate the spectrum broadening amount according to the seed light spectrum width and the target spectrum width;

[0018] Step 2: Calculate the target B integral value according to the spectrum broadening amount, and set a single crystal fiber in the single crystal fiber cascade module; the relationship formula between the spectrum broadening amount and the target B integral value B is:

[0019]

[0020] Among them, Δω out and Δω in are the frequency widths of the output and input spectra, respectively;

[0021] Step 3: Collect the laser power and laser focusing radius of the laser output from the current single crystal fiber, and calculate the self-focusing length Z of the laser in the current single crystal fiber f , expressed as:

[0022]

[0023] Where P is the laser power, ω0 is the laser focusing radius, n0 and n2 are the linear refractive index and nonlinear refractive index of the single crystal fiber respectively;

[0024] The length of the current-stage single crystal optical fiber is set to be less than the self-focusing length and greater than the preset minimum length; the minimum length is set to 30 mm;

[0025] Step 4: Collect the frequency domain characteristics, time domain characteristics and power level of the output laser of the current single crystal fiber. The frequency domain characteristics include the spectrum width and the central wavelength, and the time domain characteristics include the pulse width. Combined with the volume integral model, the effective mode volume corresponding to different signal light transmission parameters is calculated. The axial laser intensity at any position when the laser is transmitted in the current single crystal fiber is calculated based on the effective mode volume.

[0026] Step 5: Calculate the actual B integral value B′ at different amplification powers according to the B integral formula and the nonlinear refractive index and axial laser intensity of the current-stage single crystal fiber, expressed as:

[0027]

[0028] Where n2 represents the nonlinear refractive index of the single crystal fiber, I(z) represents the axial laser intensity, and λ represents the wavelength of the light emitted by the seed source;

[0029] Step 6: If the actual B integral value is less than the target B integral value, add a level of single crystal optical fiber and return to step 3 until the actual B integral value is greater than or equal to the target B integral value.

[0030] Preferably, the length of the single crystal fiber (gain medium length) L gain Less than the self-focusing length Z f , expressed as:

[0031]

[0032] Where I0 represents the axial laser intensity at the laser focusing radius ω0.

[0033] Through the above technical solutions, it can be known that compared with the prior art, the present invention discloses a single crystal fiber nonlinear cascade laser amplifier, which has a simple design structure, convenient operation, easy integration, and easy industrialization through the characteristic advantages of the single crystal fiber cascade structure and the technical characteristics of nonlinear amplification. The single crystal fiber cascade structure is composed of multiple single crystal fiber gain modules connected in series to achieve nonlinear amplification, that is, nonlinear phase shift is generated while power amplification, and spectrum broadening is achieved through nonlinear accumulation (SPM effect), thereby breaking through the gain bandwidth limitation and achieving the generation of few-cycle pulses after dispersion management. The specific beneficial effects are as follows:

[0034] 1) It is expected to solve the contradiction between high average and high peak power. With the large surface area to volume ratio, high thermal conductivity and long gain region of SCF itself, the thermal effect is effectively reduced to increase the average power; the cascade structure is used to regulate the nonlinear phase shift and self-focusing length during the amplification process, and the pulse splitting, beam distortion, light breakdown and other problems caused by the self-focusing effect are reduced. At the same time, the laser free space transmission reduces the axial light intensity of the SCF, avoids laser damage, and obtains high peak power.

[0035] 2) No additional nonlinear post-compression process is required, and ultra-wideband spectrum is obtained through nonlinear cascade to support the generation of short-cycle pulses. The self-phase modulation (SPM) effect in each SCF is used to cause nonlinear broadening of the spectrum, and the B integral is controlled to accumulate step by step rather than continuously through cascade mode, and finally the dispersion-compensated compressed pulse is at least optical period, without the need for additional nonlinear post-compression process.

[0036] 3) The structure is simple and compact, easy to operate and popularize. The nonlinear cascade structure previously used continuous laser pumping, and each level of SCF gain module was connected in series. Compared with the OPCPA system and the traditional gain medium CPA combined with nonlinear post-compression scheme, the structure is simpler and easier to operate, providing convenience for subsequent popularization and application.

