High-beam-quality and high-power picosecond ultraviolet laser

Abstract

The invention provides a high-beam-quality and high-power picosecond ultraviolet laser, and relates to the technical field of lasers, the high-beam-quality and high-power picosecond ultraviolet laser comprises a fundamental frequency light source module, an optical fiber power amplification module, a frequency conversion module and a beam quality control module, the fundamental frequency light source module is used for generating stable fundamental frequency pulse light; the optical fiber power amplification module is used for acquiring high-power fundamental frequency pulse light; the frequency conversion module and the light beam quality control module are used for sequentially performing frequency doubling and sum frequency conversion on the high-power fundamental frequency pulse light, and performing color separation and collimation on the high-power fundamental frequency pulse, the 532nm pulse light and the ultraviolet pulse light, so that the frequency conversion module only outputs the ultraviolet pulse light; and the light beam quality control module is used for receiving the ultraviolet pulse light emitted by the frequency conversion module and carrying out wavefront detection and phase compensation on the ultraviolet pulse light so as to shape the ultraviolet pulse light. According to the invention, the output power and the conversion efficiency of the ultraviolet section can be improved.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more particularly to a high beam quality, high power picosecond ultraviolet laser. Background Technology

[0002] Picosecond ultraviolet lasers, with their core advantages such as ultra-high precision machining, wide material adaptability, low thermal damage and high edge quality, multiphoton absorption effect, and high repetition rate and efficiency, are widely used in precision industrial processing, medical and biotechnology, additive manufacturing and micromachining, scientific research, and other fields. Beam quality, as a crucial parameter of a laser, largely determines its overall performance. Especially in fields such as semiconductors and medicine, beam quality is even more prioritized than power and pulse width.

[0003] Chinese Patent CN114552344B discloses a high-energy, high-beam-quality fiber-solid hybrid picosecond laser amplifier. This laser amplifier includes an all-fiber seed source, a solid-state regenerative amplifier, a spatial optical isolation system, beam shaping, a solid-state end-pumped single-pass amplifier, and a solid-state side-pumped dual-rod cascaded double-pass amplifier arranged sequentially along the optical path. While the above approach increases peak power through the solid segment, it is prone to introducing self-phase modulation, leading to spectral broadening and consequently increasing phase mismatch and ultraviolet beam quality degradation during frequency doubling. Therefore, it is essential to provide a high-beam-quality, high-power picosecond ultraviolet laser to improve ultraviolet output power and conversion efficiency. Summary of the Invention

[0004] In view of this, the present invention proposes a high beam quality, high power picosecond ultraviolet laser.

[0005] This invention provides a high-beam-quality, high-power picosecond ultraviolet laser, comprising a fundamental frequency source module, an fiber power amplification module, a frequency conversion module, and a beam quality control module, wherein... The fundamental frequency light source module is connected to the fiber optic power amplifier module, and the fundamental frequency light source module is used to generate stable fundamental frequency pulse light; The fiber optic power amplifier module is coupled to the frequency conversion module, and the fiber optic power amplifier module is used to cascade amplify the fundamental frequency pulse light to obtain high-power fundamental frequency pulse light; The frequency conversion module is coupled to the beam quality control module. The frequency conversion module is used to sequentially perform second harmonic and sum-frequency conversion on the high-power fundamental frequency pulse light to obtain second harmonic pulse light and ultraviolet pulse light. By performing color separation and collimation on the high-power fundamental frequency pulse, the second harmonic pulse light and the ultraviolet pulse light, the frequency conversion module outputs only the ultraviolet pulse light. The beam quality control module is used to receive the ultraviolet pulse light emitted by the frequency conversion module, and to perform wavefront detection and phase compensation on the ultraviolet pulse light to shape the ultraviolet pulse light.

[0006] Based on the above technical solutions, preferably, the fundamental frequency light source module includes a semiconductor saturable absorber mirror, a wavelength division multiplexer, a semiconductor single-mode pump laser, a first polarization-maintaining fiber, a chirped fiber Bragg grating, and a first polarization-maintaining fiber isolator connected in sequence. The output end of the wavelength division multiplexer is coupled to the semiconductor saturable absorber mirror, the first input end of the wavelength division multiplexer is connected to the semiconductor single-mode pump laser, the second input end of the wavelength division multiplexer is connected to one end of the chirped fiber Bragg grating through the first polarization-maintaining fiber, and the first polarization-maintaining fiber isolator is connected to the other end of the chirped fiber Bragg grating and the fiber power amplifier module.

