High-power nanosecond laser with adjustable time-domain double-pulse delay

Abstract

The invention provides a time-domain double-pulse delay-adjustable high-power nanosecond laser, which comprises a passive Q-switched resonant cavity, a single-lamp double-rod amplification module, a first single-lamp single-rod amplification module, a second single-lamp single-rod amplification module, a light beam collimation module, a half-wave plate and a delay light path control module which are arranged in sequence, the centers of the single-lamp double-rod amplification module, the first single-lamp single-rod amplification module, the second single-lamp single-rod amplification module, the light beam collimation module, the half-wave plate and the delay light path control module are arranged on the same horizontal line. According to the invention, laser pulse output with adjustable time-domain double-pulse laser delay time is realized, intelligent regulation and control of the double-pulse laser delay time are effectively realized, and the ubiquitous problems of low energy utilization rate and generation of plasma shielding effect in traditional laser shock peening are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nanosecond lasers, and particularly to a high-power nanosecond laser with adjustable time-domain double-pulse delay. Background Art

[0002] Laser shock peening is a surface strengthening technology that uses a laser beam to modify the surface of a metal material. The laser shock peening technology uses a short-pulse (ns-level) high-peak-power (GW / cm2) laser beam to pass through a transparent confinement layer and act on an absorption layer on the material surface. The absorption layer absorbs energy and vaporizes and ionizes to form a plasma in an extremely short time. The plasma continuously accumulates under the action of the confinement layer to form a plasma shock wave of GPa level and propagates into the metal interior. When the shock wave pressure exceeds the yield limit of the material, plastic deformation occurs on the material surface, causing microstructural changes such as an increase in the lattice dislocation density and grain refinement. Eventually, a residual stress layer with a depth of 0.5-2 mm is formed on the material surface. Laser shock peening can effectively improve the fatigue performance of materials and extend the service life of materials. The time-domain characteristics of the shock wave determine the actual strengthening effect on the target material. The laser shock peening technology faces the technical bottleneck of low laser energy utilization rate in practical applications, which directly restricts the effective improvement of the plasma shock wave intensity. When a high-power laser irradiates the material surface, a plasma formation process will be triggered on the nanosecond time scale, and this plasma layer has a specific thickness distribution characteristic. It is worth noting that when the plasma density exceeds the critical threshold, a significant plasma shielding effect will be triggered - this high-density plasma will strongly reflect and absorb the subsequent laser beam, hindering the efficient transmission of laser energy to the material surface, thus making it difficult to maintain a stable plasma shock wave intensity. In the existing process, the technical path of attempting to increase the power density by reducing the spot size, although theoretically capable of enhancing the shock wave intensity, will cause practical problems such as a reduction in the processing spot area and a decrease in the energy distribution uniformity, and ultimately will severely restrict the processing efficiency and the process stability of the strengthening effect. The delayed double-pulse laser can change the laser energy deposition route, regulate the evolution of the laser-induced plasma shock wave and the subsequent interaction process between the laser and the plasma, increase the plasma duration and intensity, and ultimately achieve better strengthening efficiency and effect.

[0003] To achieve stable laser output with high peak power, the currently common amplification techniques mainly include three types: CPA (chirped-pulse amplification), OPCPA (optical parametric chirped-pulse amplification), and MOPA (master oscillator power amplifier). As a revolutionary ultrashort pulse laser amplification method applied earlier, CPA can achieve high peak power output in the terawatt (TW) to petawatt (PW) range. However, its drawbacks are also relatively obvious. The CPA system requires precise control of the pulse phase and temporal characteristics, including the use of complex grating pairs to broaden and compress the pulse, which increases the complexity and cost of the system. In recent years, the MOPA technology has become the mainstream solution for high-energy all-solid-state lasers due to its significant advantages. This technology uses a stable low-power single-frequency master oscillator combined with a high-gain amplification stage. While ensuring extremely high peak power output, it features a simple system structure, convenient operation and maintenance; excellent output beam quality, high frequency stability, modular design for easy power expansion and effective suppression of nonlinear effects. Compared with the complex OPCPA technology, MOPA does not require stringent phase matching conditions, has low temperature sensitivity, and a wider working wavelength range, making it widely used in industrial processing, scientific research and other fields. Summary of the Invention

[0004] Aiming at the technical problems of low laser energy utilization rate and plasma shielding effect in traditional laser shock peening, the present invention proposes a high-power nanosecond laser with adjustable delay time for double pulses in the time domain. By intelligently regulating the delay time of the double-pulse laser, the laser energy deposition route is changed, and ultimately a better laser shock peening effect is achieved.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows: A high-power nanosecond laser with adjustable delay time for double pulses in the time domain includes a passively Q-switched resonator, a single-lamp double-rod amplification module, a first single-lamp single-rod amplification module, a second single-lamp single-rod amplification module, a beam collimation module, a half-wave plate and a delay optical path control module arranged in sequence. The centers of the single-lamp double-rod amplification module, the first single-lamp single-rod amplification module, the second single-lamp single-rod amplification module, the beam collimation module, and the half-wave plate and delay optical path control module are on the same horizontal line;