[0037] This invention will provide a new research solution for the field of few-cycle pulse generation and amplification technology. The high-performance laser pulses obtained have important application potential in basic research and large scientific facilities, micro-processing of semiconductors and transparent organic materials, ultra-long-distance reconnaissance and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0039] Figure 1 A schematic diagram of the structure of a single crystal fiber nonlinear cascade laser amplifier provided by the present invention;

[0040] Figure 2 A schematic diagram of the chirped mirror combination structure consisting of two groups of chirped mirror pairs provided by the present invention. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The embodiment of the present invention discloses a nonlinear cascade laser amplifier based on a single crystal fiber, such as Figure 1 As shown, it includes a seed source 1, a pre-chirp management module 2, a single crystal fiber cascade module 4 and a pulse compression module 5 arranged along the optical path. A pump source 3 is also arranged between the pre-chirp management module 2 and the single crystal fiber cascade module 4 to emit pump light to the optical path between the two; the single crystal fiber cascade module 4 includes a plurality of cylindrical single crystal fibers connected in series.

[0043] Furthermore, the seed source 1 is a commercial or homemade femtosecond laser with adjustable wavelength and repetition rate, which may be a solid laser, a fiber laser, or a laser based on frequency conversion technology, and its output wavelength corresponds to the emission wavelength of a single crystal optical fiber.

[0044] Furthermore, the pre-chirp management module 2 utilizes optical elements or materials with positive or color group delay dispersion to achieve dispersion control and regulate the chirp amount; the optical element may be a chirped mirror pair, and the material may be a ZnSe material.

[0045] Furthermore, the pump source 3 is a continuous laser, including a semiconductor laser and a fiber laser.

[0046] Furthermore, the doping ions of the single crystal optical fiber include Nd 3+ , Yb 3+ , Er 3+ 、Tm 3+ 、Ho 3+ The matrix materials of single crystal optical fiber include garnet and aluminate. The spectral bandwidth and output power obtained by the single crystal optical fiber cascade module are jointly determined by nonlinear accumulation, self-focusing length and dispersion management.

[0047] Furthermore, the pulse compression module 5 uses a chirped mirror combination to perform second-order and high-order dispersion compensation on the amplified pulse laser, and controls the amount of introduced dispersion by changing the number of reflections on the chirped mirror combination, thereby achieving the generation of a few-cycle pulse; the chirped mirror combination includes at least one pair of chirped mirror pairs, and the number of chirped mirrors can be set according to actual needs. The chirped mirror combination consisting of two groups of chirped mirror pairs is as follows: Figure 2 shown.

[0048] Furthermore, the chirped mirror pair includes two chirped mirrors that are offset and arranged in parallel. The input light is irradiated by the second chirped mirror and then reflected to the first chirped mirror. After multiple reflections between the two chirped mirrors, it is emitted from the first chirped mirror along the transmission path of the input light.

[0049] On the other hand, in a specific embodiment, a single crystal fiber nonlinear cascade laser amplifier is a 2-micron laser based on Ho:SCF single crystal fiber nonlinear cascade amplification. The single crystal fiber cascade module 4 uses Ho-doped single crystal fiber (Ho:SCF), and both light-passing end faces of all Ho:SCF are plated with an anti-reflection film with a transmittance of ≥99% for the pump light in the 1940 band; the absorption length of Ho:SCF is regulated according to the self-focusing length of the amplification process, usually 30 to 50 mm.

[0050] The pump source 3 is a thulium-doped all-fiber laser with an output wavelength of 1940 nm, coupled with a pigtail output, and its pumping mode is end-face pumping.

[0051] Seed source 1 is a 2μm solid-state mode-locked laser based on rare earth ion doping, in which wavelength tuning is achieved through a birefringent filter, outputting <100fs pulses close to the Fourier transform limit, and a pulse picker is used for pulse frequency selection.

[0052] Pre-chirp management module 2 uses ZnSe polycrystalline with different lengths (30-60mm) and double-ended Brewster angle cut to provide positive dispersion (GVD ~ 240fs 2 / mm), chirped mirror combination (GDD~-1000fs 2 / bounce) provides negative dispersion to perform pre-chirp management (including zero chirp) on the seed source, and regulates the dispersion of the seed source before amplification to widen the pulse to 0.3-1ps.

[0053] The pulse compression module 5 uses a chirped mirror combination to provide negative dispersion for pulse compression, measures the quality of the compressed pulse to optimize the pre-chirp management module and the dispersion compensation amount, and the chirped mirror combination includes at least one group of chirped mirrors. The pulse compression module 5 regulates the dispersion of the amplified seed source, because the seed source amplified by the single crystal fiber cascade module will introduce positive dispersion, resulting in a wider pulse, and a chirped mirror is needed to provide negative dispersion to achieve pulse width compression.

