A high-energy nanosecond laser with adjustable repetition rate and its working method

Abstract

This invention discloses a high-energy nanosecond laser with adjustable repetition rate and its operating method, belonging to the field of laser technology. The laser of this invention includes a synchronization signal controller, a nanosecond seed source, an electro-optic selection system, a first end-face pump amplification stage, a second end-face pump amplification stage, and a side-pumped dual-pass amplification stage. The synchronization signal controller generates a clock reference signal, a frequency-division synchronization signal, and a clock synchronization signal to achieve integrated control of the system signals. The clock reference signal triggers the seed source to generate nanosecond seed light pulses. By optimizing and adjusting the frequency-division synchronization signal, the electro-optic selection system selects the frequency-division seed light pulses, achieving adjustable repetition rate of the seed light pulses. Simultaneously, a pulse-pumped mode MOPA structure is adopted. The clock synchronization signal maintains the repetition rate of the pump light pulses in each amplification stage consistent with that of the undivided seed light pulses, ensuring the thermal stability of the entire system and achieving high-energy, reliable nanosecond laser output with adjustable repetition rate.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a high-energy nanosecond laser with adjustable repetition rate and its operating method. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] High-energy nanosecond lasers with tunable repetition rate have significant application value and broad market prospects in fields such as precision materials processing, optical communication, biomedicine, and scientific research. In the field of precision materials processing, the tunable repetition rate allows the laser to precisely control the cutting speed and surface quality according to the material type and processing requirements, while avoiding thermal damage to the material, achieving optimal cutting results and efficiency. Simultaneously, the high reliability and high energy of the nanosecond laser output ensure the precision, controllability, and long-term operational stability of cutting complex structures.

[0004] Currently, a common method for obtaining high-energy nanosecond laser output is to use a solid-state (or fiber-optic) seed source to output nanosecond pulses and then amplify the pulse energy using a laser amplification system to create a master oscillator power amplifier (MOPA). Depending on the pumping mode, common implementation methods are further divided into continuous pump mode MOPA and pulse pump mode MOPA.

[0005] In continuous-pump mode MOPA, patent CN117220124A discloses a high-energy, high-repetition-rate nanosecond laser system. This patent utilizes an acousto-optic Q-switched solid-state oscillator as a seed source, achieving adjustable pulse repetition rate by changing the acousto-optic modulation signal state. Then, through a single-stage end-face continuous-pump amplification and a two-stage dual-rod single-pass side-face continuous-pump amplification, high-energy nanosecond laser output with an adjustable repetition rate of 500Hz-2kHz is achieved. This patent employs a continuous-pump mode amplification module, resulting in severe thermal effects in the laser amplification system, leading to significant spot distortion and limiting its amplification capability. While the patent uses multiple soft-edge apertures in conjunction with a relay imaging system to compensate for thermal effects to some extent, this method suffers from high energy loss, low reliability, complex structure, and high cost, hindering engineering design. Furthermore, the continuous-pump mode amplification module has low energy amplification efficiency; moreover, the patent lacks special treatment for the end face of the gain medium, making it difficult to suppress spontaneous emission amplification (ASE) during amplification, affecting the signal-to-noise ratio and stability of the laser output.

[0006] In pulse-pumped mode MOPA, the pump source outputs periodic pulsed pump light through electrical signal modulation, reducing continuous heat accumulation in the gain crystal and thus mitigating the severe thermal effects of continuous-pumped mode MOPA. However, since the seed source modulation signal serves as the signal reference for the entire system, changes in its repetition rate will synchronously alter the repetition rate of the pulsed pump light in each amplification stage. This, in turn, causes changes in the thermal effects of the gain crystal, leading to fluctuations in the mode and intensity distribution during beam propagation. Consequently, this results in deterioration of the laser system's output energy stability and beam quality, and increases 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 its operating method. The laser provided by the present invention can achieve high-energy, stable and high-beam-quality nanosecond laser output with adjustable repetition rate in the range of 1Hz-5kHz. It is also highly efficient, reliable, simple in structure and low in cost, which is beneficial for 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, sequentially arranged along the optical path, a nanosecond seed source, a first optical isolation system, a first beam shaping system, an electro-optic selection system, a first end-pump amplification stage, a second end-pump amplification stage, a second beam shaping system, a second optical isolation system, and a side-pump dual-pass amplification stage; the electro-optic selection system includes a Pockel cell and a high-voltage driver; the side-pump dual-pass amplification stage includes a first side-pump module and a second side-pump module;

[0009] 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 division synchronization signal and multiple clock synchronization signals; the clock reference signal is used to trigger the nanosecond seed source; the frequency division synchronization signal is used to trigger the high-voltage driver to generate an electro-optic high-voltage signal, thereby controlling the opening or closing of the Pockel cell; the multiple clock synchronization signals are 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 amplification stage and the second end-face pump amplification stage, respectively.

