Low temporal jitter externally triggered high energy picosecond laser and working method thereof

Abstract

This invention discloses a low-time-jitter externally triggered high-energy picosecond laser and its operating method, relating to the field of laser technology. The method includes: a control module that synthesizes an external trigger signal and a supplementary trigger signal into a composite trigger signal; a gain-switched semiconductor laser that generates a seed pulse sequence driven by the composite trigger signal; an optical fiber preamplifier including at least one stage of optical fiber amplification unit for pre-amplifying the seed pulse sequence; an acousto-optic selection module that synchronously selects a target seed pulse generated by the external trigger signal from the pre-amplified seed pulse sequence according to the timing of the external trigger signal; and a solid-state main amplifier that, driven by a synchronous pump pulse matching the timing of the target seed pulse, amplifies the target seed pulse stage by stage, resolving the contradiction between optical fiber pre-amplification and low-frequency light output. By retaining the direct physical drive attribute, quantization delay errors are avoided, achieving high-energy output while ensuring extremely low time jitter, making it suitable for high-precision timing synchronization applications.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a low-time-jitter externally triggered high-energy picosecond laser and its operating method. Background Technology

[0002] High-energy picosecond lasers, with their ultrashort pulse widths and high peak power, have significant application value in precision machining, biomedical imaging, and basic scientific research. However, in complex systems involving multiple devices working together, such as inertial confinement fusion, laser-driven particle acceleration, free-electron laser diagnostics, and laser distance-gated 3D imaging, the timing synchronization accuracy between devices directly affects the overall system performance, placing extremely high demands on the low time jitter characteristics of the output optical signal relative to the external trigger electrical signal.

[0003] Short-cavity Q-switching, passive mode-locking, and gain-switching semiconductor technology are the main approaches to generating picosecond laser pulses. While short-cavity Q-switched lasers can be externally triggered, the time jitter between the output optical signal and the trigger electrical signal is significant, typically reaching nanosecond or even microsecond levels. Passively mode-locked lasers rely primarily on intracavity nonlinear elements for pulse operation, making precise synchronization with external electrical signals and on-demand triggering difficult. Compared to the former two technologies, gain-switching semiconductor technology achieves ultrashort pulse output through direct short electrical pulse drive (electromodulation). It features a short electro-optical conversion path, fast carrier response, and a compact structure, enabling extremely low time jitter on the picosecond level. However, the single-pulse output energy of this type of laser is extremely low, limiting its direct application in high-energy scenarios.

[0004] Fiber preamplification combined with solid-state main amplification is a primary technique for increasing the pulse energy of gain-switched semiconductor lasers. However, fiber preamplifiers require a high seed pulse repetition frequency; otherwise, excessive accumulation of inverted particle numbers during amplification can lead to transient over-amplification, enhanced amplified spontaneous emission (ASE), and exacerbated nonlinear effects, resulting in pulse waveform distortion, reduced amplification efficiency, and deterioration in stability and beam quality. However, high-energy picosecond lasers typically have low repetition frequencies, making it difficult for existing solutions to effectively increase pulse energy while maintaining low output time jitter relative to the external trigger signal. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a low-time-jitter externally triggered high-energy picosecond laser and its operating method. By combining the external trigger signal and a supplementary trigger signal into a composite trigger signal, a gain-switched semiconductor laser is driven to generate a high-frequency seed pulse sequence, maintaining stable operation of the fiber preamplifier. In conjunction with an acousto-optic selection module, a target seed pulse generated directly by the external trigger electrical signal is selected under synchronization signal control. Finally, the pulse is synchronously pumped and amplified by a solid-state main amplifier, achieving stable output of high-energy picosecond pulses under external triggering conditions. This satisfies the dual requirements of high-precision timing synchronization and high-energy output in complex collaborative systems, solving the problem that existing solutions struggle to simultaneously achieve low time-jitter and high-energy output under external triggering conditions, as well as the stable operation of the fiber preamplifier under low-frequency triggering, single-triggering, or no-trigger-signal conditions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a low-time jitter externally triggered high-energy picosecond laser, comprising: a control module and a gain-switching semiconductor laser, an optical fiber preamplifier, an acousto-optic menu module, and a solid-state main amplifier arranged sequentially along the optical path; The control module is used to receive external trigger signals and, in combination with a supplementary trigger signal with a preset repetition frequency, output a composite trigger signal to the gain-switching semiconductor laser. The gain-switched semiconductor laser is used to generate a seed pulse sequence under the drive of a composite trigger signal; The fiber optic preamplifier includes at least one fiber optic amplification unit for preamplifying the seed pulse sequence. The audio-visual selection module is used to synchronously select the target seed pulse generated by the external trigger signal from the pre-amplified seed pulse sequence according to the timing of the external trigger signal; The solid-state main amplifier is used to amplify the target seed pulse stage by stage under the drive of a synchronous pump pulse that is time-matched with the target seed pulse.

[0007] As an alternative implementation, when the external trigger signal is a periodic trigger signal, a supplementary trigger signal with a preset repetition frequency is generated between adjacent external trigger signals, and the external trigger signal and the supplementary trigger signal are combined into a composite trigger signal. When the external trigger signal is a single trigger signal or there is no external trigger signal, the control module automatically generates a supplementary trigger signal with a preset repetition frequency to drive the gain-switching semiconductor laser and fiber preamplifier.

[0008] As an alternative implementation, the fiber preamplifier includes at least one single-mode fiber amplification unit and at least one large-mode-field double-clad fiber amplification unit, and fiber isolators and narrowband filters are provided between adjacent amplification units. The single-mode fiber amplification unit includes a single-mode gain fiber, a pump source, and a wavelength division multiplexer. The seed pulse sequence output from the previous stage and the pump light output from the pump source are coupled into the single-mode gain fiber through the wavelength division multiplexer for amplification. The large-mode-area double-clad fiber amplification unit includes a large-mode-area ytterbium-doped double-clad fiber, a combiner, and a multimode pump source. The seed pulse sequence output from the last-stage single-mode fiber amplification unit and the pump light output from the multimode pump source are coupled into the large-mode-area ytterbium-doped double-clad fiber through the combiner for amplification.

[0009] As an alternative implementation, the acousto-optic menu module includes an optical isolation system, a first beam shaping system, an acousto-optic menu device, and a spatial filter arranged sequentially along the optical path; The optical isolation system includes a first half-wave plate, a first spatial optical isolator, and a second half-wave plate arranged sequentially along the optical path, for unidirectional transmission of pre-amplified seed pulse sequences; The first beam shaping system includes a first plano-convex lens and a first plano-concave lens arranged sequentially along the optical path, used to scale and collimate the spot size of the pre-amplified seed pulse sequence incident on the second half-wave plate; The acousto-optic selector is used to receive the pre-amplified seed pulse sequence incident by the first plano-concave lens and output the target seed pulse; The spatial filter includes a second plano-convex lens, a spatial filter aperture, and a third plano-convex lens arranged confocally along the optical path. The second plano-convex lens is used to focus the target seed pulse onto the spatial filter aperture. After passing through the spatial filter aperture, the target seed pulse is collimated by the third plano-convex lens and then injected into the solid-state main amplifier.

[0010] As an alternative implementation, the solid-state main amplifier includes a first-stage end-pumped dual-pass amplifier module, a first-stage end-pumped single-pass amplifier module, and at least one stage side-pumped dual-pass amplifier module arranged sequentially along the optical path; wherein, the first-stage end-pumped dual-pass amplifier module is used to perform primary solid-state amplification of the target seed pulse, the first-stage end-pumped single-pass amplifier module is used to increase the energy of the target seed pulse to the mJ level, and the at least one stage side-pumped dual-pass amplifier module is used to increase the energy of the target seed pulse to the hundreds of mJ level or above.

