Dual-wavelength repetition-frequency-adjustable high-energy nanosecond laser system

Abstract

The invention discloses a dual-wavelength repetition-frequency-adjustable high-energy nanosecond laser system which comprises an electro-optic Q-switched laser, a beam-expanding collimation unit, a double-pass amplification unit, a boosting stage amplification unit and a frequency multiplication unit which are arranged in sequence, and the electro-optic Q-switched laser, the double-pass amplification unit, the boosting stage amplification unit and the frequency multiplication unit are all connected with a signal control unit; laser emitted by the electro-optic Q-switched laser enters the beam expanding and collimating unit for beam expanding and collimating, then enters the double-pass amplification unit and the boosting stage amplification unit in sequence, enters the frequency doubling unit after being amplified by the double-pass amplification unit and the boosting stage amplification unit, and outputs high-energy nanosecond laser with two wavelengths through the frequency doubling unit. A multi-stage amplification structure is adopted, thermal load can be dispersed to a plurality of amplification stages, the environment stability is good, the device is suitable for long-time operation, in addition, the manufacturing and maintenance cost is low, and the device can be widely adopted and has good adaptability.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, in particular to a high-power solid laser. Background Art

[0002] According to the different pulse widths, pulse lasers can be divided into nanosecond, picosecond and femtosecond lasers. Among them, for nanosecond lasers, it can take into account the requirements of peak power and single pulse energy at the same time. In laser processing, non-contact nanosecond lasers can break through the bottleneck of low efficiency and poor precision of traditional mechanical processing; in the field of national defense, near-infrared nanosecond lasers can be used for optical recognition and photoelectric confrontation to achieve precise military strikes. In short, high-energy nanosecond pulse lasers are widely used in laser processing, laser radar, biomedicine, national defense and military. Q-switching technology is an effective way to generate nanosecond pulses, but the energy of the single laser pulse generated by Q-switching technology is low. Master oscillator power amplifier (MOPA) technology is often used to amplify the output energy of short-pulse laser pulses. For MOPA technology, the thermal lens effect of the gain module is inevitable, which deteriorates the performance of the laser and limits the adjustable output of the laser repetition frequency, and even causes damage to optical components.

[0003] In the prior art, a Chinese invention patent with publication number CN115224580A and publication date of October 21, 2022 discloses a polarization-switchable short-pulse laser system, including a laser oscillator module, a laser amplification module, and a laser frequency-doubling polarization switching module, wherein the optical input end of the laser amplification module is connected to the laser oscillator module, and the optical output end of the laser amplification module is connected to the laser frequency-doubling polarization switching module, the laser oscillator module is used to generate a nanosecond pulse laser with a wavelength of 1064nm, the laser amplification module is used to amplify the energy of the nanosecond pulse laser, and the laser frequency-doubling polarization switching module outputs a dual-wavelength polarization-state switchable laser. Although the patent can realize the use of a polarization-switchable short-pulse laser system in the fields of laser ranging, photoelectric countermeasures, and atmospheric detection, the patent has a complex structure, which is not conducive to integration, and it is difficult to compensate for thermal depolarization, which affects the life of the component. Summary of the invention

[0004] In view of the deficiencies in the above-mentioned background technology, the present invention proposes a dual-wavelength high-energy nanosecond laser system with adjustable repetition rate, which solves the problems in the prior art of thermal effects and thermal focal instability corresponding to different repetition rates of the laser during high-power operation, which easily leads to light spot deterioration or even light spot distortion, and further causes damage to components.

[0005] The technical solution of the present invention is implemented as follows: a dual-wavelength high-energy nanosecond laser system with adjustable repetition rate comprises an electro-optical Q-switched laser, a beam expansion and collimation unit, a two-way amplification unit, a booster-stage amplification unit and a frequency doubling unit which are arranged in sequence, wherein the electro-optical Q-switched laser, the two-way amplification unit, the booster-stage amplification unit and the frequency doubling unit are all controlled and connected with a signal control unit; the laser emitted by the electro-optical Q-switched laser enters the beam expansion and collimation unit for beam expansion and collimation, and then enters the two-way amplification unit and the booster-stage amplification unit in sequence, and after being amplified by the two-way amplification unit and the booster-stage amplification unit, enters the frequency doubling unit, and outputs high-energy nanosecond lasers of two wavelengths through the frequency doubling unit.

[0006] Further preferably, the electro-optical Q-switched laser comprises a resonant cavity laser side pump module and an electro-optical Q-switching which are arranged in sequence, the electro-optical Q-switching and the resonant cavity laser side pump module are coaxially arranged, a quarter wave plate 1 and a first reflector are arranged in sequence on an optical path on one side of the electro-optical Q-switching, and a resonant cavity laser side pump module, a pinhole aperture, a first polarizer and a second reflector are arranged in sequence on an optical path on the other side of the electro-optical Q-switching; photons spontaneously radiated by the resonant cavity laser side pump module oscillate between the electro-optical Q-switching, the quarter wave plate 1, the first reflector, the pinhole aperture and the first polarizer to form laser which is emitted from the second reflector.

[0007] Further preferably, the beam expansion and collimation unit comprises a beam expansion lens corresponding to the second reflector, and a collimating lens is provided at the output end of the beam expansion lens.

[0008] Further preferably, the beam expansion and collimation unit further includes a third reflector, and the laser output through the collimating lens is redirected by the third reflector and then incident on the double-pass amplification unit.