[0010] Secondly, the present invention provides a method for operating the above-mentioned high-energy nanosecond laser with adjustable repetition rate, comprising the following steps:

[0011] After being triggered by the clock reference signal of the synchronization signal controller, the nanosecond seed source outputs nanosecond seed light, which is first shaped by the first optical isolation system and the first beam shaping system.

[0012] After the nanosecond seed light is shaped and its polarization state becomes horizontal, it enters the electro-optic selection system. The high-voltage driver receives the frequency division synchronization signal from the synchronization signal controller and generates an electro-optic high-voltage signal, which boosts the Pockel cell from 0V to a quarter-wave voltage and then drops it to 0V to filter out the frequency division seed light with the required period interval. The selected frequency division seed light becomes vertically polarized and enters the first end-face pump amplification stage. It is matched with the pump light mode output and shaped by the pulse pump source of the first end-face pump amplification stage and passes through the first gain crystal in the same path. Then the laser enters the second end-face pump amplification stage and is matched with the pump light mode output and shaped by the pulse pump source of the second end-face pump amplification stage and passes through the second gain crystal in the same path.

[0013] The clock synchronization signal output by the synchronization signal controller controls the pulse pump source of the first end-face pump amplification stage to have the same pulse repetition rate as the undivided seed light pulse and the pump light pulse width to be comparable to the lifetime of the upper energy level of the first gain crystal. This optimizes the relative delay time between the clock synchronization signal and the clock reference signal, enabling the first end-face pump amplification stage to obtain the optimal amplified energy output. The pulse pump source parameters in the second end-face pump amplification stage and the laser spot size at the second gain crystal are consistent with those in the first end-face pump amplification stage.

[0014] The laser beam amplified by the second end-face pump amplification stage first passes through the second beam shaping system and the second optical isolation system, and then the polarization state of the light changes to a vertical polarization state before entering the side pump amplification stage. Both the first side pump module and the second side pump module are triggered by the clock synchronization signal output by the synchronization signal controller and undergo single-pass amplification, and then double-pass amplification. The polarization state of the amplified light changes to a horizontal polarization state, and then a high-energy nanosecond laser with adjustable repetition rate is output.

[0015] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0016] (1) The present invention uses a high-precision synchronous signal controller developed independently to generate a clock reference signal, a frequency division synchronous signal and a clock synchronization signal, thereby realizing the integrated control of the laser system signals. This makes the jitter between the three electrical signals and the jitter between the optical signal and the electrical signal less than 1ns, thus improving the overall stability and control accuracy of the system.

[0017] (2) By optimizing and adjusting the repetition rate, delay, and pulse width of the frequency division synchronization signal, this invention controls the switching operation of the electro-optical selection system in a timely manner. It can select the frequency division seed light pulse with the required period interval without changing the repetition rate of the seed source, thereby achieving flexible and adjustable repetition rate of the seed light pulse. Moreover, 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 out the ASE effect.

[0018] (3) The present invention adopts a pulse-pumped mode MOPA structure to alleviate the thermal effect of the gain crystals of each amplification stage. By triggering the pump source output of each amplification stage with the same repetition frequency as the undivided seed light pulse through the clock synchronization signal, the pump light pulse is not affected by the change of the repetition frequency of the divided seed light pulse injected into the laser amplification system, ensuring the thermal effect stability of the entire system and avoiding the thermal effect changes caused by the synchronous change of the repetition frequency of the pulse pump source and the divided seed light pulse in each amplification stage, thereby preventing damage to optical components, output energy stability and beam quality degradation.

