A few-cycle pulse generation system and method based on pulse shaping

Abstract

The scheme discloses a few-cycle pulse generation system and method based on pulse shaping, wherein: a superfast laser module is used to output a high-energy pulse laser, and the high-energy pulse laser is injected into a pulse shaping module; the pulse shaping module is used to determine a parabolic pulse waveform according to parameter configuration of a nonlinear spectral broadening module, and obtain a parabolic pulse with a steep time-domain front edge according to the parabolic pulse waveform; the nonlinear spectral broadening module is used to realize nonlinear spectral broadening, and obtain a spectral broadening pulse laser with approximate linear chirp; and a pulse compression module is used to perform dispersion compensation and pulse compression on the spectral broadening pulse laser, and obtain a target pulse laser with high energy and few cycles. The scheme can effectively solve the nonlinear chirp accumulation problem in the traditional Gaussian pulse post-compression scheme, can realize higher-quality pulse compression, thereby realizing high-energy few-cycle pulse laser transmission with a narrower pulse width, and further providing a high-performance driving light source for the generation of attosecond pulses.

Description

Technical Field

[0001] This solution relates to the field of laser technology, and in particular to a few-period pulse generation system and method based on pulse shaping. Background Technology

[0002] High-energy, few-period pulsed lasers, possessing both extremely short pulse widths and extremely high peak power, demonstrate irreplaceable value in several key fields, including precision materials processing, advanced laser medicine, and cutting-edge basic scientific research. It is particularly noteworthy that these pulsed lasers are currently the only driving source capable of generating attosecond pulses, which have crucial applications in real-time observation of ultrafast dynamics processes at the atomic and molecular levels. Currently, the main technical approaches for obtaining high-energy, few-period laser pulses include two methods: optical parametric amplification (OPA) and a combination of chirped-pulse amplification (CPA) followed by compression.

[0003] OPA technology achieves wavelength tuning through parametric processes in nonlinear crystals. Although it has the advantage of continuously adjustable output wavelength, it has extremely stringent requirements for the spatiotemporal overlap of seed light and pump light. Furthermore, the nonlinear crystal itself is sensitive to temperature fluctuations, resulting in poor system stability and high environmental requirements. Therefore, it is limited in industrial applications that require high stability.

[0004] CPA (Continuous Phase Activation) technology, combined with a post-compression system, injects a high-energy pulsed laser (typically a Gaussian pulse) from the CPA amplification chain into a nonlinear medium, utilizing the medium's nonlinear effects, such as the Kerr effect, to broaden the pulse spectrum. According to the Fourier transform limit theory, dispersion compensation can theoretically yield a narrower pulse width. However, this traditional approach has inherent limitations: when a Gaussian pulse propagates in a nonlinear gas medium, it is simultaneously subjected to self-phase modulation and self-steepening effects, accumulating significant nonlinear chirps. These chirps exhibit complex spatiotemporal coupling characteristics, making them difficult to completely cancel out by subsequent conventional dispersion compensation elements.

[0005] Since nonlinear chirp cannot be effectively compensated, the resulting compressed pulse is often accompanied by time base and waveform distortion, leading to a significant reduction in pulse peak power and a decrease in compressed pulse quality. Specifically, the pulse time-domain profile deviates from the ideal transform limit shape, exhibiting leading wing or trailing edge base. This not only significantly reduces the effective utilization rate of pulse energy after amplification by the CPA system but also severely restricts the practical performance of short-cycle pulses in high-precision applications. Summary of the Invention

[0006] This solution aims to at least address the technical problems existing in the prior art. To this end, the first aspect of this invention proposes a few-period pulse generation system based on pulse shaping. The system includes an ultrafast laser module, a pulse shaping module, a nonlinear spectral broadening module, and a pulse compression module connected sequentially; wherein: The ultrafast laser module is used to output high-energy pulsed laser and inject the high-energy pulsed laser into the pulse shaping module; The pulse shaping module is used to determine the parabolic pulse waveform according to the parameter configuration of the nonlinear spectral broadening module, and to obtain a parabolic pulse with a steep time-domain leading edge based on the parabolic pulse waveform. The nonlinear spectral broadening module is used to receive the parabolic pulse with a steep time-domain leading edge, and achieves nonlinear spectral broadening under the combined effect of self-phase modulation and self-steepening effect, to obtain a spectrally broadened pulsed laser with approximately linear chirp. The pulse compression module is used to perform dispersion compensation and pulse compression on the spectrally broadened pulsed laser to obtain a high-energy, short-period target pulsed laser.

[0007] Optionally, the pulse shaping module is a Fourier transform time-domain pulse shaper; the time-domain pulse shaper consists of a pair of gratings, a pair of lenses, and a phase plate; The dual grating pair consists of a pair of diffraction gratings, symmetrically distributed at both ends of the entire optical path; The dual lens consists of a pair of parallel lenses, wherein the object-side focal plane of the left lens coincides with the left grating, and the object-side focal plane of the right lens coincides with the phase plate. The phase plate is placed at the center of symmetry of the dual grating pair.

[0008] Optionally, the nonlinear spectral broadening module is constructed based on an air-filled hollow fiber and includes a coupling lens and an air-filled hollow fiber. The gas filling the air-filled hollow optical fiber is any one of the following: He, Ne, Ar, Kr, Xe, N2, air, or a mixture of gases in different proportions.

[0009] Optionally, the nonlinear spectral broadening module is constructed based on an inflatable multi-channel cavity, including an input coupling mirror, a concave reflector, an inflatable multi-channel chamber, and an output coupling mirror; The input coupling mirror and the output coupling mirror are located at opposite ends of the gas-filled multi-pass chamber. The concave reflector corresponds to the position of the input coupling mirror and is used to cooperate with the output coupling mirror to form a resonant structure of the multi-pass chamber, so that the light beam passes through the gas medium multiple times in the chamber, accumulating nonlinear effects to broaden the spectrum. The gas filled in the inflatable multi-channel cavity is any one of the following: He, Ne, Ar, Kr, Xe, N2, air, or a mixture of gases in different proportions.