[0007] Based on the above technical solutions, preferably, the fiber optic power amplification module includes a first power amplification unit and a second power amplification unit, wherein the first power amplification unit is connected to the baseband light source module and the second power amplification unit respectively, and the second power amplification unit is coupled to the frequency conversion module.

[0008] More preferably, the first power amplification unit includes a first signal pump combiner, a first multimode semiconductor pump laser, a second polarization-maintaining fiber, and a second polarization-maintaining fiber isolator. The first input end of the first signal pump combiner is connected to the fundamental frequency light source module, the second input end of the first signal pump combiner is connected to the first multimode semiconductor pump laser, the output end of the first signal pump combiner is connected to one end of the second polarization-maintaining fiber isolator through the second polarization-maintaining fiber, and the other end of the second polarization-maintaining fiber isolator is connected to the second power amplification unit.

[0009] More preferably, the second power amplification unit includes a mode field adapter, a second signal pump combiner, a second multimode semiconductor pump laser, a third polarization-maintaining fiber, a cladding power stripper, and a fiber collimator. One end of the mode field adapter is connected to the first power amplification unit, and the other end of the mode field adapter is connected to the first input end of the second signal pump combiner. The second input end of the second signal pump combiner is connected to the second multimode semiconductor pump laser. The output end of the second signal pump combiner is connected to the cladding power stripper through the third polarization-maintaining fiber. One end of the fiber collimator is connected to the cladding power stripper, and the other end of the fiber collimator is coupled to the frequency conversion module.

[0010] More preferably, the frequency conversion module includes a first focusing lens, a second-harmonic crystal, a second focusing lens, a third-harmonic crystal, a first dichroic mirror, a second dichroic mirror, and a collimating lens. The first focusing lens, the second-harmonic crystal, the third-harmonic crystal, and the first dichroic mirror are located on the same optical axis, and the second dichroic mirror and the collimating lens are located on the same optical axis.

[0011] More preferably, the principal plane of the second harmonic crystal is the XY plane, the crystal angle of the second harmonic crystal is θ=90°, and φ=0°, the principal plane of the third harmonic crystal is the YZ plane, and the crystal angle of the third harmonic crystal is θ=45° and φ=90°.

[0012] More preferably, the incident and exit surfaces of the second harmonic crystal are coated with antireflection films in the 1064nm and 532nm bands, and the incident and exit surfaces of the third harmonic crystal are coated with antireflection films in the 1064nm, 532nm and 355nm bands.

[0013] More preferably, both the second harmonic crystal and the third harmonic crystal are LBO crystals.

[0014] More preferably, the first polarization-maintaining fiber is a single-clad ytterbium-doped fiber, the second polarization-maintaining fiber is a 10 / 125 polarization-maintaining double-clad ytterbium-doped fiber, and the third polarization-maintaining fiber is a 25 / 250 polarization-maintaining double-clad ytterbium-doped fiber.

[0015] The high beam quality, high power picosecond ultraviolet laser provided by this invention has the following advantages over existing technologies: The fundamental frequency light source module stabilizes the output phase and energy, providing stable incident conditions for nonlinear frequency conversion. Cascaded fiber power amplification followed by sequential second harmonic and sum-frequency conversion significantly improves the output power and conversion efficiency in the ultraviolet band. Cascaded amplification increases pulse energy while maintaining mode quality, keeping pulse morphology and spectrum controllable. The sequential conversion path of second harmonic and sum-frequency conversion reduces the impact of group velocity mismatch and phase mismatch on efficiency. Under good wavefront and mode quality conditions, the coupling efficiency and stability of the nonlinear process are improved. The beam quality control module performs real-time wavefront detection and phase compensation for the ultraviolet pulse light, effectively suppressing aberrations introduced by amplification, harmonics, and thermal effects, making the beam approximately diffraction-limited, and allowing for repeated acquisition of small focal spots and high peak intensity.