[0009] Further preferably, the double-pass amplification unit includes an isolation device and a first-stage double-pass amplification module, the isolation device is coaxially arranged with the first-stage double-pass amplification module, the isolation device includes a second polarizer, a Faraday rotator, a half wave plate and a third polarizer arranged in sequence, and the second polarizer, the Faraday rotator, the half wave plate and the third polarizer are coaxially arranged, one side of the first-stage double-pass amplification module corresponds to the third polarizer, and the other side of the first-stage double-pass amplification module is provided with a quarter wave plate 2 and a fifth reflector; the laser incident from the third reflector is sequentially emitted to the second polarizer, the Faraday rotator, the half wave plate and the third polarizer, the first-stage double-pass amplification module, the quarter wave plate 2 and the fifth reflector, and is emitted to the quarter wave plate 2, the first-stage double-pass amplification module and the second polarizer through the fifth reflector, and finally emitted through the third polarizer.

[0010] Further preferably, the double-pass amplification module is further provided with a fourth reflector for changing the direction of the light path, the light source input end of the fourth reflector corresponds to the third reflector, and the light source output end of the fourth reflector corresponds to the second polarizer.

[0011] Further preferably, the booster-stage amplification unit includes a secondary one-way amplification module and a tertiary one-way amplification module which are arranged in sequence, a quartz rotor for compensating for thermal depolarization is provided between the secondary one-way amplification module and the tertiary one-way amplification module, and a fourth polarizer and a divergent lens are provided in sequence at the laser incident end of the secondary one-way amplification module; the laser emitted from the third polarizer passes through the fourth polarizer and the divergent lens in sequence and then emits to the secondary one-way amplification module and the tertiary one-way amplification module, and is emitted through the tertiary one-way amplification module.

[0012] Further preferably, the booster stage amplification unit also includes a sixth reflector and a seventh reflector for changing the direction of the light path, the light source input end of the sixth reflector corresponds to the divergent lens, the light source output end of the sixth reflector corresponds to the light source input end of the seventh reflector, and the light source output end of the seventh reflector corresponds to the light source input end of the secondary single-pass amplification module.

[0013] Further preferably, the frequency doubling unit includes a frequency doubling crystal and a DC motor, the frequency doubling crystal is mounted on a guide rail at the output end of the DC motor, and the frequency doubling crystal corresponds to the three-stage single-pass amplification module.

[0014] Further preferably, the signal control unit includes a host computer and a phase modulator, the host computer is connected to the phase modulator through a serial port server, and the resonant cavity laser side pump module, the first-stage two-way amplification module, the second-stage single-way amplification module and the third-stage single-way amplification module are all connected to the host computer through the serial port server; the phase modulator is connected to the electro-optical Q-switching, the resonant cavity laser side pump module and the second-stage single-way amplification module, the resonant cavity laser side pump module is connected to the first-stage two-way amplification module, and the second-stage single-way amplification module is connected to the third-stage single-way amplification module.

[0015] The beneficial effects of the present invention are: 1. The present invention adopts an electro-optical Q-switched laser to realize the output of seed light with adjustable repetition rate. After the laser is emitted from the electro-optical Q-switched laser, it passes through a beam expansion and collimation unit to amplify the laser spot, and then enters a double-pass amplification unit composed of an isolation device and a first-stage double-pass amplification device for energy amplification. The amplified laser passes through a plano-concave lens to further adjust the size of the spot and the divergence angle, and then enters a booster-stage amplification unit composed of a second-stage single-pass amplification module and a third-stage single-pass amplification module for energy amplification again. Finally, the amplified laser enters the frequency doubling unit to realize dual-wavelength high-energy laser output. The laser system adopts a multi-stage amplification structure, which can disperse the heat load to multiple amplification stages, and adds an adjustment element, i.e., a quartz rotor, between the amplification stages to compensate for the thermal depolarization effect.

[0016] 2. The entire frequency doubling module is placed on a horizontally movable displacement platform to achieve left and right lateral movement, thereby meeting the switching requirements of 1064nm and 532nm in the system. Through precise control of the motor, the position and angle of the crystal are ensured to be in the optimal state to obtain stable and high-quality 532nm green laser output. In order to solve the thermal effect and thermal focal length change problems caused by different repetition rates under high-power operation, a heat-insensitive cavity is designed under existing conditions. Specifically, the electro-optical Q-switched laser is optimized by the electronic control part, the electro-optical Q-switched trigger is separated from the power supply, and the electro-optical Q-switched and resonant cavity power supplies are triggered separately by the phase modulator, and the phase modulation of the two signals is completed by the phase modulator. This solution can keep the laser power supply running at 200 Hz at all times. The operating frequency of the laser can be changed by changing the electro-optical Q-switched trigger signal. At this time, the thermal effect in the laser remains stable and unchanged, and the control of the thermal problem in the laser is achieved by changing the control logic.

[0017] 3. The present invention adopts a dual-pass side pump amplifier module and two single-pass side pump amplifier modules, which have the advantages of simple design, easy manufacturing and maintenance, more compact, easy integration in a small system, and low cost. By changing the control logic, all side pump modules are operated at 200 Hz, which makes the internal heat generated by the lasers at different repetition rates consistent, and then compensated by optical elements such as quartz rotors, it can be stable under different repetition rate conditions, and the beam quality will not change greatly. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0019] Figure 1 It is a schematic diagram of the optical path structure of the present invention; Figure 2 It is a control logic diagram of the structure of the present invention.