[0011] As an alternative implementation, the first-stage end-pumped dual-pass amplification module includes a third half-wave plate, a fourth plano-convex lens, a third 45° reflector, a first thin-film polarizer, a first Nd:YAG gain crystal, a first dichroic mirror, a first pump light shaping system, a first 808 nm semiconductor laser pump source, a fourth 45° reflector, a first quarter-wave plate, and a first 0° high-reflection mirror. The target seed pulse is sequentially incident on the first Nd:YAG gain crystal through the third half-wave plate, the fourth plano-convex lens, the third 45° reflector and the first thin-film polarizer for a single amplification. The pump light output from the first 808 nm semiconductor laser pump source is focused into the first Nd:YAG gain crystal by the first pump light shaping system and the first dichroic mirror. The target seed pulse, amplified once by the first Nd:YAG gain crystal, passes sequentially through the first dichroic mirror, the fourth 45° reflector, the first quarter-wave plate, and the first 0° high-reflection mirror, before returning to the first Nd:YAG gain crystal for dual-pass amplification. The dual-pass amplified target seed pulse is then incident on the first-stage end-pumped single-pass amplification module via the first thin-film polarizer.

[0012] As an alternative implementation, the first-stage end-pumped single-pass amplification module includes a fifth 45° reflector, a sixth 45° reflector, a fifth plano-convex lens, a seventh 45° reflector, a second dichroic mirror, a second pump light shaping system, a second 808nm semiconductor laser pump source, and a second Nd:YAG gain crystal. The target seed pulse output from the first-stage end-pump dual-pass amplification module is focused sequentially by the fifth 45° reflector, the sixth 45° reflector, the fifth plano-convex lens, the seventh 45° reflector, and the second dichroic mirror onto the second Nd:YAG gain crystal for amplification. The pump light output from the second 808 nm semiconductor laser pump source is sequentially focused into the second Nd:YAG gain crystal by the second pump light shaping system and the second dichroic mirror. The target seed pulse, amplified by the second Nd:YAG gain crystal, is incident on the side-pump dual-pass amplification module.

[0013] As an alternative implementation, the side-pumped dual-pass amplification module includes a fourth half-wave plate, a second optical isolator, a fifth half-wave plate, an eighth 45° reflector, a ninth 45° reflector, a second plano-concave lens, a sixth plano-convex lens, a second thin-film polarizer, a second quarter-wave plate, a first Nd:YAG side-pumping module, a seventh plano-convex lens, a vacuum tube, an eighth plano-convex lens, a Faraday rotator, and a second 0° high-reflection mirror, arranged sequentially along the optical path. The target seed pulse, amplified by the first-stage end-pump single-pass method, is incident on the fourth half-wave plate and sequentially transmitted along the optical path to the first Nd:YAG side-pump module for amplification. After amplification, it passes sequentially through the seventh plano-convex lens, the vacuum tube, the eighth plano-convex lens, the Faraday rotator, and the second 0° high-reflection mirror, before returning to the first Nd:YAG side-pump module for double-pass amplification. The amplified target seed pulse then passes through the second quarter-wave plate and enters the second thin-film polarizer, where polarization separation and extraction are performed.

[0014] As an alternative implementation, the repetition frequency of the synchronous pump pulse in the solid-state main amplifier is consistent with the repetition frequency of the target seed pulse. After the target seed pulse is amplified step by step, a picosecond laser pulse with low time jitter relative to the external trigger signal is output. The repetition frequency of the picosecond laser pulse is adjusted in the range of 1 Hz to 1 kHz, the pulse width is less than 100 ps, ​​the single pulse energy is greater than 100 mJ, and the time jitter relative to the external trigger electrical signal is controlled within 25 ps.

[0015] Secondly, the present invention provides a method for operating a high-energy picosecond laser with low time jitter external triggering, comprising: The control module receives external trigger signals and, in conjunction with a supplementary trigger signal generated at a preset repetition frequency, outputs a composite trigger signal to the gain-switching semiconductor laser. A seed pulse sequence is generated by a gain-switched semiconductor laser driven by a composite trigger signal. The seed pulse sequence is pre-amplified using an optical fiber preamplifier; The target seed pulse triggered by the external trigger signal is synchronously selected from the pre-amplified seed pulse sequence by the audio-visual selection module according to the timing of the external trigger signal; The target seed pulse is amplified step by step by a solid-state main amplifier driven by a synchronous pump pulse that is time-matched to the target seed pulse.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention proposes a low-time-jitter externally triggered high-energy picosecond laser and its operating method. A control module inserts a supplementary trigger signal with a preset repetition frequency between adjacent external trigger signals, combining the external trigger signal and the supplementary trigger signal into a composite trigger signal. This composite trigger signal drives a gain-switched semiconductor laser to generate a high-repetition-frequency seed pulse, satisfying the operating conditions of the fiber preamplifier. When the original external trigger signal is a single trigger signal or is absent, the control module automatically generates a supplementary trigger signal with a preset repetition frequency to maintain stable operating conditions for the gain-switched semiconductor laser and the fiber preamplifier. Simultaneously, in conjunction with an acousto-optic selection module, the target seed pulse directly driven by the external trigger signal is selected synchronously, and the supplementary pulse is filtered out, ensuring that the output optical signal has extremely low time jitter relative to the external trigger signal. The target seed pulse is then injected into a solid-state main amplifier for synchronous pump energy amplification, achieving stable output of high-energy picosecond pulses under external triggering conditions, meeting the dual requirements of high-precision timing synchronization and high-energy output for complex collaborative systems. This invention resolves the contradiction between fiber preamplification and low-frequency light output. By retaining the direct physical drive properties, it avoids quantization delay errors and achieves high energy output while ensuring extremely low time jitter. It is suitable for high-precision timing synchronization applications.

[0017] This invention inserts a supplementary trigger signal with a preset repetition frequency between adjacent original external trigger signals and combines it with the original external trigger signals to form a composite trigger signal, thereby driving a gain-switched semiconductor laser to generate a high repetition frequency seed pulse sequence. By using the high repetition frequency seed pulse sequence for fiber pre-amplification, excessive accumulation of population inversion in the amplifier due to excessively low seed pulse repetition frequency can be avoided. This suppresses instantaneous over-amplification, enhanced spontaneous emission, and aggravated nonlinear effects, reducing adverse effects such as decreased output signal-to-noise ratio, spectral broadening or distortion, and enhanced stimulated Brillouin scattering. As a result, the stable operation requirements of fiber pre-amplification are met, and the stability of the pre-amplification process and the quality of the output signal are improved.

[0018] When the original external trigger signal is a single trigger signal or there is no external trigger signal, the present invention can still automatically generate a supplementary trigger signal with a preset repetition frequency by the control module, preferably 500 kHz, in order to maintain the gain-switching semiconductor laser and fiber preamplifier in a stable working state, thereby improving the system's adaptability to different triggering conditions and its working reliability.

[0019] This invention uses an acousto-optic menu module to synchronously select the target seed pulse directly triggered by the original external trigger signal from the pre-amplified high repetition frequency seed pulse sequence according to the timing of the original external trigger signal, and filters out the supplementary seed pulse triggered by the supplementary trigger signal. This ensures that the final output pulse maintains a direct trigger correspondence with the original external trigger signal, thereby effectively avoiding the additional time uncertainty introduced by regenerating the pulse after internal timing processing, and ensuring that the output optical signal has extremely low time jitter characteristics relative to the original external trigger signal.

[0020] This invention employs a multi-stage amplification structure combining fiber optic pre-amplification and solid-state main amplification. The pre-stage fiber optic pre-amplifier can achieve stable pre-amplification of low-energy seed pulses under high repetition frequency conditions. The subsequent solid-state main amplifier achieves progressive pulse energy enhancement through a first-stage end-pumped double-pass amplification, a first-stage end-pumped single-pass amplification, and at least a first-stage side-pumped double-pass amplification. Simultaneously, each stage pump source of the solid-state main amplifier is controlled by a second synchronization control signal. The repetition frequency of its synchronization pump pulse is consistent with the target output repetition frequency corresponding to the original external trigger signal, but different from the repetition frequency of the high-repetition-frequency seed pulse sequence in the previous stage. Therefore, the solid-state main amplifier only effectively amplifies the target seed pulse, which can reduce the heat accumulation, energy waste, and amplification instability problems caused by ineffective pumping of supplementary seed pulses.

[0021] This invention enables low-time jitter, high-energy picosecond laser output that supports external triggering. The output repetition frequency can be adjusted within the range of 1 Hz to 1 kHz, the pulse width is less than 100 ps, ​​the output energy is greater than 100 mJ, and the time jitter of the output optical signal relative to the external trigger electrical signal can be controlled within 25 ps, thereby meeting the application requirements of high-precision timing synchronization and high-energy picosecond laser output.