[0016] Using LBO as the second and third harmonic crystals, and selecting appropriate orientations for the second and third harmonic crystals respectively, efficient phase matching and low group velocity mismatch were achieved in the target band. At the same time, the beam waist and effective nonlinear coefficient under critical phase matching were optimized, which improved the conversion efficiency and stability of the second and sum frequencies. In addition, LBO has the material advantages of high damage threshold, low absorption and good thermal conductivity. Under this orientation, thermally induced phase mismatch and thermal lensing effect are more easily controlled, which is beneficial to high average power, long-term operation pointing and energy stability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a high beam quality, high power picosecond ultraviolet laser provided by the present invention.

[0019] Figure reference numerals: 1. Fundamental frequency light source module; 11. Semiconductor saturable absorber mirror; 12. Wavelength division multiplexer; 13. Semiconductor single-mode pumped laser; 14. First polarization-maintaining fiber; 15. Chirped fiber Bragg grating; 16. First polarization-maintaining fiber isolator; 2. Fiber power amplifier module; 21. First power amplifier unit; 211. First signal pump combiner; 212. First multimode semiconductor pumped laser; 213. Second polarization-maintaining fiber; 214. Second polarization-maintaining fiber isolator; 2 2. Second power amplifier unit; 221. Mode field adapter; 222. Second signal pump combiner; 223. Second multimode semiconductor pump laser; 224. Third polarization-maintaining fiber; 225. Cladding power stripper; 226. Fiber collimator; 3. Frequency conversion module; 31. First focusing lens; 32. Second frequency harmonic crystal; 33. Second focusing lens; 34. Third frequency harmonic crystal; 35. First dichroic mirror; 36. Second dichroic mirror; 37. Collimating lens; 4. Beam quality control module. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1This invention provides a polarization-tunable green laser, comprising a fundamental frequency source module 1, an optical fiber power amplification module 2, a frequency conversion module 3, and a beam quality control module 4, wherein... The fundamental frequency light source module 1 is connected to the fiber power amplifier module 2. The fundamental frequency light source module 1 is used to generate stable fundamental frequency pulsed light. The fundamental frequency light source module 1 includes a semiconductor saturable absorber mirror 11, a wavelength division multiplexer 12, a semiconductor single-mode pump laser 13, a first polarization-maintaining fiber 14, a chirped fiber Bragg grating 15, and a first polarization-maintaining fiber isolator 16 connected in sequence. The output end of the wavelength division multiplexer 12 is coupled to the semiconductor saturable absorber mirror 11. The first input end of the wavelength division multiplexer 12 is connected to the semiconductor single-mode pump laser 13. The second input end of the wavelength division multiplexer 12 is connected to one end of the chirped fiber Bragg grating 15 through the first polarization-maintaining fiber 14. The first polarization-maintaining fiber isolator 16 is connected to the other end of the chirped fiber Bragg grating 15 and the fiber power amplifier module 2.

[0022] In this embodiment, a single-mode pump laser in the fundamental frequency light source module 1 is injected into the polarization-maintaining fiber cavity through a wavelength division multiplexer 12. Passive mode-locking is achieved in conjunction with a semiconductor saturable absorber mirror 11 (SESAM) to generate a stable short-pulse fundamental frequency seed. A chirped fiber Bragg grating 15 (CFBG) manages the pulse dispersion and chirp to optimize the time and frequency domain characteristics. The end polarization-maintaining fiber isolator provides unidirectional operation, suppresses backlash and self-oscillation, thereby outputting a polarization-stable fundamental frequency pulse signal.

[0023] The fiber optic power amplifier module 2 is coupled to the frequency conversion module 3. The fiber optic power amplifier module 2 is used to cascade amplify the fundamental frequency pulse light to obtain high-power fundamental frequency pulse light. The fiber optic power amplifier module 2 includes a first power amplifier unit 21 and a second power amplifier unit 22. The first power amplifier unit 21 is connected to the fundamental frequency light source module 1 and the second power amplifier unit 22, respectively. The second power amplifier unit 22 is coupled to the frequency conversion module 3.

