Repetition-frequency-adjustable high-energy nanosecond laser and working method thereof

Abstract

The invention discloses a repetition-frequency-adjustable high-energy nanosecond laser and a working method thereof, and belongs to the technical field of lasers. The laser comprises a synchronizing signal controller, a nanosecond seed source, an electro-optical selection system, a first end face pumping amplification stage, a second end face pumping amplification stage and a side face pumping bi-pass amplification stage, the synchronizing signal controller is adopted to generate a clock reference signal, a frequency division synchronizing signal and a clock synchronizing signal, and integrated control over system signals is achieved. The clock reference signal is used for triggering the seed source to generate nanosecond seed light pulses, the frequency division synchronizing signal is optimized and adjusted to control the electro-optical menu system to screen out frequency division seed light pulses, and the repetition frequency of the seed light pulses is adjustable. Meanwhile, a pulse pumping mode MOPA structure is adopted, the repetition frequency of each amplification stage pumping light pulse and the repetition frequency of the non-frequency-divided seed light pulse are kept consistent through a clock synchronization signal, it is ensured that the heat effect of the whole system is stable, and repetition frequency adjustable nanosecond laser output with high energy and good reliability is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a high-energy nanosecond laser with adjustable repetition rate and a working method thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] High-energy nanosecond lasers with adjustable repetition rates have important application value and broad market prospects in the fields of precision material processing, optical communications, biomedicine, and scientific research. In the field of precision material processing, the adjustable repetition rate function enables the laser to accurately control the cutting speed and surface quality according to the material type and processing requirements and avoid thermal damage to the material, thereby achieving the best cutting effect and efficiency. At the same time, the high-reliability, high-energy nanosecond laser output ensures the precision, controllability, and long-term stability of cutting complex structures.

[0004] At present, the common method to obtain high-energy nanosecond laser output is to use a master oscillator power amplifier (MOPA) that outputs nanosecond pulses from a solid (or optical fiber) seed source and amplifies the pulse energy through a laser amplification system. Depending on the pumping mode, the common implementation methods are divided into continuous pumping mode MOPA and pulse pumping mode MOPA.

[0005] In the continuous pumping mode MOPA, the patent with publication number CN117220124A discloses a high-energy and high-repetition-rate nanosecond laser system. The patent uses an acousto-optic Q-switched solid oscillator as a seed source, and realizes adjustable pulse repetition rate by changing the state of the acousto-optic modulation signal. Then, through the first-stage end face continuous pumping amplification and the two-stage double-rod single-pass side face continuous pumping amplification, high-energy and adjustable repetition rate nanosecond laser output is realized. The patent adopts a continuous pumping mode amplification module, and the laser amplification system has serious thermal effects, resulting in serious spot distortion and limiting its amplification ability. The patent uses multiple sets of soft-edge apertures in conjunction with a relay imaging system to compensate for the thermal effect to a certain extent. However, this method has large energy loss, low reliability, complex structure and high cost, which is not conducive to engineering design. At the same time, the continuous pumping mode amplification module has low energy amplification efficiency; and the patent does not specially treat the end face of the gain medium, making it difficult to suppress the spontaneous emission amplification (ASE) effect during the amplification process, affecting the signal-to-noise ratio and stability of the laser output.

[0006] In pulse pump mode MOPA, the pump source outputs periodic pulse pump light through electrical signal modulation, which reduces the continuous heat accumulation of the gain crystal, thereby improving the serious thermal effect problem of continuous pump mode MOPA. However, the seed source modulation signal is used as the signal reference of the entire system. When the repetition frequency changes, it will synchronously change the repetition frequency of the pulse pump light in each amplifier stage, which will cause the change of the thermal effect of the gain crystal, causing the mode and intensity distribution to fluctuate during the propagation of the beam, resulting in the degradation of the output energy stability and beam quality of the laser system, and increasing the risk of damage to optical components. Summary of the invention

[0007] In view of this, the present invention provides a high-energy nanosecond laser with adjustable repetition rate and a working method thereof. The laser provided by the present invention can achieve nanosecond laser output with high energy, good stability and beam quality with adjustable repetition rate in the range of 1 Hz-5 kHz, and has high efficiency, good reliability, simple structure and low cost, which is conducive to engineering design.

[0008] In a first aspect, the present invention provides a high-energy nanosecond laser with adjustable repetition rate, comprising a synchronization signal controller and a nanosecond seed source, a first optical isolation system, a first beam shaping system, an electro-optical selection system, a first end-pump amplifier stage, a second end-pump amplifier stage, a second beam shaping system, a second optical isolation system and a side-pumped double-pass amplifier stage, wherein the electro-optical selection system comprises a Pockels cell and a high-voltage driver; and the side-pumped double-pass amplifier stage comprises a first side-pumping module and a second side-pumping module; The synchronization signal controller uses the digital signal generated by the internal crystal oscillator phase-locked loop as the clock reference signal and synchronously generates a frequency-divided synchronization signal and a multi-channel clock synchronization signal; the clock reference signal is used to trigger the nanosecond seed source; the frequency-divided synchronization signal is used to trigger the high-voltage driver to generate an electro-optical high-voltage signal, thereby controlling the opening or closing of the Pockels cell; the multi-channel clock synchronization signal is used to provide trigger signals for the pulse pump source, the first side pump module, and the second side pump module in the first end-face pump amplifier stage and the second end-face pump amplifier stage, respectively.