[0010] Optionally, the pulse compression module is a pair of chirped mirrors or a pair of dual gratings; the reflectivity of the chirped mirrors is greater than or equal to 99.9%, and the pair of dual gratings adopts a multilayer dielectric film grating with a reflectivity greater than or equal to 99.9%.

[0011] A second aspect of this invention proposes a few-period pulse generation method based on pulse shaping, wherein the method is applied to the few-period pulse generation system based on pulse shaping described in the first aspect, the system comprising: an ultrafast laser module, a pulse shaping module, a nonlinear spectral broadening module, and a pulse compression module, and the method comprising: The ultrafast laser module outputs high-energy pulsed laser and injects the high-energy pulsed laser into the pulse shaping module; The pulse shaping module shapes the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a pre-determined parabolic pulse waveform; the parabolic pulse waveform is determined according to the parameter configuration of the nonlinear spectral broadening module. The parabolic pulse with a steep time-domain leading edge is coupled into a nonlinear spectral broadening module for transmission. Nonlinear spectral broadening is achieved under the combined effect of self-phase modulation and self-steepening effect of the nonlinear spectral broadening module, resulting in a spectrally broadened pulsed laser with approximately linear chirp. The spectrally broadened pulsed laser is injected into a pulse compression module for pulse compression to obtain a high-energy, short-period target pulsed laser.

[0012] Optionally, when the nonlinear spectral broadening module is constructed based on an air-filled hollow fiber, the parabolic pulse waveform is determined by the length of the air-filled hollow fiber, the type of the air-filling medium, and the air-filling pressure. When the nonlinear broadening module is constructed based on an inflatable multi-pass cavity, the parabolic pulse waveform is determined by the number of passes, length, and inflation pressure of the inflatable multi-pass cavity.

[0013] Optionally, the pulse shaping module is a Fourier transform time-domain pulse shaper; the pulse shaping module shapes the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a predetermined parabolic pulse waveform, including: When the high-energy pulsed laser passes through the first grating of the double grating pair, the different frequencies of the high-energy pulsed laser are spatially separated to obtain pulsed lasers of each frequency component. The pulsed lasers of each frequency component are incident on the first lens of the lens pair and focused onto the phase plate by the first lens; The phase plate modulates the amplitude and phase of the pulsed laser of each frequency component according to a predetermined parabolic pulse waveform to obtain a modulated pulse. The modulation pulse is incident on the second lens of the lens pair and then focused by the second lens onto the second grating; The second grating compresses and resynthesizes the modulation pulse to obtain a parabolic pulse with a steep leading edge in the time domain.

[0014] Optionally, the nonlinear spectral broadening module is constructed based on an air-filled hollow fiber, and the nonlinear spectral broadening achieved under the combined effect of self-phase modulation and self-steepening of the nonlinear spectral broadening module includes: The parabolic pulse with a steep time-domain leading edge is injected into the air-filled hollow fiber through a coupling lens; During the transmission of the parabolic pulse with a steep time-domain leading edge in the air-filled hollow fiber, the high-intensity light field in the air-filled hollow fiber interacts with the gas molecules. Under the combined effect of self-phase modulation and self-steepening, the spectrum is broadened towards the red and blue ends, achieving nonlinear spectral broadening.

[0015] Optionally, the nonlinear spectral broadening module is constructed based on an inflatable multi-cavity structure. The nonlinear spectral broadening achieved under the combined effect of self-phase modulation and self-steepening of the nonlinear spectral broadening module includes: The parabolic pulse with a steep time-domain leading edge modulates the beam to match the intrinsic mode of the multi-pass cavity through a concave reflector, and then guides it into the inflatable multi-pass cavity through a coupling input mirror. The parabolic pulse with a steep time-domain leading edge is transmitted and refracted multiple times between two concave mirrors inside the gas-filled multi-pass cavity, and interacts with the gas inside the cavity. Under the combined effect of self-phase modulation and self-steepening, nonlinear spectral broadening is achieved.

[0016] The embodiments of the present invention have the following beneficial effects: This invention provides a few-period pulse generation system based on pulse shaping. The system includes an ultrafast laser module, a pulse shaping module, a nonlinear spectral broadening module, and a pulse compression module connected in sequence. The ultrafast laser module outputs a high-energy pulsed laser and injects it into the pulse shaping module. The pulse shaping module determines a parabolic pulse waveform based on the parameter configuration of the nonlinear spectral broadening module and obtains a parabolic pulse with a steep time-domain leading edge based on the parabolic pulse waveform. The nonlinear spectral broadening module receives the parabolic pulse with a steep time-domain leading edge and achieves nonlinear spectral broadening under the combined effect of self-phase modulation and self-steepening, resulting in a spectrally broadened pulsed laser with approximately linear chirp. The pulse compression module performs dispersion compensation and pulse compression on the spectrally broadened pulsed laser to obtain a high-energy, few-period target pulsed laser. This scheme can effectively solve the nonlinear chirp accumulation problem in the traditional Gaussian pulse compression scheme, and can achieve higher quality pulse compression, thereby realizing high-energy, short-period pulse laser transmission with narrower pulse width, and thus providing a high-performance driving light source for the generation of attosecond pulses. Attached Figure Description

[0017] Figure 1 A schematic diagram of a few-period pulse generation system based on pulse shaping provided in an embodiment of the present invention; Figure 2 This is a simulation result diagram of pulse evolution according to an embodiment of the present invention; Figure 3 A comparison of the compression results of a traditional Gaussian pulse and a shaped parabolic pulse with a steep time-domain leading edge, provided for embodiments of the present invention, after passing through an air-filled hollow fiber and dispersion compensation. Figure 4 This is a schematic diagram of a Fourier transform time-domain pulse shaper provided in an embodiment of the present invention; Figure 5 A schematic diagram of another few-period pulse generation system based on pulse shaping provided in an embodiment of the present invention; Figure 6 The flowchart illustrates the steps of a few-period pulse generation method based on pulse shaping, as provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present solution, and not all embodiments. Based on the embodiments of the present solution, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present solution.

