High-fidelity energy boosting of ultra-short laser pulse sequences and methods

Abstract

The application belongs to the technical field of laser, and proposes a high-fidelity energy boosting device and method for ultra-short laser pulse sequence. A mode-locked fiber oscillator, a pulse stretching fiber, a pulse sequence generation module, a fiber preamplification module, a regenerative amplification optical path, a double-pass traveling wave amplification optical path and a dispersion compensation device are arranged along a main light path. The pulse sequence generation module divides the stretched pulse into a main pulse branch and a phase modulation sub-pulse branch through a 20:80 two-way fiber coupler. The main pulse branch generates N uniform sub-pulses, and the phase modulation sub-pulse branch is combined with the main pulse sequence after phase modulation by an acousto-optic modulator to generate an N+1 type uniform pulse sequence. The acousto-optic modulator is driven by a FPGA direct digital synthesis radio frequency generator, and accurate phase programming control of a single sub-pulse is realized. The application realizes high-fidelity energy boosting output.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a high-fidelity energy enhancement device and method for ultrashort laser pulse sequences. Background Technology

[0002] Ultrashort laser pulse sequences are the core light source carriers for many cutting-edge fields such as nonlinear spectroscopy detection, molecular dynamics manipulation, and precision materials processing. Various advanced experimental scenarios continuously place higher demands on the intra-sequence repetition rate (INR) and sub-pulse energy of these pulse sequences. Currently, the mainstream optical path architectures used to generate high INR pulse sequences fall into two categories: free-space and fiber optic paths. Both types of paths can achieve multi-sub-pulse laser output based on techniques such as pulse shaping, laser beam splitting delay, medium birefringence, interferometers, and high-frequency oscillators. Furthermore, they can be combined with fiber optic and solid-state chirped pulse amplification paths to achieve pulse energy boosting. Fiber optic paths have a compact overall structure and superior stability compared to multi-path free-space beam splitting structures, making them more suitable for experimental scenarios requiring long-term continuous operation. Solid-state gain media can handle higher single-pulse energy while avoiding excessive accumulation of nonlinear phase. The combination of these two approaches has become the mainstream development direction for generating high-energy, high INR pulse sequences, and various fiber optic pulse sequence generation devices combined with solid-state chirped pulse amplification schemes have been widely studied and implemented.

[0003] When processing high-repetition-rate (IRR) pulse sequences, especially those with a repetition rate greater than 100 GHz, existing optical fiber architectures with solid-state amplification suffer from coherent superposition of sub-pulses in the time domain after stretching. This results in high-intensity time-domain spikes. In nonlinear media, the nonlinear phase accumulation caused by these spikes continuously alters the pulse's spectral shape. After pulse compression, redundant satellite pulse sidelobes are generated, distorting the pulse sequence's time-domain waveform. Conventional optical paths cannot avoid this time-domain shape distortion during the energy enhancement process of high IRR pulse sequences. Furthermore, the lower pulse time-domain contrast and the generation of redundant satellite pulses lead to decreased nonlinear detection accuracy and sensitivity, failure of molecular manipulation techniques such as phase and delay adjustments, and excessive ablation and heat accumulation during material processing. These issues severely hinder the development of high IRR laser pulse sequences in numerous application fields. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-fidelity energy enhancement device and method for ultrashort laser pulse sequences. By applying phase modulation to the laser pulse sequence, optical field spikes caused by coherent superposition during pulse sequence amplification are suppressed, achieving high-fidelity pulse energy enhancement. A beam splitting-phase modulation-beam combining architecture combined with an N+1 pulse allocation scheme is designed, which relaxes the phase modulation requirement for individual sub-pulses from an ultrafast time scale (picosecond level) to a macroscopic time scale (nanosecond level and above), significantly reducing the requirements for the response speed of active phase modulation devices and simplifying system complexity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a high-fidelity energy enhancement device for ultrashort laser pulse sequences.

[0006] A high-fidelity energy enhancement device for ultrashort laser pulse sequences comprises, in sequence, an optical fiber mode-locked oscillator, a pulse broadening fiber, a pulse sequence generation module, an optical fiber preamplifier module, a regenerative amplification optical path, a dual-pass wave amplification optical path, and a dispersion compensation device arranged along the main optical path of laser forward transmission. The internal components of the pulse sequence generation module are arranged along the optical path to form an N+1 pulse beam splitting phase modulation optical path. The N+1 pulse beam splitting phase modulation optical path receives the broadened pulse output from the pulse broadening fiber. Through beam splitting, single-path sub-pulse phase modulation, generation of N sub-pulses, and beam combining, the phase modulation of the pulse sequence is achieved, reducing pulse interference spikes, thereby realizing high-fidelity energy enhancement of high-repetition-rate ultrashort laser pulse sequences.

[0007] In one implementation of the first aspect of the present invention, in the pulse sequence generation module, the incident light is connected to a 20:80 1-to-2 fiber coupler, and the 20:80 1-to-2 fiber coupler splits the light into two beams; one of the beams passes through a pulse splitter and a polarization-dependent fiber isolator in sequence and is connected to the first input port of a 50:50 1-to-2 fiber coupler. One 20% stream passes sequentially through an acousto-optic modulator and an adjustable fiber optic attenuator to the second input port of a 50:50 1-to-2 fiber optic coupler; the acousto-optic modulator is electrically connected to an RF power amplifier, and the RF power amplifier is electrically connected to a field-programmable gate array direct digital synthesis RF generator. The 20:80 1-to-2 fiber coupler, pulse splitter, polarization-dependent fiber isolator, acousto-optic modulator, adjustable fiber attenuator, and 50:50 1-to-2 fiber coupler together constitute the optical path for generating N+1 pulse sequences with programmable phase.

[0008] In one implementation of the first aspect of the present invention, the fiber preamplifier module includes a single-mode fiber-coupled semiconductor laser, a wavelength division multiplexer, a ytterbium-doped gain fiber, and a fiber isolator. The pump light output from the single-mode fiber-coupled semiconductor laser is coupled into the main optical path via a wavelength division multiplexer. A ytterbium-doped gain fiber is placed between the wavelength division multiplexer and the fiber isolator. The fiber isolator is placed between the ytterbium-doped gain fiber and the regenerative amplification optical path to perform primary amplification of the pulse sequence.

[0009] In one implementation of the first aspect of the present invention, in the regenerative amplification optical path, the fiber collimator receives the output beam of the fiber isolator and collimates it into a free space parallel beam before it is incident on the first polarization beam splitter. The output beam of the first polarization beam splitter passes through the first Faraday rotating mirror and the first half-wave plate in sequence before being output to the second polarization beam splitter. The output beam of the second polarizing beam splitter passes sequentially through the second Faraday rotating mirror and the second half-wave plate before being incident on the first 45-degree dielectric film reflector. The light beam reflected by the first 45-degree dielectric film mirror is incident on the third polarization beam splitter. One output beam of the third polarization beam splitter passes through the Pockels cell and arrives at the fourth polarization beam splitter. The Pockels cell controls the injection and pouring of the pulse sequence into the cavity through the electro-optic effect. The transmitted beam from the fourth polarizing beam splitter is incident on the first 0~45° dielectric film reflector. The beam reflected by the first 0~45° dielectric film reflector passes sequentially through the first plano-convex lens and the dielectric film dichroic mirror before being incident on the first gain crystal. The first gain crystal transmits the beam into the concave dielectric film mirror, which reflects the beam to the second 0-45° dielectric film mirror. The second 0-45° dielectric film mirror reflects the beam through the fourth plano-convex lens and into the second 0° dielectric film mirror. The beam is then reflected by the second 0° dielectric film mirror along the original path back to the first 0° dielectric film mirror, completing the round trip within the cavity. The regenerative amplification optical path is configured with a first multimode fiber-coupled semiconductor laser. The pump light output from the first multimode fiber-coupled semiconductor laser is coupled to the first gain crystal via a third plano-convex lens, a second plano-convex lens, and a dielectric film dichroic mirror. The beam accumulates gain by going back and forth multiple times in the cavity and is output outward after being reversed in the Pockels cell state.