[0006] The passive Q-switching resonator generates seed light, which undergoes four-stage power amplification through a single-lamp double-rod amplification module, a first single-lamp single-rod amplification module, and a second single-lamp single-rod amplification module. Subsequently, it enters the beam collimation module to correct the wavefront distortion accumulated during the power amplification process, compressing the beam divergence angle to the diffraction limit level to generate high-energy and high-power laser pulses. The half-wave plate is rotated to dynamically adjust the light energy distribution between the normal optical path and the delay optical path. The delay optical path control module changes the laser energy deposition route by adjusting the pulse delay time Δt between the normal optical path and the delay optical path, regulating the evolution of the laser-induced plasma shock wave and the subsequent interaction process between the laser and the plasma.

[0007] Preferably, a quartz rotor is provided between the first single-lamp single-rod amplification module and the second single-lamp single-rod amplification module. The quartz rotor performs thermal effect compensation to correct the thermal lens effect generated by the first single-lamp single-rod amplification module and maintain the beam quality.

[0008] Preferably, an optical isolator is provided between the passive Q-switching resonator and the single-lamp double-rod amplification module. The center point of the optical isolator is on the same horizontal line as the center points of the passive Q-switching resonator and the single-lamp double-rod amplification module. A first beam expansion module is provided between the optical isolator and the single-lamp double-rod amplification module, and the center point of the first beam expansion module is on the same horizontal line as the center points of the optical isolator and the single-lamp double-rod amplification module. A second beam expansion module is provided between the single-lamp double-rod amplification module and the first single-lamp single-rod amplification module, and the center point of the second beam expansion module is on the same horizontal line as the center points of the single-lamp double-rod amplification module and the first single-lamp single-rod amplification module. A third beam expansion module is provided between the first single-lamp single-rod amplification module and the quartz rotor, and the center point of the third beam expansion module is on the same horizontal line as the center points of the first single-lamp single-rod amplification module and the quartz rotor.

[0009] Preferably, the single-lamp double-rod amplification module, the first single-lamp single-rod amplification module, and the second single-lamp single-rod amplification module are all realized by neodymium-doped yttrium aluminum garnet laser crystal rods.

[0010] The quartz rotor is a quartz crystal.

[0011] Preferably, the first beam expansion module, the second beam expansion module, and the third beam expansion module each include a first negative lens and a first positive lens arranged in sequence. The center points of the first negative lens and the first positive lens are on the same horizontal line as the center point of the single-lamp double-rod amplification module, and the distance between the first negative lens and the first positive lens is equal to the difference between the focal lengths of the first negative lens and the first positive lens.

[0012] Preferably, the passive Q-switching resonator includes a 0° total reflection mirror, an LD side-pumping module, a passive Q-switching, a fifth polarization beam splitter, a small hole, and an output mirror arranged in sequence. The centers of the 0° total reflection mirror, the LD side-pumping module, the passive Q-switching, the fifth polarization beam splitter, the small hole, and the output mirror are on the same horizontal line. The 0° total reflection mirror and the output mirror form a resonator. Under the action of the LD side-pumping module, the gain medium continuously accumulates inverted population. At this time, the saturable absorber maintains a high-loss state to suppress laser oscillation. When the energy storage reaches the threshold, the absorber suddenly becomes saturated and transparent, and the number of photons in the resonator increases avalanche-like, forming a nanosecond-level giant pulse. The passive Q-switching enables the resonator to output a larger seed light. The fifth polarization beam splitter and the small hole work together to ensure linearly polarized and fundamental mode output, and the high-peak power and narrow pulse-width seed light are coupled and output through the output mirror (1-6).

[0013] Preferably, the beam collimation module includes a second positive lens and a second negative lens arranged in sequence. The centers of the second positive lens and the second negative lens are on the same horizontal line. The second positive lens converts the divergent beam output by the second single-lamp single-rod amplification module into a converging beam, and the second negative lens readjusts the converging beam into a collimated parallel light. The distance between the second positive lens and the second negative lens is the sum of the focal lengths of the positive and negative lenses.

[0014] Preferably, the delay optical path control module includes a third polarization beam splitter, a fourth polarization beam splitter, and a reflection component. The centers of the half-wave plate, the third polarization beam splitter, and the fourth polarization beam splitter are on the same horizontal line. The reflection component is arranged on the delay optical path between the third polarization beam splitter and the fourth polarization beam splitter.

[0015] Preferably, the reflection component includes a first 45° total reflection mirror and a second 45° total reflection mirror. The first 45° total reflection mirror is arranged on the reflection optical path of the third polarization beam splitter. The centers of the first 45° total reflection mirror and the second 45° total reflection mirror are on the same horizontal line. The fourth polarization beam splitter is arranged on the reflection optical path of the second 45° total reflection mirror.