[0009] In a second aspect, the present invention provides a method for operating the above-mentioned high-energy nanosecond laser with adjustable repetition rate, comprising the following process: After the nanosecond seed source is triggered by the clock reference signal of the synchronization signal controller, the output nanosecond seed light is first shaped by the first optical isolation system and the first beam shaping system; After the shaping, the polarization state of the nanosecond seed light changes to horizontal polarization and enters the electro-optical selection system. The high-voltage driver receives the frequency division synchronization signal of the synchronization signal controller to trigger and generate an electro-optical high-voltage signal, so that the Pockels cell is boosted from 0V to a quarter-wave voltage, and then reduced to 0V, and the frequency division seed light of the required period interval time is screened out; the polarization state of the selected frequency division seed light changes to vertical polarization, enters the first end-face pump amplifier stage, and matches the pump light mode output and shaped by the pulse pump source of the first end-face pump amplifier stage and passes through the first gain crystal in the same way; then the laser enters the second end-face pump amplifier stage, and matches the pump light mode output and shaped by the pulse pump source of the second end-face pump amplifier stage and passes through the second gain crystal in the same way; The clock synchronization signal output by the synchronization signal controller controls the pulse pump source pump light of the first end-face pump amplifier stage to be consistent with the pulse repetition frequency of the un-frequency-divided seed light, and the pulse width of the pump light to be equivalent to the energy level lifetime on the first gain crystal, and optimizes the relative delay time between the clock synchronization signal and the clock reference signal, so that the first end-face pump amplifier stage obtains the optimal amplification energy output; the pulse pump source parameters in the second end-face pump amplifier stage and the laser spot size at the second gain crystal are consistent with those in the first end-face pump amplifier stage; The laser amplified by the second end face pump amplifier stage first passes through the second beam shaping system and the second optical isolation system, and then the light polarization state changes to a vertical polarization state and enters the side pump amplifier stage; the first side pump module and the second side pump module are both triggered by the clock synchronization signal output by the synchronization signal controller and perform single-pass amplification, and then perform double-pass amplification, the amplified light polarization state changes to a horizontal polarization state, and then outputs high-energy nanosecond laser with adjustable repetition rate.

[0010] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The present invention adopts a self-developed high-precision synchronization signal controller to generate a clock reference signal, a frequency division synchronization signal and a clock synchronization signal, thereby realizing integrated control of the laser system signal, so that the jitter between the three electrical signals and the jitter between the optical signal and the electrical signal are all less than 1ns, thereby improving the overall stability and control accuracy of the system.

[0011] (2) The present invention optimizes and adjusts the repetition rate, delay and pulse width of the frequency division synchronization signal trigger, and timely controls the switch working state of the electro-optical selection system, so as to select the frequency division seed light pulses with the required period interval time without changing the repetition rate of the seed source, thereby realizing the flexible adjustment of the repetition rate of the seed light pulse. In addition, the use of the electro-optical selection system improves the signal-to-noise ratio of the frequency division seed light pulse and can chop and filter the ASE effect.

[0012] (3) The present invention adopts a pulse pump mode MOPA structure to alleviate the thermal effect of the gain crystal of each amplifier stage. The pump source of each amplifier stage is triggered by a clock synchronization signal to output a pump light pulse that is consistent with the repetition frequency of the un-frequency-divided seed light pulse, so that it is not affected by the change in the repetition frequency of the frequency-divided seed light pulse injected into the laser amplification system, ensuring the stability of the thermal effect of the entire system, avoiding the change in the thermal effect caused by the synchronous change of the repetition frequency of the pulse pump source and the frequency-divided seed light pulse in each amplifier stage, and thus preventing damage to optical components, output energy stability and beam quality degradation.