[0010] In one implementation of the first aspect of the present invention, in the dual-pass-through-wave amplification optical path, the beam output from the second polarization beam splitter arrives at the fifth polarization beam splitter after being incident on the third half-wave plate. The first branch of the fifth polarization beam splitter is connected in sequence to the first quarter-wave plate and the chirped Bragg grating; The second branch of the fifth polarization beam splitter is connected in sequence to the second quarter-wave plate, the second forty-five-degree dielectric film mirror, the fifth plano-convex lens, the plano-concave lens, the second gain crystal, and the 0° dielectric film dichroic mirror. The dual-pass-wave amplification optical path is configured with a second multimode fiber-coupled semiconductor laser. The pump port of the 0° dielectric film dichroic mirror is connected to the second multimode fiber-coupled semiconductor laser, which is coupled to the second gain crystal by the sixth and seventh plano-convex lenses. The chirped volume Bragg grating is one implementation of the dispersion compensation device.

[0011] In one implementation of the first aspect of the present invention, the pulse broadening fiber is a polarization-maintaining fiber, the output end of the polarization-maintaining fiber is connected to the input port of the pulse sequence generation module, and the dispersion of the polarization-maintaining fiber is matched with the dispersion of the dispersion compensation device. The pulse splitter is located on 80% of the output optical path of the 20:80 1-to-2 fiber coupler within the pulse sequence generation module. The pulse splitter is selected from any pulse splitting method such as fiber pulse shaper, beam splitter, and active fiber delay loop. It is used to split a single pulse into multiple sub-pulses and adapt the repetition frequency within the target sequence by adjusting the time domain interval of the sub-pulses.

[0012] In one implementation of the first aspect of the present invention, a dispersion compensation device is arranged at the beam output end of the dual-pass-wave amplification optical path. The dispersion compensation device is selected from any one of a dispersion prism, a transmission diffraction grating, a reflection diffraction grating, and a chirped volume Bragg grating. It is used to receive the amplified pulse sequence and complete dispersion compensation, thereby compressing the pulse time domain width.

[0013] Secondly, the present invention provides a high-fidelity energy enhancement method for ultrashort laser pulse sequences.

[0014] A high-fidelity energy enhancement method for ultrashort laser pulse sequences, utilizing the high-fidelity energy enhancement device for ultrashort laser pulse sequences according to the first aspect of this invention, includes the following processes: An ultrashort seed pulse is output from an optical fiber mode-locked oscillator, and the incident pulse of the ultrashort seed pulse is used to broaden the optical fiber to complete the time-domain broadening. The broadened pulse is fed into the pulse sequence generation module, which uses the phase-programmable N+1 pulse sequence to generate an optical path to complete beam splitting, phase modulation and beam combining, generating an N+1 type uniform pulse sequence. The N+1 type uniform pulse sequence is fed into the fiber preamplifier module to complete the primary amplification, and then sequentially fed into the regenerative amplification optical path and the dual-pass wave amplification optical path to increase the pulse energy step by step. The pulse sequence after energy enhancement is fed into a dispersion compensation device to complete dispersion compensation and compression, and outputs a high-fidelity pulse sequence with high intra-sequence repetition frequency, low satellite pulse intensity, and high signal-to-noise ratio.

[0015] In one implementation of the second aspect of the present invention, a 20:80 split-to-2 fiber optic coupler is used to split the broadened pulse into two transmission beams; 80% of one beam is transmitted through a pulse splitter and a polarization-dependent fiber optic isolator, and 20% of the other beam is transmitted through an acousto-optic modulator and an adjustable fiber optic attenuator. The field-programmable gate array direct digital synthesis RF generator outputs an RF signal, which is amplified by an RF power amplifier and drives an acousto-optic modulator to apply phase modulation to a single beam; the two beams are combined via a 50:50 1-to-2 fiber coupler to obtain an N+1 type uniform pulse sequence. The acquisition process of the RF signal output by the field-programmable gate array direct digital synthesis RF generator is as follows: a portion of the ultra-short seed pulse is extracted from the output beam of the fiber mode-locked oscillator and sent to the photodetector to be converted into an electrical pulse. The electrical pulse is converted into a square wave signal by a comparator. The square wave signal is converted into parallel data by the gigabit transceiver port and sent to the field-programmable gate array direct digital synthesis RF generator. The field-programmable gate array (FPGA) direct digital synthesis RF generator retrieves a sine wave template, combines it with input parallel data to generate four-channel weighted waveform data, performs serial conversion and weighted superposition on the four-channel weighted waveform data to generate a gated sine signal, and sends the gated sine signal to the RF power amplifier to complete power amplification before driving the acousto-optic modulator.

[0016] In one implementation of the second aspect of the present invention, the phase offset matching logic for applying phase modulation to a single sub-pulse is as follows: the most effective interference spike suppression is determined by comparative simulation calculation, which is to apply an additional π phase to the single sub-pulse, and the applied phase of the sub-pulse is set by optimizing the time delay between the AOM driving RF pulse signal and the single pulse signal. The calculated phase offset value is loaded into the field programmable gate array direct digital synthesis RF generator, and the acousto-optic modulator applies the corresponding phase perturbation to the single sub-pulse to suppress the interference spikes generated by the coherent superposition of pulses.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes a fiber mode-locked oscillator, a pulse-stretching fiber, and a pulse sequence generation module connected in series with two stages of solid-state amplification and dispersion compensation devices to form a complete optical path. The phase-programmable N+1 pulse sequence generated within the pulse sequence generation module produces a processed and stretched pulse. This allows for phase modulation of individual sub-pulses before beam combining, which can mitigate optical field spikes caused by the temporal coherence superposition of sub-pulses to a certain extent. The nonlinear optical field changes caused by these spikes are alleviated, the accumulated nonlinear phase during pulse transmission is reduced, the number and intensity of redundant satellite pulses generated during the compression stage are decreased, and the pulse contrast is improved. The temporal waveform fidelity of the amplified high-repetition-rate ultrashort laser pulse sequence is improved. This invention eliminates the need for separate phase modulation devices for all sub-pulses; interference suppression can be achieved with only a single sub-pulse phase modulation branch. This simplifies the configuration of active control devices within the optical path and reduces the complexity of optical path setup and debugging. Simultaneously, the N+1 pulse allocation scheme reduces the response speed requirements of the electro-optic modulation devices. The all-fiber beam splitting and control structure is directly connected to the subsequent solid-state amplification optical path. Compared with multiple free-space optical paths, the stable state of the optical path is easier to maintain over long-term operation, making it suitable for long-term experiments such as spectral detection, molecular manipulation, and materials processing. The overall optical path can maintain the original temporal domain shape of the pulse while raising the energy of the high-repetition-frequency pulse, making it suitable for various laser applications that require high-fidelity pulse output.