[0016] Preferably, both the third polarization beam splitter and the first 45° total reflection mirror are arranged on the first electric displacement platform. The first 45° total reflection mirror is arranged on the slider of the first electric displacement platform. Both the fourth polarization beam splitter and the second 45° total reflection mirror are arranged on the first electric displacement platform. The second 45° total reflection mirror is arranged on the slider of the second electric displacement platform.

[0017] The third polarization beam splitter receives the linearly polarized light from the half-wave plate. The third polarization beam splitter has a high transmittance for P-polarized light and directly enters the normal optical path. The third polarization beam splitter has a high reflectivity for S-polarized light and deflects it by 90° to enter the delay optical path L1, enters the delay optical path L2 through the first 45° total reflection mirror, and enters the delay optical path L3 through the second 45° total reflection mirror. After recombining with the P-polarized light at the fourth polarization beam splitter, a time-domain double pulse is formed; the S-polarized light is introduced into an optical path difference ΔL = L1 + L2 + L3 - L4 through the first 45° total reflection mirror and the second 45° total reflection mirror, and the adjustable range of the double-pulse laser delay time is realized within a certain range according to the optical path difference;

[0018] The pulse delay time Δt satisfies: Δt = (L1 + L2 + L3 - L4) / c; where, the adjustable range of the pulse delay time Δt is 0 - 10 ns, L4 is the length of the normal optical path, L1 + L2 + L3 is the length of the delay optical path, and c is the speed of light;

[0019] Calculate the optical path difference ΔL = c·Δt according to the preset pulse delay time Δt, and determine the displacement amount between the first 45° total reflection mirror and the third polarization beam splitter and between the second 45° total reflection mirror and the fourth polarization beam splitter as ΔL / 2;

[0020] By rotating the half-wave plate to adjust the energy ratio of the optical paths where the P-polarized light and the S-polarized light are located in the delay optical path control module, the relationship between the rotation angle θ of the half-wave plate and the energy ratio is:

[0021] where, φ0 is the initial phase offset, and the precise adjustment of P-polarized light:S-polarized light from 1:1 to 10:1 is realized by controlling the rotation angle θ; E1 represents the energy of the P-polarized light, and E2 represents the energy of the S-polarized light.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The structure of the present invention is simple and has good stability. The MOPA technology is adopted to generate high-peak-power laser and combined with the intelligent regulation of the delay optical path control module, which solves the problem of reduced processing efficiency caused by the plasma shielding effect. It can enable the laser to fully utilize the laser energy to generate plasma shock waves under the same input energy and spot size, thereby significantly improving the efficiency and effect of laser shock peening. The present invention realizes the output of laser pulses with adjustable time-domain double-pulse laser delay time, effectively realizes the intelligent regulation of the double-pulse laser delay time, and improves the problems of low energy utilization rate and plasma shielding effect commonly existing in traditional laser shock peening. Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic structural diagram of the present invention.

[0025] Figure 2 is Figure 1 a schematic structural diagram of the passive Q-switching resonator shown.

[0026] Figure 3 is Figure 1 a schematic structural diagram of the beam expander module shown.

[0027] Figure 4 is Figure 1 a schematic structural diagram of the beam collimation module shown

[0028] Figure 5 is Figure 1 a schematic structural diagram of the optical path delay control module shown.

[0029] In the figure, 1 is the passive Q-switching resonator, 2 is the optical isolator, 3 is the first beam expander module, 4 is the single-lamp double-rod amplification module, 5 is the second beam expander module, 6 is the first single-lamp single-rod amplification module, 7 is the third beam expander module, 8 is the quartz rotor, 9 is the second single-lamp single-rod amplification module, 10 is the beam collimation module, 11 is the half-wave plate, 12 is the optical path delay control module, 1-1 is the 0° total reflection mirror, 1-2 is the LD side-pumping module, 1-3 is the passive Q-switch, 1-4 is the polarization beam splitter, 1-5 is the small hole, 1-6 is the output mirror, 3-1 is the negative lens, 3-2 is the positive lens, 10-1 is the positive lens, 10-2 is the negative lens, 12-1 is the third polarization beam splitter, 12-2 is the fourth polarization beam splitter, 12-3 is the first 45° total reflection mirror, 12-4 is the second 45° total reflection mirror. L1, L2 and L3 are the delay optical path lengths, and L4 is the reference optical path length. Detailed implementation manners