[0019] (4) The high-energy nanosecond laser with adjustable repetition rate provided by the present invention can achieve high energy, high stability and good beam quality nanosecond laser output with adjustable repetition rate in the range of 1Hz-5kHz. It is efficient, reliable, simple in structure and low in cost, and more conducive to engineering design. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0021] Figure 1 This is a schematic diagram of the structure of the high-energy nanosecond laser with adjustable repetition rate according to Embodiment 1 of the present invention;

[0022] Figure 2 This is a timing diagram of the synchronization signal controller and optical pulse in the high-energy nanosecond laser with adjustable repetition rate according to Embodiment 1 of the present invention;

[0023] Figure 3 This is a schematic diagram of the beam quality output by the high-energy nanosecond laser with adjustable repetition rate according to Embodiment 1 of the present invention;

[0024] Figure 4 This is a far-field intensity distribution diagram of the output beam of the high-energy nanosecond laser with adjustable repetition rate according to Embodiment 1 of the present invention;

[0025] Figure 5 This is a schematic diagram of the energy stability of the high-energy nanosecond laser with adjustable repetition rate according to Embodiment 1 of the present invention;

[0026] In the diagram: 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. Fourth dichroic mirror; 604. Second pump beam shaping system; 605. Second pulse pump source; 606. Third 45° total reflection mirror; 7. Second beam shaping system; 701. Fourth plano-convex lens; 702. Second pinhole aperture; 703. Fifth plano-convex lens; 8. Second optical isolation system; 801. Third half-wave plate; 802. Second optical isolator; 803. Fourth half-wave plate; 901. Fourth 45° total reflection mirror; 902. Second polarizer; 903. First side pump module; 904. Thermal compensation lens; 905. 90° quartz rotator; 906. Second side pump module; 907. Faraday rotator; 908. Second 0° total reflection mirror; 10. Synchronization signal controller; 11. High voltage driver. Detailed Implementation

[0027] 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.

[0028] This invention provides a high-energy nanosecond laser with adjustable repetition rate, comprising a synchronization signal controller and, sequentially arranged along the optical path, a nanosecond seed source, a first optical isolation system, a first beam shaping system, an electro-optic selection system, a first end-pump amplification stage, a second end-pump amplification stage, a second beam shaping system, a second optical isolation system, and a side-pump dual-pass amplification stage; the electro-optic selection system includes a Pockel cell and a high-voltage driver; the side-pump dual-pass amplification stage includes a first side-pump module and a second side-pump module;

[0029] The synchronization signal controller is connected to the nanosecond seed source, the electro-optic menu system, the pulse pump source, the first side pump module, and the second side pump module in the first end-face pump amplification stage and the second end-face pump amplification stage, respectively.

[0030] 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 division synchronization signal and multiple clock synchronization signals; the clock reference signal is used to trigger the nanosecond seed source; the frequency division synchronization signal is used to trigger the high-voltage driver to generate an electro-optic high-voltage signal, thereby controlling the opening or closing of the Pockel cell; the multiple clock synchronization signals are 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 amplification stage and the second end-face pump amplification stage, respectively.

[0031] In this invention, the nanosecond seed source is a seed source with an electro-optic or acousto-optic Q-switched solid-state laser oscillator or an electrically modulated semiconductor laser plus a multi-stage fiber pre-amplification stage structure, used to generate highly reliable nanosecond seed light.

[0032] In this invention, the first optical isolation system includes a first half-wave plate, a first optical isolator, and a second half-wave plate arranged sequentially along the optical path, used to block unselected seed light and amplified return light from damaging the seed source and optical components after electro-optical selection.

[0033] In this invention, the first beam shaping system includes a first plano-convex lens, a first pinhole aperture, and a second plano-convex lens arranged sequentially along the optical path. These are used to shape the nanosecond pulse seed source spot to match the aperture of the Pockels cell in the electro-optic menu system and to filter out stray light and the substrate around the seed spot.

[0034] In this invention, the electro-optical selection system includes a first polarizer, a Pockel cell, and a first 0° total reflection mirror arranged sequentially along the optical path. These components are used to select seed light pulses with a desired periodic interval for injection into the laser amplification system, thereby adjusting the repetition frequency of the seed light pulses. A high-voltage driver in the electro-optical selection system provides the Pockel cell with a high-voltage signal whose amplitude and duration are adjustable.

[0035] More preferably, the Pockel cell uses an electro-optic crystal of one of KTP, BBO, RTP or LiNbO3.