[0013] (4) The high-energy nanosecond laser with adjustable repetition rate provided by the present invention can achieve nanosecond laser output with high energy, stability and good beam quality with adjustable repetition rate in the range of 1 Hz-5 kHz, high efficiency, good reliability, simple structure and low cost, which is more conducive to engineering design. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0015] Figure 1 is a schematic structural diagram of a high-energy nanosecond laser with adjustable repetition rate according to Example 1 of the present invention; Figure 2 It is a timing diagram of a synchronization signal controller and optical pulses in a high-energy nanosecond laser with adjustable repetition rate according to Example 1 of the present invention; Figure 3 Schematic diagram of the beam quality output by the high-energy nanosecond laser with adjustable repetition rate according to Example 1 of the present invention; Figure 4 This is a far-field intensity distribution diagram of the light spot of the output light beam of the high-energy nanosecond laser with adjustable repetition rate according to Example 1 of the present invention; Figure 5 Schematic diagram of energy stability outputted by a high-energy nanosecond laser with adjustable repetition rate according to Example 1 of the present invention; In the figure; 1, nanosecond seed source; 2, first optical isolation system; 201, first half-wave plate; 202, first optical isolator; 203, second half-wave plate; 3, first beam shaping system; 301, first plano-convex lens; 302, first pinhole aperture; 303, second plano-convex lens; 401, first polarizer; 402, Pockels cell; 403, first 0° total reflection mirror; 501, first 45° total reflection mirror; 502, third plano-convex lens; 503, second 45° total reflection mirror; 504, first pulse pump source; 505, first pump beam shaping system; 506, first dichroic mirror; 507, first gain crystal; 508, second dichroic mirror; 601, third dichroic mirror; 602, second gain crystal; 60 3. The fourth dichroic mirror; 604. The second pump beam shaping system; 605. The second pulse pump source; 606. The third 45° total reflection mirror; 7. The second beam shaping system; 701. The fourth plano-convex lens; 702. The second pinhole aperture; 703. The fifth plano-convex lens; 8. The second optical isolation system; 801. The third half-wave plate; 802. The second optical isolator; 803. The fourth half-wave plate; 901. The fourth 45° total reflection mirror; 902. The second polarizer; 903. The first side pump module; 904. The thermal compensation lens; 905. The 90° quartz rotator; 906. The second side pump module; 907. The Faraday rotator; 908. The second 0° total reflection mirror; 10. The synchronization signal controller; 11. The high-voltage driver. DETAILED DESCRIPTION

[0016] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0017] The present invention provides a high-energy nanosecond laser with adjustable repetition rate, comprising a synchronization signal controller and a nanosecond seed source, a first optical isolation system, a first beam shaping system, an electro-optical selection system, a first end-pump amplifier stage, a second end-pump amplifier stage, a second beam shaping system, a second optical isolation system and a side-pumped double-pass amplifier stage, which are sequentially arranged along an optical path; the electro-optical selection system comprises a Pockels cell and a high-voltage driver; the side-pumped double-pass amplifier stage comprises a first side-pumping module and a second side-pumping module; The synchronization signal controller is respectively connected to the nanosecond seed source, the electro-optical selection system, the pulse pump source in the first end-pump amplifier stage and the second end-pump amplifier stage, the first side pump module and the second side pump module; The synchronization signal controller uses the digital signal generated by the internal crystal oscillator phase-locked loop as the clock reference signal and synchronously generates a frequency-divided synchronization signal and a multi-channel clock synchronization signal; the clock reference signal is used to trigger the nanosecond seed source; the frequency-divided synchronization signal is used to trigger the high-voltage driver to generate an electro-optical high-voltage signal, thereby controlling the opening or closing of the Pockels cell; the multi-channel clock synchronization signal is used to provide trigger signals for the pulse pump source, the first side pump module, and the second side pump module in the first end-face pump amplifier stage and the second end-face pump amplifier stage, respectively.

[0018] In the present invention, the nanosecond seed source adopts an electro-optical or acousto-optic Q-switched solid laser oscillator or an electrically modulated semiconductor laser plus a multi-stage optical fiber pre-amplification structure seed source to generate high-reliability nanosecond seed light.

[0019] In the present invention, the first optical isolation system includes a first half-wave plate, a first optical isolator and a second half-wave plate arranged in sequence along the optical path, which are used to block the unselected seed light after electro-optical selection and the amplified return light from damaging the seed source and optical components.

[0020] In the present invention, the first beam shaping system includes a first plano-convex lens, a first pinhole aperture and a second plano-convex lens arranged in sequence along the optical path, which are used to shape the nanosecond pulse seed source spot to match the light aperture of the Pockels cell in the electro-optical selection system, and filter out stray light and background around the seed spot.

[0021] In the present invention, the electro-optical selection system includes a first polarizer, a Pockels cell and a first 0° total reflection mirror arranged in sequence along the optical path, which is used to select seed light pulses with a required period interval time and inject them into the laser amplification system to adjust the repetition frequency of the seed light pulses. The high-voltage driver in the electro-optical selection system is used to provide the Pockels cell with a high-voltage signal with adjustable amplitude and duration.

[0022] Further preferably, the electro-optical crystal used in the Pockels cell is one of KTP, BBO, RTP or LiNbO3.