[0019] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0020] The purpose of this invention is to provide a few-period pulse generation system based on pulse shaping. By using pulse shaping, a parabolic pulse with a steep leading edge in the time domain is obtained. Then, in a post-compression device, under the combined effect of self-phase modulation and self-steepening effect, it gradually evolves into a pulsed laser with approximately linear chirp. This can solve the problem of nonlinear chirp accumulation in the traditional Gaussian pulse post-compression scheme, thereby realizing the transmission of high-energy few-period pulsed lasers with narrower pulse widths, and thus providing a high-performance driving light source for the generation of attosecond pulses.

[0021] Figure 1 This is a schematic diagram of a few-period pulse generation system based on pulse shaping, provided as an embodiment of the present invention.

[0022] like Figure 1 As shown, the system includes an ultrafast laser module 10, a pulse shaping module 11, a nonlinear spectral broadening module 12, and a pulse compression module 13 connected in sequence; wherein: The ultrafast laser module is used to output high-energy pulsed laser and inject the high-energy pulsed laser into the pulse shaping module; The pulse shaping module is used to determine the parabolic pulse waveform according to the parameter configuration of the nonlinear spectral broadening module, and to obtain a parabolic pulse with a steep time-domain leading edge based on the parabolic pulse waveform. The nonlinear spectral broadening module is used to receive the parabolic pulse with a steep time-domain leading edge, and achieves nonlinear spectral broadening under the combined effect of self-phase modulation and self-steepening effect, to obtain a spectrally broadened pulsed laser with approximately linear chirp. The pulse compression module is used to perform dispersion compensation and pulse compression on the spectrally broadened pulsed laser to obtain a high-energy, short-period target pulsed laser.

[0023] The core objective of this scheme is to overcome the pulse width limitation of conventional ultrafast lasers and obtain ultrashort pulses with fewer cycles (generally <10 optical cycles, or even 2-3 optical cycles), high energy, and high peak power.

[0024] The overall technical route of the scheme is: high-energy pulsed laser → pre-shaping into a "parabolic pulse with a steep time-domain leading edge" → nonlinear spectral broadening module (self-phase modulation + self-steepening) → generating an approximately linearly chirped pulsed laser → chirp compensation by dispersive element → short-period high peak power pulse.

[0025] Ultrafast laser modules typically use near-Gaussian time-domain waveforms and conventional pulses with narrow spectra. For example, a high-energy pulsed laser has a center wavelength of 800 nm, a repetition rate of 1000 Hz, a pulse energy of 15 mJ, and a pulse width of 30 fs.

[0026] The pulse shaping module is an acousto-optic programmable dispersion filter or a Fourier transform time-domain pulse shaper. It belongs to the joint modulation of time domain and spectral domain and can simultaneously control the pulse's time-domain waveform, amplitude distribution, initial chirp, and leading / trailing slope.

[0027] Parabolic pulses are theoretically among the best pre-shaped waveforms in ultrafast nonlinear optics. The time-domain amplitude distribution of a parabolic pulse is a quadratic function. When propagating in a nonlinear medium, the self-phase modulation does not affect the shape of the time-domain pulse. Therefore, parabolic pulses can suppress the distortion of nonlinear chirps at the source and are naturally adapted to subsequent linear chirped output targets.

[0028] A single parabolic pulse is not enough. This scheme additionally steepens the time-domain leading edge. Its core function is to suppress the steepness of the pulse trailing edge caused by the self-steepening effect in nonlinear transmission. The steepness of the pulse trailing edge distorts the linear chirp of the pulse. Steepening the leading edge can pre-compensate for the steepness of the trailing edge caused by the self-steepening effect, making the time-domain symmetry of the pulse after spectral broadening more controllable and avoiding chirp disorder caused by the steepness of the trailing edge.

[0029] Figure 2 This is a simulation result diagram of pulse evolution according to an embodiment of the present invention.

[0030] in, Figure 2 (a) is a standard parabolic pulse. Figure 2 (b) is a parabolic pulse with a steep time-domain leading edge generated after passing through the pulse shaping module; Figure 2 (c) The solid line represents the pulse waveform obtained after the parabolic pulse with a steep time-domain leading edge is transmitted through an air-filled hollow fiber, and the dashed line represents the corresponding approximate linear chirped distribution.

[0031] The pulse shaping module reversely sets the peak power, leading edge slope, pulse width, and energy of the parabolic pulse based on the material, length, and air pressure of the nonlinear medium at the back end, so that the pulse reaches the optimal width in the nonlinear medium, achieving precise matching in engineering.

[0032] The pre-shaped parabolic pulse with a steep time-domain leading edge is coupled into a nonlinear spectral broadening module, which generates an approximately linear chirp through self-phase modulation (SPM) and self-steepening.

[0033] Self-phase modulation is the core of spectral broadening. When a pulse propagates in a nonlinear medium, the light intensity induces an instantaneous change in the refractive index of the medium. The light intensity is different at different times of the pulse, and the corresponding instantaneous frequency is different, which generates instantaneous phase modulation, ultimately broadening the narrow spectrum into a wide spectrum. This is the basic effect of ultrafast spectral broadening.