[0022] 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

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of a high-energy picosecond laser with low time jitter external triggering provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the timing relationship between the original external trigger signal, the supplementary trigger signal, the composite trigger signal, the high repetition frequency seed pulse sequence, the first synchronization control signal, the target seed pulse after the menu, and the second synchronization control signal provided in Embodiment 1 of the present invention. Figure 3 The oscilloscope measured timing diagram of the original external trigger signal, the composite trigger signal and the first synchronization control signal provided in Embodiment 1 of the present invention; Figure 4 An oscilloscope test result of the time jitter between the original external trigger signal and the final output optical signal provided in Embodiment 1 of the present invention; The components include: 1. Control module; 2. Gain-switched semiconductor laser; 3. Polarization-maintaining fiber circulator; 4. First 976 nm semiconductor laser pump source; 5. First wavelength division multiplexer; 6. First polarization-maintaining ytterbium-doped single-mode gain fiber; 7. First fiber isolator; 8. First narrowband filter; 9. Second 976 nm semiconductor laser pump source; 10. Second wavelength division multiplexer; 11. Second polarization-maintaining ytterbium-doped single-mode gain fiber; 12. Second fiber isolator; 13. Second narrowband filter; 14. Third 976 nm semiconductor laser pump source; 15. First wavelength division multiplexer; 16. Second polarization-maintaining ytterbium-doped single-mode gain fiber; 17. Second fiber isolator; 18. Second narrowband filter; 19. Third 976 nm semiconductor laser pump source; 20. Gain-switched semiconductor laser; 21. Second gain-switched semiconductor laser; 22. Second gain-switched semiconductor laser; 3. Polarization-maintaining fiber circulator; 23. Second gain-switched semiconductor laser; 4. First 976 nm semiconductor laser pump source; 5. First wavelength division multiplexer; 10. Second wavelength division multiplexer; 11. Second polarization-maintaining ytterbium-doped single-mode gain fiber; 12. Second fiber isolator; 13. Second narrowband filter; 14. Third 976 nm semiconductor laser pump source; 15. Second wavelength division multiplexer; 16. Second gain-switched semiconductor laser; 17. Second gain-switched semiconductor laser; 18. Second gain-switched semiconductor laser; 19. Second gain-switched semiconductor laser; 10. Second wavelength division multiplexer; 11. Second polarization-maintaining ytterbium-doped single-mode 15. nm semiconductor laser pump source; 16. Beam combiner; 17. Large mode area ytterbium-doped double-clad fiber; 18. Pump light stripper; 19. Fiber collimator; 20. First 45° mirror; 21. Second 45° mirror; 22. First half-wave plate; 23. First spatial optical isolator; 24. Second half-wave plate; 25. First plano-convex lens; 26. First plano-concave lens; 27. Acousto-optic selector; 28. Second plano-convex lens; 29. ​​Spatial filter aperture; 30. Third plano-convex lens; 31. Fourth plano-convex lens; 32. Third 45° mirror; 33. First thin-film polarizer; 34. First Nd:YAG gain crystal; 35. First dichroic mirror; 36. First pump light shaping system; 37. First 808 nm semiconductor laser pump source; 38, fourth 45° reflector; 39, first quarter-wave plate; 40, first 0° high-reflection mirror; 41, fifth 45° reflector; 42, sixth 45° reflector; 43, fifth plano-convex lens; 44, seventh 45° reflector; 45, second dichroic mirror; 46, second pump light shaping system; 47, second 808 48. Nd:YAG semiconductor laser pump source; 49. Second Nd:YAG gain crystal; 50. Fourth half-wave plate; 51. Second optical isolator; 52. Fifth half-wave plate; 53. Eighth 45° mirror; 54. Ninth 45° mirror; 55. Second plano-concave lens; 56. Sixth plano-convex lens; 57. Second thin-film polarizer; 58. Second quarter-wave plate; 59. First Nd:YAG side-pump module; 60. Seventh plano-convex lens; 61. Vacuum tube; 62. Eighth plano-convex lens; 63. Faraday rotator; 64. Second 0° high-reflection mirror. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0026] 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.

[0027] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. Furthermore, it should be understood that the terms “comprising” and “including”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0028] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0029] Example 1 This embodiment provides a low-time-jitter externally triggered high-energy picosecond laser, such as... Figure 1 As shown, it includes: a control module 1, and a gain-switching semiconductor laser 2, an optical fiber preamplifier, an acousto-optic selector module, and a solid-state main amplifier arranged sequentially along the optical path.

[0030] In this embodiment, the control module 1 is used to receive the original external trigger signal and, in combination with the generated supplementary trigger signal with a preset repetition frequency, output a composite trigger signal to the gain-switching semiconductor laser 2; and also outputs a first synchronization control signal and a second synchronization control signal, which are used to control the acousto-optic menu module and the solid-state main amplifier to work synchronously, respectively.

[0031] Specifically: The control module 1 is equipped with a trigger signal synthesis module. When the original external trigger signal is a periodic trigger signal, the control module 1 generates a supplementary trigger signal with a preset repetition frequency between adjacent original external trigger signals. The original external trigger signal and the supplementary trigger signal are combined into a composite trigger signal through the trigger signal synthesis module. The composite trigger signal is output to the gain-switched semiconductor laser 2 to drive the gain-switched semiconductor laser 2 to generate a seed pulse sequence with a high repetition frequency.

[0032] When the original external trigger signal is a single trigger signal or there is no external trigger signal, the control module 1 automatically generates a supplementary trigger signal with a preset repetition frequency, preferably 500 kHz, to maintain the gain-switching semiconductor laser 2 and the fiber preamplifier at a repetition frequency suitable for stable operation, and to avoid excessive accumulation of population inversion in the fiber preamplifier due to long-term low repetition frequency or no seed input.

[0033] The control module 1 also outputs a first synchronization control signal (audio-visual menu control signal) and a second synchronization control signal (synchronous pump control signal) that are synchronized with the original external trigger signal. The first synchronization control signal is used to control the audio-visual menu module to perform synchronous menu selection according to the timing of the original external trigger signal, and the second synchronization control signal is used to control the solid-state main amplifier to perform synchronous pumping according to the target seed pulse repetition frequency corresponding to the original external trigger signal.

[0034] In the absence of an external trigger signal, since there is no target seed pulse directly triggered by the external trigger signal, the acousto-optic menu module does not perform target pulse selection, and the solid-state main amplifier does not perform effective synchronous amplification output. Only when a valid original external trigger signal is detected will corresponding first and second synchronization control signals be generated based on the external trigger signal, which are used for acousto-optic menu selection and solid-state main amplifier synchronous pumping.

[0035] In this embodiment, the gain-switched semiconductor laser 2 is used to generate a corresponding high repetition frequency seed pulse sequence through electro-optic conversion under the drive of the composite trigger signal. The high repetition frequency seed pulse sequence includes a target seed pulse directly triggered by the original external trigger signal and a supplementary seed pulse triggered by the supplementary trigger signal.

[0036] Specifically: the center wavelength of the seed pulse output by the gain-switched semiconductor laser 2 is 1064.3±0.3 nm, the seed pulse width is less than 100 ps, ​​the output polarization state is linearly polarized, and the 3dB spectral width of the output spectrum is less than 0.1 nm.

[0037] Furthermore, by adjusting the temperature control parameters of the gain-switched semiconductor laser 2, the center wavelength of the output spectrum can be adjusted; at the same time, a narrower seed spectrum helps to suppress spectral broadening during subsequent amplification, thereby improving the spectral stability and amplification quality of the output pulse.

[0038] In this embodiment, a polarization-maintaining fiber circulator 3 is also provided at the output end of the gain-switched semiconductor laser 2. The seed pulse sequence output by the gain-switched semiconductor laser 2 first enters the polarization-maintaining fiber circulator 3. The polarization-maintaining fiber circulator 3 is used to guide the seed pulse sequence into the subsequent fiber preamplifier and to isolate the back propagation light from the subsequent amplification link and export it from the corresponding port, thereby preventing the back light from returning to the seed source and affecting the stable operation of the gain-switched semiconductor laser 2, and improving the safety and stability of the seed output of the front stage.