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] Such as Figure 1As shown in the figure, a high-power nanosecond laser with adjustable time-domain double-pulse delay includes a passive Q-switching resonator 1, a single-lamp double-rod amplification module 4, a first single-lamp single-rod amplification module 6, a quartz rotor 8, a second single-lamp single-rod amplification module 9, a beam collimation module 10, a half-wave plate 11, and a delay optical path control module 12, which are arranged in sequence. All the optical elements of the single-lamp double-rod amplification module 4, the first single-lamp single-rod amplification module 6, the second single-lamp single-rod amplification module 9, the beam collimation module 10, the half-wave plate 11, and the delay optical path control module 12 are set on the same horizontal line to realize the transmission of the seed light. The passive Q-switching resonator 1 generates the seed light, which undergoes four-stage power amplification through the single-lamp double-rod amplification module 4, the first single-lamp single-rod amplification module 6, and the second single-lamp single-rod amplification module 9, and then enters the beam collimation module 10 to generate high-power laser pulses with high beam quality and large energy. The delay optical path control module 12 divides the laser pulse into a normal optical path and a delay optical path, changes the laser energy deposition route by adjusting the pulse delay time Δt, controls the evolution of the laser-induced plasma shock wave and the subsequent interaction process between the laser and the plasma, and dynamically adjusts the optical energy distribution of the two paths by rotating the half-wave plate 11.

[0032] The main function of the passive Q-switching resonator 1 is to realize the dynamic output of the seed light through the nonlinear characteristics of the saturable absorber. The single-lamp double-rod amplification module 4 serves as the first-stage amplification. The double-rod design makes the pumping more uniform, improves the energy extraction efficiency, and enables more sufficient amplification. The first single-lamp single-rod amplification module 6 and the second single-lamp single-rod amplification module 9 serve as the second-stage and third-stage amplifications respectively, gradually increasing the pulse energy. The main function of the beam collimation module 10 is to correct the wavefront aberration accumulated in the amplification process of the previous second single-lamp single-rod amplification module 9 and compress the beam divergence angle to the diffraction limit level. The main function of the delay optical path control module 12 is to change the laser energy deposition route by adjusting the pulse delay time Δt, control the evolution of the laser-induced plasma shock wave and the subsequent interaction process between the laser and the plasma, improve the energy deposition efficiency, the plasma duration and intensity, and weaken the influence of the plasma shielding effect.

[0033] The single-lamp double-rod amplification module 4, the first single-lamp single-rod amplification module 6, and the second single-lamp single-rod amplification module 9 are realized by neodymium-doped yttrium aluminum garnet (Nd:YAG) laser crystal rods.

[0034] A quartz rotor 8 is provided between the first single-lamp single-rod amplification module 6 and the second single-lamp single-rod amplification module 9. The quartz rotor 8 compensates for the thermal effect and can improve the thermal lens effect by rotation, correct the thermal lens effect generated by the previous first single-lamp single-rod amplification module 6, that is, the asymmetric thermal distortion, and maintain the beam quality. The quartz rotor 8 is a quartz crystal.

[0035] An optical isolator 2 is provided between the passive Q-switching resonator 1 and the single-lamp double-rod amplification module 4. The center point of the optical isolator 2 is on the same horizontal line as the center points of the passive Q-switching resonator 1 and the single-lamp double-rod amplification module 4. The function of the optical isolator 2 is to prevent the reverse-transmitted light from damaging the passive Q-switching resonator 1 and ensure the unidirectional transmission of the emitted seed light. The optical isolator 2 is composed of a first polarization beam splitter, a Faraday rotator, and a second polarization beam splitter arranged in sequence. The center points of the first polarization beam splitter, the Faraday rotator, and the second polarization beam splitter group are on the same horizontal line as the center point of the passive Q-switching resonator 1. The functions of the first polarization beam splitter, the Faraday rotator, and the second polarization beam splitter are respectively to prevent the reverse-transmitted light from damaging the passive Q-switching resonator 1 and ensure unidirectional transmission.

[0036] A first beam expansion module 3 is provided between the optical isolator 2 and the single-lamp double-rod amplification module 4. The center point of the first beam expansion module 3 is on the same horizontal line as the center points of the optical isolator 2 and the single-lamp double-rod amplification module 4. A second beam expansion module 5 is provided between the single-lamp double-rod amplification module 4 and the first single-lamp single-rod amplification module 6. The center point of the second beam expansion module 5 is on the same horizontal line as the center points of the single-lamp double-rod amplification module 4 and the first single-lamp single-rod amplification module 6. A third beam expansion module 7 is provided between the first single-lamp single-rod amplification module 6 and the quartz rotor 8. The center point of the third beam expansion module 7 is on the same horizontal line as the center points of the first single-lamp single-rod amplification module 6 and the quartz rotor 8. The functions of the first beam expansion module 3, the second beam expansion module 5, and the third beam expansion module 7 are all to match the crystal aperture of the pre-stage amplification module, avoid optical damage, and at the same time ensure that the light beam covers the effective area of the gain medium.