[0034] The self-steepening effect not only broadens the spectrum asymmetrically but also makes the pulse time domain steeper towards the trailing edge. Self-steepening is caused by the change in the group velocity of the pulse in the medium with light intensity: the group velocity is slow at the peak intensity of the pulse and fast at the leading / trailing edge, eventually causing the pulse peak to shift towards the trailing edge of the pulse, resulting in a steeper waveform.

[0035] The approximately linearly chirped pulse after spectral broadening theoretically corresponds to a narrower Fourier transform-limited pulse width. The linear chirping needs to be canceled by a dispersive element to compress the time-domain pulse to an extremely narrow width at the Fourier transform limit, i.e., a few-period pulse.

[0036] The pulse compression module addresses linear chirp by using dispersion compensation elements to compensate for dispersion, delaying the leading wavelength and advancing the lagging wavelength, synchronizing all spectral components in the time domain, eliminating chirp, and compressing the pulse to its narrowest limit.

[0037] Figure 3 A comparison of the compression results of a traditional Gaussian pulse and a shaped parabolic pulse with a steep time-domain leading edge, provided in an embodiment of the present invention, after passing through an air-filled hollow fiber and dispersion compensation.

[0038] Figure 3 (a) The solid line represents the traditional Gaussian pulse output by the ultrafast laser module. Figure 3 (a) The dashed line represents the short-period pulse waveform output after the Gaussian pulse passes through an air-filled hollow fiber and undergoes dispersion compensation. Figure 3 (b) The solid line represents the parabolic pulsed laser with a steep time-domain leading edge obtained by the pulse shaping module. Figure 3 (b) The dashed line represents the short-period pulse waveform output after a parabolic pulse with a steep time-domain leading edge passes through an air-filled hollow fiber with the same configuration and dispersion compensation.

[0039] from Figure 3It is not difficult to see that when the initial pulse is a traditional Gaussian pulse, the final output pulse width obtained by compression using hollow fiber is 8.8 fs, and the pulse has a leading edge; when the initial pulse is shaped into a parabolic pulse with a steep leading edge in the time domain using the present invention, the final output pulse width after compression using hollow fiber with the same configuration is 6.5 fs, and the pulse distortion is smaller.

[0040] The simulation results above show that the short-period pulses obtained by shaping the pulses into parabolic pulses with steep leading edges in the time domain, as proposed in this invention, have significantly better pulse quality than the traditional Gaussian pulse scheme.

[0041] As an optional embodiment, the pulse shaping module is a Fourier transform time-domain pulse shaper; the time-domain pulse shaper consists of a pair of gratings, a pair of lenses, and a phase plate; the pair of gratings consists of a pair of diffraction gratings, symmetrically distributed at both ends of the entire optical path; the pair of lenses consists of a pair of parallel lenses, wherein the object-side focal plane of the left lens coincides with the left grating, and the object-side focal plane of the right lens coincides with the phase plate; the phase plate is placed at the center of symmetry of the pair of gratings.

[0042] Figure 4 This is a schematic diagram of a Fourier transform time-domain pulse shaper provided in an embodiment of the present invention.

[0043] like Figure 4 As shown, this system is a typical 4f Fourier transform pulse shaping system. The dual-grating pair consists of a pair of diffraction gratings symmetrically distributed at both ends of the optical path. Their function is to diffuse the incident ultrashort pulse, spatially separating light components of different frequencies, allowing the phase plate to independently modulate the intensity and phase of each frequency component, thereby obtaining the target shaped pulse.

[0044] The double lens is located at the center between the two grating pairs and is parallel to the grating pairs. Its function is to focus the different frequency light components diffracted by the grating pairs onto their focal plane, forming a Fourier surface.

[0045] The phase plate is placed at the focal plane of the lens, precisely at the center of symmetry of the double grating pair. It is the core component of pulse shaping, which shapes the pulse time-domain waveform by applying specific amplitude and phase modulation to light at different spatial positions (corresponding to different frequencies).

[0046] The high-energy pulse output from the ultrafast laser module is first coupled into the Fourier transform time-domain pulse shaper. After passing through the first grating, the pulse's frequencies are dispersed laterally. The phase plate independently modulates the amplitude and phase of each frequency component. The pulse modulated by the phase plate is then incident on the second lens and focused onto the second grating. After compression by the grating, the target-shaped pulse waveform is output, which is a parabolic pulse waveform with a steep leading edge in the time domain.

[0047] As an optional embodiment, the nonlinear spectral broadening module is constructed based on an inflatable hollow fiber and includes a coupling lens and an inflatable hollow fiber; the gas filled in the inflatable hollow fiber is any one of the following: He, Ne, Ar, Kr, Xe, N2, air, or a mixture of gases in different proportions.

[0048] like Figure 1 As shown, the nonlinear spectral broadening module includes a coupling lens and an air-filled hollow fiber.

[0049] The coupling lens is located at the front end of the gas-filled hollow fiber. Its function is to efficiently focus the incident ultrafast laser pulse and couple it into the core of the hollow fiber, ensuring that the beam is transmitted in single mode within the fiber and maximizing the interaction intensity between the light and the gas medium.

[0050] Gas-filled hollow optical fiber is the core component of the module. The fiber has a hollow structure inside, filled with a specific gas. When light propagates in the fiber core, it undergoes nonlinear interactions with gas molecules, thereby broadening the spectrum.

[0051] The modules can be filled with gases including He, Ne, Ar, Kr, Xe, N2, air, or mixtures of gases in different proportions. The selection of different gases is based on the third-order nonlinear coefficient, dispersion characteristics, and gas pressure regulation. The intensity of the nonlinear effect can be controlled by flexibly adjusting the gas pressure.