[0054] The single crystal fiber cascade module 4 adopts a four-stage nonlinear cascade. Assuming that the average power after amplification by the fourth-stage single crystal fiber (SCF) is 100W, the repetition rate is 1MHz, the spectrum half width is about 50nm, and the spot radius reaching the fourth-stage SCF is ω0=350μm. The self-focusing length can be calculated to be about 55mm using the self-focusing length formula. Therefore, it is necessary to control the length of the fourth-stage SCF within 55mm to ensure that the beam distortion, pulse splitting or light breakdown will not be caused during the amplification process. At the same time, the corresponding B-integral value of this stage is calculated to be about π using the B-integral formula. According to the spectrum broadening factor, when the B-integral is greater than 2.5, the broadening factor is linearly related to the B-integral value. In order to effectively guarantee the beam transmission parameters, the size parameters of the first three-stage SCF and the focusing parameters of the pump light and the laser are adjusted so that the B-integral value inside the SCF is less than π. The spectrum broadening factor formula is used to calculate that the fourth-order broadening is 3 times the input spectrum, and the half-peak width Δλ is ~150nm, which is enough to support the generation of 50fs pulses. The total four-level nonlinear accumulation is about 3.5π. If the last stage uses a high nonlinear (n2) undoped aluminate SCF to enhance the SPM effect, the corresponding B integral value will be larger, and the total phase shift of the four-level nonlinear cascade is much larger than 3.5π. After spectrum broadening, it can cover 1850nm-2400nm, the Fourier transform limit width is ~16fs, and three-cycle pulses are generated.

[0055] On the other hand, the specific process of determining the arrangement of each level of single crystal optical fibers in the single crystal optical fiber cascade module is as follows:

[0056] S1: The pre-chirp management module 2 stretches the seed source 1 pulse to the picosecond level, collects the seed light spectrum width of the seed source, sets the target spectrum width of the amplified laser, and calculates the spectrum stretching amount according to the seed light spectrum width and the target spectrum width;

[0057] S2: Calculate the target B integral value according to the spectrum broadening amount, and set a single crystal fiber in the single crystal fiber cascade module;

[0058] The spectral broadening can be calculated as:

[0059]

[0060] where Δω out and Δω in are the frequency widths of the output and input spectra, respectively, and B is the calculated B integral;

[0061] S3: Measure the laser power and laser focusing radius of the single-stage single-crystal fiber output laser, and calculate the self-focusing length Z of the laser in the current-stage single-crystal fiber f , expressed as:

[0062]

[0063] Wherein, P is the laser power, which is the data obtained by measurement; ω0 is the laser focusing radius, which is the data obtained by measurement; n0 and n2 are the linear refractive index and nonlinear refractive index of the single crystal fiber, respectively, which are the data known from the single crystal fiber material;

[0064] The length of the current-stage single crystal optical fiber is set to be less than the self-focusing length and greater than the preset minimum length; the minimum length is set to 30 mm;

[0065] S4: Measure the frequency domain, time domain characteristics and power level of the laser after the nonlinear cascade of a single-stage single-crystal fiber. The frequency domain characteristics include the spectrum width and central wavelength, and the time domain characteristics include the pulse width. The effective mode volume corresponding to different signal light transmission parameters is calculated through the volume integral model, and the axial laser intensity at any position when the laser is transmitted in the current stage of the single-crystal fiber is calculated based on the effective mode volume;

[0066] S5: According to the B integral formula and the nonlinear refractive index and axial laser intensity of the current-stage single-crystal fiber, the actual B integral value B′ under different amplification powers is calculated and expressed as:

[0067]

[0068] Wherein, n2 represents the nonlinear refractive index of the single crystal fiber, which is the data known from the single crystal fiber material; I(z) represents the axial laser intensity, which is the data obtained by measurement; λ represents the wavelength of the light emitted by the seed source, which is the data known from the selected seed source; B integral is used to calculate the nonlinear phase shift after each level, and the nonlinear accumulation is regulated by optimizing the axial light intensity distribution, thereby controlling the nonlinear broadening degree of the pulse spectrum during the amplification process;

[0069] S6: If the actual B-integral value is less than the target B-integral value, an additional single-crystal optical fiber is added, and the process returns to S3. The frequency domain and time domain characteristics of the laser after the two-stage, three-stage, and four-stage nonlinear cascades are measured in turn, and the B-integral values ​​at different amplification powers are calculated until the actual B-integral value is greater than or equal to the target B-product.