[0024] The first power amplifier unit 21 includes a first signal pump combiner 211, a first multimode semiconductor pump laser 212, a second polarization-maintaining fiber 213, and a second polarization-maintaining fiber isolator 214. The first input terminal of the first signal pump combiner 211 is connected to the fundamental frequency light source module 1, the second input terminal of the first signal pump combiner 211 is connected to the first multimode semiconductor pump laser 212, the output terminal of the first signal pump combiner 211 is connected to one end of the second polarization-maintaining fiber isolator 214 through the second polarization-maintaining fiber 213, and the other end of the second polarization-maintaining fiber isolator 214 is connected to the second power amplifier unit 22.

[0025] In this embodiment, the first power amplification unit 21 adopts a cascaded structure of a first signal pump combiner 211, a multimode semiconductor pump, a second polarization-maintaining fiber 213, and a second polarization-maintaining fiber isolator 214 to achieve efficient combining of the pump and signal and low insertion loss amplification. The front-end obtains high gain to improve the signal-to-noise ratio and suppress ASE. At the same time, full polarization-maintaining transmission ensures high PER linear polarization and stable mode quality, directly improving the nonlinear conversion efficiency and consistency of subsequent frequency doubling. Interstage isolation effectively blocks backlight, avoiding parasitic oscillations and cavity length disturbances and protecting the pump and combiner, enhancing system reliability. The graded gain and polarization maintenance together improve the SBS threshold, reduce the accumulation of nonlinearities such as SPM and stimulated Raman, reduce spectral broadening and time-domain distortion, and maintain excellent wavefront and pointing stability, thereby providing high-power, high-SNR, and high-PER high-quality input for subsequent amplification, significantly improving the efficiency, stability, and long-term robustness of the final ultraviolet output.

[0026] The second power amplification unit 22 includes a mode field adapter 221, a second signal pump combiner 222, a second multimode semiconductor pump laser 223, a third polarization-maintaining fiber 224, a cladding power stripper 225, and an fiber collimator 226. One end of the mode field adapter 221 is connected to the first power amplification unit 21, and the other end of the mode field adapter 221 is connected to the first input end of the second signal pump combiner 222. The second input end of the second signal pump combiner 222 is connected to the second multimode semiconductor pump laser 223. The output end of the second signal pump combiner 222 is connected to the cladding power stripper 225 through the third polarization-maintaining fiber 224. One end of the fiber collimator 226 is connected to the cladding power stripper 225, and the other end of the fiber collimator 226 is coupled to the frequency conversion module 3. The first polarization-maintaining fiber 14 is a single-clad ytterbium-doped fiber, the second polarization-maintaining fiber 213 is a 10 / 125 polarization-maintaining double-clad ytterbium-doped fiber, and the third polarization-maintaining fiber 224 is a 25 / 250 polarization-maintaining double-clad ytterbium-doped fiber.

[0027] In this embodiment, the second power amplification unit 22 achieves high-power, low-distortion amplification oriented towards frequency doubling output through device cascading. The second signal pump combiner 222 is efficiently coupled with the high-power multimode pump to achieve high-power gain extension of the cladding pump. At the same time, the third polarization-maintaining fiber 224 provides a higher SBS threshold and thermal carrying capacity, supporting higher average power, peak power, and longer operating stability. Through the link design of progressively increasing fiber diameter, mode quality and power scalability are balanced, and high PER linear polarization is maintained to improve the effective nonlinear coefficient utilization of subsequent SHG / SFG. The cladding power stripper 225 efficiently removes residual pump and cladding stray light, suppresses heat accumulation and parasitic oscillations, and improves the safety and reliability of the laser. The fiber collimator 226 stably collimates the high-power output and is optimally matched with the frequency conversion module 3 to ensure beam pointing and wavefront quality, and reduce coupling loss and thermal aberration. The overall effect is high-efficiency high-power amplification, controlled nonlinearity and thermal effects, stable polarization and mode quality, improved frequency conversion coupling efficiency, and long-term robust operation.

[0028] In this implementation, the fiber power amplifier module 2 employs a two-stage polarization-maintaining doped fiber amplification. The first stage uses a multimode semiconductor pump to couple the signal into the active polarization-maintaining fiber in a combiner for pre-amplification, and an isolator suppresses reflection. The second stage introduces a higher-power pump after mode field adaptation to complete the main amplification. At the same time, a cladding power stripper 225 removes residual pump and thermal load. Finally, a fiber collimator 226 converts the high-power signal into a free-space collimated beam, ensuring high efficiency and polarization maintenance.