[0020] In the figure: 1: electro-optic Q-switched laser; 1-1: first reflector; 1-2: quarter wave plate 1; 1-3: electro-optic Q-switching; 1-4: resonant cavity laser side pump module; 1-5: pinhole aperture; 1-6: first polarizer; 1-7: second reflector; 2: beam expansion and collimation unit; 2-1: beam expansion lens; 2-2: collimation lens; 2-3: third reflector; 3: double-pass amplification unit; 3-1: fourth reflector; 3-2: second polarizer; 3-3: Faraday rotator; 3-4: half wave plate; 3-5: third polarizer; 3-6: first-stage double-pass amplification module; 3-7: quarter wave plate II; 3-8: fifth reflector; 4: booster-stage amplification unit; 4-1: fourth polarizer; 4-2: divergent lens; 4-3: sixth reflector; 4-4: seventh reflector; 4-5: second-stage single-pass amplification module; 4-6: quartz rotor; 4-7: third-stage single-pass amplification module; 5: frequency doubling unit; 5-1: frequency doubling crystal; 5-2: DC motor. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] like Figure 1~2As shown, in Example 1, a dual-wavelength repetition rate adjustable high-energy nanosecond laser system comprises an electro-optical Q-switched laser 1, a beam expansion collimation unit 2, a two-way amplification unit 3, a booster-stage amplification unit 4 and a frequency doubling unit 5 which are arranged in sequence, and the electro-optical Q-switched laser 1, the two-way amplification unit 3, the booster-stage amplification unit 4 and the frequency doubling unit 5 are all connected to the signal control unit for control; the signal control unit can send a communication signal and a trigger signal to control the electro-optical Q-switched laser 1, the two-way amplification unit 3, the booster-stage amplification unit 4 and the frequency doubling unit 5, thereby achieving 1064 nm near-infrared or 532 nm green light output or 1064 nm near-infrared and 532 nm green light output simultaneously. The laser emitted by the electro-optical Q-switched laser 1 enters the beam expansion collimation unit 2 for beam expansion and collimation, and then enters the two-way amplification unit 3, the booster-stage amplification unit 4 in sequence, and after being amplified by the two-way amplification unit 3 and the booster-stage amplification unit 4, enters the frequency doubling unit 5, and outputs high-energy nanosecond lasers of two wavelengths through the frequency doubling unit 5. An electro-optical Q-switched laser 1 is used to realize the output of seed light with adjustable repetition rate. After the laser is emitted from the electro-optical Q-switched laser 1, it passes through the beam expansion and collimation unit 2 to amplify the laser spot, and then enters the double-pass amplification unit 3 composed of an isolation device and a first-stage double-pass amplification module 3-6 for energy amplification. The amplified laser passes through a plano-concave lens to further adjust the size of the spot and the divergence angle, and then enters the booster-stage amplification unit 4 composed of a second-stage single-pass amplification module 4-5 and a third-stage single-pass amplification module 4-7 for energy amplification again. Finally, the amplified laser enters the frequency doubling unit to realize dual-wavelength high-energy laser output. The laser system adopts a multi-stage amplification structure, which can disperse the heat load to multiple amplification stages, and adds adjustment elements, namely quartz rotors 4-6, between the amplification stages to compensate for the thermal depolarization effect.

[0023] In this embodiment, the electro-optical Q-switched laser 1 includes a resonant cavity laser side pump module 1-4 and an electro-optical Q switch 1-3 which are arranged in sequence, the electro-optical Q switch is coaxially arranged with the resonant cavity laser side pump module 1-4, a quarter wave plate 1-2 and a first reflector 1-1 are arranged in sequence on one side optical path of the electro-optical Q switch 1-3, and a resonant cavity laser side pump module 1-4, a pinhole aperture 1-5, a first polarizer 1-6 and a second reflector 1-7 are arranged in sequence on the other side optical path of the electro-optical Q switch 1-3; the laser emitted by the resonant cavity laser side pump module 1-4 oscillates between the electro-optical Q switch 1-3, the quarter wave plate 1-2, the first reflector 1-1, the pinhole aperture 1-5 and the first polarizer 1-6, and then is emitted from the second reflector 1-7. The first reflector 1-1 is a full reflector, the second reflector 1-7 is a partial reflector, and the flat cavity electro-optical Q-switched laser 1 composed of the full reflector and the partial reflector, the signal control unit can design the electric control part, that is, the control logic, so that the side pump module always operates at 200 Hz, and the repetition rate is dynamically adjustable at 1-200 Hz by changing the trigger of the electro-optical Q-switching 1-3, and the internal heat problem of the laser is effectively solved. In addition, the flat cavity design is relatively simple, easy to manufacture and adjust, suitable for rapid experiments and applications, and has high environmental stability, suitable for long-term operation, and low manufacturing and maintenance costs. It can be widely adopted and has good adaptability.