[0023] In the present invention, the first end-pump amplifier stage includes a first 45° total reflection mirror, a third plano-convex lens, a second 45° total reflection mirror, a first dichroic mirror, a first gain crystal, and a second dichroic mirror, which are sequentially arranged along the optical path, and also includes a first pulse pump source and a first pump beam shaping system. Further preferably, the first pulse pump source adopts a semiconductor laser with fiber-coupled output, and the semiconductor laser adopts a pulse pumping working mode to provide pump energy for the first gain crystal; the light output by the first pulse pump source is expanded by the first pump beam shaping system and then injected into the center of the first gain crystal after passing through the first dichroic mirror; and light absorbers for collecting unabsorbed pump light are arranged at corresponding positions of the first dichroic mirror and the second dichroic mirror.

[0024] In the present invention, the second end-pump amplifier stage includes a third dichroic mirror, a second gain crystal, a fourth dichroic mirror and a third 45° total reflection mirror arranged in sequence along the optical path, and also includes a second pulse pump source and a second pump beam shaping system. Further preferably, the second pulse pump source adopts a semiconductor laser with fiber-coupled output, and the semiconductor laser adopts a pulse pumping working mode to provide pump energy for the second gain crystal; the light output by the second pulse pump source is expanded by the second pump beam shaping system and injected into the center of the second gain crystal after passing through the fourth dichroic mirror; and light absorbers for collecting unabsorbed pump light are arranged at corresponding positions of the third dichroic mirror and the fourth dichroic mirror.

[0025] In the present invention, the semiconductor laser center wavelength used by the first pulse pump source and the second pulse pump source is one of 808nm, 880nm or 888nm.

[0026] In the present invention, the first gain crystal and the second gain crystal are Nd:YVO4 crystals, and both end faces of the first gain crystal and the second gain crystal are cut with wedge angles to suppress the ASE effect during the amplification process.

[0027] In the present invention, the second beam shaping system includes a fourth plano-convex lens, a second pinhole aperture and a fifth plano-convex lens, which are used to expand and collimate the light spot output by the second end-pump amplifier stage to match the aperture of the first side-pump module.

[0028] In the present invention, the second optical isolation system comprises a third half-wave plate, a second optical isolator and a fourth half-wave plate, which are used to prevent the return light amplified by the side pump amplifier stage from damaging the optical elements in the optical path.

[0029] In the present invention, the side-pumped double-pass amplifier stage includes a fourth 45° total reflection mirror, a second polarizer, a first side-pumping module, a thermal compensation lens, a 90° quartz rotator, a second side-pumping module, a Faraday rotator, and a second 0° total reflection mirror, which are sequentially arranged along the optical path. The thermal compensation lens adopts a plano-concave lens to compensate for the thermal lens effect of the gain crystal under high-power operation of the first side-pumping module and the second side-pumping module; the 90° quartz rotator and the Faraday rotator are used to compensate for the thermal depolarization effect of the gain crystal under high-power operation of the first side-pumping module and the second side-pumping module. The present invention uses thermal lens compensation technology and thermal depolarization compensation technology to compensate for the thermal effect of the gain crystal in each amplifier stage, avoiding complex beam shaping and imaging.

[0030] The gain crystals used in the first side pump module and the second side pump module of the present invention are both large-aperture Nd:YAG crystal rods, and the pump center wavelength is 808 nm.

[0031] The present invention also provides a working method of the above-mentioned high-energy nanosecond laser with adjustable repetition rate, comprising the following process: After the nanosecond seed source is triggered by the clock reference signal of the synchronization signal controller, the output nanosecond seed light is first shaped by the first optical isolation system and the first beam shaping system; After the shaping, the polarization state of the nanosecond seed light changes to horizontal polarization and enters the electro-optical selection system. The high-voltage driver receives the frequency division synchronization signal of the synchronization signal controller to trigger and generate an electro-optical high-voltage signal, so that the Pockels cell is boosted from 0V to a quarter-wave voltage, and then reduced to 0V, and the frequency division seed light of the required period interval time is screened out; the polarization state of the selected frequency division seed light changes to vertical polarization, enters the first end-face pump amplifier stage, and matches the pump light mode output and shaped by the pulse pump source of the first end-face pump amplifier stage and passes through the first gain crystal in the same way; then the laser enters the second end-face pump amplifier stage, and matches the pump light mode output and shaped by the pulse pump source of the second end-face pump amplifier stage and passes through the second gain crystal in the same way; The clock synchronization signal output by the synchronization signal controller controls the pulse pump source pump light of the first end-face pump amplifier stage to be consistent with the pulse repetition frequency of the un-frequency-divided seed light, and the pulse width of the pump light to be equivalent to the energy level lifetime on the first gain crystal, and optimizes the relative delay time between the clock synchronization signal and the clock reference signal, so that the first end-face pump amplifier stage obtains the optimal amplification energy output; the pulse pump source parameters in the second end-face pump amplifier stage and the laser spot size at the second gain crystal are consistent with those in the first end-face pump amplifier stage; The laser amplified by the second end face pump amplifier stage first passes through the second beam shaping system and the second optical isolation system, and then the light polarization state changes to a vertical polarization state and enters the side pump amplifier stage; the first side pump module and the second side pump module are both triggered by the clock synchronization signal output by the synchronization signal controller and perform single-pass amplification, and then perform double-pass amplification, the amplified light polarization state changes to a horizontal polarization state, and then outputs high-energy nanosecond laser with adjustable repetition rate.