[0039] In this embodiment, the fiber preamplifier includes a first-stage single-mode fiber amplification unit, a second-stage single-mode fiber amplification unit, and a third-stage large-mode-field double-clad fiber amplification unit arranged sequentially along the optical path. The seed pulse sequence output by the polarization-maintaining fiber circulator 3 enters the two-stage single-mode fiber amplification unit and the first-stage large-mode-field double-clad fiber amplification unit sequentially.

[0040] Fiber optic preamplifiers are used to preamplify high-repetition-frequency seed pulse sequences to increase seed pulse energy and avoid excessive accumulation of population inversion within the amplifier due to excessively low seed pulse repetition frequency. This suppresses transient overamplification, enhanced spontaneous emission, and aggravated nonlinear effects, thereby reducing adverse effects such as decreased signal-to-noise ratio, spectral broadening or distortion, and enhanced stimulated Brillouin scattering of the output signal.

[0041] The first-stage single-mode fiber amplification unit and the second-stage single-mode fiber amplification unit are used to pre-amplify the high repetition frequency seed pulse sequence step by step, so as to achieve a steady increase in seed pulse energy while ensuring high amplification efficiency and good beam quality. The third-stage large mode field double-clad fiber amplification unit is used to further increase the pulse energy under high power conditions and reduce the peak power density by using a larger mode field area, thereby reducing the limitation of nonlinear effects on output performance during high power amplification.

[0042] Specifically: Both the first-stage single-mode fiber amplification unit and the second-stage single-mode fiber amplification unit include a single-mode gain fiber, a pump source, and a wavelength division multiplexer for coupling the pump light into the corresponding gain fiber; preferably, the single-mode gain fiber is a polarization-maintaining ytterbium-doped gain fiber, and the pump source is a semiconductor laser pump source with a wavelength in the 976 nm band.

[0043] The third-stage large-mode-area double-clad fiber amplification unit includes a large-mode-area ytterbium-doped double-clad fiber, a combiner, and a multimode pump source. The pulse signal output from the second-stage single-mode fiber amplification unit is coupled into the large-mode-area ytterbium-doped double-clad fiber via the combiner, and is further pumped by the multimode pump source with high power to achieve a further increase in pulse energy. Preferably, the large-mode-area ytterbium-doped double-clad fiber is a polarization-maintaining fiber.

[0044] Fiber optic isolators and narrowband filters are installed between adjacent fiber optic amplification units. The fiber optic isolators suppress the influence of backpropagating light from subsequent stages on the preceding amplification links and seed source, while the narrowband filters filter out the amplified spontaneous emission background generated during amplification, improve the output pulse signal-to-noise ratio, and suppress spectral broadening or distortion caused by amplification bandwidth expansion. The fiber optic isolators and narrowband filters enhance the stability of the multi-stage single-mode pre-amplification process and improve the output signal quality.

[0045] Furthermore, the first-stage single-mode fiber amplification unit and the second-stage single-mode fiber amplification unit constitute a two-stage single-mode step-by-step amplification structure to achieve step-by-step gain accumulation of low-energy seed pulses while maintaining good polarization characteristics and beam quality of the output laser. The third-stage large-mode-field double-clad fiber amplification unit uses a larger mode field area to reduce peak power density and weaken the limitations imposed on the amplification process by self-phase modulation, stimulated Brillouin scattering, and other nonlinear effects.

[0046] As an alternative implementation, the output end of the third-stage large-mode-field double-clad fiber amplification unit is also provided with a pump light stripper 17 and a fiber collimator 18; wherein, the pump light stripper 17 is used to remove the unabsorbed residual pump light and clad stray light, and the fiber collimator 18 is used to output the amplified pulsed laser as a collimated beam for subsequent injection into the acousto-optic menu module.

[0047] like Figure 1 As shown, the fiber optic preamplifier specifically includes: The first-stage single-mode fiber amplification unit includes a first 976 nm semiconductor laser pump source 4, a first wavelength division multiplexer 5, and a first polarization-maintaining ytterbium-doped single-mode gain fiber 6. The first input terminal of the first wavelength division multiplexer 5 is connected to the output terminal of the polarization-maintaining fiber circulator 3, and the second input terminal is connected to the output terminal of the first 976 nm semiconductor laser pump source 4. The output terminal of the first wavelength division multiplexer 5 is connected to the first polarization-maintaining ytterbium-doped single-mode gain fiber 6. The output terminal of the first polarization-maintaining ytterbium-doped single-mode gain fiber 6 is connected to the second-stage single-mode fiber amplification unit in sequence through the first fiber isolator 7 and the first narrowband filter 8.

[0048] The second-stage single-mode fiber amplification unit includes a second 976 nm semiconductor laser pump source 9, a second wavelength division multiplexer 10, and a second polarization-maintaining ytterbium-doped single-mode gain fiber 11. The first input terminal of the second wavelength division multiplexer 10 is connected to the output terminal of the first narrowband filter 8, and the second input terminal is connected to the output terminal of the second 976 nm semiconductor laser pump source 9. The output terminal of the second wavelength division multiplexer 10 is connected to the second polarization-maintaining ytterbium-doped single-mode gain fiber 11. The output terminal of the second polarization-maintaining ytterbium-doped single-mode gain fiber 11 is connected to the third-stage large-mode-field double-clad fiber amplification unit in sequence through the second fiber isolator 12 and the second narrowband filter 13.

[0049] The third-stage large-mode-area double-clad fiber amplification unit includes a third 976 nm semiconductor laser pump source 14, a beam combiner 15, and a large-mode-area ytterbium-doped double-clad fiber 16.

[0050] The first input terminal of the beam combiner 15 is connected to the output terminal of the second narrowband filter 13, the second input terminal is connected to the output terminal of the third 976 nm semiconductor laser pump source 14, and the output terminal of the beam combiner 15 is connected to the large mode area ytterbium-doped double-clad fiber 16.

[0051] Specifically: The seed pulse output from the polarization-maintaining fiber circulator 3 and the pump light output from the first 976 nm semiconductor laser pump source 4 are amplified by entering the first polarization-maintaining ytterbium-doped single-mode gain fiber 6 through the first wavelength division multiplexer 5. The first 976 nm semiconductor laser pump source 4 provides pump energy to the first polarization-maintaining ytterbium-doped single-mode gain fiber 6 through the first wavelength division multiplexer 5, realizing the first-stage single-mode fiber pre-amplification.

[0052] After being amplified in the first stage, the seed pulse passes through the first fiber isolator 7 and the first narrowband filter 8 in sequence before entering the second stage single-mode fiber amplification unit. In the second-stage single-mode fiber amplification unit, the pulse output from the first narrowband filter 8 and the pump light output from the second 976 nm semiconductor laser pump source 9 are amplified by entering the second polarization-maintaining ytterbium-doped single-mode gain fiber 11 through the second wavelength division multiplexer 10. The second 976 nm semiconductor laser pump source 9 provides pump energy to the second polarization-maintaining ytterbium-doped single-mode gain fiber 11 through the second wavelength division multiplexer 10, thereby realizing the second-stage single-mode fiber pre-amplification.

[0053] The seed pulse after the second stage amplification passes through the second fiber isolator 12 and the second narrowband filter 13 in sequence before entering the third stage large mode field double cladding fiber amplification unit. In the third-stage large-mode-area double-clad fiber amplification unit, the pulse output from the second narrowband filter 13 and the pump light output from the third 976nm semiconductor laser pump source 14 are amplified by the beam combiner 15 into the large-mode-area ytterbium-doped double-clad fiber 16, thereby further enhancing the energy.

[0054] Finally, the seed pulse, after being amplified in the third stage, is removed by the pump light stripper 17 to remove the remaining pump light and cladding stray light, and is then output as a free-space collimated beam by the fiber collimator 18.

[0055] As an alternative implementation, the optical fibers and fiber optic device pigtails used in the optical fiber preamplifier are all polarization-maintaining fibers, thereby improving the overall environmental stability and polarization maintenance capability of the device.