[0024] In this embodiment, the beam expansion and collimation unit 2 includes a beam expansion lens 2-1 corresponding to the second reflector 1-7, and a collimating lens 2-2 is provided at the output end of the beam expansion lens 2-1. The light beam output by the electro-optical Q-switched laser 1 passes through the beam expansion and collimation unit 2 at the rear end, and the diameter of the light beam increases from the original 1.8 mm to 3.3 mm, and is in a slightly divergent state after beam expansion to achieve the maximum amplification efficiency and make the light beam output more collimated. The beam expansion and collimation unit 2 also includes a third reflector 2-3, and the laser output through the collimating lens 2-2 is redirected by the third reflector 2-3 and then injected into the double-pass amplification unit 3. The third reflector 2-3 is a full-reflection mirror set at an angle of 45°, which is used to change the emission direction of the light path, deflect the light path by 90 degrees, and make the system structure more compact.

[0025] In this embodiment, the double-pass amplification unit 3 includes an isolation device and a first-stage double-pass amplification module 3-6. The first-stage double-pass amplification module is an LD side pump module for amplification. The isolation device is coaxially arranged with the first-stage double-pass amplification module 3-6. The isolation device includes a Faraday rotator 3-3. The laser input end of the Faraday rotator 3-3 is provided with a second polarizer 3-2. The laser output end of the Faraday rotator 3-3 is provided with a half-wave plate 3-4 and a third polarizer 3-5 corresponding to the first-stage double-pass amplification module 3-6. A quarter wave plate 2 3-7 and a fifth reflector 3-8 are provided on the other side of the module 3-6; the laser beam incident from the third reflector 2-3 is sequentially directed to the second polarizer 3-2, the Faraday rotator 3-3, the half wave plate 3-4 and the third polarizer 3-5, the first double-pass amplification module 3-6, the quarter wave plate 2 3-7 and the fifth reflector 3-8, and is directed to the quarter wave plate 2 3-7, the first double-pass amplification module 3-6 and the second polarizer 3-2 through the fifth reflector 3-8, and finally exits through the third polarizer 3-5. In the double-pass amplification unit 3, the light beam also needs to be processed by an isolation device. Although polarizers are used for light splitting during the double-pass amplification process, in the case of high-power laser amplification, the thermal gradient will cause thermally induced double deflection, causing thermal depolarization of the laser, which may generate return light through the polarizer, causing damage to the front-end equipment. Therefore, a single-pass isolation system including a half wave plate 3-4, two polarizers and an optical rotator is built to protect the safety of the front-end devices. Then, the seed light is amplified in the first-stage double-pass amplification device, and finally a laser output with a single pulse energy of 77 mJ is achieved. The first-stage double-pass amplification module is also provided with a fourth reflector 3-1 for changing the direction of the light path. The light source input end of the fourth reflector 3-1 corresponds to the third reflector 2-3, and the light source output end of the fourth reflector 3-1 corresponds to the second polarizer 3-2. The fourth reflector 3-1 is a full reflector set at an angle of 45°, which is used to change the direction of the light path and deflect the light path by 90 degrees. The third reflector 2-3 cooperates with the fourth reflector 3-1 to achieve a 180-degree change in the direction of the light path.

[0026] In this embodiment, the booster stage amplification unit 4 includes a secondary one-way amplification module 4-5 and a tertiary one-way amplification module 4-7 which are arranged in sequence. Both the secondary one-way amplification module 4-5 and the tertiary one-way amplification module 4-7 are LD side pump modules for amplification. A quartz rotor 4-6 for compensating thermal depolarization is arranged between the secondary one-way amplification module 4-5 and the tertiary one-way amplification module 4-7. A fourth polarizer 4-1 and a divergent lens 4-2 are arranged in sequence at the laser incident end of the secondary one-way amplification module 4-5. The laser emitted from the third polarizer 3-5 is emitted to the secondary one-way amplification module 4-5 and the tertiary one-way amplification module 4-7 after passing through the fourth polarizer 4-1 and the divergent lens 4-2 in sequence, and then emitted through the tertiary one-way amplification module 4-7. The third polarizer 3-5 is parallel to the fourth polarizer 4-1, and is used to inject the laser in the dual-way amplification unit 3 into the booster stage amplification unit 4. The booster-stage amplifier unit 4 also includes a sixth reflector 4-3 and a seventh reflector 4-4 for changing the direction of the optical path. The light source input end of the sixth reflector 4-3 corresponds to the divergent lens 4-2, the light source output end of the sixth reflector 4-3 corresponds to the light source input end of the seventh reflector 4-4, and the light source output end of the seventh reflector 4-4 corresponds to the light source input end of the secondary single-pass amplifier module 4-5. The sixth reflector 4-3 and the seventh reflector 4-4 are two total reflectors that are relatively arranged and tilted at 45°, which change the laser direction by 180 degrees, thereby making the structure more compact. In the booster-stage amplifier unit 4, the light beam is also expanded before amplification, that is, a plano-concave divergent lens 4-2 is used to make the light spot smaller than the crystal rod diameter, and the divergence angle is slightly divergent, thereby compensating for the thermal focal length in the secondary amplification process. Subsequently, after passing through the secondary single-pass amplifier module 4-5, the quartz rotor 4-6 and the tertiary single-pass amplifier module 4-7, a laser output of more than 320 mJ is achieved. A quartz rotor 4-6 is added between the secondary single-pass amplification module 4-5 and the tertiary single-pass amplification module 4-7. This configuration is intended to compensate for thermal focal length changes and beam offset problems caused by thermal depolarization and thermal effects, thereby effectively reducing depolarization and improving the beam quality of the amplified light. By precisely controlling the amplified power of the secondary single-pass amplification module 4-5 and the tertiary single-pass amplification module 4-7, the best compensation state can be achieved during the thermal depolarization compensation process of the laser. This adjustment helps to optimize the stability and accuracy of the laser output, and increase the proportion of subsequent linearly polarized light, thereby improving the frequency doubling efficiency.