[0018] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0020] Figure 1 A schematic diagram of the main optical path of a high-fidelity energy enhancement device for ultrashort laser pulse sequences provided as an exemplary embodiment of the present invention; Figure 2 A schematic diagram of a dual-pass wave amplification optical path provided for an exemplary embodiment of the present invention; Figure 3 A detailed optical path structure diagram of a pulse sequence generated using a beam splitting-pulse modulation-beam combining path is provided as an exemplary embodiment of the present invention, illustrating the sub-pulse configuration of N=4+1 and the phase modulation method of a single sub-pulse; Figure 4 The evolution of the time-domain shape of a pulse sequence after high-intensity pulse amplification without phase modulation, as provided in an exemplary embodiment of the present invention; Figure 5 A comparative simulation calculation result is provided as an exemplary embodiment of the present invention to compare the interference spikes generated by the coherent superposition of broadened subpulses in pulse sequences whether or not they have undergone phase modulation. Figure 5 (a) in the figure is a comparison of the time-domain normalized light intensity of the broadened pulse sequence with and without phase modulation. Figure 5 (b) in the figure is a comparison of the normalized light intensity of the frequency domain spectrum corresponding to the pulse sequence with and without phase modulation. Figure 5 (c) in the figure is a comparison of the time-domain normalized light intensity of the final output pulse sequence after compression. Figure 5 (d) in the diagram represents the relative phase histogram corresponding to each of the five sub-pulses in the pulse sequence. Figure 6 A schematic diagram of high-precision AOM drive signal generation and a result analysis diagram of the adjustment of the generated radio frequency signal are provided as an exemplary embodiment of the present invention, wherein... Figure 6 (a) in the diagram is a schematic diagram of the complete generation process of AOM radio frequency drive signals. Figure 6 (b) shows the FPGA output drive voltage waveform under different RF cycle delays. Figure 6 In the diagram, (c) shows the final output sinusoidal radio frequency signal waveform under different trigger delays (0.0 to 2.5 cycles). Figure 6 (d) in the figure is a timing comparison diagram of the FPGA output RF pulse and the mode-locked trigger synchronization signal; Figure 7 The following is a flowchart of an FPGA program provided for an exemplary embodiment of the present invention, wherein FDR is the frequency division ratio and LUT is a lookup table; The components include: 1. Fiber mode-locked oscillator; 2. Pulse-stretching fiber; 3. Pulse sequence generation module; 4. Single-mode fiber-coupled semiconductor laser; 5. Wavelength division multiplexer; 6. Fiber isolator; 7. Fiber collimator; 8. First polarization beam splitter; 9. First Faraday rotator mirror; 10. First half-wave plate; 11. Second polarization beam splitter; 12. Second Faraday rotator mirror; 13. Second half-wave plate; 14. First 45° dielectric film mirror; 15. First 0° dielectric film mirror; 16. Third polarization beam splitter; 17. Pockels cell; 18. Fourth polarization beam splitter; 19. First 0~45° dielectric film mirror; 20. First plano-convex lens; 21. Dielectric film dichroic mirror; 22. Second plano-convex lens; 23. Third plano-convex lens; 24. First multimode fiber-coupled semiconductor laser; 25. First gain crystal; 26. Concave dielectric film mirror; 27. 28. Second 0-45° dielectric film reflector; 29. ​​Fourth plano-convex lens; 30. Second 0° dielectric film reflector; 31. Third half-wave plate; 32. Fifth polarization beam splitter; 33. First quarter-wave plate; 34. Chirped volume Bragg grating; 35. Second quarter-wave plate; 36. Second 45° dielectric film reflector; 37. Fifth plano-convex lens; 38. Plano-concave lens; 39. Second gain crystal; 40. 0° dielectric film dichroic mirror; 41. Sixth plano-convex lens; 42. Seventh plano-convex lens; 43. Second multimode fiber-coupled semiconductor laser; 44. 20:80 1-to-2 fiber coupler; 45. Acousto-optic modulator; 46. RF power amplifier; 47. Field-programmable gate array direct digital synthesis RF generator; 48. Adjustable fiber attenuator; 49. Pulse splitter; 50. Polarization-dependent fiber isolator; 51. 50:50 1-to-2 fiber coupler. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] In view of the problems existing in the current solution, the present invention provides a high-fidelity energy enhancement device and method for ultrashort laser pulse sequences. Its core technical concept lies in addressing the high-intensity interference spikes and satellite pulses induced by the coherent superposition of adjacent broadened sub-pulses during the amplification process of chirped pulses under high repetition frequency conditions within the sequence. This is achieved by introducing an N+1 pulse beam splitting phase modulation optical path in the pulse sequence generation stage, and using an acousto-optic modulator to apply programmable phase perturbation to each sub-pulse, fundamentally disrupting the coherent superposition condition within the broadened pulse sequence. This suppresses nonlinear phase accumulation during the amplification process, achieving high-fidelity energy enhancement and pulse compression output. Different embodiments are analyzed below.

[0024] Example 1: Reference Figure 1 , Figure 2 and Figure 3 In one embodiment, the present invention provides a high-fidelity energy enhancement device for ultrashort laser pulse sequences. The device comprises, sequentially arranged along the main optical path of the laser forward transmission, an optical fiber mode-locked oscillator 1, a pulse broadening optical fiber 2, a pulse sequence generation module 3, an optical fiber preamplifier module, a regenerative amplification optical path, a dual-pass wave amplification optical path, and a dispersion compensation device, forming a complete ultrashort pulse sequence energy enhancement system.

[0025] The fiber optic mode-locked oscillator 1 operates based on a nonlinear polarization rotation mode-locking mechanism, enabling stable output of linearly polarized ultrashort seed pulses with ultrawide spectral bandwidth. Due to its all-fiber cavity structure, the output pulses exhibit excellent amplitude stability and phase consistency, laying the foundation for uniform splitting and high-fidelity amplification of subsequent pulse sequences. A small amount of sampled light is extracted from the output port of the fiber optic mode-locked oscillator 1 through an asymmetric splitting ratio fiber coupler. This sampled light is converted into an electrical pulse signal by a photodetector, and then shaped into a square wave trigger signal with a fixed amplitude by a comparator. This signal provides a precise switching trigger timing reference for subsequent electro-optic and acousto-optic devices.

[0026] Pulse-stretching fiber 2 is a polarization-maintaining fiber, and its output port is directly connected to the input port of pulse sequence generation module 3. Utilizing its large group velocity dispersion, the polarization-maintaining fiber significantly broadens the femtosecond to picosecond-level ultrashort pulses output from fiber mode-locked oscillator 1 in the time domain to hundreds of picoseconds or even nanoseconds. The physical mechanism of this broadening lies in the fact that ultrashort pulses have a wide spectrum, and different frequency components within the pulse propagate at different group velocities in the polarization-maintaining fiber, causing the pulse's time-domain envelope to be stretched. The peak power of the broadened pulse is significantly reduced, effectively preventing irreversible damage to optical components in subsequent solid-state amplifiers due to high peak power, while also significantly increasing the threshold for nonlinear effects such as self-phase modulation. The dispersion of pulse-stretching fiber 2 is matched with the dispersion of the dispersion compensation device, ensuring that the amplified broadened pulse can be sufficiently compressed to near its transform-limit pulse width.

[0027] Reference Figure 3 The internal components of the pulse sequence generation module 3 are arranged along the optical path to form a phase-programmable N+1 pulse sequence generation optical path. After the broadened pulse enters the pulse sequence generation module 3, it is first incident on the 20:80 1-to-2 fiber coupler 43. This coupler splits the incident beam into two paths according to a preset power ratio: a first beam with a power ratio of 80% and a second beam with a power ratio of 20%. The two beams are transmitted along independent optical paths, forming a main pulse branch and a phase-modulated sub-pulse branch.

[0028] The first beam passes sequentially along the main pulse branch through the pulse splitter 48 and the polarization-dependent fiber isolator 49, and finally connects to the first input port of the 50:50 1-to-2 fiber coupler 50. The pulse splitter 48 is responsible for splitting a single broadened pulse into N time-uniformly spaced sub-pulses, forming a main pulse sequence with a high intra-sequence repetition frequency. The polarization-dependent fiber isolator 49 is located at the output end of the pulse splitter 48. Its function is twofold: firstly, to perform polarization selection when generating the pulse sequence using fiber birefringence; and secondly, to block the back-propagating beam, preventing back-reflected light from interfering with the uniformity and stability of the main pulse sequence and protecting upstream fiber optic devices from damage caused by backlight.