[0032] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0033] Example 1 Figure 1 Schematic diagram of the structure of the high-energy nanosecond laser with adjustable repetition rate of this embodiment, including a nanosecond seed source 1, a first optical isolation system 2, a first beam shaping system 3, an electro-optical selection system, a first end-pump amplifier stage, a second end-pump amplifier stage, a second beam shaping system 7, a second optical isolation system 8, a side-pumped dual-pass amplifier stage and a synchronization signal controller 10.

[0034] In this embodiment, the nanosecond seed source 1 uses an electro-optical Q-switched solid laser oscillator to generate high-reliability nanosecond seed light, with an output pulse width of 4ns, a repetition rate of 5kHz, a single pulse energy of 0.5mJ, and a central wavelength of 1064.3nm.

[0035] In this embodiment, the first optical isolation system 2 includes a first half-wave plate 201, a first optical isolator 202 and a second half-wave plate 203 arranged in sequence along the optical path, and is used to block the unselected seed light after the electro-optical selection and the amplified return light from damaging the nanosecond seed source 1 and the optical elements.

[0036] In this embodiment, the first beam shaping system 3 includes a first plano-convex lens 301, a first pinhole aperture 302 and a second plano-convex lens 303 arranged in sequence along the optical path, and is used to shape the light spot of the nanosecond seed source 1. The light spot after shaping is 1 mm collimated light, which is used to match the aperture of the Pockels cell 402 in the electro-optical selection system. The 4f system composed of the first plano-convex lens 301 and the second plano-convex lens 303 is added with a first pinhole aperture 302 with a diameter of 0.8 mm to realize spatial filtering, which can filter out stray light and background around the seed spot.

[0037] In this embodiment, the electro-optical selection system includes a first polarizer 401, a Pockels cell 402, a first 0° total reflection mirror 403 and a high-voltage driver 11 for providing the Pockels cell 402 with a high-voltage signal with adjustable amplitude and duration.

[0038] The horizontally polarized seed light emitted from the first optical isolation system 2 enters the electro-optical selection system and is transmitted through the first polarizer 401. When the Pockels cell 402 is closed, the seed light still maintains a horizontal polarization state after traveling back and forth through the electro-optical selection system. Therefore, it is transmitted through the first polarizer 401 and is blocked at the first optical isolation system 2 to prevent the return from damaging the nanosecond seed source 1.

[0039] When the Pockels cell 402 is opened, the process of boosting and reducing the voltage of the Pockels cell 402 needs to be started when the seed light pulse of the required periodic interval passes through the Pockels cell 402 for the first time, and closed after being reflected by the first 0° total reflection mirror 403 and passing through the Pockels cell 402 for the second time, so that the polarization state of the selected frequency-divided seed light pulse changes to vertical polarization after traveling back and forth between the electro-optical selection system, and is reflected by the first polarizer 401 and enters the laser amplification system.

[0040] In this embodiment, the first end-pump amplifier stage includes a first 45° total reflection mirror 501, a third plano-convex lens 502, a second 45° total reflection mirror 503, a first dichroic mirror 506, a first gain crystal 507 and a second dichroic mirror 508, which are arranged in sequence along the optical path, and also includes a first pulse pump source 504 and a first pump beam shaping system 505.

[0041] The first pulse pump source 504 is a semiconductor laser with fiber-coupled output, which adopts a pulse pumping working mode to provide pump energy for the first gain crystal 507. The pump light is expanded and shaped by the first pump beam shaping system 505 and then injected into the center of the first gain crystal 507 after passing through the first dichroic mirror 506; light absorbers for collecting unabsorbed pump light are arranged at corresponding positions of the first dichroic mirror 506 and the second dichroic mirror 508.

[0042] In this embodiment, the second end-pumped amplifier stage includes a third dichroic mirror 601 , a second gain crystal 602 , a fourth dichroic mirror 603 and a third 45° total reflection mirror 606 arranged in sequence along the optical path, and also includes a second pulse pump source 605 and a second pump beam shaping system 604 .

[0043] The second pulse pump source 605 adopts a semiconductor laser with fiber-coupled output and adopts a pulse pumping working mode to provide pump energy for the second gain crystal 602; the pump light is expanded and shaped by the second pump beam shaping system 604 and then injected into the center of the second gain crystal 602 after passing through the fourth dichroic mirror 603; and light absorbers for collecting unabsorbed pump light are arranged at corresponding positions of the third dichroic mirror 601 and the fourth dichroic mirror 603.

[0044] In this embodiment, the working center wavelength of the first pulse pump source 504 and the second pulse pump source 605 is 808 nm, the peak power is 300 W, and the pump pulse width is 100 μs.