[0027] In this embodiment, the frequency doubling unit 5 includes a frequency doubling crystal 5-1 and a DC motor 5-2. The frequency doubling crystal 5-1 is mounted on the guide rail at the output end of the DC motor 5-2. The frequency doubling crystal 5-1 corresponds to the three-stage single-pass amplification module 4-7. The frequency doubling crystal is mounted on a temperature-controlled furnace, which is mounted on the guide rail. Through the control of the DC motor, a displacement platform capable of moving the frequency doubling crystal is formed to achieve 1064 nm near-infrared output or 532 nm green light output. The amplified 1064nm laser is incident on the LBO crystal, and 532nm frequency doubling laser output is achieved under the phase matching condition. The fundamental frequency light and the frequency doubling light reflected by the color separation mirror are absorbed by the light absorption bucket constructed of aluminum alloy, and the frequency doubling light is output after being transmitted by the color separation mirror. The entire frequency doubling module is placed on a horizontally movable displacement platform to achieve left and right lateral movement, thereby meeting the switching requirements of 1064nm and 532nm in the system. Specifically, the frequency doubling crystal 5-1 is fixed on a motor, which can realize the switching of the frequency doubling crystal 5-1 through precise movement control. Through the precise control of the motor, the position and angle of the crystal are ensured to be in the optimal state to obtain stable and high-quality 532 nm green laser output. By controlling the frequency doubling crystal 5-1 through the movement of the motor, the wavelength of the laser output can be flexibly adjusted to adapt to different experimental needs or application scenarios. In addition, the frequency doubling crystal 5-1 is placed on a temperature-controlled furnace to constantly control the crystal temperature to ensure the efficiency of the energy conversion process and the stability of the laser output, which not only improves the flexibility of the laser system, but also provides a reliable solution for precisely adjusting the laser characteristics.

[0028] In this embodiment, the signal control unit includes a host computer and a phase modulator, the host computer is connected to the phase modulator through a serial port server, the resonant cavity laser side pump module 1-4, the first-stage double-pass amplification module 3-6, the second-stage single-pass amplification module 4-5 and the third-stage single-pass amplification module 4-7 are all connected to the host computer through the serial port server; the phase modulator is connected to the electro-optical Q-switching 1-3, the resonant cavity laser side pump module 1-4 and the second-stage single-pass amplification module, the resonant cavity laser side pump module 1-4 is connected to the first-stage double-pass amplification module 3-6, and the second-stage single-pass amplification module 4-5 is connected to the third-stage single-pass amplification module 4-7. The host computer sends a communication signal, and the phase modulator sends a trigger signal. The communication signals sent by the host computer are respectively transmitted to the power supplies of the phase modulator, the resonant cavity laser side pump module 1-4, the first-stage two-way amplification module 3-6, the second-stage single-way amplification module 4-5 and the third-stage single-way amplification module 4-7. The phase modulator sends a trigger signal which is respectively transmitted to the electro-optical Q switching 1-3, the resonant cavity laser side pump module 1-4 and the second-stage single-way amplification module power supply. After receiving the trigger signal, the resonant cavity laser side pump module 1-4 transmits it to the first-stage two-way amplification module 3-6. After receiving the trigger signal, the second-stage single-way amplification module 4-5 transmits it to the third-stage single-way amplification module 4-7.

[0029] The present invention uses a seed laser source with a wavelength of 1064 nm as the starting laser source, and the parameters of the output laser are: the repetition frequency ranges from 1 Hz to 200 Hz, the single pulse energy is about 10 mJ, and the pulse width is about 11.8 ns. The laser first passes through the beam expansion collimating lens 2-2 unit to expand and collimate the spot of the laser pulse. After that, the laser passes through the isolation device to achieve unidirectional laser output. Then it enters the first-level double-pass amplification module 3-6, where the laser is double-pass amplified, and the final output single pulse energy can reach a maximum of 77 mJ. Then, the laser enters the second-level single-pass amplification module 4-5 after the divergent lens 4-2 expands the beam to further amplify the laser. After this series of amplifications, the laser enters the third-level amplification module through the quartz rotor 4-6 for amplification, and finally achieves 1064 nm laser output with a repetition frequency range of 1 Hz to 200 Hz, a pulse width of about 12 ns, and a single pulse energy reaching or exceeding 320 mJ. Finally, the laser is converted into a wavelength by LBO frequency doubling crystal 5-1, and a laser output with a wavelength of 532 nm is realized, and the output energy is 150 mJ. The frequency doubling crystal 5-1 is mounted on a displacement platform, and the output wavelength of the laser is controlled by adjusting the position of the platform.