[0029] The pulse splitter 48 is selected from any one of the pulse splitting methods, such as fiber pulse shapers, beam splitters, and active fiber delay loops. Fiber pulse shapers split a single pulse into multiple equally spaced sub-pulses through a specific fiber delay structure; beam splitters achieve binary multiplication of sub-pulse splitting through a tree-like cascade of multiple 1×2 fiber couplers; and active fiber delay loops generate a programmable number of sub-pulses through a controlled fiber loop. All three schemes can achieve uniform sub-pulse splitting within an all-fiber structure, and the number of sub-pulses can be flexibly adjusted according to the repetition frequency within the target sequence, covering a wide range of configurations from several to hundreds of sub-pulses.

[0030] The second beam passes sequentially along the phase-modulated sub-pulse branch through the acousto-optic modulator 44 and the adjustable fiber optic attenuator 47, and finally connects to the second input port of the 50:50 1-to-2 fiber optic coupler 50. The acousto-optic modulator 44 applies precise phase modulation to the light pulse passing through it through an acousto-optic interaction mechanism: when the radio frequency drive signal is applied to the piezoelectric transducer of the acousto-optic modulator 44, the transducer excites an ultrasonic traveling wave in the medium. The ultrasonic traveling wave causes a periodic change in the refractive index of the medium. During the propagation of the light pulse, an additional optical phase directly related to the phase of the radio frequency signal is accumulated, thereby realizing precise programming control of the phase of a single sub-pulse.

[0031] An adjustable fiber optic attenuator 47 is arranged at the output end of the acousto-optic modulator 44 to finely adjust the power of the single-path sub-pulse after phase modulation, so that it is consistent with the power of each sub-pulse in the main pulse sequence, and ensure the amplitude uniformity of each sub-pulse in the N+1 type uniform pulse sequence after beam combining.

[0032] The field-programmable gate array (FPGA) direct digital synthesizer (RF generator) 46 and the RF power amplifier 45 form the drive control link for the acousto-optic modulator 44. The output of the FPGA direct digital synthesizer RF generator 46 is electrically connected to the RF power amplifier 45, and the output of the RF power amplifier 45 is electrically connected to the acousto-optic modulator 44.

[0033] Reference Figure 6 and Figure 7 The working principle of the field-programmable gate array (FPGA) direct digital synthesis RF generator 46 is as follows: an ultra-short seed pulse is extracted from the sampling output of the mode-locked fiber optic oscillator 1, converted into an electrical pulse by a photodetector, shaped into a square wave signal by a comparator, and then converted into parallel digital data by a gigabit transceiver port and sent to the FPGA; the FPGA internally retrieves a pre-stored sine waveform lookup table and combines it with the input parallel data to generate four-channel weighted waveform data; after serial conversion of the four-channel weighted waveform data, a gated sine signal with a fixed frequency is synthesized by weighted superposition; the gated sine signal is sent to the RF power amplifier 45 to complete power amplification and then drives the acousto-optic modulator 44.

[0034] The core advantage of the aforementioned direct digital synthesis architecture lies in the fact that the gate width, delay, and phase of the RF signal can all be independently programmed and controlled through the internal program of the field-programmable gate array (FPGA). Its timing control precision reaches the nanosecond or even sub-nanosecond level, far exceeding the picosecond time intervals between sub-pulses within a pulse sequence. Therefore, phase modulation operations on a single sub-pulse do not need to be completed within a picosecond timescale, but rather implemented on a macroscopic timescale through pre-programming. This fundamentally removes the stringent limitations on the response speed of active phase modulation devices, significantly reducing the system's implementation difficulty and cost.

[0035] The 50:50 1-to-2 fiber coupler 50 combines the main pulse sequence from the first input port with the phase-modulated single-path sub-pulse from the second input port, outputting a uniform pulse sequence with a total of N+1 sub-pulses. In the combined pulse sequence, the N main pulse sub-pulses and 1 phase-modulated sub-pulse are uniformly arranged in the time domain, forming a complete initial pulse sequence with a high intra-sequence repetition frequency. The phase state of the phase-modulated sub-pulse has a controlled difference from the other N sub-pulses.

[0036] Reference Figure 1The fiber preamplifier module is positioned between the output of the pulse sequence generation module 3 and the input of the regenerative amplification optical path. The fiber preamplifier module includes a single-mode fiber-coupled semiconductor laser 4, a wavelength division multiplexer 5, a ytterbium-doped gain fiber, and a fiber isolator 6. The pump light output from the single-mode fiber-coupled semiconductor laser 4 is combined with the main optical path signal light via wavelength division multiplexing in the fiber after being wavelength divided by the wavelength division multiplexer 5. The pump light and signal light propagate together in the ytterbium-doped gain fiber. In the ytterbium-doped gain fiber, ytterbium ions undergo population inversion under the excitation of the pump light, amplifying the signal pulse sequence through stimulated emission and boosting the low-power pulse sequence from the pulse sequence generation module 3 to a power level sufficient for injection into the solid-state regenerative amplifier. The fiber isolator 6 is positioned between the output of the ytterbium-doped gain fiber and the regenerative amplification optical path to block backscattered light from the solid-state amplifier, preventing damage to the fiber optic devices in the fiber preamplifier module and protecting the ytterbium-doped gain fiber from interference from backscattered spontaneous emission.

[0037] In the regenerative amplification optical path, the output beam of the fiber isolator 6 first enters the fiber collimator 7, which collimates the Gaussian beam transmitted in the fiber into a free-space parallel beam, completing the coupling conversion between fiber transmission and free-space transmission. The collimated beam enters the first polarization beam splitter 8, which separates the beam into a specific polarization state. The beam then passes sequentially through the first Faraday rotator mirror 9 and the first half-wave plate 10, which rotates and transforms the polarization state of the beam before outputting it to the second polarization beam splitter 11. The output beam of the second polarization beam splitter 11 passes sequentially through the second Faraday rotator mirror 12 and the second half-wave plate 13. The combination of the second Faraday rotator mirror and the second half-wave plate precisely controls the polarization state of the beam, causing it to enter the first 45-degree dielectric film reflector 14 with a specific polarization state. The first 45-degree dielectric film reflector 14 then refracts the light path before it enters the third polarization beam splitter 16.

[0038] The third polarization beam splitter 16 splits the incident beam into two directions: transmission and reflection. One path passes through the Pockels cell 17 and reaches the fourth polarization beam splitter 18. The Pockels cell 17 is the core electro-optic switching device of the regenerative amplification cavity. By applying or removing a high-voltage electric field, it changes the polarization state of the beam passing through it using the electro-optic effect, thereby controlling the transmission or reflection direction of the beam at the fourth polarization beam splitter 18, realizing the injection of the pulse sequence into the regenerative amplification cavity and the output of the accumulated gain pulse sequence within the cavity; the other path enters the first 0° dielectric film reflector 15.

[0039] The beam transmitted by the fourth polarization beam splitter 18 is incident on the first 0-45° dielectric film reflector 19, and after being refracted, it passes sequentially through the first plano-convex lens 20 and the dielectric film dichroic mirror 21, finally illuminating the first gain crystal 25. The first gain crystal 25 serves as the gain medium of the regenerating amplification cavity, and is pumped by the first multimode fiber-coupled semiconductor laser 24. The pump light output from the first multimode fiber-coupled semiconductor laser 24 is coupled sequentially through the third plano-convex lens 23, the second plano-convex lens 22, and the dielectric film dichroic mirror 21 to the first gain crystal 25, establishing population inversion within the crystal.

[0040] The transmitted beam from the first gain crystal 25 is incident on the concave dielectric film reflector 26. The concave dielectric film reflector 26 reflects and focuses the beam, which then enters the second 0-45° dielectric film reflector 27. After being refracted, it passes through the fourth plano-convex lens 28 and enters the second 0° dielectric film reflector 29, where it is reflected along its original path, completing one round trip within the cavity. The beam accumulates gain through multiple round trips within the cavity, extracting energy from population inversion each time it passes through the first gain crystal 25, achieving exponential energy amplification. When the pulse sequence accumulates to a predetermined gain level within the cavity, the polarization state is switched by the Pockels cell 17, causing the amplified pulse sequence to be reflected out from the fourth polarization beam splitter 18, completing the regenerative amplification process.