[0037] Such as Figure 3As shown in the figure, the first beam expander module 3, the second beam expander module 5, and the third beam expander module 7 each include a first negative lens 3-1 and a first positive lens 3-2 arranged in sequence. The centers of the first negative lens 3-1 and the first positive lens 3-2 are on the same horizontal line as the center of the single-lamp double-rod amplification module 4. The position where the lenses are placed is such that the distance between the first negative lens 3-1 and the first positive lens 3-2 is equal to the difference between the focal lengths of the first negative lens 3-1 and the first positive lens 3-2. The first negative lens 3-1 diverges the incident parallel light, and the first positive lens 3-2 reconverts the light beam diverged by the first negative lens 3-1 into parallel light and simultaneously enlarges the beam diameter. The first beam expander module 3 gently expands the seed beam to prepare for the high-power amplification of the subsequent single-lamp double-rod amplification module 4. The expanded beam enters the single-lamp double-rod amplification module 4, where the laser first obtains a significant energy boost. The double-rod structure design not only saves space but also effectively suppresses the thermal lens effect, providing stable first-stage gain for the system. The second beam expander module 5 gently expands the seed beam to match the crystal aperture of the first single-lamp single-rod amplification module 6, avoiding optical damage and reducing the power density after beam expansion, and the energy is amplified for the second time. Subsequently, the beam enters the first single-lamp single-rod amplification module 6. This stage focuses on further extraction of energy, and the third beam expander module 7 maintains the beam quality during this process to prevent nonlinear effects caused by excessive power density.

[0038] Among them, as Figure 2 shown, the passive Q-switching resonator 1 includes a 0° total reflection mirror 1-1, an LD side-pumping module 1-2, a passive Q-switch 1-3, a fifth polarization beam splitter 1-4, a small hole 1-5, and an output mirror 1-6 arranged in sequence. The centers of the 0° total reflection mirror 1-1, the LD side-pumping module 1-2, the passive Q-switch 1-3, the fifth polarization beam splitter 1-4, the small hole 1-5, and the output mirror 1-6 are on the same horizontal line. The seed light is output from the output mirror 1-6 and enters the optical isolator 2. The passive Q-switching resonator 1 forms a resonator using the 0° total reflection mirror 1-1 and the output mirror 1-6. Under the action of the LD side-pumping module 1-2, the gain medium continuously accumulates inverted population. At this time, the saturable absorber maintains a high-loss state to suppress laser oscillation. When the energy storage reaches the threshold, the absorber suddenly becomes saturated and transparent, and the number of photons in the cavity increases avalanche-like, forming a nanosecond-level giant pulse; finally, it is coupled and output through the output mirror 1-6 with a high peak power (10 5 -10 7W), high-quality seed light with a narrow pulse width (5 - 20 ns). The LD side-pumping module 1 - 2 is pumped by an LD, and the passive Q-switch 1 - 3 enables the resonant cavity to output a larger seed light, laying a foundation for subsequent amplification. The fifth polarization beam splitter 1 - 4 and the small hole 1 - 5 work together to ensure linearly polarized and fundamental mode output, providing an ideal laser source for the subsequent amplification system. The light reflected by the fifth polarization beam splitter 1 - 4 is useless. The polarization beam splitter 1 - 4 and the small hole 1 - 5 work together to ensure that the light output from the passive Q-switch resonant cavity 1 is linearly polarized light and fundamental mode light, providing an ideal seed light for the subsequent amplification system. The seed light enters the optical isolator 2 from the passive Q-switch resonant cavity 1. The main function of the optical isolator 2 is to block the backward-transmitted light using the polarization principle, ensuring unidirectional passage of the incident light and protecting the passive Q-switch resonant cavity 1.

[0039] The main functions of the first beam expansion module 3, the second beam expansion module 5, and the third beam expansion module 7 are to achieve precise matching of the beam parameters with the amplification link: the seed light is gradually amplified through multi-stage gradient beam expansion to match the crystal apertures of the single-lamp double-rod amplification module 4, the first single-lamp single-rod amplification module 6, and the second single-lamp single-rod amplification module 9. While reducing the power density to protect the optical components, it ensures sufficient overlap of the beam with the gain region. The quartz rotor 8 compensates for the thermal effect and corrects the thermal lens effect generated by the previous-stage amplification module, maintaining the beam quality. The second single-lamp single-rod amplification module 9 performs final-stage energy enhancement. At this time, the precise regulation of the beam expansion module ensures that the amplification process is always carried out under the optimal beam parameters, providing an ideal optical input for the delay optical path control module.

[0040] As Figure 4 shown, the beam collimation module 10 includes a second positive lens 10 - 1 and a second negative lens 10 - 2 arranged in sequence. The center points of the second positive lens 10 - 1 and the second negative lens 10 - 2 are set on the same horizontal line. The second positive lens 10 - 1 converts the divergent beam (due to the thermal lens effect or natural divergence) output from the previous-stage amplification module into a convergent beam, and the second negative lens 10 - 2 readjusts the convergent beam formed by the second positive lens 10 - 1 into parallel light (collimated state). The distance between the second positive lens 10 - 1 and the second negative lens 10 - 2 is the sum of the focal lengths of the positive and negative lenses, converting the divergent beam output from the previous-stage second single-lamp single-rod amplification module 9 into parallel light. The main function of the beam collimation module 10 is to correct the wavefront aberration accumulated during the amplification process of the previous-stage second single-lamp single-rod amplification module 9, compress the beam divergence angle to the diffraction limit level, and the characteristics of the collimated beam directly affect the laser shock peening effect.