[0045] In this embodiment, the first gain crystal 507 and the second gain crystal 602 are Nd:YVO4 crystals with a length of 20 mm and a doping concentration of 0.2 at.%. Both end faces of the first gain crystal 507 and the second gain crystal 602 are cut with wedge angles to suppress ASE effect during amplification.

[0046] In this embodiment, the second beam shaping system 7 includes a fourth plano-convex lens 701 , a second pinhole aperture 702 and a fifth plano-convex lens 703 , which expands and collimates the light spot output by the second end-face pump amplifier stage to a diameter of 5 mm to match the aperture of the first side pump module 903 .

[0047] In this embodiment, the second optical isolation system 8 includes a third half-wave plate 801, a second optical isolator 802 and a fourth half-wave plate 803, which are used to prevent the returned depolarized light and ASE light after amplification by the side-pumped double-pass amplifier stage from damaging the optical components in the optical path.

[0048] In this embodiment, the side-pumped double-pass amplifier stage includes a fourth 45° total reflection mirror 901, a second polarizer 902, a first side-pumping module 903, a thermal compensation lens 904, a 90° quartz rotator 905, a second side-pumping module 906, a Faraday rotator 907 and a second 0° total reflection mirror 908, which are sequentially arranged along the optical path; The gain crystals used in the first side pump module 903 and the second side pump module 906 are both Nd:YAG crystal rods with a diameter of 11mm, a pump center wavelength of 808nm, a peak power of 7000W, and a pump pulse width of 230μs. The thermal compensation lens 904 is a plano-concave lens with a focal length of f=-300mm, which is used to compensate for the thermal lens effect of the Nd:YAG crystal rod when the first side pump module 903 and the second side pump module 906 are running at high power. The 90° quartz rotator 905 and the Faraday rotator 907 are used to compensate for the thermal depolarization effect of the gain crystal when the first side pump module 903 and the second side pump module 906 are running at high power; the second 0° total reflection mirror 908 is used to reflect the laser after single-pass amplification and perform double-pass amplification, finally achieving a repetition rate of hundreds of mJ with an adjustable range of 1Hz-5kHz and a beam quality of M 2 <1.5, operation stability RMS<1% and laser output with pulse width of 4ns.

[0049] In this embodiment, the synchronization signal controller 10 is respectively connected to the nanosecond seed source 1, the electro-optical selection system, the first pulse pump source 504 and the second pulse pump source 605, the first side pump module 903 and the second side pump module 906, and is used to provide a clock reference and a trigger signal for the system. Figure 2 FIG. 1 is a timing diagram of the synchronization signal controller 10 and the optical pulse in the high-energy nanosecond laser with adjustable repetition rate in this embodiment. Figure 2 , the timing of the synchronization signal controller 10 and the optical pulse of the present invention is described in detail.

[0050] The synchronization signal controller 10 uses the digital signal generated by the internal crystal oscillator phase-locked loop as a clock reference signal and synchronously generates a frequency-divided synchronization signal and a multi-channel clock synchronization signal.

[0051] By setting the pulse width and repetition rate of the clock reference signal, it is used to trigger the electro-optical Q-switched solid-state oscillator to generate nanosecond seed light, such as Figure 2 As shown in the “seed light pulse”, the repetition frequency of the seed light pulse is consistent with the clock reference signal. Correspondingly, the period of the seed light pulse is τ a .

[0052] At the same time, the synchronization signal controller 10 generates a frequency-divided synchronization signal in synchronization with the clock reference signal, which is used to trigger the high-voltage driver 11 in the electro-optical selection system to generate an electro-optical high-voltage signal. By adjusting the delay, frequency division number and pulse width of the frequency-divided synchronization signal relative to the clock reference signal, the high-voltage duration t, voltage increase and voltage reduction of the electro-optical high-voltage signal are controlled, so that the Pockels cell 402 is turned on or off at a reasonable time, and the frequency-divided seed light pulses with the required period interval time are screened out. Correspondingly, the pulse period after frequency division is τ b ,like Figure 2 As shown in the “Electro-optical high voltage signal” and “Output light pulse”.

[0053] The synchronization signal controller 10 generates multiple clock synchronization signals according to the clock reference signal, and provides trigger signals to generate pump light pulses for the first pulse pump source 504 and the second pulse pump source 605, the first side pump module 903, and the second side pump module 906. Figure 2 As shown in the "Pump Light Pulse" in the figure, the repetition frequency of the clock synchronization signal and the clock reference signal are synchronized and the same, so that the repetition frequency of the pump light pulse is consistent with that of the seed light pulse before frequency division. The pump pulse width T is adjusted to match the upper energy level lifetime of each amplifier stage gain crystal, and then the delay time Δt between the pump light pulse and the seed light pulse after frequency division is optimized, so that each amplifier stage can obtain the best amplification efficiency and maximum amplification energy.