[0030] The large energy amplification under short pulses, the frequency doubling efficiency under large energy, and the change of repetition rate lead to the change of thermal focal length of the laser. To solve these problems, a phase modulator is used to adjust the resonant cavity power supply and the electro-optical Q1-3 delay respectively, and the large energy amplification of short pulses is achieved through three-stage amplifier amplification. At the same time, the frequency doubling crystal 5-1 and the frequency doubling structure are optimized, and the phase matching conditions are adjusted to increase the frequency doubling efficiency to more than 50%. In the optical design, the influence of thermal depolarization and thermal focusing is reduced, and the thermal focusing is compensated and the thermal depolarization is suppressed by adding negative lenses and quartz rotors 4-6. Through these measures, the output energy of 1064 nm is ≥320mJ, the pulse width is 12 ns, and the output energy of 532 nm is ≥150mJ. This technical solution is efficient, stable and reliable, and has broad application prospects in the fields of laser striking, optical communications, medical devices, etc. in the future.

[0031] Embodiment 2, a dual-wavelength high-energy nanosecond laser system with adjustable repetition rate comprises Figure 1 Optical path and Figure 2 The circuit is composed of Figure 1As shown, the laser is generated by an electro-optical Q-switched laser, which is composed of a first reflector, a quarter wave plate, an electro-optical Q-switching, a resonant cavity laser side pump module, a pinhole aperture, a first polarizer and a second reflector. The output laser enters the beam expansion and collimation unit composed of a beam expansion lens, a collimating lens and a third reflector to amplify the laser spot. Then it enters the double-pass amplification unit to amplify the laser energy. The system includes an isolation device and a first-stage double-pass amplification device, wherein the isolation device is composed of a second polarizer, a Faraday rotator, a half wave plate and a third polarizer, and the first-stage double-pass amplification device is composed of a first-stage double-pass amplification module, a quarter wave plate and a fifth reflector. The output laser is reflected by the third polarizer and enters the booster-stage amplification unit. Specifically, the laser is first reflected by the fourth polarizer, and then the size of the spot and the divergence angle is adjusted by a plano-concave lens, and then it enters the second-stage single-pass amplification module through the sixth reflector and the seventh reflector for energy amplification, and then the quartz rotor compensates for its thermal depolarization effect, and finally enters the third-stage single-pass amplification module for energy amplification again. The laser after three-stage amplification can output a laser with a wavelength of 532 nm after being frequency-doubled by a frequency-doubling crystal. The frequency-doubling crystal is fixed on a movable base plate controlled by a DC motor. By moving the base plate and controlling the triggering of the electro-optical Q switching, high-energy nanosecond laser output with adjustable repetition rate can be achieved.

[0032] like Figure 2 As shown in the figure, the circuit part of the laser system uses a three-channel phase modulator to trigger and control electro-optical Q-switching and multiple power supplies, where the three channels trigger the electro-optical Q-switching, the resonant cavity power supply and the secondary amplifier power supply respectively, and the primary amplifier power supply and the tertiary amplifier power supply are triggered by the resonant cavity power supply and the secondary amplifier power supply respectively. Compared with the triggering method of traditional lasers, this scheme separates the triggering of electro-optical Q-switching and the resonant cavity power supply, so that the laser power supply can always operate at 200 Hz. At this time, the thermal effect and thermal focal length of the laser remain stable and unchanged. The operating frequency of the laser can be changed by changing the triggering of electro-optical Q-switching, which effectively improves the spot morphology and beam quality under different repetition rates.

[0033] A high-energy nanosecond laser system with dual wavelengths and adjustable repetition rate consists of an electro-optical Q-switched laser, a beam expansion and collimation unit, a double-pass amplification unit, a booster-stage amplification unit and a frequency doubling unit.

[0034] The electro-optical Q-switched laser uses side LD pumping combined with electro-optical Q-switching technology to achieve the oscillation output of high-energy 1064 nm laser. Specifically, the laser consists of a total reflector, a quarter-wave plate, an electro-optical Q-switching, a resonant cavity laser side pump module, a small aperture, a P polarizer and a partial reflector. In order to adjust the working phase delay between the laser LD side pump module and the electro-optical Q-switching, the system is equipped with two phase modulator channels, which output two signals respectively. This adjustment mechanism enables the stimulated radiation to be re-amplified when the population inversion in the cavity reaches the maximum value; at the same time, this adjustment mechanism can keep the side pump LD module running at 200 Hz at all times. By changing the trigger signal of the electro-optical Q-switching, the operating frequency of the laser can be changed, which can effectively control the internal heat problem of the laser. In addition, the cavity length of the laser is determined to be 26 cm by calculation, and the size of the small aperture is finally determined to be 2 mm after adjustment to obtain the best beam quality and output energy. Finally, the laser achieves a giant pulse output with a single pulse energy of 10 mJ and a spot size of 1.8 mm.

[0035] The light beam output by the electro-optical Q-switched laser passes through the rear-end beam expansion and collimation unit. The diameter of the beam increases from the original 1.8 mm to 3.3 mm, and is slightly divergent after beam expansion to achieve maximum amplification efficiency and make the beam output more collimated.

[0036] In the double-pass amplification unit, the light beam also needs to be processed through an isolation device. Although polarizers are used for beam splitting during the double-pass amplification process, in the case of high-power laser amplification, thermal gradients can lead to thermally induced birefringence, causing thermal depolarization of the laser, which may generate return light through the polarizer and cause damage to the front-end equipment. Therefore, a single-pass isolation system consisting of a half-wave plate, two polarizers, and an optical rotator was built to protect the safety of the front-end devices. Subsequently, the seed light was amplified in the first-stage double-pass amplification device, and finally a laser output with a single pulse energy of 77 mJ was achieved.