[0056] Furthermore, by optimizing the coiling radius and controlling the stress of the large-mode-area ytterbium-doped double-clad fiber 16, the influence of high-order mode transmission on beam quality and polarization characteristics can be reduced, providing high-quality seed pulses for subsequent acousto-optic selection and solid-state main amplification.

[0057] As an alternative implementation, the fiber optic preamplifier adopts a structure combining two-stage single-mode amplification and one-stage large-mode-field double-clad amplification to achieve stable pre-amplification of high-repetition-frequency, low-energy seed pulses in the front stage, and to balance high output energy and low nonlinear effects in the rear stage, providing the acousto-optic selector module and solid-state main amplifier with input pulses that are energy-rich, have good spectral quality, and are amplified stably.

[0058] It should be noted that since the first two stages of single-mode fiber amplification have completed the stable pre-amplification of the seed pulse while ensuring good beam quality and polarization characteristics, and the final stage amplification needs to further increase the pulse energy, this embodiment adopts a large mode field double-clad fiber amplification structure to reduce the peak power density by utilizing the larger mode field area, weaken the limitation of nonlinear effects on output performance during high-power amplification, and improve the power carrying capacity of the final stage amplification.

[0059] In this embodiment, the pulse output after being collimated by the fiber optic collimator 18 is deflected by the first 45° reflector 19 and the second 45° reflector 20 before entering the audio-visual menu module.

[0060] Driven by the first synchronization control signal, the audio-visual selection module performs synchronous selection on the high repetition frequency seed pulse sequence amplified by the fiber optic preamplifier according to the timing sequence of the original external trigger signal. It synchronously selects the target seed pulse directly triggered by the original external trigger signal from the preamplified seed pulse sequence and diffracts it. It filters out the supplementary seed pulse triggered by the supplementary trigger signal and the supplementary seed pulse propagates along the original optical path.

[0061] Since the selected target seed pulse is directly physically driven by the original external trigger signal, the quantization delay error and additional time uncertainty introduced by triggering the pulse after clock sampling, timing determination and signal reconstruction by the digital control system are avoided, thus ensuring that the output optical signal has extremely low time jitter characteristics relative to the original external trigger signal.

[0062] Specifically: The audio-visual menu module includes an optical isolation system, a first beam shaping system, an audio-visual menu 26, and a spatial filter arranged sequentially along the optical path.

[0063] The optical isolation system includes a first half-wave plate 21, a first spatial optical isolator 22 and a second half-wave plate 23 arranged sequentially along the optical path. It is used for unidirectional transmission of pre-amplified seed pulse sequences and to block the reverse backlight or self-excited oscillation light generated by the subsequent solid-state main amplifier at high gain, thereby protecting the upstream fiber optic link and semiconductor seed source from photo-induced damage.

[0064] The first beam shaping system includes a first plano-convex lens 24 and a first plano-concave lens 25 arranged sequentially along the optical path. These are used to match and scale and collimate the spot size of the pre-amplified seed pulse sequence output by the second half-wave plate 23, so that the spatial distribution characteristics of the beam meet the optimal operating conditions of the subsequent acousto-optic selector 26, thereby providing a spatial size basis for improving the acousto-optic diffraction efficiency.

[0065] The acousto-optic selector 26 is connected to the first plano-concave lens 25 and is used to receive the pre-amplified seed pulse sequence after spatial shaping and polarization matching. Under the drive of the first synchronization control signal, the time-matched target seed pulse undergoes acousto-optic diffraction, while the unselected supplementary seed pulse and the beam without a driving signal propagate along the original optical path.

[0066] The spatial filter includes a second plano-convex lens 27, a spatial filter aperture 28, and a third plano-convex lens 29 arranged confocally along the optical path. The second plano-convex lens 27 is used to focus the target seed pulse output by the acousto-optic selector 26 onto the spatial filter aperture 28. The spatial filter aperture 28 is used to position the selected diffraction light focal point to allow the target seed pulse to pass through and filter out unselected light and amplified spontaneous emission background light transmitted along different spatial optical paths. Subsequently, after the selected target seed pulse passes through the spatial filter aperture 28, it is re-collimated by the third plano-convex lens 29 and injected into the solid-state main amplifier, thereby effectively filtering out unselected light and background stray light.

[0067] Furthermore, the second half-wave plate 23 is also used to adjust the polarization state of the beam input to the acousto-optic selector 26 to improve the acousto-optic diffraction efficiency. This is because the diffraction efficiency of the acousto-optic selector 26 is sensitive to the polarization direction of the incident light. By rotating the second half-wave plate 23 to match its polarization state with the optimal diffraction axis of the acousto-optic selector 26, the energy utilization rate during selection can be further improved.

[0068] In this embodiment, the solid-state main amplifier is used to perform final energy amplification on the selected target seed pulse under the synchronous pumping driven by the second synchronous control signal, so as to output a picosecond laser pulse with high energy and low time jitter relative to the original external trigger signal.

[0069] The solid-state main amplifier includes a first-stage end-pumped dual-pass amplifier module, a first-stage end-pumped single-pass amplifier module, and at least one stage side-pumped dual-pass amplifier module arranged sequentially along the optical path. The first-stage end-pumped dual-pass amplifier module is used to perform primary solid-state amplification of the target seed pulse output by the acousto-optic selector module. The first-stage end-pumped single-pass amplifier module is used to further increase the pulse energy to the order of several mJ. The at least one stage side-pumped dual-pass amplifier module is used to further increase the pulse energy to obtain high-energy picosecond laser pulses with energies of hundreds of mJ or even higher.

[0070] Specifically: The target seed pulse output by the acousto-optic selector module first enters the first-stage end-pumped dual-pass amplification module, which includes: a third half-wave plate 30, a fourth plano-convex lens 31, a third 45° reflector 32, a first thin-film polarizer 33, a first Nd:YAG gain crystal 34, a first dichroic mirror 35, a first pump light shaping system 36, a first 808 nm semiconductor laser pump source 37, a fourth 45° reflector 38, a first quarter-wave plate 39, and a first 0° high-reflection mirror 40.

[0071] The third half-wave plate 30 receives the target seed pulse and is used to adjust the polarization direction of the target seed pulse; the fourth plano-convex lens 31 is used to shape the spot of the target seed pulse to improve its spatial matching with the first Nd:YAG gain crystal 34.

[0072] The target seed pulse output by the fourth plano-convex lens 31 is sequentially incident into the first Nd:YAG gain crystal 34 through the third 45° reflector 32 and the first thin film polarizer 33; at the same time, the pump light output by the first 808 nm semiconductor laser pump source 37 is sequentially focused into the first Nd:YAG gain crystal 34 through the first pump light shaping system 36 and the first dichroic mirror 35. The target seed pulse, amplified by the first Nd:YAG gain crystal 34, passes sequentially through the first dichroic mirror 35, the fourth 45° reflector 38, the first quarter-wave plate 39, and the first 0° high-reflection mirror 40. Then, it passes through the first 0° high-reflection mirror 40, the first quarter-wave plate 39, the fourth 45° reflector 38, and the first dichroic mirror 35 before returning to the first Nd:YAG gain crystal 34 for secondary amplification. The target seed pulse after secondary amplification is then incident on the first-stage end-pumped single-pass amplification module via the first thin-film polarizer 33.

[0073] As an alternative implementation, the third 45° reflector 32, the first thin-film polarizer 33, the fourth 45° reflector 38, the first quarter-wave plate 39, and the first 0° high-reflection mirror 40 together constitute a dual-pass amplification optical path to realize primary solid-state amplification of the target seed pulse and polarization control and output of the amplified pulse.

[0074] The first 808 nm semiconductor laser pump source 37 is preferably a quasi-continuous wave semiconductor laser with fiber-coupled output, used to provide end-face pump energy to the first Nd:YAG gain crystal 34.

[0075] The first pump light shaping system 36 is used to adjust the spot size and divergence characteristics of the pump light to meet the end-face pump coupling requirements of the first Nd:YAG gain crystal 34.

[0076] The first dichroic mirror 35 is used to couple the shaped pump light output from the first pump light shaping system 36 to the first Nd:YAG gain crystal 34. That is, after the first 808 nm semiconductor laser pump source 37 is shaped by the first pump light shaping system 36, it is coupled into the first Nd:YAG gain crystal 34 by the first dichroic mirror 35 to perform end-face pumping.