[0041] As Figure 5As shown in the figure, the delay optical path control module 12 includes a third polarization beam splitter 12-1, a fourth polarization beam splitter 12-2, a first 45° total reflection mirror 12-3, and a second 45° total reflection mirror 12-4. The centers of the half-wave plate 11, the third polarization beam splitter 12-1, and the fourth polarization beam splitter 12-2 are set on the same horizontal line. The first 45° total reflection mirror 12-3 is set on the reflection optical path of the third polarization beam splitter 12-1. The centers of the first 45° total reflection mirror 12-3 and the second 45° total reflection mirror 12-4 are set on the same horizontal line. The fourth polarization beam splitter 12-2 is set on the reflection optical path of the second 45° total reflection mirror 12-4. The functions of the first 45° total reflection mirror 12-3 and the second 45° total reflection mirror 12-4 are to vertically reflect the reflected light of the third polarization beam splitter 12-1 twice and then enter the fourth polarization beam splitter 12-2. The function of the fourth polarization beam splitter 12-2 is to combine the P-polarized light and the S-polarized light to achieve delayed output. The third polarization beam splitter 12-1, the fourth polarization beam splitter 12-2, the first 45° total reflection mirror 12-3, and the second 45° total reflection mirror 12-4 are all set on the intelligent electric displacement platform. The third polarization beam splitter 12-1 receives the linearly polarized light from the previous-stage half-wave plate 11. The third polarization beam splitter 12-1 has a high transmittance for P-polarized light and directly enters the optical path L4. The third polarization beam splitter 12-1 has a high reflectivity for S-polarized light and deflects it by 90° to enter the delay optical path L1. The delay optical path L1 is perpendicular to the optical path L4. The S-polarized light is introduced into the optical path difference ΔL = L1 + L2 + L3 - L4 through the adjustable mirror group, that is, the first 45° total reflection mirror 12-3 and the second 45° total reflection mirror 12-4. Specifically, it enters the delay optical path L2 through the first 45° total reflection mirror 12-3 and enters the delay optical path L3 through the second 45° total reflection mirror 12-4, and forms a time-domain double pulse after recombining with the P-polarized light in the fourth polarization beam splitter 12-2. By rotating the half-wave plate 11 to change the incident polarization direction, the energy distribution of the two paths of light is dynamically adjusted. The intelligent electric displacement platform can accurately control the positions of the third polarization beam splitter 12-1, the first 45° total reflection mirror 12-3, the second 45° total reflection mirror 12-4, and the fourth polarization beam splitter 12-2, and the double-pulse laser delay time can be adjusted within a range according to the optical path difference. The pulse delay time Δt realized by the delay optical path control module 12 satisfies:

[0042] Δt = (L1 + L2 + L3 - L4) / c

[0043] Among them, the adjustment range of the pulse delay time Δt is 0 - 10 ns. L4 is the reference optical path length, L1 + L2 + L3 is the delay optical path length, and c is the speed of light. The continuous adjustment of the delay time is achieved by adjusting the delay optical path length through the intelligent electric displacement platform. The positioning accuracy of the high-precision motor-driven intelligent electric displacement platform is better than 20 μm to meet the requirement of precise control of the double-pulse laser delay time. Specifically, the reference optical path length L4 and the delay optical path length L2 are equal. Therefore, it is necessary to adjust the distance between the third polarization beam splitter 12-1 and the first 45° total reflection mirror 12-3, and the distance between the fourth polarization beam splitter 12-2 and the second 45° total reflection mirror 12-4. The third polarization beam splitter 12-1 and the first 45° total reflection mirror 12-3 are both set on the first electric displacement platform, and the fourth polarization beam splitter 12-2 and the second 45° total reflection mirror 12-4 are both set on the second electric displacement platform. The first 45° total reflection mirror 12-3 is set on the slider of the first electric displacement platform, and the second 45° total reflection mirror 12-4 is set on the corresponding slider of the second electric displacement platform. After the user inputs the target pulse delay time Δt, the software of the electric displacement platform automatically calculates the optical path difference according to the formula ΔL = c·Δt, and can determine that the displacement of each total reflection mirror relative to the polarization beam splitter on its respective electric displacement platform is ΔL / 2. The electric displacement platform drives the slider to move the first 45° total reflection mirror 12-3 and the second 45° total reflection mirror 12-4 to the corresponding positions according to the displacement amount. The first 45° total reflection mirror 12-3 and the second 45° total reflection mirror 12-4 are always on the same horizontal line, realizing the automatic adjustment of the double-pulse laser delay time. The model of the intelligent electric displacement platform is PA1000. By adjusting the pulse delay time Δt, the laser energy deposition route is changed, the evolution of the laser-induced plasma shock wave and the subsequent interaction process between the laser and the plasma are regulated, the energy deposition efficiency, the plasma duration and intensity are improved, and the influence of the plasma shielding effect is weakened.