[0041] Reference Figure 2 The pulse sequence output from the regenerated amplification optical path is incident on the third half-wave plate 30 and arrives at the fifth polarization beam splitter 31. The fifth polarization beam splitter 31 splits the beam into two paths: the first branch is connected in sequence to the first quarter-wave plate 32 and the chirped Bragg grating 33; the second branch is connected in sequence to the second quarter-wave plate 34, the second forty-five-degree dielectric film mirror 35, the fifth plano-convex lens 36, the plano-concave lens 37, the second gain crystal 38, the 0° dielectric film dichroic mirror 39, the sixth plano-convex lens 40, and the seventh plano-convex lens 41, forming a dual-pass-wave amplification optical path.

[0042] In the second branch, the fifth plano-convex lens 36 and the plano-concave lens 37 form a beam waist adjustment combination, adjusting the beam waist diameter of the incident beam to match the pump spot size in the second gain crystal 38, thereby achieving optimal spatial gain extraction efficiency. The second gain crystal 38 is pumped by the second multimode fiber-coupled semiconductor laser 42 through the pump port of the 0° dielectric film dichroic mirror 39, establishing population inversion within the crystal. After the beam completes its first single-pass amplification in the second gain crystal 38, it is reflected by the 0° dielectric film dichroic mirror 39, shaped by the sixth plano-convex lens 40 and the seventh plano-convex lens 41, and then undergoes a second single-pass amplification through the second gain crystal 38, achieving a further significant increase in pulse sequence energy through the dual-pass wave amplification structure.

[0043] The pulse sequence, amplified by the dual-pass wave, returns to the fifth polarization beam splitter 31. Due to the two passes of the second quarter-wave plate 34, the polarization state is rotated by ninety degrees. The pulse sequence is then output from the first branch of the fifth polarization beam splitter 31 and enters the dispersion compensation device composed of the first quarter-wave plate 32 and the chirped Bragg grating 33. The chirped Bragg grating 33 provides negative dispersion that matches the dispersion of the pulse-stretching fiber 2, compensating for the time delay difference of different frequency components in the amplified stretched pulse sequence. This allows the pulse sequence to be recompressed in the time domain to an ultrashort pulse width close to the transform limit, outputting a high-fidelity pulse sequence with high intra-sequence repetition frequency and low satellite pulses.

[0044] The aforementioned device, through the core design of the N+1 pulse beam splitting phase modulation optical path, achieves the following technical effects: First, compared to the free-space beam splitting scheme, the all-fiber structure pulse sequence generation module 3 eliminates pulse interval fluctuations and sub-pulse intensity non-uniformity caused by mechanical vibration, thermal drift, and airflow disturbance in the free-space optical path, significantly improving system stability and sub-pulse consistency. Second, the N+1 pulse allocation scheme shifts the phase modulation operation from the ultrafast response requirement of the picosecond timescale to the macroscopic timescale of nanoseconds and above, enabling programmable phase control based on the acousto-optic modulator 44 to be realized under existing device technology conditions, greatly reducing system complexity. Third, by applying controlled phase perturbation to a single sub-pulse, the coherent superposition condition of the broadened pulse sequence during the chirped pulse amplification process is disrupted, effectively suppressing the formation of high-intensity interference spikes, thereby reducing nonlinear phase accumulation caused by self-phase modulation, and ultimately suppressing the generation of compressed satellite pulses, achieving high-fidelity pulse sequence energy enhancement with high temporal contrast.

[0045] Example 2: Reference Figure 3 In one embodiment, the pulse splitter 48 in the pulse sequence generation module 3 is implemented using a fiber pulse shaper. The fiber pulse shaper uses a fiber delay line array of a specific length to split a single broadened pulse into multiple sub-pulses with fixed time intervals in the time domain. The sub-pulse time interval is determined by the length of the delay fiber. By adjusting the length of the delay fiber, the repetition frequency within the sequence can be continuously adjusted over a wide range, covering a frequency range from hundreds of gigahertz to terahertz. The number of sub-pulses can be customized by the number of stages in the delay line array, achieving a flexible configuration from tens to hundreds of sub-pulses. The advantages of the fiber pulse shaper scheme are its simple structure, lack of active control, all-fiber integration with the main optical path, and superior system compactness and long-term stability compared to free-space beam splitting schemes.

[0046] In another embodiment, the pulse splitter 48 is implemented using an active fiber delay loop. The active fiber delay loop uses active switching devices within the fiber loop to control the pulse's circulation within the loop, generating one sub-pulse output per cycle. The number of cycles determines the number of sub-pulses. The advantage of the active fiber delay loop scheme is that the number of sub-pulses can be dynamically adjusted online by controlling the number of cycles, allowing for flexible reconfiguration of the sub-pulse number without hardware changes. This is suitable for applications requiring frequent switching of pulse sequence parameters. By adjusting the on-time of the active switches, the relative time intervals of each sub-pulse can be finely controlled, further enhancing the programmability and flexibility of the pulse sequence parameters. Both alternative implementations of the pulse splitter 48 described above can work in conjunction with the acousto-optic modulator 44 and the field-programmable gate array direct digital synthesis RF generator 46 in the N+1 pulse beam splitting phase modulation optical path to achieve high-fidelity amplification of high-repetition-frequency pulse sequences.

[0047] Example 3: In one implementation, the field-programmable gate array (FPGA) direct digital synthesis (DDS) RF generator 46 applies a π-phase shift to the phase modulation of the single-channel sub-pulse. The physical meaning of the π-phase shift is that the phase difference between the phase-modulated single-channel sub-pulse and adjacent sub-pulses in the main pulse sequence is exactly π. During chirped pulse amplification, the broadened sub-pulses overlap in the time domain. If the phases of the sub-pulses are consistent, constructive interference occurs in the overlapping region, forming a time-domain spike with extremely high peak power. When the (N+1)th sub-pulse carries the π-phase shift, this sub-pulse undergoes local destructive interference with adjacent sub-pulses in the overlapping region, effectively suppressing the formation of high-intensity interference spikes. The elimination of interference spikes directly reduces the peak light intensity in the amplification medium, thereby reducing the accumulation of its nonlinear phase. The reduction in nonlinear phase accumulation means a decrease in the spectral distortion of the pulse sequence. The compressed spectrum does not contain periodic modulation caused by the nonlinear phase, thus effectively suppressing the generation of satellite pulses and ultimately achieving a high-fidelity pulse sequence output with high time-domain contrast.

[0048] Figure 4 This shows the evolution of the time-domain shape of a pulse sequence after it has undergone high-intensity pulse amplification without phase modulation. (Refer to...) Figure 5 By comparing the temporal intensity distribution of the broadened pulse sequences before and after applying the π phase shift, it can be clearly seen that without phase modulation, the broadened pulse sequences produce obvious high-intensity interference spikes due to coherent superposition; after applying the π phase shift, the interference spikes are effectively suppressed. Correspondingly, significant changes before and after introducing the π phase can also be clearly observed in the spectral domain of the pulse sequences.

[0049] Furthermore, the field-programmable gate array direct digital synthesis RF generator 46 can apply other custom phase perturbation values ​​besides the π phase offset to a single subpulse. By optimizing the phase offset, the optimal phase perturbation scheme can be precisely matched for pulse sequences with different numbers of subpulses, different repetition frequencies within the sequence, and different amplification gain conditions, further improving the interference spike suppression effect and the satellite pulse suppression depth.