[0036] In this invention, the first end-face pump amplification 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 arranged sequentially along the optical path. It also includes a first pulse pump source and a first pump beam shaping system. More preferably, the first pulse pump source is an optical fiber-coupled semiconductor laser, which operates in pulse pump mode to provide pump energy to the first gain crystal. The light output from the first pulse pump source is expanded by the first pump beam shaping system, passes through the first dichroic mirror, and is injected into the center of the first gain crystal. Optical absorbers are positioned at corresponding locations on the first and second dichroic mirrors to collect unabsorbed pump light.

[0037] In this invention, the second end-face pump amplification stage includes a third dichroic mirror, a second gain crystal, a fourth dichroic mirror, and a third 45° total reflection mirror arranged sequentially along the optical path. It also includes a second pulse pump source and a second pump beam shaping system. More preferably, the second pulse pump source is an optical fiber-coupled semiconductor laser, operating in pulse pump mode to provide pump energy to the second gain crystal. The light output from the second pulse pump source is expanded by the second pump beam shaping system, passes through the fourth dichroic mirror, and is injected into the center of the second gain crystal. Optical absorbers are positioned at corresponding locations on the third and fourth dichroic mirrors to collect unabsorbed pump light.

[0038] In this invention, the semiconductor lasers used in the first and second pulse pump sources have a center wavelength of 808nm, 880nm, or 888nm.

[0039] In this 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.

[0040] In this invention, the second beam shaping system includes a fourth plano-convex lens, a second pinhole aperture, and a fifth plano-convex lens, used to expand and collimate the beam spot output from the second end-face pump amplification stage to match the aperture of the first side-face pump module.

[0041] In this invention, the second optical isolation system includes a third half-wave plate, a second optical isolator, and a fourth half-wave plate, used to block the return light after amplification by the side pump amplification stage from damaging the optical components in the optical path.

[0042] In this invention, the side-pumped dual-pass amplification 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 arranged sequentially along the optical path. The thermal compensation lens is a plano-concave lens used to compensate for the thermal lensing effect of the gain crystal under high-power operation of the first and second side-pumping modules. 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 and second side-pumping modules. This invention uses thermal lensing compensation technology and thermal depolarization compensation technology to compensate for the thermal effect of the gain crystal in each amplification stage, avoiding complex beam shaping and imaging.

[0043] The first and second side pump modules of this invention both use large-diameter Nd:YAG crystal rods as the gain crystal, with a pump center wavelength of 808nm.

[0044] The present invention also provides a method for operating the above-mentioned high-energy nanosecond laser with adjustable repetition rate, comprising the following steps:

[0045] After being triggered by the clock reference signal of the synchronization signal controller, the nanosecond seed source outputs nanosecond seed light, which is first shaped by the first optical isolation system and the first beam shaping system.

[0046] After the nanosecond seed light is shaped and its polarization state becomes horizontal, it enters the electro-optic selection system. The high-voltage driver receives the frequency division synchronization signal from the synchronization signal controller and generates an electro-optic high-voltage signal, which boosts the Pockel cell from 0V to a quarter-wave voltage and then drops it to 0V to filter out the frequency division seed light with the required period interval. The selected frequency division seed light becomes vertically polarized and enters the first end-face pump amplification stage. It is matched with the pump light mode output and shaped by the pulse pump source of the first end-face pump amplification stage and passes through the first gain crystal in the same path. Then the laser enters the second end-face pump amplification stage and is matched with the pump light mode output and shaped by the pulse pump source of the second end-face pump amplification stage and passes through the second gain crystal in the same path.

[0047] The clock synchronization signal output by the synchronization signal controller controls the pulse pump source of the first end-face pump amplification stage to have the same pulse repetition rate as the undivided seed light pulse and the pump light pulse width to be comparable to the lifetime of the upper energy level of the first gain crystal. This optimizes the relative delay time between the clock synchronization signal and the clock reference signal, enabling the first end-face pump amplification stage to obtain the optimal amplified energy output. The pulse pump source parameters in the second end-face pump amplification stage and the laser spot size at the second gain crystal are consistent with those in the first end-face pump amplification stage.

[0048] The laser beam amplified by the second end-face pump amplification stage first passes through the second beam shaping system and the second optical isolation system, and then the polarization state of the light changes to a vertical polarization state before entering the side pump amplification stage. Both the first side pump module and the second side pump module are triggered by the clock synchronization signal output by the synchronization signal controller and undergo single-pass amplification, and then double-pass amplification. The polarization state of the amplified light changes to a horizontal polarization state, and then a high-energy nanosecond laser with adjustable repetition rate is output.