[0077] As an alternative implementation, the first Nd:YAG gain crystal 34 has dimensions of 3 mm × 3 mm × 8 mm and a doping concentration of 0.6 at.% Nd³. + The coating is doped and its end face has high transmittance for both 1064 nm and 808 nm.

[0078] As an alternative implementation, the coating parameters of the first dichroic mirror 35 are 808 nm high transmittance and 1064 nm high reflectance.

[0079] As an alternative implementation, the first 808 nm semiconductor laser pump source 37 has an output peak power of 100 W, a pump pulse width of 230 μs, and maintains timing matching with the target seed pulse under the control of the second synchronization control signal.

[0080] In this embodiment, the first-stage end-pumped single-pass amplification module includes a fifth 45° reflector 41, a sixth 45° reflector 42, a fifth plano-convex lens 43, a seventh 45° reflector 44, a second dichroic mirror 45, a second pump light shaping system 46, a second 808 nm semiconductor laser pump source 47, and a second Nd:YAG gain crystal 48.

[0081] The target seed pulse output by the first-stage end-pump dual-pass amplification module is shaped by the fifth 45° reflector 41, the sixth 45° reflector 42 and the fifth plano-convex lens 43, and then enters the seventh 45° reflector 44. It is then focused by the seventh 45° reflector 44 and the second dichroic mirror 45 into the second Nd:YAG gain crystal 48. Meanwhile, the pump light output from the second 808 nm semiconductor laser pump source 47 is focused into the second Nd:YAG gain crystal 48 by the second pump light shaping system 46 and the second dichroic mirror 45 in sequence. The target seed pulse, amplified by the second Nd:YAG gain crystal 48, is incident on the side-pump dual-pass amplification module.

[0082] The second 808 nm semiconductor laser pump source 47 is preferably a quasi-continuous wave semiconductor laser with fiber-coupled output, used to provide end-face pump energy to the second Nd:YAG gain crystal 48.

[0083] The second pump light shaping system 46 and the second dichroic mirror 45 are used to shape the pump light and couple it into the second Nd:YAG gain crystal 48.

[0084] The fifth plano-convex lens 43 is used to shape the target seed pulse output by the first-stage end-pumped dual-pass amplification module to improve its spatial matching with the second Nd:YAG gain crystal 48.

[0085] The second Nd:YAG gain crystal 48 is used to amplify the input target seed pulse in a single pass under synchronous end-face pumping, so as to further increase the pulse energy to several mJ.

[0086] As an alternative implementation, the second Nd:YAG gain crystal 48 has dimensions of 3 mm × 3 mm × 8 mm and a doping concentration of 0.6 at.% Nd³. + The coating is doped and its end face has high transmittance for both 1064 nm and 808 nm.

[0087] As an alternative implementation, the coating parameters of the second dichroic mirror 45 are 808 nm high transmittance and 1064 nm high reflectance.

[0088] As an alternative implementation, the second 808 nm semiconductor laser pump source 47 has an output peak power of 300 W, a pump pulse width of 230 μs, and maintains timing matching with the input pulse under the control of the second synchronization control signal.

[0089] The target seed pulse, after being amplified by a single-pass amplification by a first-stage end pump, enters at least a first-stage dual-pass amplification module by a side pump. This embodiment uses... Figure 1 Taking the first-stage side-pumped dual-pass amplification module as an example, it includes a fourth half-wave plate 49, a second optical isolator 50, a fifth half-wave plate 51, an eighth 45° reflector 52, a ninth 45° reflector 53, a second plano-concave lens 54, a sixth plano-convex lens 55, a second thin-film polarizer 56, a second quarter-wave plate 57, a first Nd:YAG side-pump module 58, a seventh plano-convex lens 59, a vacuum tube 60, an eighth plano-convex lens 61, a Faraday rotator 62, and a second 0° high-reflection mirror 63, arranged sequentially along the optical path.

[0090] The target seed pulse, amplified by the first-stage end-pump single-pass method, is incident on the fourth half-wave plate 49 and sequentially transmitted along the optical path to the first Nd:YAG side-pump module 58 for amplification. After amplification, it passes sequentially through the seventh plano-convex lens 59, the vacuum tube 60, the eighth plano-convex lens 61, the Faraday rotator 62, and the second 0° high-reflection mirror 63. Then, it returns to the first Nd:YAG side-pump module 58 for double-pass amplification via the second 0° high-reflection mirror 63, the Faraday rotator 62, the eighth plano-convex lens 61, the vacuum tube 60, and the seventh plano-convex lens 59. The amplified target seed pulse then enters the second thin-film polarizer 56 through the second quarter-wave plate 57. The second thin-film polarizer 56 performs polarization separation and extraction of the target seed pulse returned after double-pass amplification.

[0091] Specifically: The fourth half-wave plate 49 and the fifth half-wave plate 51 are respectively disposed on the front and rear sides of the second optical isolator 50 to adjust the polarization direction of the pulse light in the second optical isolator 50 and the subsequent amplification optical path.

[0092] The second optical isolator 50 is used to suppress the influence of the amplified return light on the preamplifier link and front-end optical components.

[0093] The second plano-concave lens 54 and the sixth plano-convex lens 55 constitute the second beam shaping system, which is used to expand, collimate and shape the target seed pulse output by the first-stage end-pumped single-pass amplification module so that the input beam aperture matches the effective light transmission aperture of the first Nd:YAG side-pumped module 58.

[0094] The second thin-film polarizer 56 is used to achieve polarization separation and output of the return pulse after dual-pass amplification.

[0095] The second quarter-wave plate 57 is used to reduce the nonlinear interaction of the laser in the gain medium and other optical components, thereby reducing the risk of optical damage and small-scale self-focusing effects.

[0096] The first Nd:YAG side-pumping module 58 is an integrated side-pumping amplification module. It uses a large-aperture Nd:YAG crystal as the laser gain medium and is provided with side-pumping energy by an 808 nm quasi-continuous wave semiconductor laser pump source. The first Nd:YAG side-pumping module 58 is controlled by a second synchronization control signal to output a synchronization pump pulse that matches the target seed pulse selected by the acousto-optic selector module and to amplify the target seed pulse with high energy.

[0097] The seventh plano-convex lens 59 and the eighth plano-convex lens 61 constitute a 4f relay imaging system. The vacuum tube 60 is disposed between the seventh plano-convex lens 59 and the eighth plano-convex lens 61, and a spatial filter aperture is provided in the middle of the vacuum tube 60. The 4f relay imaging system is used to perform relay imaging and beam shaping on the spatial transmission state of high-energy pulses during side-pumped dual-pass amplification, so as to reduce diffraction spread and beam distortion during long optical path transmission. The vacuum tube 60 is used to reduce the risk of breakdown of high peak power lasers in air, and the spatial filter aperture is used to filter out spatial stray light and improve the output beam quality.

[0098] The Faraday rotator 62 is used to compensate for thermal depolarization under high power amplification conditions.

[0099] The second 0° high-reflection mirror 63 is used to reflect the fundamental frequency light after single-pass amplification in order to achieve double-pass amplification.

[0100] As an alternative implementation, at least one side-pumped dual-pass amplification module can be configured as a single-stage or multi-stage series structure. When a single-stage side-pumped dual-pass amplification module is used, the output pulse energy can be increased to the level of hundreds of mJ. When multiple stages of side-pumped dual-pass amplification modules are connected in series, each stage of the side-pumped dual-pass amplification module is arranged sequentially along the optical path to further increase the pulse energy to the level of hundreds of mJ or even J while maintaining good beam quality and amplification stability.

[0101] As an alternative implementation, the first Nd:YAG side pump module 58 is an integrated side pump amplification module, which uses a 7 mm diameter Nd:YAG rod as the gain medium and is cooled by 20 °C circulating water.

[0102] As an alternative implementation, the first Nd:YAG side-pumping module 58 is side-pumped by an 808 nm quasi-continuous wave semiconductor laser pump source with an output peak power of 7000 W and a pump pulse width of 230 μs.