[0050] Reference Figure 6 The gate width, delay, and phase of the RF drive signal output by the field-programmable gate array (FPGA) direct digital synthesis RF generator 46 can all be independently programmed and set through the FPGA's internal program. These three parameters together determine the time window, trigger delay, and phase offset of the acousto-optic modulator 44 applying phase modulation to a single sub-pulse. The gate width parameter controls the duration of phase modulation applied to a single sub-pulse, ensuring that phase modulation only acts on the target sub-pulse without affecting adjacent sub-pulses. The delay parameter controls the time offset of phase modulation relative to the trigger signal, achieving precise synchronization between the phase modulation timing and the pulse sequence. The phase parameter directly sets the optical phase offset applied to the target sub-pulse. The independent programmable control of these three parameters gives the system comprehensive adjustment capabilities for the phase modulation scheme.

[0051] Example 4: In one embodiment, the operation of the high-fidelity energy enhancement device is as follows: The fiber mode-locked oscillator 1 continuously outputs an ultrashort seed pulse. The seed pulse incident on the fiber 2 is broadened using the group velocity dispersion of the polarization-maintaining fiber in the time domain, resulting in a significant reduction in peak power. The broadened pulse enters the pulse sequence generation module 3, and is split into a main pulse branch and a phase modulation sub-pulse branch by a 20:80 1-to-2 fiber coupler 43.

[0052] In the main pulse branch, the broadened pulse is split into N uniform sub-pulses by the pulse splitter 48, and then filtered for reverse interference by the polarization-dependent fiber isolator 49 before entering the first input port of the 50:50 1-to-2 fiber coupler 50. In the phase-modulated sub-pulse branch, the broadened pulse is subjected to phase modulation pre-programmed by the field-programmable gate array direct digital synthesis RF generator 46 by the acousto-optic modulator 44, and then its power is adjusted by the adjustable fiber attenuator 47 to match the amplitude of each sub-pulse in the main pulse sequence before entering the second input port of the 50:50 1-to-2 fiber coupler 50. The 50:50 1-to-2 fiber coupler 50 combines the two beams and outputs a uniform pulse sequence with a total of N+1 sub-pulses, where the (N+1)th sub-pulse carries a pre-programmed phase shift.

[0053] The synthesized N+1 type uniform pulse sequence is fed into the fiber preamplifier module, where it undergoes primary amplification via ytterbium-doped gain fiber and is pumped by a single-mode fiber-coupled semiconductor laser 4. The power is increased to a level meeting the injection requirements of the solid-state amplifier. After isolation by fiber isolator 6, the pulse sequence is output to free space. The pulse sequence is then collimated by fiber collimator 7 and injected into the regenerative amplification optical path. Pockels cell 17 is activated under trigger signal control, injecting the pulse sequence into the regenerative amplification cavity. The pulse sequence travels back and forth within the cavity multiple times, extracting energy from population inversion each time it passes through the first gain crystal 25, achieving exponential energy accumulation. When the energy of the pulse sequence within the cavity reaches a predetermined level, Pockels cell 17 switches its polarization state again, reversing the amplified pulse sequence from the cavity, completing the main energy amplification.

[0054] The outflowing high-energy pulse sequence enters the dual-pass-wave amplification optical path. After the beam waist is adjusted by the fifth plano-convex lens 36 and plano-concave lens 37, it passes twice through the second gain crystal 38 to further extract energy from the population inversion established by the second multimode fiber-coupled semiconductor laser 42, achieving another significant increase in the total energy of the pulse sequence. Finally, the high-energy broadened pulse sequence enters the dispersion compensation device. The chirped Bragg grating 33 provides negative dispersion compensation that matches the dispersion of the pulse broadening fiber 2, compressing the broadened pulse sequence to an ultrashort pulse width close to the transform limit, outputting a high-fidelity pulse sequence with high intra-sequence repetition frequency and low satellite pulses. Since the coherent superposition interference spikes and nonlinear phase accumulation during the amplification process have been effectively suppressed by phase modulation in the pulse sequence generation module 3, the compressed pulse sequence has excellent temporal contrast, and the satellite pulse component is at an extremely low level.

[0055] Example 5: In one embodiment, the present invention provides a high-fidelity energy enhancement method for ultrashort laser pulse sequences, implemented using the aforementioned device, comprising the following processes: An ultrashort seed pulse is output from an optical fiber mode-locked oscillator 1, and the ultrashort seed pulse is incident on an optical fiber 2 to achieve time-domain broadening. The broadened pulse is sent to a pulse sequence generation module 3, where beam splitting, phase modulation, and beam combining are performed using an N+1 pulse beam splitting phase modulation optical path to generate an N+1 type uniform pulse sequence. The N+1 type uniform pulse sequence is passed to an optical fiber preamplifier module for primary amplification, and then sequentially passed to a regenerative amplification optical path and a dual-passing-wave amplification optical path to progressively increase the pulse energy. The energy-enhanced pulse sequence is passed to a dispersion compensation device for dispersion compensation compression, outputting a high-fidelity pulse sequence with high intra-sequence repetition frequency and low satellite pulses.

[0056] Specifically, the broadened pulse is split into two transmission beams by a 20:80 1-to-2 fiber coupler 43: one beam is transmitted via a pulse splitter 48 and a polarization-dependent fiber isolator 49, and the other beam is transmitted via an acousto-optic modulator 44 and an adjustable fiber attenuator 47. A field-programmable gate array (FPGA) direct digital synthesizer (RF generator) 46 outputs an RF signal, which is amplified by an RF power amplifier 45 and then drives the acousto-optic modulator 44 to apply phase modulation to the single beam. The two beams are then combined via a 50:50 1-to-2 fiber coupler 50 to obtain an N+1 type uniform pulse sequence.

[0057] The acquisition process of the RF signal output by the field-programmable gate array (FPGA) direct digital synthesis RF generator 46 is as follows: a portion of the ultrashort seed pulse is extracted from the output beam of the fiber mode-locked oscillator 1 and sent to the photodetector to be converted into an electrical pulse. The electrical pulse is converted into a square wave signal by a comparator. The square wave signal is converted into parallel data by the gigabit transceiver port and sent to the FPGA direct digital synthesis RF generator 46. The FPGA direct digital synthesis RF generator 46 retrieves a sine wave template and combines it with the input parallel data to generate four-channel weighted waveform data. The four-channel weighted waveform data is serially converted and weighted to generate a gated sine wave signal. The gated sine wave signal is sent to the RF power amplifier 45 to complete power amplification and drive the acousto-optic modulator 44 to apply corresponding phase perturbation to the single sub-pulse to suppress interference spikes generated by pulse coherent superposition.

[0058] When applying phase modulation to a single sub-pulse, the calculated phase offset value is loaded into the field-programmable gate array direct digital synthesis RF generator 46, and the acousto-optic modulator 44 applies the corresponding phase perturbation to the single sub-pulse. Through precise calculation and fine-tuning of the phase offset in experiments, it can be ensured that the phase modulation scheme is compatible with the specific amplifier crystal parameters, achieving the optimal satellite pulse suppression effect for different solid-state amplification systems.

[0059] Example 6: In one embodiment, the high-fidelity energy enhancement device and method of the present invention have significant application value in the field of nonlinear spectroscopy. In stimulated Raman scattering spectroscopy, pulse sequences with high intra-sequence repetition frequencies exhibit spectral characteristics similar to optical frequency combs, with pulse energy concentrated on several narrow spectral lines, forming a comb-like spectrum with high spectral intensity. The high-energy, high intra-sequence repetition frequency pulse sequence provided by the present invention can significantly improve the pumping efficiency of the stimulated Raman scattering process. Simultaneously, the high-fidelity characteristics ensure the spectral purity of the pulse sequence, avoiding interference from spectral background noise introduced by satellite pulses on weak Raman signals, and significantly improving the signal-to-noise ratio and detection sensitivity of stimulated Raman scattering spectroscopy.