[0049] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0050] Example 1

[0051] Figure 1 This is a schematic diagram of the structure of the high-energy nanosecond laser with adjustable repetition rate in this embodiment, including a nanosecond seed source 1, a first optical isolation system 2, a first beam shaping system 3, an electro-optic selection system, a first end-face pump amplification stage, a second end-face pump amplification stage, a second beam shaping system 7, a second optical isolation system 8, a side-pumped dual-pass amplification stage, and a synchronization signal controller 10.

[0052] In this embodiment, the nanosecond seed source 1 uses an electro-optic Q-switched solid-state laser oscillator to generate highly reliable nanosecond seed light, with an output pulse width of 4ns, a repetition rate of 5kHz, a single pulse energy of 0.5mJ, and a center wavelength of 1064.3nm.

[0053] 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 sequentially along the optical path, which are used to block the seed light not selected after the electro-optical selection and the amplified return light from damaging the nanosecond seed source 1 and optical components.

[0054] 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 sequentially along the optical path. These are used to shape the light spot of the nanosecond seed source 1. The shaped light spot is a 1mm collimated light used to match the aperture of the Pockels cell 402 in the electro-optic menu system. The 4f system composed of the first plano-convex lens 301 and the second plano-convex lens 303 incorporates the first pinhole aperture 302 with a diameter of 0.8mm to achieve spatial filtering, which can filter out stray light and substrate around the seed light spot.

[0055] In this embodiment, the electro-optic menu system includes a first polarizer 401, a Pockel cell 402, a first 0° total reflection mirror 403 arranged sequentially along the optical path, and a high-voltage driver 11 for providing the Pockel cell 402 with an adjustable amplitude and duration high-voltage signal.

[0056] The horizontally polarized seed light emitted from the first optical isolation system 2 is incident on the electro-optic selection system and transmitted through the first polarizer 401. When the Pockel cell 402 is closed, the seed light remains horizontally polarized after traveling back and forth through the electro-optic selection system. Therefore, it is transmitted through the first polarizer 401 and blocked at the first optical isolation system 2 to prevent it from returning and damaging the nanosecond seed source 1.

[0057] When the Pockel cell 402 is opened, the voltage boosting and deboosting processes of the Pockel cell 402 need to be activated when the seed light pulse of the required period interval first passes through the Pockel cell 402, and then closed after the second pass through the Pockel cell 402 after being reflected by the first 0° total reflection mirror 403. This causes the polarization state of the selected frequency-divided seed light pulse to become vertically polarized after traveling back and forth through the electro-optic selection system, and then enter the laser amplification system after being reflected by the first polarizer 401.

[0058] In this embodiment, the first end-face pump amplification 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 arranged sequentially along the optical path. It also includes a first pulse pump source 504 and a first pump beam shaping system 505.

[0059] The first pulse pump source 504 is a semiconductor laser with fiber-coupled output. It uses pulse pumping mode to provide pump energy to the first gain crystal 507. The pump light is expanded and shaped by the first pump beam shaping system 505 and 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 set at corresponding positions of the first dichroic mirror 506 and the second dichroic mirror 508.

[0060] In this embodiment, the second end-face pump amplification 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 sequentially along the optical path, and also includes a second pulse pump source 605 and a second pump beam shaping system 604.

[0061] The second pulse pump source 605 is a semiconductor laser with fiber-coupled output, operating in pulse pump mode, used 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 injected into the center of the second gain crystal 602 after passing through the fourth dichroic mirror 603; light absorbers are set at corresponding positions of the third dichroic mirror 601 and the fourth dichroic mirror 603 to collect unabsorbed pump light.

[0062] In this embodiment, the first pulse pump source 504 and the second pulse pump source 605 have a working center wavelength of 808nm, a peak power of 300W, and a pump pulse width of 100μs.

[0063] 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 the ASE effect during the amplification process.

[0064] 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. The beam of the light spot output from the second end-face pump amplification stage is expanded and collimated to a diameter of 5mm to match the aperture of the first side pump module 903.

[0065] 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 block the depolarized light returning after amplification by the side-pumped dual-pass amplifier stage and the optical components in the ASE light damage optical path.

[0066] In this embodiment, the side-pumped dual-pass amplification 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 arranged sequentially along the optical path.