[0052] For example, the hollow fiber is 5 m long, the core diameter is 1 mm, and the core is filled with nitrogen gas at a pressure of 0.2 bar.

[0053] As an optional embodiment, the nonlinear spectral broadening module is constructed based on an inflatable multi-channel cavity, including an input coupling mirror, a concave reflector, an inflatable multi-channel chamber, and an output coupling mirror; The input coupling mirror and the output coupling mirror are located at opposite ends of the gas-filled multi-pass chamber. The concave reflector corresponds to the position of the input coupling mirror and is used to cooperate with the output coupling mirror to form a resonant structure of the multi-pass chamber, allowing the light beam to pass through the gas medium multiple times within the chamber, accumulating nonlinear effects to broaden the spectrum. The gas filled in the gas-filled multi-pass chamber is any one of the following: He, Ne, Ar, Kr, Xe, N2, air, or a mixture of gases in different proportions.

[0054] Figure 5 This is a schematic diagram of another few-period pulse generation system based on pulse shaping, provided in an embodiment of the present invention.

[0055] like Figure 5 As shown, the nonlinear spectral broadening module includes an input coupling mirror, a concave mirror, an inflatable multi-pass chamber, and an output coupling mirror.

[0056] For example, 211 is a pair of high-reflectivity concave mirrors (reflectivity ≥99.9%), 212 is a coupling input mirror, 213 is a gas-filled multi-channel chamber (cavity length 1 m, cavity mirror curvature radius 500 mm, cavity mirror coated with a film with reflectivity ≥99.99%, operating wavelength range 600-1000 nm), and 214 is a coupling output mirror, with 0.8 bar of Ar gas filling the chamber; in the pulse compression module 22, 221 is a pair of high-reflectivity multilayer dielectric film gratings (reflectivity ≥99.9%).

[0057] As an optional embodiment, the pulse compression module is a pair of chirped mirrors or a pair of dual gratings; the reflectivity of the chirped mirrors is greater than or equal to 99.9%, and the pair of dual gratings adopts a multilayer dielectric film grating with a reflectivity greater than or equal to 99.9%.

[0058] Specifically, the pulse compression module consists of a pair of chirped mirrors. To ensure minimal energy transmission loss, the reflectivity of the chirped mirrors is generally above 99.9%. The laser is reflected back and forth multiple times between the two chirped mirrors to achieve dispersion compensation.

[0059] The pulse compression module can also be a pair of gratings. In order to ensure low energy transmission loss, the gratings are generally multilayer dielectric film gratings with a reflectivity of ≥99.9%.

[0060] In summary, the pulse shaping-based few-period pulse generation system provided by this invention includes an ultrafast laser module, a pulse shaping module, a nonlinear spectral broadening module, and a pulse compression module connected in sequence. Specifically: the ultrafast laser module outputs a high-energy pulsed laser and injects it into the pulse shaping module; the pulse shaping module determines a parabolic pulse waveform based on the parameter configuration of the nonlinear spectral broadening module and obtains a parabolic pulse with a steep time-domain leading edge based on the parabolic pulse waveform; the nonlinear spectral broadening module receives the parabolic pulse with a steep time-domain leading edge and achieves nonlinear spectral broadening under the combined effect of self-phase modulation and self-steepening effect, resulting in a spectrally broadened pulsed laser with approximately linear chirp; the pulse compression module performs dispersion compensation and pulse compression on the spectrally broadened pulsed laser to obtain a high-energy, few-period target pulsed laser. This scheme can effectively solve the nonlinear chirp accumulation problem in the traditional Gaussian pulse compression scheme, and can achieve higher quality pulse compression, thereby realizing high-energy, short-period pulse laser transmission with narrower pulse width, and thus providing a high-performance driving light source for the generation of attosecond pulses.

[0061] Figure 6 The flowchart illustrates the steps of a few-period pulse generation method based on pulse shaping, as provided in an embodiment of the present invention.

[0062] This method is applied to Figure 1 The system for generating few-period pulses based on pulse shaping includes: an ultrafast laser module, a pulse shaping module, a nonlinear spectral broadening module, and a pulse compression module.

[0063] like Figure 6 As shown, the method includes: Step 101: The ultrafast laser module outputs a high-energy pulsed laser and injects the high-energy pulsed laser into the pulse shaping module.

[0064] Ultrafast laser modules typically use near-Gaussian time-domain waveforms and conventional pulses with narrow spectra.

[0065] Step 102: The pulse shaping module shapes the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a pre-determined parabolic pulse waveform; the parabolic pulse waveform is determined according to the parameter configuration of the nonlinear spectral broadening module. The pulse shaping module is an acousto-optic programmable dispersion filter or a Fourier transform time-domain pulse shaper. It belongs to the joint modulation of time domain and spectral domain and can simultaneously control the pulse's time-domain waveform, amplitude distribution, initial chirp, and leading / trailing slope.

[0066] The pulse shaping module reversely sets the peak power, leading edge slope, pulse width, and energy of the parabolic pulse based on the material, length, and air pressure of the nonlinear medium at the back end, so that the pulse reaches the optimal width in the nonlinear medium, achieving precise matching in engineering.

[0067] Parabolic pulses are theoretically among the best pre-shaped waveforms in ultrafast nonlinear optics. The time-domain amplitude distribution of a parabolic pulse is a quadratic function. When propagating in a nonlinear medium, the self-phase modulation does not affect the shape of the time-domain pulse. Therefore, parabolic pulses can suppress the distortion of nonlinear chirps at the source and are naturally adapted to subsequent linear chirped output targets.