[0044] By rotating the half-wave plate 11, the energy ratio of the optical paths where the P-polarized light and the S-polarized light are located in the delay optical path control module 12 is adjusted. The relationship between the rotation angle θ of the half-wave plate 11 and the energy ratio

[0045]

[0046] Among them, φ0 is the initial phase offset. The precise adjustment of the P-polarized light:S-polarized light from 1:1 to 10:1 is achieved by controlling the rotation angle θ. E1 represents the energy of the P-polarized light, and E2 represents the energy of the S-polarized light.

[0047] In summary, the present invention proposes a high-power nanosecond laser with adjustable time-domain double-pulse delay. Based on the MOPA architecture, it integrates a passive Q-switching resonator, a multi-stage amplification module, and a delay optical path control module, realizing the dynamic distribution of double-pulse delay and energy, effectively improving the laser shock peening effect. This system has both high stability and programmability and is suitable for the field of precision material processing.

[0048] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-power nanosecond laser with adjustable time-domain double-pulse delay, characterized in that, It includes a passive Q-switching resonator (1), a single-lamp double-rod amplification module (4), a first single-lamp single-rod amplification module (6), a second single-lamp single-rod amplification module (9), a beam collimation module (10), a half-wave plate (11) and a delay optical path control module (12) arranged in sequence. The centers of the single-lamp double-rod amplification module (4), the first single-lamp single-rod amplification module (6), the second single-lamp single-rod amplification module (9), the beam collimation module (10), the half-wave plate (11) and the delay optical path control module (12) are on the same horizontal line; The passive Q-switching resonator (1) generates seed light, and the seed light undergoes four-stage power amplification through the single-lamp double-rod amplification module (4), the first single-lamp single-rod amplification module (6), and the second single-lamp single-rod amplification module (9). Subsequently, it enters the beam collimation module (10) to correct the wavefront distortion accumulated during the power amplification process, compress the beam divergence angle to the diffraction limit level, and generate high-energy and high-power laser pulses. The half-wave plate (11) is rotated to dynamically adjust the light energy distribution between the normal optical path and the delay optical path, and the delay optical path control module (12) controls the pulse delay time of the laser pulse between the normal optical path and the delay optical path Δt to change the laser energy deposition route, regulate the evolution of the laser-induced plasma shock wave, and the subsequent laser-plasma interaction process.

2. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 1, wherein A quartz rotor (8) is provided between the first single-lamp single-rod amplification module (6) and the second single-lamp single-rod amplification module (9). The quartz rotor (8) performs thermal effect compensation to correct the thermal lens effect generated by the first single-lamp single-rod amplification module (6) and maintain the beam quality.

3. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 2, characterized in that, An optical isolator (2) is provided between the passive Q-switching resonator (1) and the single-lamp double-rod amplification module (4). The center point of the optical isolator (2) and the center points of the passive Q-switching resonator (1) and the single-lamp double-rod amplification module (4) are on the same horizontal line; A first beam expansion module (3) is provided between the optical isolator (2) and the single-lamp double-rod amplification module (4). The center point of the first beam expansion module (3) and the center points of the optical isolator (2) and the single-lamp double-rod amplification module (4) are on the same horizontal line; A second beam expansion module (5) is provided between the single-lamp double-rod amplification module (4) and the first single-lamp single-rod amplification module (6). The center point of the second beam expansion module (5) and the center points of the single-lamp double-rod amplification module (4) and the first single-lamp single-rod amplification module (6) are on the same horizontal line; A third beam expansion module (7) is provided between the first single-lamp single-rod amplification module (6) and the quartz rotor (8). The center point of the third beam expansion module (7) and the center points of the first single-lamp single-rod amplification module (6) and the quartz rotor (8) are on the same horizontal line.

4. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 3, characterized in that, The single-lamp double-rod amplification module (4), the first single-lamp single-rod amplification module (6), and the second single-lamp single-rod amplification module (9) are all realized by neodymium-doped yttrium aluminum garnet laser crystal rods; The quartz rotor (8) is a quartz crystal.

5. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 3 or 4, characterized in that, The first beam expansion module (3), the second beam expansion module (5), and the third beam expansion module (7) all include a first negative lens (3-1) and a first positive lens (3-2) arranged in sequence. The center points of the first negative lens (3-1) and the first positive lens (3-2) and the center point of the single-lamp double-rod amplification module (4) are on the same horizontal line. The distance between the first negative lens (3-1) and the first positive lens (3-2) is equal to the difference between the focal lengths of the first negative lens (3-1) and the first positive lens (3-2).

6. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to any one of claims 1-4, characterized in that, The passive Q-switching resonator (1) includes a 0° total reflection mirror (1-1), an LD side pumping module (1-2), a passive Q-switching switch (1-3), a fifth polarization beam splitter (1-4), a small hole (1-5) and an output mirror (1-6) arranged in sequence. The central points of the 0° total reflection mirror (1-1), the LD side pumping module (1-2), the passive Q-switching switch (1-3), the fifth polarization beam splitter (1-4), the small hole (1-5) and the output mirror (1-6) are on the same horizontal line. The 0° total reflection mirror (1-1) and the output mirror (1-6) form a resonator. Under the action of the LD side pumping module (1-2), the gain medium continuously accumulates inverted population. At this time, the saturable absorber maintains a high-loss state to suppress laser oscillation. When the energy storage reaches the threshold, the absorber suddenly saturates and becomes transparent, and the number of photons in the resonator increases avalanche-like, forming a nanosecond-level giant pulse. The passive Q-switching switch (1-3) enables the resonator to output a larger seed light. The combined action of the fifth polarization beam splitter (1-4) and the small hole (1-5) ensures linearly polarized and fundamental mode output, and the high-peak power and narrow pulse-width seed light is coupled and output through the output mirror (1-6).

7. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 1, characterized in that, The beam collimation module (10) includes a second positive lens (10-1) and a second negative lens (10-2) arranged in sequence. The central points of the second positive lens (10-1) and the second negative lens (10-2) are on the same horizontal line. The second positive lens (10-1) converts the divergent beam output by the second single-lamp single-rod amplification module (9) into a converging beam, and the second negative lens (10-2) readjusts the converging beam into a collimated parallel light. The distance between the second positive lens (10-1) and the second negative lens (10-2) is the sum of the focal lengths of the positive and negative lenses.

8. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 1 or 7, characterized in that, The delay optical path control module (12) includes a third polarization beam splitter (12-1), a fourth polarization beam splitter (12-2) and a reflection component. The central points of the half-wave plate (11), the third polarization beam splitter (12-1) and the fourth polarization beam splitter (12-2) are on the same horizontal line. The reflection component is arranged on the delay optical path between the third polarization beam splitter (12-1) and the fourth polarization beam splitter (12-2).

9. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 8, wherein, The reflection component includes a first 45° total reflection mirror (12-3) and a second 45° total reflection mirror (12-4). The first 45° total reflection mirror (12-3) is arranged on the reflection optical path of the third polarization beam splitter (12-1). The central points of the first 45° total reflection mirror (12-3) and the second 45° total reflection mirror (12-4) are on the same horizontal line. The fourth polarization beam splitter (12-2) is arranged on the reflection optical path of the second 45° total reflection mirror (12-4).

10. The high-power nanosecond laser with adjustable time-domain double-pulse delay according to claim 9, characterized in that, The third polarization beam splitter (12-1) and the first 45° total reflection mirror (12-3) are both arranged on the first electric displacement platform. The first 45° total reflection mirror (12-3) is arranged on the slider of the first electric displacement platform. The fourth polarization beam splitter (12-2) and the second 45° total reflection mirror (12-4) are both arranged on the first electric displacement platform. The second 45° total reflection mirror (12-4) is arranged on the slider of the second electric displacement platform; The third polarization beam splitter (12-1) receives the linearly polarized light from the half-wave plate (11). The third polarization beam splitter (12-1) has a high transmittance for P-polarized light and directly enters the normal optical path. The third polarization beam splitter (12-1) has a high reflectance for S-polarized light and deflects it by 90° to enter the optical path with time delay L1, enters the optical path with time delay L2 through the first 45° total reflection mirror (12-3), and enters the optical path with time delay L3 through the second 45° total reflection mirror (12-4). After recombining with the P-polarized light at the fourth polarization beam splitter (12-2), a time-domain double pulse is formed. The S-polarized light is introduced into an optical path difference through the first 45° total reflection mirror (12-3) and the second 45° total reflection mirror (12-4). According to the optical path difference, the delay time of the double-pulse laser is adjustable within a certain range; The pulse delay time Δt satisfies: ; where, the pulse delay time Δt has an adjustment range of 0 - 10 ns, L 4 is the normal optical path length, L 1 +L 2 +L 3 is the delay optical path length, c is the speed of light; According to the preset pulse delay time Δt Calculate the optical path difference ΔL = c ·Δ t , and determine that the displacement between the first 45° total reflection mirror (12-3) and the third polarization beam splitter (12-1) and between the second 45° total reflection mirror (12-4) and the fourth polarization beam splitter (12-2) is ΔL / 2; Adjust the energy ratio of the optical paths where the P-polarized light and the S-polarized light are located in the delay optical path control module (12) by rotating the half-wave plate (11). The relationship between the rotation angle θ of the half-wave plate (11) and the energy ratio is: ; wherein, ϕ 0 is the initial phase shift, and by controlling the rotation angle θ, the P-polarized light: S-polarized light is precisely adjusted from 1:1 to 10:1; E1 represents the energy of the P-polarized light, and E2 represents the energy of the S-polarized light.

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