[0067] The first side pump module 903 and the second side pump module 906 both use Nd:YAG crystal rods with a diameter of 11 mm, a pump center wavelength of 808 nm, a peak power of 7000 W, and a pump pulse width of 230 μs. The thermal compensation lens 904 is a plano-concave lens with a focal length of f = -300 mm, used to compensate for the thermal lensing effect of the Nd:YAG crystal rods under high-power operation of the first side pump module 903 and the second side pump module 906. A 90° quartz rotator 905 and a Faraday rotator 907 are used to compensate for the thermal depolarization effect of the gain crystals under high-power operation of the first side pump module 903 and the second side pump module 906. The second 0° total reflection mirror 908 is used to reflect the laser beam after single-pass amplification for double-pass amplification, ultimately achieving a repetition rate adjustable in the range of 1 Hz to 5 kHz on the order of hundreds of mJ and a beam quality M 2 <1.5, operational stability RMS <1%, and laser output with a pulse width of 4ns.

[0068] In this embodiment, the synchronization signal controller 10 is connected to the nanosecond seed source 1, the electro-optical menu system, the first pulse pump source 504, the second pulse pump source 605, the first side pump module 903, and the second side pump module 906, respectively, to provide the system with a clock reference and trigger signal. Figure 2 The diagram shown is a timing sequence diagram of the synchronization signal controller 10 and the optical pulse in the high-energy nanosecond laser with adjustable repetition rate in this embodiment. The following is in conjunction with... Figure 2 The timing of the synchronization signal controller 10 and the optical pulse of the present invention will be described in detail.

[0069] The synchronization signal controller 10 uses the digital signal generated by the internal crystal phase-locked loop as the clock reference signal and synchronously generates frequency division synchronization signal and multiple clock synchronization signals.

[0070] By setting the pulse width and repetition rate of the clock reference signal, a nanosecond seed light is generated by triggering an electro-optic Q-switched solid-state oscillator. Figure 2 As shown in the "seed light pulse" diagram, the repetition frequency of the seed light pulse is consistent with the clock reference signal, and correspondingly, the period of the seed light pulse is τ. a .

[0071] Simultaneously, the synchronization signal controller 10 generates a frequency-divided synchronization signal based on the clock reference signal, which triggers the high-voltage driver 11 in the electro-optical menu system to generate an electro-optical high-voltage signal. By adjusting the delay, division number, and pulse width of the frequency-divided synchronization signal relative to the clock reference signal, the high-voltage duration t, voltage boosting, and voltage bucking of the electro-optical high-voltage signal are controlled, causing the Pockel cell 402 to turn on or off at a reasonable time, thus filtering out the frequency-divided seed optical pulses with the required period interval. Correspondingly, the pulse period after frequency division is τ. b ,like Figure 2 The terms "electro-optic high voltage signal" and "output optical pulse" are shown in the figure.

[0072] The synchronization signal controller 10 generates multiple clock synchronization signals based on the clock reference signal, which provide trigger signals to the first pulse pump source 504, the second pulse pump source 605, the first side pump module 903, and the second side pump module 906 to generate pump light pulses. For example... Figure 2 As shown in the diagram of the "pump light pulse," the repetition frequency of the clock synchronization signal is synchronized and identical with that of the clock reference signal, ensuring 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 level lifetime of the gain crystals of each amplification stage. Then, the delay time Δt between the pump light pulse and the seed light pulse after frequency division is optimized to ensure that each amplification stage achieves optimal amplification efficiency and maximum amplification energy.

[0073] like Figure 3 The diagram shown illustrates the beam quality of the high-energy nanosecond laser with adjustable repetition rate in this embodiment. The system of this invention exhibits stable thermal effects and employs a pulse-pumped MOPA structure combined with thermal lens compensation and thermal depolarization compensation techniques, ensuring that the final output beam maintains good beam quality. The beam quality M along both axes... 2 They are 1.38 and 1.46 respectively; Figure 4 The image shows the far-field intensity distribution of the output beam of the high-energy nanosecond laser with adjustable repetition rate in this embodiment. It can be seen that the beam can still maintain a good Gaussian intensity distribution in the far field.

[0074] Figure 5 This is a schematic diagram of the energy stability of the high-energy nanosecond laser with adjustable repetition rate in this embodiment. According to the application requirements, when the output pulse repetition rate is 500Hz, the power stability test of the laser is carried out for 8 hours at an output energy of hundreds of mJ. The RMS of the laser is 0.59% after 8 hours of operation.