[0103] As an alternative implementation, the pump sources in the first 808 nm semiconductor laser pump source 37, the second 808 nm semiconductor laser pump source 47, and the first Nd:YAG side-pump module 58 are all controlled by a second synchronization control signal to output a synchronization pump pulse that matches the target seed pulse selected by the acousto-optic menu module. The repetition frequency of the synchronization pump pulse is consistent with the target output repetition frequency corresponding to the original external trigger signal, but different from the repetition frequency of the high repetition frequency seed pulse sequence in the preceding stage. This allows the solid-state main amplifier to effectively amplify only the target seed pulse and reduces the heat accumulation, energy waste, and amplification instability problems caused by ineffective pumping of the supplementary seed pulse.

[0104] like Figure 2The diagram illustrates the timing relationship between the original external trigger signal, the supplementary trigger signal, the composite trigger signal, the high repetition frequency seed pulse sequence, the first synchronization control signal (audio-visual menu control signal), the target seed pulse after menu selection, and the second synchronization control signal (synchronization pump control signal) in this embodiment. It should be noted that... Figure 2 It is mainly used to illustrate the relative timing relationships between various signals, and is not used to define the complete workflow of the system.

[0105] When there is a periodic original external trigger signal, after receiving the original external trigger signal, the control module 1 generates a supplementary trigger signal with a preset repetition frequency between adjacent original external trigger signals, and combines the original external trigger signal and the supplementary trigger signal into a composite trigger signal through the internal trigger signal synthesis module, which drives the gain-switching semiconductor laser 2 to output a high repetition frequency seed pulse sequence.

[0106] At the same time, the control module 1 outputs a first synchronous control signal (audio-visual menu control signal) to drive the audio-visual menu 26, so that the target seed pulse after selection corresponds to the original external trigger signal; at the same time, it outputs a second synchronous control signal (synchronous pump control signal) to drive the pump sources of each stage of the solid-state main amplifier, so that they match the timing of the selected target seed pulse.

[0107] Preferably, the repetition frequency of the original external trigger signal can be adjusted in the range of 1 Hz to 1 kHz, and the repetition frequency of the supplementary trigger signal is preferably 500 kHz; the second synchronization control signal is output 230 μs ahead of the target seed pulse after the selection, so as to ensure that the solid-state main amplifier establishes an effective gain that matches the target seed pulse.

[0108] When the original external trigger signal is a single trigger signal or there is no external trigger signal, the control module 1 automatically outputs a supplementary trigger signal with a preset repetition frequency to maintain the gain-switched semiconductor laser 2 and the fiber preamplifier at a repetition frequency suitable for stable operation. This avoids excessive accumulation of population inversion, instantaneous over-amplification, enhanced amplified spontaneous emission, and aggravated nonlinear effects in the fiber preamplifier due to low repetition frequency operation. Under this condition, the main function is to maintain the stable operation of the pre-stage seed source and the fiber preamplifier.

[0109] like Figure 3 The diagram shows the oscilloscope-measured timing diagrams of the original external trigger signal, the composite trigger signal, and the first synchronization control signal in this embodiment. It can be seen that the composite trigger signal inserts a high-repetition-frequency supplementary trigger signal between adjacent original external trigger signals, while the first synchronization control signal is synchronized with the original external trigger signal in time, used to drive the audio-visual selector to select the target seed pulse. The above test results verify the correctness of the trigger signal synthesis and synchronization control mechanism in this embodiment.

[0110] like Figure 4 As shown, under periodic external triggering conditions, the time jitter of the final output optical signal in this embodiment relative to the original external triggering signal is tested. Figure 4 The oscilloscope test results for the original external trigger signal (C2) and the final output optical signal (C1) are presented. Statistical analysis of the time interval between the two signals shows that the standard deviation of the time jitter is approximately 23 ps. The test results indicate that the output optical signal in this embodiment has lower time jitter characteristics compared to the original external trigger signal.

[0111] Furthermore, this embodiment can realize low-time jitter high-energy picosecond laser output that supports external triggering, with its output repetition frequency adjustable in the range of 1 Hz to 1 kHz, pulse width less than 100 ps, ​​and single pulse energy greater than 100 mJ.

[0112] Furthermore, this embodiment has good scalability in its main amplification structure. By reserving and optimizing the amplification stage based on the existing main amplification structure design, and further adding two main amplification stages composed of gain crystals with a diameter of 15 mm, the output energy is expected to be further increased to the 1 J level. This provides greater flexibility for subsequent system upgrades and higher power and higher energy application requirements, thereby meeting the needs of higher energy applications.

[0113] Example 2 This embodiment provides a method for operating a high-energy picosecond laser with low timing jitter external triggering as described in Embodiment 1. It should be noted that the operating method described in this embodiment corresponds to the structure described in Embodiment 1, and the signal timing relationship can be referenced. Figure 2 and Figure 3 The content shown.

[0114] The timing relationship between the original external trigger signal, the supplementary trigger signal, the composite trigger signal, the high repetition frequency seed pulse sequence, the first synchronization control signal (audio-visual menu control signal), the target seed pulse after menu selection, and the second synchronization control signal (synchronous pump control signal) is as follows: Figure 2 As shown.

[0115] Specifically: The system receives the original external trigger signal and generates a supplementary trigger signal with a preset repetition frequency between adjacent original external trigger signals. When the original external trigger signal is a single trigger signal or there is no external trigger signal, the control module 1 automatically generates a supplementary trigger signal with a preset repetition frequency, preferably 500 kHz, and simultaneously outputs a first synchronization control signal and a second synchronization control signal that are synchronized with the original external trigger signal.

[0116] Subsequently, the original external trigger signal and the supplementary trigger signal are combined into a composite trigger signal, and the composite trigger signal is used to drive the gain-switched semiconductor laser 2 to generate a high repetition frequency seed pulse sequence. The high repetition frequency seed pulse sequence includes a target seed pulse directly triggered by the original external trigger signal and a supplementary seed pulse triggered by the supplementary trigger signal.

[0117] Furthermore, the high repetition frequency seed pulse sequence is sequentially fed into polarization-maintaining fiber circulator 3, two-stage single-mode fiber amplification unit and one-stage large-mode-field double-clad fiber amplification unit for step-by-step pre-amplification, so as to improve the seed pulse energy and maintain the stability of the previous amplification process.

[0118] The pre-amplified high repetition frequency seed pulse sequence enters the audio-visual menu module, and under the control of the first synchronization control signal, it performs synchronous menu selection according to the timing of the original external trigger signal, selects the target seed pulse directly triggered by the original external trigger signal, and filters out the supplementary seed pulse triggered by the supplementary trigger signal, thereby obtaining the target seed pulse after menu selection that is synchronized with the original external trigger signal.

[0119] Finally, the selected target seed pulse is injected into the solid-state main amplifier, and under the synchronous pumping controlled by the second synchronous control signal, it is sequentially amplified through a first-stage end-pumped dual-pass amplifier module, a first-stage end-pumped single-pass amplifier module, and at least a first-stage side-pumped dual-pass amplifier module, ultimately outputting a high-energy picosecond laser pulse with low time jitter relative to the original external trigger signal.

[0120] In this embodiment, by inserting a supplementary trigger signal between the low-frequency original external trigger signals, the original low repetition frequency external trigger seed is transformed into a high repetition frequency seed pulse sequence suitable for fiber pre-amplification, thereby avoiding problems such as excessive accumulation of population inversion in the amplifier, instantaneous over-amplification, enhanced amplified spontaneous emission, and aggravated nonlinear effects caused by the seed pulse repetition frequency being too low. Meanwhile, since the pulse that is ultimately retained and enters the solid-state main amplifier is the target seed pulse after the menu is directly triggered by the original external trigger signal, the additional time uncertainty introduced by regenerating the pulse after internal timing processing can be effectively avoided, thereby ensuring that the output optical signal has extremely low time jitter characteristics relative to the original external trigger signal.