[0060] In applications of resonance-enhanced multiphoton ionization and infrared resonance multiphoton dissociation, precise pulse timing and phase consistency are crucial for achieving multiphoton processes. The pulse sequence generated by the device of this invention exhibits excellent sub-pulse uniformity and low satellite pulse background, ensuring that the coherent superposition effect of each sub-pulse during multiphoton excitation is predictable and controllable, effectively improving the quantum efficiency of multiphoton ionization and dissociation processes. In laser-induced breakdown spectroscopy applications, high-energy pulse sequences can generate stable plasmas on the surface of target materials, and the high repetition frequency characteristic within the sequence creates a synergistic enhancement effect between each sub-pulse and the plasma excitation and maintenance process. The high-fidelity pulse sequence provided by this invention has extremely low satellite pulse components, avoiding interference from satellite pulses on the plasma excitation timing and ensuring the time resolution and elemental analysis accuracy of the laser-induced breakdown spectral signal.

[0061] In one embodiment, the high-fidelity energy enhancement device and method of the present invention have unique advantages in the field of molecular dynamics manipulation. Molecular rotation and vibrational dynamics occur on a picosecond timescale, requiring a pulse sequence with a repetition frequency precisely matched to the molecular rotation or vibration period to achieve coherent manipulation of the molecular motion state. The device of the present invention, by adjusting the delay parameter of the pulse divider 48, can precisely set the repetition frequency within the sequence to an integer multiple of the target molecule's rotation or vibration frequency, achieving resonance matching between the pulse sequence and the molecular dynamics process. The high-fidelity characteristics ensure that the phase relationship of each sub-pulse in the pulse sequence is strictly controlled, and the absence of satellite pulses avoids the destruction of molecular quantum state coherence by non-resonant excitation, significantly improving the efficiency and fidelity of the molecular orientation and alignment control process.

[0062] In plasma wave generation applications, high-energy, high-repetition-rate ultrashort pulse sequences can excite coherently superimposed plasma waves in plasma. The temporal synergistic enhancement of the plasma wave excitation by each sub-pulse results in plasma waves with amplitudes far exceeding those of single-pulse excitation. In the high-fidelity pulse sequence generated by the device of this invention, the amplitude uniformity and phase controllability of each sub-pulse ensure the coherent superposition efficiency of the plasma wave excitation process, while the low satellite pulse background avoids unintended plasma disturbances, which is beneficial for generating high-amplitude, high-purity plasma waves and providing a high-quality driving light source for cutting-edge applications such as laser plasma accelerators.

[0063] In one embodiment, the high-fidelity energy enhancement device and method of the present invention have broad application prospects in the field of precision material processing. Ultrashort pulse sequence processing has unique thermal management advantages compared to single-pulse processing: the high repetition frequency of the pulse sequence can establish an electron temperature distribution in the material similar to quasi-continuous excitation, while the time interval between each sub-pulse is short enough that the material lattice has not yet completed thermal relaxation. Thus, while maintaining the non-thermal ablation characteristics of ultrashort pulses, the material removal rate of a single processing operation is improved through the synergistic effect of multiple sub-pulses. The high-energy pulse sequence provided by the present invention provides sufficient driving energy for the above-mentioned synergistic processing effect, the high-fidelity characteristics ensure precise control of the temporal structure of the pulse sequence, and the effective suppression of satellite pulses avoids the impact of unintended material excitation on the processing morphology accuracy.

[0064] In pulsed laser deposition applications, high-energy pulse sequences can generate high-density plasma plumes on the target surface. The high repetition rate within the sequence allows for precise timing control of the plasma plume generation and propagation process. The uniform sub-pulse sequence generated by the device of this invention ensures the uniformity of target ablation during each laser deposition process, which is beneficial for improving the compositional uniformity and crystal quality of the deposited film. This has significant application value in precision manufacturing fields such as functional thin film preparation and semiconductor epitaxial growth. In free-electron laser seed source applications, free-electron lasers place extremely high demands on the temporal structure and phase stability of the seed laser. The high repetition rate pulse sequence generated by the device of this invention can provide a seed light with a precise temporal structure for the free-electron laser. High fidelity ensures that the temporal waveform of the seed pulse sequence faithfully reflects the design parameters. Low satellite pulse background avoids interference from parasitic seeds in the free-electron laser gain process. The high stability of the all-fiber front-end structure ensures the long-term reliable operation of the seed light, meeting the stringent requirements for seed source stability in large-scale free-electron laser devices.

[0065] It is understood that the dispersion compensation device in the above embodiments is not limited to the chirped Bragg grating 33. Depending on the actual application requirements, any one of the dispersion prism, transmission diffraction grating or reflection diffraction grating can be selected, as long as the dispersion provided by it matches the dispersion of the pulse broadening fiber 2 and can complete the dispersion compensation and compression of the amplified broadened pulse sequence.

[0066] It is understood that the gain medium in the regenerative amplification optical path and the dual-pass-wave amplification optical path in the above embodiments can be other solid-state gain media such as Yb:YAG, Yb:KGW, Yb:CALGO, Nd:YAG or Ti:Sapphire. The pump source wavelength, seed source center wavelength and cavity mirror coating parameters can be adjusted accordingly. This is also applicable to the N+1 pulse beam splitting phase modulation scheme of the present invention and the programmable phase modulation technology based on the acousto-optic modulator 44 and the field-programmable gate array direct digital synthesis RF generator 46.

[0067] It is understood that the mode-locked fiber oscillator 1 in the above embodiments is not limited to a ytterbium-doped fiber oscillator based on a nonlinear polarization rotation mode-locking mechanism. It can also employ a semiconductor saturable absorber mirror mode-locking mechanism or other mode-locking mechanisms. The gain medium can also be selected from erbium-doped fiber or thulium-doped fiber, etc., according to the target operating wavelength, and the operating wavelength can be adjusted accordingly. This also applies to the pulse sequence high-fidelity energy enhancement scheme proposed in this invention. Where there is no conflict, the technical features of the foregoing embodiments can be combined to achieve the optimal system configuration for specific application scenarios.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-fidelity energy enhancement device for ultrashort laser pulse sequences, characterized in that... ， A high-fidelity energy enhancement device for ultrashort laser pulse sequences comprises, in sequence, an optical fiber mode-locked oscillator, a pulse broadening fiber, a pulse sequence generation module, an optical fiber preamplifier module, a regenerative amplification optical path, a dual-pass wave amplification optical path, and a dispersion compensation device arranged along the main optical path of laser forward transmission. The internal components of the pulse sequence generation module are arranged along the optical path to form an N+1 pulse beam splitting phase modulation optical path. The N+1 pulse beam splitting phase modulation optical path receives the broadened pulse output from the pulse broadening fiber. Through beam splitting, single-path sub-pulse phase modulation, generation of N sub-pulses, and beam combining, the phase modulation of the pulse sequence is achieved, which weakens the pulse coherent interference spikes, thereby realizing high-fidelity energy enhancement of the high-repetition-rate ultrashort laser pulse sequence.

2. The high-fidelity energy enhancement device for ultrashort laser pulse sequences as described in claim 1, characterized in that, In the pulse sequence generation module, the incident light is fed into a 20:80 1-to-2 fiber coupler, which splits the light into two beams; one of the beams, 80%, passes through a pulse splitter and a polarization-dependent fiber isolator in sequence and is connected to the first input port of a 50:50 1-to-2 fiber coupler. One 20% stream passes sequentially through an acousto-optic modulator and an adjustable fiber optic attenuator to the second input port of a 50:50 1-to-2 fiber optic coupler; the acousto-optic modulator is electrically connected to an RF power amplifier, and the RF power amplifier is electrically connected to a field-programmable gate array direct digital synthesis RF generator. The 20:80 1-to-2 fiber optic coupler, pulse splitter, polarization-dependent fiber optic isolator, acousto-optic modulator, adjustable fiber optic attenuator, and 50:50 1-to-2 fiber optic coupler together constitute the optical path for generating N+1 pulse sequences with programmable phase.