[0075] Example 2

[0076] This embodiment provides a method for operating the high-energy nanosecond laser with adjustable repetition rate as described in Embodiment 1, including the following process:

[0077] 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. The first beam shaping system 3 shapes the seed light into collimated light, matches the light aperture of the Pockel cell 402 and filters out stray light and substrate around the seed light.

[0078] After being shaped, the seed light enters the electro-optic selection system. After passing through the first polarizer 401, the seed light becomes horizontally polarized. The high-voltage driver 11 receives the frequency division synchronization signal from the synchronization signal controller 10 and is triggered to generate an electro-optic high-voltage signal, causing the Pockel cell 402 to be boosted from 0V to a quarter-wave voltage and then debossed to 0V. The boosting and debouncing processes end when the main pulse passes through the Pockel cell 402 for the first time and after passing through the first 0° total reflection mirror 403 and then through the Pockel cell 402 again. By adjusting the pulse width and delay of the high-voltage signal, the frequency-divided seed light with the required period interval is selected to ensure that no pre-pulse or tail pulse enters the boosting and debouncing process. At this time, the unselected seed light is still horizontally polarized and is blocked in the first optical isolation system 2 after being transmitted through the first polarizer 401. The selected frequency-divided seed light becomes vertically polarized and is reflected and injected into the laser amplification system after passing through the first polarizer 401 again.

[0079] After frequency division, the seed light enters the first end-face pump amplification stage. The third plano-convex lens 502 shapes the seed light to match the pump light mode output by the first pulse pump source 504 and shaped by the first pump beam shaping system 505, and the two beams pass through the first gain crystal 507. The clock synchronization signal output by the synchronization signal controller 10 controls the pump light of the first pulse pump source 504 to have the same pulse repetition rate as the undivided seed light, and the pump light pulse width to be comparable to the lifetime of the upper energy level of the first gain crystal 507. This optimizes the relative delay time between the clock synchronization signal and the clock reference signal, so that the first end-face pump amplification stage obtains the optimal amplification energy output. At the same time, in order to achieve thermal lens compensation of the two-stage end-face pump amplification stage, the parameters of the second pulse pump source 605 and the laser spot size at the second gain crystal 602 in the second end-face pump amplification stage need to be consistent with those of the first end-face pump amplification stage.

[0080] After passing through two stages of end-pump amplification, the laser first passes through the second beam shaping system 7 and the second optical isolation system 8. Then, the light polarization state is vertically polarized and enters the side-pump amplification stage through the second polarizer 902. The first side-pump module 903 and the second side-pump module 906 are both triggered by the clock synchronization signal output by the synchronization signal controller 10 and perform single-pass amplification. The thermal lensing effect generated by the first side-pump module 903 and the second side-pump module 906 under high-power operation is compensated by the thermal compensation lens 904. 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 it passes through the second polarizer 902 again, the polarization state of the amplified light becomes horizontally polarized. The high-energy nanosecond laser with adjustable repetition rate is output from the second polarizer 902.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-energy nanosecond laser with adjustable repetition rate, characterized in that, The synchronous signal controller and nanosecond seed source, first optical isolation system, first optical beam shaping system, electro-optical gating system, first end-pumped amplification stage, second end-pumped amplification stage, second optical beam shaping system, second optical isolation system and side-pumped double-pass amplification stage are sequentially arranged along the light path; the electro-optical gating system comprises a Pockels cell and a high-voltage driver; the side-pumped double-pass amplification stage comprises a first side-pumped module and a second side-pumped module; The first end-pumped amplification stage comprises a first gain crystal and a first pulse pumping source; the second end-pumped amplification stage comprises a second gain crystal and a second pulse pumping source. The nanosecond seed source adopts an electro-optical or acousto-optical Q-switched solid laser oscillator or an electrically modulated semiconductor laser with a multi-stage optical fiber pre-amplification stage structure; the electro-optical gating system comprises a first polarizer, a Pockels cell and a first 0° full reflection mirror sequentially arranged along the light path. The synchronous signal controller generates a digital signal as a clock reference signal by an internal crystal oscillator phase-locked loop and synchronously generates a frequency division synchronous signal and a multi-path clock synchronous signal; the clock reference signal is used to trigger the nanosecond seed source; The frequency division synchronous 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-path clock synchronous signal is synchronized with and identical to the clock reference signal in frequency, and is used to provide a trigger signal for the pulse pumping source in the first end-pumped amplification stage and the second end-pumped amplification stage, the first side-pumped module and the second side-pumped module, respectively, so that the pumping source outputs pumping light pulses consistent with the repetition frequency of the undivided seed light pulses, and the first pulse pumping source has a pumping light pulse width equivalent to the energy level lifetime of the first gain crystal; the second pulse pumping source has parameters consistent with those of the first pulse pumping source.