[0121] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A high-energy picosecond laser with low time jitter external triggering, characterized in that, include: The control module, along with a gain-switching semiconductor laser, fiber optic preamplifier, acousto-optic selector module, and solid-state main amplifier arranged sequentially along the optical path; The control module is used to receive external trigger signals and, in combination with a supplementary trigger signal with a preset repetition frequency, output a composite trigger signal to the gain-switching semiconductor laser. The gain-switched semiconductor laser is used to generate a seed pulse sequence under the drive of a composite trigger signal; The fiber optic preamplifier includes at least one fiber optic amplification unit for preamplifying the seed pulse sequence. The audio-visual selection module is used to synchronously select the target seed pulse generated by the external trigger signal from the pre-amplified seed pulse sequence according to the timing of the external trigger signal; The acousto-optic menu module includes an optical isolation system, a first beam shaping system, an acousto-optic menu selector, and a spatial filter arranged sequentially along the optical path. The optical isolation system includes a first half-wave plate, a first spatial optical isolator, and a second half-wave plate arranged sequentially along the optical path, for unidirectional transmission of pre-amplified seed pulse sequences; The first beam shaping system includes a first plano-convex lens and a first plano-concave lens arranged sequentially along the optical path, used to scale and collimate the spot size of the pre-amplified seed pulse sequence incident on the second half-wave plate; The acousto-optic selector is used to receive the pre-amplified seed pulse sequence incident by the first plano-concave lens and output the target seed pulse; The spatial filter includes a second plano-convex lens, a spatial filter aperture, and a third plano-convex lens arranged confocally along the optical path. The second plano-convex lens is used to focus the target seed pulse onto the spatial filter aperture. After passing through the spatial filter aperture, the target seed pulse is collimated by the third plano-convex lens and then injected into the solid-state main amplifier. The solid-state main amplifier is used to amplify the target seed pulse stage by stage under the drive of a synchronous pump pulse that is time-matched with the target seed pulse. The solid-state main amplifier includes a first-stage end-pumped dual-pass amplifier module, a first-stage end-pumped single-pass amplifier module, and at least one stage side-pumped dual-pass amplifier module arranged sequentially along the optical path. The first-stage end-pumped dual-pass amplifier module is used to perform primary solid-state amplification of the target seed pulse, the first-stage end-pumped single-pass amplifier module is used to increase the energy of the target seed pulse to the mJ level, and the at least one stage side-pumped dual-pass amplifier module is used to increase the energy of the target seed pulse to the hundreds of mJ level or above.

2. A low-time-jitter externally triggered high-energy picosecond laser as described in claim 1, characterized in that, When the external trigger signal is a periodic trigger signal, a supplementary trigger signal with a preset repetition frequency is generated between adjacent external trigger signals, and the external trigger signal and the supplementary trigger signal are combined into a composite trigger signal; When the external trigger signal is a single trigger signal or there is no external trigger signal, the control module automatically generates a supplementary trigger signal with a preset repetition frequency to drive the gain-switching semiconductor laser and fiber preamplifier.

3. A low-time-jitter externally triggered high-energy picosecond laser as described in claim 1, characterized in that, The fiber optic preamplifier includes at least one single-mode fiber amplification unit and at least one large-mode-field double-clad fiber amplification unit, and fiber optic isolators and narrowband filters are provided between adjacent amplification units. The single-mode fiber amplification unit includes a single-mode gain fiber, a pump source, and a wavelength division multiplexer. The seed pulse sequence output from the previous stage and the pump light output from the pump source are coupled into the single-mode gain fiber through the wavelength division multiplexer for amplification. The large-mode-area double-clad fiber amplification unit includes a large-mode-area ytterbium-doped double-clad fiber, a combiner, and a multimode pump source. The seed pulse sequence output from the last-stage single-mode fiber amplification unit and the pump light output from the multimode pump source are coupled into the large-mode-area ytterbium-doped double-clad fiber through the combiner for amplification.

4. A low-time-jitter externally triggered high-energy picosecond laser as described in claim 1, characterized in that, The first-stage end-pumped dual-pass amplification module includes a third half-wave plate, a fourth plano-convex lens, a third 45° reflector, a first thin-film polarizer, a first Nd:YAG gain crystal, a first dichroic mirror, a first pump light shaping system, a first 808 nm semiconductor laser pump source, a fourth 45° reflector, a first quarter-wave plate, and a first 0° high-reflection mirror. The target seed pulse is sequentially incident on the first Nd:YAG gain crystal through the third half-wave plate, the fourth plano-convex lens, the third 45° reflector and the first thin-film polarizer for a single amplification. The pump light output from the first 808 nm semiconductor laser pump source is focused into the first Nd:YAG gain crystal by the first pump light shaping system and the first dichroic mirror. The target seed pulse, amplified once by the first Nd:YAG gain crystal, passes sequentially through the first dichroic mirror, the fourth 45° reflector, the first quarter-wave plate, and the first 0° high-reflection mirror, before returning to the first Nd:YAG gain crystal for dual-pass amplification. The dual-pass amplified target seed pulse is then incident on the first-stage end-pumped single-pass amplification module via the first thin-film polarizer.

5. A high-energy picosecond laser with low time jitter external triggering as described in claim 1, characterized in that, The first-stage end-pumped single-pass amplification module includes a fifth 45° reflector, a sixth 45° reflector, a fifth plano-convex lens, a seventh 45° reflector, a second dichroic mirror, a second pump light shaping system, a second 808 nm semiconductor laser pump source, and a second Nd:YAG gain crystal. The target seed pulse output from the first-stage end-pump dual-pass amplification module is focused sequentially by the fifth 45° reflector, the sixth 45° reflector, the fifth plano-convex lens, the seventh 45° reflector, and the second dichroic mirror onto the second Nd:YAG gain crystal for amplification. The pump light output from the second 808 nm semiconductor laser pump source is sequentially focused into the second Nd:YAG gain crystal by the second pump light shaping system and the second dichroic mirror. The target seed pulse, amplified by the second Nd:YAG gain crystal, is incident on the side-pump dual-pass amplification module.

6. A low-time-jitter externally triggered high-energy picosecond laser as described in claim 1, characterized in that, The side-pumped dual-pass amplification module includes, in sequence along the optical path, a fourth half-wave plate, a second optical isolator, a fifth half-wave plate, an eighth 45° reflector, a ninth 45° reflector, a second plano-concave lens, a sixth plano-convex lens, a second thin-film polarizer, a second quarter-wave plate, a first Nd:YAG side-pumping module, a seventh plano-convex lens, a vacuum tube, an eighth plano-convex lens, a Faraday rotator, and a second 0° high-reflection mirror; The target seed pulse, amplified by the first-stage end-pump single-pass method, is incident on the fourth half-wave plate and sequentially transmitted along the optical path to the first Nd:YAG side-pump module for amplification. After amplification, it passes sequentially through the seventh plano-convex lens, the vacuum tube, the eighth plano-convex lens, the Faraday rotator, and the second 0° high-reflection mirror, before returning to the first Nd:YAG side-pump module for double-pass amplification. The amplified target seed pulse then passes through the second quarter-wave plate and enters the second thin-film polarizer, where polarization separation and extraction are performed.

7. A low-time-jitter externally triggered high-energy picosecond laser as described in claim 1, characterized in that, The repetition frequency of the synchronous pump pulse in the solid-state main amplifier is consistent with the repetition frequency of the target seed pulse. After the target seed pulse is amplified step by step, a picosecond laser pulse with low time jitter relative to the external trigger signal is output. The repetition frequency of the picosecond laser pulse is adjusted in the range of 1 Hz to 1 kHz, the pulse width is less than 100 ps, ​​the single pulse energy is greater than 100 mJ, and the time jitter relative to the external trigger electrical signal is controlled within 25 ps.

8. A method for operating a high-energy picosecond laser with low timing jitter external triggering as described in any one of claims 1-7, characterized in that, include: The control module receives external trigger signals and, in conjunction with a supplementary trigger signal generated at a preset repetition frequency, outputs a composite trigger signal to the gain-switching semiconductor laser. A seed pulse sequence is generated by a gain-switched semiconductor laser driven by a composite trigger signal. The seed pulse sequence is pre-amplified using an optical fiber preamplifier; The target seed pulse triggered by the external trigger signal is synchronously selected from the pre-amplified seed pulse sequence by the audio-visual selection module according to the timing of the external trigger signal; The target seed pulse is amplified step by step by a solid-state main amplifier driven by a synchronous pump pulse that is time-matched to the target seed pulse.

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