[0068] A single parabolic pulse is not enough. This scheme additionally steepens the time-domain leading edge. Its core function is to suppress the steepness of the pulse trailing edge caused by the self-steepening effect in nonlinear transmission. The steepness of the pulse trailing edge distorts the linear chirp of the pulse. Steepening the leading edge can pre-compensate for the steepness of the trailing edge caused by the self-steepening effect, making the time-domain symmetry of the pulse after spectral broadening more controllable and avoiding chirp disorder caused by the steepness of the trailing edge.

[0069] Step 103: The parabolic pulse with a steep time-domain leading edge is coupled into the nonlinear spectral broadening module for transmission. Nonlinear spectral broadening is achieved under the combined effect of self-phase modulation and self-steepening effect of the nonlinear spectral broadening module, resulting in a spectrally broadened pulsed laser with approximately linear chirp.

[0070] For example, the high-energy Gaussian pulse output by the ultrafast laser module is shaped by an acousto-optic programmable dispersion filter to obtain a target-shaped pulse waveform, namely a parabolic pulse with a steep leading edge in the time domain, such as... Figure 2 As shown in (b).

[0071] The parabolic pulse with a steep leading edge in the time domain is coupled into the nonlinear spectral broadening module after the spot transformation is completed by a lens with a focal length of 30 mm. During the transmission of the optical fiber, the pulse spectrum is broadened, and the trailing edge of the time domain pulse will gradually become steeper and carry an approximately linear chirp (as shown in Figure 2(c)).

[0072] The nonlinear spectral broadening module generates an approximately linear chirp through self-phase modulation (SPM) and self-steepening.

[0073] Self-phase modulation is the core of spectral broadening. When a pulse propagates in a nonlinear medium, the light intensity induces an instantaneous change in the refractive index of the medium. The light intensity is different at different times of the pulse, and the corresponding instantaneous frequency is different, which generates instantaneous phase modulation, ultimately broadening the narrow spectrum into a wide spectrum. This is the basic effect of ultrafast spectral broadening.

[0074] The self-steepening effect not only broadens the spectrum asymmetrically but also makes the pulse time domain steeper towards the trailing edge. Self-steepening is caused by the change in the group velocity of the pulse in the medium with light intensity: the group velocity is slow at the peak intensity of the pulse and fast at the leading / trailing edge, eventually causing the pulse peak to shift towards the trailing edge of the pulse, resulting in a steeper waveform.

[0075] Step 104: Inject the broadened pulse laser into the pulse compression module to compress the pulse, thereby obtaining a high-energy, short-period target pulse laser.

[0076] The pulse compression module addresses linear chirp by using dispersion compensation elements to compensate for dispersion, delaying the leading wavelength and advancing the lagging wavelength, synchronizing all spectral components in the time domain, eliminating chirp, and compressing the pulse to its narrowest limit.

[0077] As an optional embodiment, when the nonlinear spectral broadening module is constructed based on an inflatable hollow fiber, the parabolic pulse waveform is determined by the length of the inflatable hollow fiber, the type of inflatable medium, and the inflatable pressure; when the nonlinear broadening module is constructed based on an inflatable multi-channel cavity, the parabolic pulse waveform is determined by the number of channels, the length, and the inflatable pressure of the inflatable multi-channel cavity.

[0078] Specifically, when the nonlinear spectral broadening module is constructed based on gas-filled hollow fiber, the parabolic pulse waveform can be uniquely determined by the hollow fiber length, the type of gas filling medium, and the gas filling pressure, and its expression is:

[0079] in, , . f For standard parabolic functions, it represents the temporal envelope shape of the pulse (e.g., Figure 2 (a) shown), in Valid within the interval; T0 represents the pulse width. It is a parameter related to pulse energy. The time coordinates representing the pulse. , It is determined by both the type of gas and the pressure (e.g.) (This is the third-order nonlinear coefficient for nitrogen at a pressure of 0.2 bar). The center frequency of the pulse. The intensity of the pulsed laser. This represents the length of the hollow fiber.

[0080] When the nonlinear broadening module is constructed based on an inflatable multi-pass cavity, the parabolic pulse waveform is determined by the number of passes, length, and inflation pressure of the inflatable multi-pass cavity.

[0081] As an optional embodiment, the pulse shaping module is an acousto-optic programmable dispersion filter. The pulse shaping module shapes the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a predetermined parabolic pulse waveform, including: The dispersive filter maps a predetermined parabolic pulse waveform into a radio frequency control signal that drives its internal acousto-optic crystal based on the internal physical conversion relationship. The dispersive filter generates a dynamic diffraction grating internally according to the radio frequency control signal. When the ultrafast laser pulse passes through the dynamic diffraction grating, different frequency components of the ultrafast laser pulse are diffracted at corresponding spatiotemporal points according to the Bragg diffraction condition to obtain diffracted light. The diffracted light is spatially synthesized to obtain a parabolic pulse with a steep leading edge in the time domain.

[0082] Specifically, the pulse shaping module can be an acousto-optic programmable dispersion filter (AOPDF), whose core is based on the acousto-optic Bragg diffraction effect. By precisely controlling the frequency domain amplitude and phase of the pulse, it can realize the construction of a custom complex pulse waveform in the time domain.

[0083] As an optional embodiment, the pulse shaping module is a Fourier transform time-domain pulse shaper; in step 102, the pulse shaping module shapes the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a predetermined parabolic pulse waveform, including: Step 1021: When the high-energy pulsed laser passes through the first grating of the dual grating pair, the different frequencies of the high-energy pulsed laser are spatially separated to obtain pulsed lasers of each frequency component; Step 1022: After the pulsed laser of each frequency component is incident on the first lens of the lens pair, it is focused onto the phase plate by the first lens; Step 1023: The phase plate modulates the amplitude and phase of the pulsed laser of each frequency component according to a predetermined parabolic pulse waveform to obtain a modulated pulse; Step 1024: After the modulation pulse is incident on the second lens of the lens pair, it is focused by the second lens onto the second grating; Step 1025: The second grating compresses and resynthesizes the modulation pulse to obtain a parabolic pulse with a steep leading edge in the time domain.