3. The high-fidelity energy enhancement device for ultrashort laser pulse sequences as described in claim 1, characterized in that, The fiber preamplifier module includes a single-mode fiber-coupled semiconductor laser, a wavelength division multiplexer, a ytterbium-doped gain fiber, and a fiber isolator. The pump light output from the single-mode fiber-coupled semiconductor laser is coupled into the main optical path via a wavelength division multiplexer. A ytterbium-doped gain fiber is placed between the wavelength division multiplexer and the fiber isolator. The fiber isolator is placed between the ytterbium-doped gain fiber and the regenerative amplification optical path to perform primary amplification of the pulse sequence.

4. The high-fidelity energy enhancement device for ultrashort laser pulse sequences as described in claim 1, characterized in that, In the regenerative amplification optical path, the fiber collimator receives the output beam of the fiber isolator and collimates it into a free-space parallel beam before it is incident on the first polarization beam splitter. The output beam of the first polarization beam splitter passes through the first Faraday rotating mirror and the first half-wave plate in sequence before being output to the second polarization beam splitter. The output beam of the second polarizing beam splitter passes sequentially through the second Faraday rotating mirror and the second half-wave plate before being incident on the first 45-degree dielectric film reflector. The light beam reflected by the first 45-degree dielectric film mirror is incident on the third polarization beam splitter. One output beam of the third polarization beam splitter passes through the Pockels cell and arrives at the fourth polarization beam splitter. The Pockels cell controls the injection and pouring of the pulse sequence into the cavity through the electro-optic effect. The transmitted beam from the fourth polarizing beam splitter is incident on the first 0~45° dielectric film reflector. The beam reflected by the first 0~45° dielectric film reflector passes through the first plano-convex lens and the dielectric film dichroic mirror in sequence before being incident on the first gain crystal. The first gain crystal transmits the beam into the concave dielectric film mirror, which reflects the beam to the second 0-45° dielectric film mirror. The beam reflected by the second 0-45° dielectric film mirror passes through the fourth plano-convex lens and enters the second 0° dielectric film mirror. The beam is then reflected by the second 0° dielectric film mirror along the original path and transmitted to the first 0° dielectric film mirror to complete the round trip within the cavity. The regenerative amplification optical path is configured with a first multimode fiber-coupled semiconductor laser. The pump light output from the first multimode fiber-coupled semiconductor laser is coupled to the first gain crystal via a third plano-convex lens, a second plano-convex lens, and a dielectric film dichroic mirror. The beam accumulates gain by circling back and forth multiple times within the cavity before being output outward.

5. The high-fidelity energy enhancement device for ultrashort laser pulse sequences as described in claim 1, characterized in that, In the dual-pass-wave amplification optical path, the beam output from the second polarization beam splitter of the regenerated amplification optical path arrives at the fifth polarization beam splitter after being incident on the third half-wave plate; The first branch of the fifth polarization beam splitter is connected in sequence to the first quarter-wave plate and the chirped Bragg grating; The second branch of the fifth polarization beam splitter is connected in sequence to the second quarter-wave plate, the second forty-five-degree dielectric film mirror, the fifth plano-convex lens, the plano-concave lens, the second gain crystal, and the 0° dielectric film dichroic mirror. The dual-pass wave amplification optical path is configured with a second multimode fiber-coupled semiconductor laser. The pump port of the 0° dielectric film dichroic mirror is connected to the second multimode fiber-coupled semiconductor laser, which is coupled to the second gain crystal by the sixth and seventh plano-convex lenses. The chirped volume Bragg grating is one implementation of the dispersion compensation device.

6. The high-fidelity energy enhancement device for ultrashort laser pulse sequences as described in claim 1, characterized in that, The pulse broadening fiber is a polarization-maintaining fiber. The output end of the polarization-maintaining fiber is connected to the input port of the pulse sequence generation module. The dispersion of the polarization-maintaining fiber is matched with the dispersion of the dispersion compensation device. The pulse splitter is located on 80% of the output optical path of the 20:80 1-to-2 fiber coupler within the pulse sequence generation module. The pulse splitter is selected from any pulse splitting method such as fiber pulse shaper, beam splitter, and active fiber delay loop. It is used to split a single pulse into multiple sub-pulses and adapt the repetition frequency within the target sequence by adjusting the time-domain interval of the sub-pulses.

7. The high-fidelity energy enhancement device for ultrashort laser pulse sequences as described in claim 1, characterized in that, The dispersion compensation device is arranged at the beam output end of the dual-pass-wave amplification optical path. The dispersion compensation device is selected from any one of the dispersion prism, transmission diffraction grating, reflection diffraction grating, and chirped volume Bragg grating. It is used to receive the amplified pulse sequence and complete dispersion compensation, compressing the pulse time domain width.

8. A high-fidelity energy enhancement method for ultrashort laser pulse sequences, characterized in that, Using the high-fidelity energy enhancement device for ultrashort laser pulse sequences as described in any one of claims 1-7, Includes the following processes: An ultrashort seed pulse is output from an optical fiber mode-locked oscillator, and the incident pulse of the ultrashort seed pulse is used to broaden the optical fiber to complete the time-domain broadening. The broadened pulse is fed into the pulse sequence generation module, which uses the phase-programmable N+1 pulse sequence to generate an optical path to complete beam splitting, phase modulation and beam combining, generating an N+1 type uniform pulse sequence. The N+1 type uniform pulse sequence is fed into the fiber preamplifier module to complete the primary amplification, and then sequentially fed into the regenerative amplification optical path and the dual-pass wave amplification optical path to increase the pulse energy step by step. The pulse sequence after energy enhancement is fed into a dispersion compensation device to complete dispersion compensation and compression, and outputs a high-fidelity pulse sequence with high intra-sequence repetition frequency, low satellite pulse intensity, and high signal-to-noise ratio.

9. The high-fidelity energy enhancement method for ultrashort laser pulse sequences as described in claim 8, characterized in that, The broadened pulse beam is split into two transmission beams by a 20:80 1-to-2 fiber coupler; 80% of one beam is transmitted through a pulse splitter and a polarization-dependent fiber isolator, and the other 20% of the beam is transmitted through an acousto-optic modulator and an adjustable fiber attenuator. The field-programmable gate array direct digital synthesis RF generator outputs an RF signal, which is amplified by an RF power amplifier and drives an acousto-optic modulator to apply phase modulation to a single beam; the two beams are combined via a 50:50 1-to-2 fiber coupler to obtain an N+1 type uniform pulse sequence. The acquisition process of the RF signal output by the field-programmable gate array direct digital synthesis RF generator is as follows: a portion of the ultra-short seed pulse is extracted from the output beam of the fiber mode-locked oscillator and sent to the photodetector to be converted into an electrical pulse. The electrical pulse is converted into a square wave signal by a comparator. The square wave signal is converted into parallel data by the gigabit transceiver port and sent to the field-programmable gate array direct digital synthesis RF generator. The field-programmable gate array (FPGA) direct digital synthesis RF generator retrieves a sine wave template, combines it with input parallel data to generate four-channel weighted waveform data, performs serial conversion and weighted superposition on the four-channel weighted waveform data to generate a gated sine signal, and sends the gated sine signal to the RF power amplifier to complete power amplification before driving the acousto-optic modulator.

10. The high-fidelity energy enhancement method for ultrashort laser pulse sequences as described in claim 8, characterized in that, The phase offset matching logic for applying phase modulation to a single sub-pulse is as follows: the most effective interference spike suppression is determined by comparative simulation calculations, which is to apply an additional π phase to the single sub-pulse. The applied phase of the sub-pulse is set by optimizing the time delay between the AOM driving RF pulse signal and the single pulse signal. The calculated phase offset value is loaded into the field programmable gate array direct digital synthesis RF generator, and the acousto-optic modulator applies the corresponding phase perturbation to the single sub-pulse to suppress the interference spikes generated by the coherent superposition of pulses.

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