2. The repetition rate tunable high energy nanosecond laser of claim 1, wherein, The first optical isolation system comprises a first half-wave plate, a first optical isolator and a second half-wave plate sequentially arranged along the light path; the first optical beam shaping system comprises a first plano-convex lens, a first pinhole diaphragm and a second plano-convex lens sequentially arranged along the light path.

3. The repetition rate tunable high energy nanosecond laser of claim 1, wherein, The first end-pumped amplification stage comprises a first 45° full reflection mirror, a third plano-convex lens, a second 45° full reflection mirror, a first dichroic mirror, a first gain crystal and a second dichroic mirror sequentially arranged along the light path, and further comprises a first pumping beam shaping system; The second end-pumped amplification stage comprises a third dichroic mirror, a second gain crystal, a fourth dichroic mirror and a third 45° full reflection mirror sequentially arranged along the light path, and further comprises a second pumping beam shaping system.

4. The repetition rate tunable high energy nanosecond laser of claim 3, wherein, The first pulse pumping source and the second pulse pumping source adopt a semiconductor laser with a center wavelength of one of 808 nm, 880 nm or 888 nm; the first gain crystal and the second gain crystal are both Nd:YVO4 crystals.

5. The repetition rate tunable high energy nanosecond laser of claim 1, wherein, The second optical beam shaping system comprises a fourth plano-convex lens, a second pinhole diaphragm and a fifth plano-convex lens; the second optical isolation system comprises a third half-wave plate, a second optical isolator and a fourth half-wave plate.

6. The repetition rate tunable high energy nanosecond laser of claim 1, wherein, The side-pumping double-pass amplification stage comprises, in sequence along an optical path, a fourth 45° full 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° full mirror.

7. The repetition rate tunable high energy nanosecond laser of claim 1, wherein, The gain crystal used by the first side-pumping module and the second side-pumping module is an Nd:YAG crystal rod.

8. The method of operating a repetition rate tunable high energy nanosecond laser of any of claims 1-7, wherein, The method comprises the following processes: The nanosecond seed light output after the nanosecond seed source is triggered by the clock reference signal of the synchronization signal controller firstly passes through a first light isolation system and a first light beam shaping system for shaping; After the polarization state of the shaped nanosecond seed light becomes horizontal polarization, the nanosecond seed light enters an electro-optical selection system; a high-voltage driver receives the frequency division synchronization signal of the synchronization signal controller and generates an electro-optical high-voltage signal to make a Pockels cell rise from 0V to a quarter-wave voltage and then drop to 0V, thereby screening the frequency-division seed light with a required period interval time; The polarization state of the selected frequency-division seed light becomes vertical polarization, and the frequency-division seed light enters a first end-pumping amplification stage and matches the pump light output and shaped by the pulse pump source of the first end-pumping amplification stage and passes through a first gain crystal in the same path; then the laser enters a second end-pumping amplification stage and matches the pump light output and shaped by the pulse pump source of the second end-pumping amplification stage and passes through a second gain crystal in the same path; The clock synchronization signal output by the synchronization signal controller controls the pulse pump source of the first end-pumping amplification stage to have the same pulse repetition frequency as the non-frequency-division seed light and the same pulse width as the lifetime of the upper level of the first gain crystal, and the relative delay time between the clock synchronization signal and the clock reference signal is optimized to make the first end-pumping amplification stage obtain optimal amplification energy output; the parameters of the pulse pump source in the second end-pumping amplification stage and the laser spot size at the second gain crystal are consistent with those in the first end-pumping amplification stage; The laser amplified by the second end-pumping amplification stage firstly passes through a second light beam shaping system and a second light isolation system, and then enters a side-pumping amplification stage with a vertical polarization state; the first side-pumping module and the second side-pumping module are triggered by the clock synchronization signal output by the synchronization signal controller and perform single-pass amplification, and then perform double-pass amplification; the polarization state of the amplified light becomes a horizontal polarization state, and then the high-energy nanosecond laser with adjustable repetition frequency is output.

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