[0037] In the booster-stage amplification unit, the beam is also expanded before amplification, that is, a plano-concave divergent lens is used to make the light spot smaller than the crystal rod diameter, and the divergence angle is slightly divergent, so as to compensate for the thermal focal length during the secondary amplification process. Subsequently, after passing through the secondary single-pass amplification module, the quartz rotor and the tertiary single-pass amplification module, a laser output of more than 320 mJ is achieved. A quartz rotor is added between the secondary and tertiary amplification modules. This configuration is designed to compensate for the thermal focal length change and beam offset problems caused by thermal depolarization and thermal effects, thereby effectively reducing the depolarization phenomenon and improving the beam quality of the amplified light. By precisely controlling the secondary and tertiary amplification powers, the optimal compensation state can be achieved during the thermal depolarization compensation process of the laser. This adjustment helps to optimize the stability and accuracy of the laser output, and increase the proportion of subsequent linearly polarized light, thereby improving the frequency doubling efficiency.

[0038] Regarding the frequency doubling unit, the amplified 1064nm laser is incident on the LBO crystal, and the 532nm frequency doubling laser output is achieved under the phase matching condition. The fundamental frequency light and the frequency doubling light are reflected by the color separation mirror. The fundamental frequency light is absorbed by the light absorption bucket made of aluminum alloy, and the frequency doubling light is output after being transmitted by the color separation mirror. The entire frequency doubling module is placed on a horizontally movable displacement platform to achieve left and right lateral movement, thereby meeting the switching requirements of 1064nm and 532nm in the system, and then achieving 1064nm or 532nm laser output. Specifically, the frequency doubling crystal is fixed on a motor, which can realize the switching of the frequency doubling crystal through precise movement control. Through the precise control of the motor, the position and angle of the crystal are ensured to be in the optimal state to obtain stable and high-quality 532 nm green laser output. By controlling the frequency doubling crystal through the movement of the motor, the wavelength of the laser output can be flexibly adjusted to adapt to different experimental needs or application scenarios. In addition, the frequency doubling crystal is placed in a temperature-controlled furnace to constantly control the crystal temperature to ensure the efficiency of the energy conversion process and the stability of the laser output. This not only improves the flexibility of the laser system, but also provides a reliable solution for precisely adjusting the laser characteristics.

[0039] In general, the laser system uses a seed laser source with a wavelength of 1064 nm as the starting laser source, and the parameters of its output laser are: the repetition frequency ranges from 1 Hz to 200 Hz, the single pulse energy is about 10 mJ, and the pulse width is about 11.8 ns. The laser first passes through the beam expansion and collimation lens system to expand and collimate the laser pulse spot. After that, the laser passes through the isolation device to achieve unidirectional laser output. Then it enters the first-stage double-pass amplification module, where the laser is double-pass amplified, and the final output single pulse energy can reach up to 77 mJ. Subsequently, the laser enters the second-stage single-pass amplification module after the divergent lens expands the beam to further amplify the laser. After this series of amplifications, the laser enters the third-stage amplification module through the quartz rotor for amplification, and finally achieves 1064nm laser output with a repetition frequency range of 1 Hz to 200 Hz, a pulse width of about 12 ns, and a single pulse energy of 320 mJ or more. Finally, the laser is converted to a wavelength of 532 nm by using an LBO frequency-doubling crystal, and the output energy is 150 mJ. The frequency-doubling crystal is mounted on a displacement platform, and the output wavelength of the laser is controlled by adjusting the position of the platform.

[0040] The large energy amplification under short pulses, the frequency doubling efficiency under large energy, and the change of repetition rate lead to the change of thermal focal length of the laser. To solve these problems, a phase modulator is used to adjust the resonant cavity power supply and electro-optical Q-switching delay respectively, and the large energy amplification of short pulses is achieved through three-stage amplifier amplification. At the same time, the frequency doubling crystal and the frequency doubling structure are optimized, and the phase matching conditions are adjusted to increase the frequency doubling efficiency to more than 50%. In the optical design, the influence of thermal depolarization and thermal focusing is reduced, and the thermal focusing is compensated and the thermal depolarization is suppressed by adding negative lenses and quartz rotors. Through these measures, the output energy of 1064 nm is ≥320mJ, the pulse width is 12 ns, and the output energy of 532 nm is ≥150mJ. This technical solution is efficient, stable and reliable, and has broad application prospects in the fields of laser strike, optical communication, medical equipment, etc. in the future.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A dual-wavelength high-energy nanosecond laser system with adjustable repetition rate, characterized in that: It comprises an electro-optical Q-switched laser (1), a beam expansion and collimation unit (2), a two-way amplification unit (3), a booster stage amplification unit (4) and a frequency doubling unit (5) which are arranged in sequence, and the electro-optical Q-switched laser (1), the two-way amplification unit (3), the booster stage amplification unit (4) and the frequency doubling unit (5) are all connected to a signal control unit; Laser light emitted from an electro-optical Q-switched laser (1) enters a beam expansion and collimation unit (2) for beam expansion and collimation, and then sequentially enters a double-pass amplification unit (3) and a booster-stage amplification unit (4). After being amplified by the double-pass amplification unit (3) and the booster-stage amplification unit (4), the laser light enters a frequency doubling unit (5), and outputs high-energy nanosecond laser light of two wavelengths through the frequency doubling unit (5).

2. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 1 is characterized in that: The electro-optical Q-switched laser (1) comprises a resonant cavity laser side pump module (1-4) and an electro-optical Q-switch (1-3) which are arranged in sequence; the electro-optical Q-switch (1-3) and the resonant cavity laser side pump module (1-4) are coaxially arranged; a quarter wave plate (1-2) and a first reflector (1-1) are arranged in sequence on one side optical path of the electro-optical Q-switch (1-3); and a resonant cavity laser side pump module (1-4), a pinhole aperture (1-5), a first polarizer (1-6) and a second reflector (1-7) are arranged in sequence on the other side optical path of the electro-optical Q-switch (1-3); Photons spontaneously radiated by the resonant cavity laser side pump module oscillate between the electro-optical Q switch (1-3), the quarter wave plate 1 (1-2), the first reflector (1-1), the pinhole aperture (1-5) and the first polarizer (1-6) to form laser light, which is then emitted from the second reflector (1-7).

3. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 2, characterized in that: The beam expansion and collimation unit (2) comprises a beam expansion lens (2-1) corresponding to the second reflector (1-7), and a collimating lens (2-2) is provided at the output end of the beam expansion lens (2-1).

4. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 3 is characterized in that: The beam expansion and collimation unit (2) further comprises a third reflector (2-3), and the laser light outputted by the collimating lens (2-2) is directed by the third reflector (2-3) and then incident on the double-pass amplification unit (3).

5. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 4 is characterized in that: The double-pass amplification unit (3) comprises an isolation device and a first-stage double-pass amplification module (3-6), the isolation device and the first-stage double-pass amplification module (3-6) are coaxially arranged, the isolation device comprises a second polarizer (3-2), a Faraday rotator (3-3), a half-wave plate (3-4) and a third polarizer (3-5) arranged in sequence, and the second polarizer (3-2), the Faraday rotator (3-3), the half-wave plate (3-4) and the third polarizer (3-5) are coaxially arranged, one side of the first-stage double-pass amplification module (3-6) corresponds to the third polarizer (3-5), and the other side of the first-stage double-pass amplification module (3-6) is provided with a second quarter-wave plate (3-7) and a fifth reflector (3-8); The laser light incident from the third reflector (2-3) is incident on the second polarizer (3-2), the Faraday rotator (3-3), the half wave plate (3-4), the third polarizer (3-5), the first double-pass amplification module (3-6), the second quarter wave plate (3-7), and the fifth reflector (3-8) in sequence, and is then incident on the second quarter wave plate (3-7), the first double-pass amplification module (3-6), and the second polarizer (3-2) through the fifth reflector (3-8), and finally is incident on the third polarizer (3-5).

6. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 5, characterized in that: The double-pass amplification module is also provided with a fourth reflector (3-1) for changing the direction of the light path; the light source input end of the fourth reflector (3-1) corresponds to the third reflector (2-3); and the light source output end of the fourth reflector (3-1) corresponds to the second polarizer (3-2).

7. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 5 or 6, characterized in that: The booster-stage amplification unit (4) comprises a secondary one-way amplification module (4-5) and a tertiary one-way amplification module (4-7) which are arranged in sequence, a quartz rotor (4-6) for compensating for thermal depolarization is arranged between the secondary one-way amplification module (4-5) and the tertiary one-way amplification module (4-7), and a fourth polarizer (4-1) and a divergent lens (4-2) are arranged in sequence at the laser incident end of the secondary one-way amplification module (4-5); The laser light emitted from the third polarizer (3-5) passes through the fourth polarizer (4-1) and the diverging lens (4-2) in sequence, and then is emitted to the secondary one-way amplification module (4-5) and the tertiary one-way amplification module (4-7), and then is emitted through the tertiary one-way amplification module (4-7).

8. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 7, characterized in that: The booster-stage amplification unit (4) further comprises a sixth reflector (4-3) and a seventh reflector (4-4) for changing the direction of the light path; the light source input end of the sixth reflector (4-3) corresponds to the divergent lens (4-2); the light source output end of the sixth reflector (4-3) corresponds to the light source input end of the seventh reflector (4-4); and the light source output end of the seventh reflector (4-4) corresponds to the light source input end of the secondary single-pass amplification module (4-5).

9. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to claim 8, characterized in that: The frequency doubling unit (5) comprises a frequency doubling crystal (5-1) and a DC motor (5-2); the frequency doubling crystal (5-1) is mounted on a guide rail at the output end of the DC motor (5-2); the frequency doubling crystal (5-1) corresponds to a three-stage single-pass amplification module (4-7).

10. The dual-wavelength high-energy nanosecond laser system with adjustable repetition rate according to any one of claims 1 to 6, 8 or 9, characterized in that: The signal control unit comprises a host computer and a phase modulator, the host computer is connected to the phase modulator via a serial port server, and the resonant cavity laser side pump module (1-4), the first-stage double-pass amplification module (3-6), the second-stage single-pass amplification module (4-5) and the third-stage single-pass amplification module (4-7) are all connected to the host computer via the serial port server; The electro-optical Q-switching (1-3), the resonant cavity laser side pump module (1-4) and the secondary single-pass amplification module are all connected to the phase modulator, the resonant cavity laser side pump module (1-4) is connected to the primary double-pass amplification module (3-6), and the secondary single-pass amplification module (4-5) is connected to the tertiary single-pass amplification module (4-7).

Images