[0029] The frequency conversion module 3 is coupled to the beam quality control module 4. The frequency conversion module 3 is used to sequentially perform second harmonic and sum-frequency conversion on the high-power fundamental frequency pulse light to obtain second harmonic pulse light and ultraviolet pulse light. By performing dichroism separation and collimation on the high-power fundamental frequency pulse light, second harmonic pulse light, and ultraviolet pulse light, the frequency conversion module 3 outputs only ultraviolet pulse light. The frequency conversion module 3 includes a first focusing lens 31, a second harmonic crystal 32, a second focusing lens 33, a third harmonic crystal 34, a first dichroic mirror 35, a second dichroic mirror 36, and a collimating lens 37. The first focusing lens 31, the second harmonic crystal 32, the second focusing lens 33, the third harmonic crystal 34, and the first dichroic mirror 35 are located on the same optical axis, and the second dichroic mirror 36 and the collimating lens 37 are located on the same optical axis.

[0030] The coupling scheme between the frequency conversion module 3 and the beam quality control module 4 achieves efficient cascade conversion of the second harmonic and sum-frequency of high-power picosecond pulses through a coaxial linear two-segment optical axis layout. The second harmonic pulse light and the fundamental frequency are highly coincident in time and space to improve the coupling efficiency of the third harmonic, thus maintaining high conversion efficiency and low thermal aberration at high average power. The dichroic mirror separates the unconverted fundamental frequency and second harmonic components and suppresses parasitic nonlinear processes. The collimating lens 37 at the end outputs a stable-pointing and spectrally pure ultraviolet pulse, which is convenient for efficient coupling with the downstream beam quality control module 4 to implement wavefront detection and phase compensation, ultimately obtaining an output containing only the ultraviolet spectrum.

[0031] In this embodiment, both the second-harmonic crystal 32 and the third-harmonic crystal 34 are LBO crystals. The principal plane of the second-harmonic crystal 32 is the XY plane, and the crystal angles of the second-harmonic crystal 32 are θ=90° and φ=0°. The principal plane of the third-harmonic crystal 34 is the YZ plane, and the crystal angles of the third-harmonic crystal 34 are θ=45° and φ=90°. Furthermore, the output end face of the third-harmonic crystal 34 has no Brewster angle, thereby reducing the walk-off effect and decreasing the ellipticity of the output ultraviolet laser beam. The incident and exit surfaces of the second-harmonic crystal 32 are coated with antireflection films in the 1064nm and 532nm wavelength bands, respectively, while the incident and exit surfaces of the third-harmonic crystal 34 are coated with antireflection films in the 1064nm, 532nm, and 355nm wavelength bands, respectively.

[0032] Using LBO as the second and third harmonic crystals 34, and selecting the orientations of the second and third harmonic crystals 34 respectively, efficient phase matching and low group velocity mismatch are achieved in the target band. At the same time, the beam waist and effective nonlinear coefficient under critical phase matching are optimized, which improves the conversion efficiency and stability of the second harmonic and sum frequency. In particular, the Brewster angle design is eliminated at the output end face of the third harmonic crystal 34, which significantly reduces polarization-dependent walk-off and spatial walk-off caused by oblique incidence. Combined with the above orientation, birefringence walk-off and angular walk-off in the crystal are suppressed, thereby effectively reducing the ellipticity of the ultraviolet output spot and improving the circular symmetry of the beam spot. At the same time, LBO has the material advantages of high damage threshold, low absorption and good thermal conductivity. Under this orientation, thermal phase mismatch and thermal lensing effect are more easily controlled, which is conducive to high average power, long-term operation, pointing and energy stability.

[0033] Furthermore, the pulsed light after fiber collimation in frequency conversion module 3 is focused by the first lens into the second harmonic crystal 32 to generate the second harmonic. Then, the second lens focuses the fundamental frequency and the second harmonic together onto the third harmonic crystal 34 to perform the sum-frequency process and obtain the third harmonic. Subsequently, two dichroic mirrors are used to separate and purify the ω, 2ω, and 3ω components according to wavelength. Finally, the collimating lens 37 shapes the desired frequency-doubled output beam.