[0070] Furthermore, by controlling the axial laser intensity and SCF length during nonlinear amplification, it can be operated in a state between spectrum broadening and pulse splitting, that is, to control the SCF length (gain medium length) L gain Smaller than the self-focusing length Z in the SCF f :

[0071]

[0072] I0 represents the axial laser intensity at the laser focusing radius ω0; the overall system needs to optimize the cascade number, SCF size parameters of each level, and focusing parameters of pump light and laser according to the amplification power level, spectral nonlinear broadening and beam quality. Among them, the power amplification level is related to the axial laser intensity I(z) of the formula, and is proportional. The higher the amplification power level, the greater the B integral; the spectral nonlinear broadening is the change in the spectral half-width before and after amplification, which corresponds to the frequency broadening F; the self-focusing effect may deteriorate the beam quality during the amplification process, and the self-focusing length Z f Affects the beam quality.

[0073] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0074] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A single crystal fiber nonlinear cascade laser amplifier, characterized in that: It includes a seed source, a pre-chirp management module, a single crystal fiber cascade module and a pulse compression module arranged along the optical path; A pump source is also arranged between the pre-chirp management module and the single crystal fiber cascade module, and the pump source emits pump light to the optical path between the pre-chirp management module and the single crystal fiber cascade module; the single crystal fiber cascade module includes a plurality of cylindrical single crystal fibers connected in series.

2. The single crystal fiber nonlinear cascade laser amplifier according to claim 1, characterized in that: The seed source is a femtosecond laser with adjustable wavelength and repetition rate, including a solid-state laser, a fiber laser or a laser based on frequency conversion technology.

3. The single crystal fiber nonlinear cascade laser amplifier according to claim 1, characterized in that: The pre-chirp management module uses chirped mirror pairs or ZnSe materials with positive or negative group delay dispersion.

4. The single crystal fiber nonlinear cascade laser amplifier according to claim 1, characterized in that: The pump source adopts a continuous laser, including a semiconductor laser or a fiber laser.

5. The single crystal fiber nonlinear cascade laser amplifier according to claim 1, characterized in that: The doping ions of single crystal optical fibers include Nd 3+ , Yb 3+ , Er 3+ 、Tm 3+ 、Ho 3+ One of them; the matrix materials of single crystal optical fiber include garnet and aluminate.

6. The single crystal fiber nonlinear cascade laser amplifier according to claim 1, characterized in that: The pulse compression module adopts a chirped mirror combination, including a plurality of chirped mirror pairs, and the plurality of chirped mirror pairs are arranged along the optical path.

7. A single crystal fiber based nonlinear cascade laser amplifier according to claim 3 or 6, characterized in that: The chirped mirror pair includes two chirped mirrors that are offset and arranged in parallel. After the input light is irradiated by the second chirped mirror, it is reflected to the first chirped mirror. After multiple reflections between the two chirped mirrors, it is emitted from the first chirped mirror along the transmission path of the input light.

8. The single crystal fiber nonlinear cascade laser amplifier according to claim 1, characterized in that: By regulating the self-focusing length during nonlinear accumulation and amplification by the size of the single crystal fiber and the number of cascade stages in the single crystal fiber cascade module, a pulsed laser with a broadband spectrum and high peak power is generated.

9. The single crystal fiber nonlinear cascade laser amplifier according to claim 8, characterized in that: The arrangement method of single crystal fiber cascade modules is: Step 1: Collect the seed light spectrum width of the seed source, set the target spectrum width of the amplified laser, and calculate the spectrum broadening amount according to the seed light spectrum width and the target spectrum width; Step 2: Calculate the target B integral value according to the spectrum broadening amount, and set a single crystal fiber in the single crystal fiber cascade module; Step 3: Collect the laser power and laser focusing radius of the laser output from the current single crystal fiber, and calculate the self-focusing length Z of the laser in the current single crystal fiber f , expressed as: Where P is the laser power, ω0 is the laser focusing radius, n0 and n2 are the linear refractive index and nonlinear refractive index of the single crystal fiber respectively; The length of the current-stage single crystal optical fiber is set to be less than the self-focusing length and greater than the preset minimum length; Step 4: Collect the frequency domain characteristics, time domain characteristics and power level of the output laser of the current single crystal fiber, and calculate the effective mode volume corresponding to different signal light transmission parameters in combination with the volume integral model, and calculate the axial laser intensity at any position when the laser is transmitted in the current single crystal fiber according to the effective mode volume; Step 5: Calculate the actual B integral value B′ at different amplification powers according to the B integral formula and the nonlinear refractive index and axial laser intensity of the current-stage single crystal fiber, expressed as: Where n2 represents the nonlinear refractive index of the single crystal fiber, I(z) represents the axial laser intensity, and λ represents the wavelength of the light emitted by the seed source; Step 6: If the actual B integral value is less than the target B integral value, add a level of single crystal optical fiber and return to step 3 until the actual B integral value is greater than or equal to the target B integral value.

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