[0084] In steps 1021-1025, the pulse shaping module can be a Fourier transform time-domain pulse shaper, which separates different frequencies of the incident pulse through a combination of dual gratings, and uses a phase plate to independently modulate the amplitude and phase of each frequency component, thereby achieving modulation of arbitrary time-domain pulse waveforms.

[0085] As shown in Figure 5, the shaped parabolic pulse with a steep temporal leading edge is coupled into a nonlinear spectral broadening module to achieve nonlinear spectral broadening. First, mode matching is achieved through a concave mirror, then the pulse is introduced into a gas-filled multi-pass chamber via a coupling input mirror. After multiple round trips, it is exported by a coupling output mirror. At this point, the pulse has evolved into a pulsed laser with an approximately linear chirped distribution. This pulse then undergoes dispersion compensation via a dual-grating pair, ultimately resulting in a high-energy, short-period pulsed laser output.

[0086] As an optional embodiment, the nonlinear spectral broadening module is constructed based on an air-filled hollow fiber. Step 103, which achieves nonlinear spectral broadening through the combined effects of self-phase modulation and self-steepening of the nonlinear spectral broadening module, includes: Step 1031: The parabolic pulse with a steep time-domain leading edge is injected into the air-filled hollow fiber through a coupling lens; Step 1032: During the transmission of the parabolic pulse with a steep time-domain leading edge in the air-filled hollow fiber, the high-intensity light field in the air-filled hollow fiber interacts with the gas molecules. Under the combined effect of self-phase modulation and self-steepening, the spectrum is broadened towards the red and blue ends, achieving nonlinear spectral broadening.

[0087] In steps 1031-1032, the coupling lens focuses the spatial light pulse onto the core region of the hollow fiber, ensuring high coupling efficiency. The core region of the gas-filled hollow fiber is hollow and can be filled with high-pressure gas. The intensity of the nonlinear effect can be adjusted according to the gas pressure, which is beneficial for the generation of linear chirp.

[0088] When the pulse enters the hollow fiber, the light field intensity is extremely high, and it will undergo third-order nonlinear optical interaction with the gas molecules. Under the combined effect of self-phase modulation effect and self-steepening effect, the spectrum is broadened towards the red and blue ends, realizing nonlinear spectral broadening.

[0089] As an optional embodiment, the nonlinear spectral broadening module is constructed based on an inflatable multi-cavity structure. Step 103, which achieves nonlinear spectral broadening through the combined effects of self-phase modulation and self-steepening of the nonlinear spectral broadening module, includes: Step 1033: The parabolic pulse with a steep time-domain leading edge is modulated to match the eigenmode of the multi-pass cavity by a concave reflector, and then introduced into the inflatable multi-pass cavity through a coupling input mirror; Step 1034: The parabolic pulse with a steep time-domain leading edge is transmitted back and forth multiple times between the two concave mirrors in the gas-filled multi-pass cavity and interacts with the gas in the cavity. Under the combined effect of self-phase modulation effect and self-steepening effect, nonlinear spectral broadening is achieved.

[0090] In steps 1033-1034, a multi-pass cavity is an optical structure, typically composed of two or more mirrors, that allows the light beam to travel back and forth multiple times within it, thereby increasing the effective action length. The cavity is filled with a nonlinear gas (such as argon, nitrogen, krypton, etc.), which has a moderate nonlinear coefficient and a high damage threshold, making it suitable for the nonlinear action of high peak power pulses. Within the multi-pass cavity, the pulse can travel back and forth dozens to hundreds of times, significantly accumulating a nonlinear phase shift, thus achieving spectral broadening.

[0091] In summary, the pulse shaping-based few-period pulse generation method provided by this invention includes: an ultrafast laser module outputting a high-energy pulsed laser and injecting the high-energy pulsed laser into a pulse shaping module; the pulse shaping module shaping the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a predetermined parabolic pulse waveform; the parabolic pulse waveform being determined based on the parameter configuration of a nonlinear spectral broadening module; the parabolic pulse with a steep leading edge in the time domain being coupled into the nonlinear spectral broadening module for transmission, achieving nonlinear spectral broadening under the combined effect of self-phase modulation and self-steepening effect of the nonlinear spectral broadening module, resulting in a spectrally broadened pulsed laser with approximately linear chirp; and the spectrally broadened pulsed laser being injected into a pulse compression module for pulse compression, resulting in a high-energy, few-period target pulsed laser. This solution effectively solves the problem of nonlinear chirp accumulation in traditional Gaussian pulse post-compression schemes, achieving higher quality pulse compression, thereby enabling the transmission of high-energy, few-period pulsed lasers with narrower pulse widths, and thus providing a high-performance driving light source for attosecond pulse generation.

[0092] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0093] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A few-period pulse generation system based on pulse shaping, characterized in that, The system comprises an ultrafast laser module, a pulse shaping module, a nonlinear spectral broadening module, and a pulse compression module connected in sequence; wherein: The ultrafast laser module is used to output high-energy pulsed laser and inject the high-energy pulsed laser into the pulse shaping module; The pulse shaping module is used to determine the parabolic pulse waveform according to the parameter configuration of the nonlinear spectral broadening module, and to obtain a parabolic pulse with a steep time-domain leading edge based on the parabolic pulse waveform. The nonlinear spectral broadening module is used to receive the parabolic pulse with a steep time-domain leading edge, and achieves nonlinear spectral broadening under the combined effect of self-phase modulation and self-steepening effect, to obtain a spectrally broadened pulsed laser with approximately linear chirp. The pulse compression module is used to perform dispersion compensation and pulse compression on the spectrally broadened pulsed laser to obtain a high-energy, short-period target pulsed laser.