[0054] like Figure 3 The figure is a schematic diagram of the beam quality of the high-energy nanosecond laser output with adjustable repetition rate in this embodiment. The thermal effect of the system of the present invention is stable and the pulse pumping mode MOPA structure is used in combination with the thermal lens compensation technology and the thermal depolarization compensation technology, so that the final output beam still maintains a good beam quality. The beam quality M of the two axes is 2 They are 1.38 and 1.46 respectively; Figure 4 This is a far-field intensity distribution diagram of the light spot of the output light beam of the high-energy nanosecond laser with adjustable repetition rate in this embodiment. It can be seen that the light spot can still maintain a good Gaussian intensity distribution in the far field.

[0055] Figure 5 This is a schematic diagram of the energy stability of the high-energy nanosecond laser output with adjustable repetition rate of this embodiment. According to application requirements, when the output pulse repetition rate is 500Hz, the laser is subjected to an 8-hour power stability test at an output energy of hundreds of mJ. The RMS working stability of the laser for 8 hours is 0.59%.

[0056] Example 2 This embodiment provides a working method of the high-energy nanosecond laser with adjustable repetition rate as described in Embodiment 1, including the following process: After the nanosecond seed source 1 is triggered by the clock reference signal of the synchronization signal controller 10, the output nanosecond seed light first passes through the first optical isolation system 2 and the first beam shaping system 3, wherein the first beam shaping system 3 shapes the seed light into collimated light, matches the clear aperture of the Pockels cell 402 and filters out the stray light and substrate around the seed light; The shaped seed light enters the electro-optical selection system. After passing through the first polarizer 401, the polarization state of the seed light is horizontal polarization. The high-voltage driver 11 receives the frequency-divided synchronization signal of the synchronization signal controller 10 to trigger and generate an electro-optical high-voltage signal, so that the Pockels cell 402 is boosted from 0V to a quarter-wave voltage and then reduced to 0V. The boosting and reducing processes are respectively ended when the main pulse passes through the Pockels cell 402 for the first time and after passing through the first 0° total reflection mirror 403 and passing through the Pockels cell 402 again. By adjusting the pulse width and delay of the high-voltage signal, the frequency-divided seed light with the required periodic interval time is screened out to ensure that no pre-pulse and tail pulse enter the boosting and reducing processes. At this time, the polarization state of the unselected seed light is still horizontal polarization, transmitted through the first polarizer 401, and blocked in the first optical isolation system 2, while the polarization state of the selected frequency-divided seed light becomes vertical polarization, and is reflected and injected into the laser amplification system after passing through the first polarizer 401 again.

[0057] The frequency-divided seed light enters the first end-face pump amplifier stage, and the third plano-convex lens 502 shapes the seed light so that it matches the pump light mode output by the first pulse pump source 504 and shaped by the first pump beam shaping system 505 and passes through the first gain crystal 507 in the same way; the clock synchronization signal output by the synchronization signal controller 10 controls the first pulse pump source 504 pump light to have the same pulse repetition frequency as the un-frequency-divided seed light, and the pump light pulse width to be equivalent to the energy level lifetime on the first gain crystal 507, optimizes the relative delay time between the clock synchronization signal and the clock reference signal, and enables the first end-face pump amplifier stage to obtain the optimal amplification energy output; at the same time, in order to realize the thermal lens compensation of the two-stage end-face pump amplifier stage, the parameters of the second pulse pump source 605 in the second end-face pump amplifier stage and the laser spot size at the second gain crystal 602 need to be consistent with those of the first end-face pump amplifier stage.

[0058] The laser after the two-stage end-face pumping amplifier stage first passes through the second beam shaping system 7 and the second optical isolation system 8, and then the light polarization state is a vertical polarization state and enters the side pumping amplifier stage through the second polarizer 902. The first side pumping module 903 and the second side pumping module 906 are triggered by the clock synchronization signal output by the synchronization signal controller 10 and perform single-pass amplification. The thermal lens effect generated by the first side pumping module 903 and the second side pumping module 906 under high-power operation is compensated by the thermal compensation lens 904, and the thermal depolarization effect is compensated by the 90° quartz rotator 905 and the Faraday rotator 907. Then the second 0° total reflection mirror 908 reflects the single-pass amplified laser again for double-pass amplification. When passing through the second polarizer 902 again, the amplified light polarization state becomes a horizontal polarization state, and high-energy nanosecond laser with adjustable repetition rate is output from the second polarizer 902.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-energy nanosecond laser with adjustable repetition rate, characterized in that: It includes a synchronization signal controller and a nanosecond seed source, a first optical isolation system, a first beam shaping system, an electro-optical selection system, a first end-pump amplifier stage, a second end-pump amplifier stage, a second beam shaping system, a second optical isolation system and a side-pumped double-pass amplifier stage, wherein the electro-optical selection system includes a Pockels cell and a high-voltage driver, and the side-pumped double-pass amplifier stage includes a first side-pumping module and a second side-pumping module. The synchronization signal controller uses the digital signal generated by the internal crystal oscillator phase-locked loop as a clock reference signal and synchronously generates a frequency-divided synchronization signal and a multi-channel clock synchronization signal; the clock reference signal is used to trigger a nanosecond seed source; The frequency-divided synchronization signal is used to trigger the high-voltage driver to generate an electro-optical high-voltage signal, thereby controlling the opening or closing of the Pockels cell; The multi-channel clock synchronization signal is used to provide trigger signals for the pulse pump source, the first side pump module, and the second side pump module in the first end-pump amplifier stage and the second end-pump amplifier stage respectively.

2. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 1, characterized in that: The nanosecond seed source adopts an electro-optical or acousto-optical Q-switched solid laser oscillator or an electrically modulated semiconductor laser plus a multi-stage optical fiber pre-amplification structure.

3. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 1, characterized in that: The first optical isolation system includes a first half-wave plate, a first optical isolator and a second half-wave plate arranged in sequence along the optical path; the first beam shaping system includes a first plano-convex lens, a first pinhole stop and a second plano-convex lens arranged in sequence along the optical path.

4. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 1, characterized in that: The electro-optical selection system comprises a first polarizer, a Pockels cell and a first 0° total reflection mirror which are sequentially arranged along the optical path.

5. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 1, characterized in that: The first end-pump amplifier stage includes a first 45° total reflection mirror, a third plano-convex lens, a second 45° total reflection mirror, a first dichroic mirror, a first gain crystal, and a second dichroic mirror, which are sequentially arranged along the optical path, and also includes a first pulse pump source and a first pump beam shaping system; The second end-pump amplifier stage includes a third dichroic mirror, a second gain crystal, a fourth dichroic mirror and a third 45° total reflection mirror arranged in sequence along the optical path, and also includes a second pulse pump source and a second pump beam shaping system.

6. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 5, characterized in that: The semiconductor laser center wavelength used by the first pulse pump source and the second pulse pump source is one of 808nm, 880nm or 888nm; the first gain crystal and the second gain crystal are both Nd:YVO4 crystals.

7. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 1, characterized in that: The second beam shaping system includes a fourth plano-convex lens, a second aperture stop and a fifth plano-convex lens; the second optical isolation system includes a third half-wave plate, a second optical isolator and a fourth half-wave plate.

8. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 1, characterized in that: The side-pumped double-pass amplifier stage includes a fourth 45° total reflection mirror, a second polarizer, a first side-pumping module, a thermal compensation lens, a 90° quartz rotator, a second side-pumping module, a Faraday rotator and a second 0° total reflection mirror, which are sequentially arranged along the optical path.

9. The high-energy nanosecond laser with adjustable repetition rate as claimed in claim 1, characterized in that: The gain crystals used in the first side pump module and the second side pump module are both Nd:YAG crystal rods.

10. The operating method of a high-energy nanosecond laser with adjustable repetition rate according to any one of claims 1 to 9, characterized in that: The process includes: After the nanosecond seed source is triggered by the clock reference signal of the synchronization signal controller, the output nanosecond seed light is first shaped by the first optical isolation system and the first beam shaping system; After the nanosecond seed light is shaped, its polarization state changes to horizontal polarization and enters the electro-optical selection system. The high-voltage driver receives the frequency-divided synchronization signal from the synchronization signal controller and generates an electro-optical high-voltage signal, which causes the Pockels cell to step up from 0V to a quarter-wave voltage and then step down to 0V, thereby selecting the frequency-divided seed light with the required period interval. The polarization state of the selected frequency-divided seed light changes to vertical polarization, enters the first end-pump amplifier stage, matches the pump light mode output and shaped by the pulse pump source of the first end-pump amplifier stage, and passes through the first gain crystal on the same path; then the laser enters the second end-pump amplifier stage, matches the pump light mode output and shaped by the pulse pump source of the second end-pump amplifier stage, and passes through the second gain crystal on the same path; The clock synchronization signal output by the synchronization signal controller controls the pulse pump source pump light of the first end-face pump amplifier stage to be consistent with the pulse repetition frequency of the un-frequency-divided seed light, and the pulse width of the pump light to be equivalent to the energy level lifetime on the first gain crystal, and optimizes the relative delay time between the clock synchronization signal and the clock reference signal, so that the first end-face pump amplifier stage obtains the optimal amplification energy output; the pulse pump source parameters in the second end-face pump amplifier stage and the laser spot size at the second gain crystal are consistent with those in the first end-face pump amplifier stage; The laser amplified by the second end face pump amplifier stage first passes through the second beam shaping system and the second optical isolation system, and then the light polarization state changes to a vertical polarization state and enters the side pump amplifier stage; the first side pump module and the second side pump module are both triggered by the clock synchronization signal output by the synchronization signal controller and perform single-pass amplification, and then perform double-pass amplification, the amplified light polarization state changes to a horizontal polarization state, and then outputs high-energy nanosecond laser with adjustable repetition rate.

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