2. The system according to claim 1, characterized in that, The pulse shaping module is a Fourier transform time-domain pulse shaper; the time-domain pulse shaper consists of a pair of gratings, a pair of lenses, and a phase plate; The dual grating pair consists of a pair of diffraction gratings, symmetrically distributed at both ends of the entire optical path; The dual lens consists of a pair of parallel lenses, wherein the object-side focal plane of the left lens coincides with the left grating, and the object-side focal plane of the right lens coincides with the phase plate. The phase plate is placed at the center of symmetry of the dual grating pair.

3. The system according to claim 1, characterized in that, The nonlinear spectral broadening module is constructed based on an air-filled hollow fiber, including a coupling lens and an air-filled hollow fiber. The gas filling the air-filled hollow optical fiber is any one of the following: He, Ne, Ar, Kr, Xe, N2, air, or a mixture of gases in different proportions.

4. The system according to claim 1, characterized in that, The nonlinear spectral broadening module is constructed based on an inflatable multi-cavity structure, including an input coupling mirror, a concave reflector, an inflatable multi-cavity chamber, and an output coupling mirror. The input coupling mirror and the output coupling mirror are located at opposite ends of the gas-filled multi-pass chamber. The concave reflector corresponds to the position of the input coupling mirror and is used to cooperate with the output coupling mirror to form a resonant structure of the multi-pass chamber, so that the light beam passes through the gas medium multiple times in the chamber, accumulating nonlinear effects to broaden the spectrum. The gas filled in the inflatable multi-channel cavity is any one of the following: He, Ne, Ar, Kr, Xe, N2, air, or a mixture of gases in different proportions.

5. The system according to claim 1, characterized in that, The pulse compression module is a pair of chirped mirrors or a pair of dual gratings; the reflectivity of the chirped mirrors is greater than or equal to 99.9%, and the pair of dual gratings uses a multilayer dielectric film grating with a reflectivity greater than or equal to 99.9%.

6. A method for generating few-period pulses based on pulse shaping, characterized in that, The method is applied to the few-period pulse generation system based on pulse shaping as described in any one of claims 1-5, the system comprising: an ultrafast laser module, a pulse shaping module, a nonlinear spectral broadening module, and a pulse compression module, the method comprising: The ultrafast laser module outputs high-energy pulsed laser and injects the high-energy pulsed laser into the pulse shaping module; The pulse shaping module shapes the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a pre-determined parabolic pulse waveform; the parabolic pulse waveform is determined according to the parameter configuration of the nonlinear spectral broadening module. The parabolic pulse with a steep time-domain leading edge is coupled into a nonlinear spectral broadening module for transmission. Nonlinear spectral broadening is achieved under the combined effect of self-phase modulation and self-steepening effect of the nonlinear spectral broadening module, resulting in a spectrally broadened pulsed laser with approximately linear chirp. The spectrally broadened pulsed laser is injected into a pulse compression module for pulse compression to obtain a high-energy, short-period target pulsed laser.

7. The method according to claim 6, characterized in that, When the nonlinear spectral broadening module is constructed based on an air-filled hollow fiber, the parabolic pulse waveform is determined by the length of the air-filled hollow fiber, the type of the air-filling medium, and the air-filling pressure. When the nonlinear broadening module is constructed based on an inflatable multi-pass cavity, the parabolic pulse waveform is determined by the number of passes, length, and inflation pressure of the inflatable multi-pass cavity.

8. The method according to claim 6, characterized in that, The pulse shaping module is a Fourier transform time-domain pulse shaper; The pulse shaping module shapes the high-energy pulsed laser into a parabolic pulse with a steep leading edge in the time domain according to a predetermined parabolic pulse waveform, including: When the high-energy pulsed laser passes through the first grating of the double grating pair, the different frequencies of the high-energy pulsed laser are spatially separated to obtain pulsed lasers of each frequency component. The pulsed lasers of each frequency component are incident on the first lens of the lens pair and focused onto the phase plate by the first lens; The phase plate modulates the amplitude and phase of the pulsed laser of each frequency component according to a predetermined parabolic pulse waveform to obtain a modulated pulse. The modulation pulse is incident on the second lens of the lens pair and then focused by the second lens onto the second grating; The second grating compresses and resynthesizes the modulation pulse to obtain a parabolic pulse with a steep leading edge in the time domain.

9. The method according to claim 6, characterized in that, The nonlinear spectral broadening module is constructed based on air-filled hollow fiber. Nonlinear spectral broadening is achieved through the combined effects of self-phase modulation and self-steepening, including: The parabolic pulse with a steep time-domain leading edge is injected into the air-filled hollow fiber through a coupling lens; During the transmission of the parabolic pulse with a steep time-domain leading edge in the air-filled hollow fiber, the high-intensity light field in the air-filled hollow fiber interacts with the gas molecules. Under the combined effect of self-phase modulation and self-steepening, the spectrum is broadened towards the red and blue ends, achieving nonlinear spectral broadening.

10. The method according to claim 6, characterized in that, The nonlinear spectral broadening module is constructed based on an inflatable multi-cavity structure. The nonlinear spectral broadening is achieved through the combined effects of self-phase modulation and self-steepening, including: The parabolic pulse with a steep time-domain leading edge modulates the beam to match the intrinsic mode of the multi-pass cavity through a concave reflector, and then guides it into the inflatable multi-pass cavity through a coupling input mirror. The parabolic pulse with a steep time-domain leading edge is transmitted and refracted multiple times between two concave mirrors inside the gas-filled multi-pass cavity, and interacts with the gas inside the cavity. Under the combined effect of self-phase modulation and self-steepening, nonlinear spectral broadening is achieved.

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