[0034] The beam quality control module 4 receives the ultraviolet pulse light emitted from the frequency conversion module 3 and performs wavefront detection and phase compensation to shape the ultraviolet pulse light. The high beam quality of the picosecond ultraviolet laser output is achieved by a 355nm spatial light modulator. By real-time detection of the phase distribution of the ultraviolet laser and using algorithms such as deep learning to transform the phase distribution loaded on the spatial light modulator, the beam quality of the ultraviolet laser is controlled, thus achieving high beam quality picosecond ultraviolet laser output.

[0035] In one example, the fundamental frequency light source module 1 consists of a semiconductor saturable absorber mirror 11, a wavelength division multiplexer 12, a semiconductor single-mode pump laser 13, a first polarization-maintaining fiber 14, a chirped fiber Bragg grating 15, and a first polarization-maintaining fiber isolator 16. The wavelength division multiplexer 12 is forward-pumped and contains 1% tap at the signal end. This device is entirely made of PM980 fiber. The first polarization-maintaining fiber 14 is an active single-clad ytterbium-doped fiber with a core diameter of 6 μm, a cladding diameter of 125 μm, a mode field diameter of approximately 7.5 μm, and a core numerical aperture (NA) of 0.11. All of the above devices are connected by fiber fusion splicing.

[0036] The first power amplification unit 21 in the fiber optic power amplification module 2 consists of a first signal pump combiner 211, a 9W semiconductor multimode pump laser, a second polarization-maintaining fiber 213, and a second polarization-maintaining fiber isolator 214. The first signal pump combiner 211 is of type 2+1×1, and the signal end and common end pigtails of the first signal pump combiner 211 are passive double-clad optical fibers. The core diameter of the first signal pump combiner 211 is 10μm, and the inner cladding diameter is 125μm. The pump end pigtail of the first signal pump combiner 211 is a multimode fiber with a core diameter of 105 μm, a cladding diameter of 125 μm, and a core numerical aperture of 0.22. The second polarization-maintaining fiber 213 is an active double-clad YDF with a core diameter of 10 μm, an inner cladding diameter of 125 μm, a core numerical aperture of 0.08, and a fiber length of 2 m. The fiber of the second polarization-maintaining fiber isolator 214 is a PM980 fiber. All of the above devices are connected by fiber fusion splicing.

[0037] The second power amplification unit 22 in the fiber optic power amplification module 2 consists of a mode field adapter 221, a second signal pump combiner 222, a 130W second multimode semiconductor pump laser 223, a third polarization-maintaining fiber 224, a cladding power stripper 225, and a fiber collimator 226. The mode field adapter 221 is drawn from PLMA-GDF-10 / 125-M and PLMA-GDF-25 / 250-M optical fibers. The second signal pump combiner 222 is a 2+1×1 type, and the signal and common ends of the second signal pump combiner 222 are passive double-clad optical fibers. The first pump combiner 222 has a core diameter of 25 μm and an inner cladding diameter of 250 μm. Its pump end pigtail is a multimode fiber with a core diameter of 105 μm, a cladding diameter of 125 μm, and a core numerical aperture of 0.22. The third polarization-maintaining fiber 224 is an active double-clad YDF with a core diameter of 25 μm, an inner cladding diameter of 250 μm, a core numerical aperture of 0.075, and a fiber length of 2 m. The pigtails of the cladding power stripper 225 and the fiber collimator 226 are both passive double-clad fibers with a core diameter of 25 μm and an inner cladding diameter of 250 μm. All of the above devices are connected by fiber fusion splicing.

[0038] The frequency conversion module 3 consists of a first focusing lens 31, a second-harmonic crystal 32 and its heating furnace, a second focusing lens 33, a third-harmonic crystal 34 and its heating furnace, a first dichroic mirror 35 and a 355nm collimating lens 37. The temperature of the second-harmonic heating furnace, the length, position and angle of the second-harmonic crystal are optimized by the green light power. The temperature of the third-harmonic heating furnace, the length, position and angle of the third-harmonic crystal 34 are optimized by the 355nm laser power. The focal length of the first focusing lens 31 is determined by the green light power. The focal lengths of the second focusing lens 33 and the 355nm collimating lens 37 are determined by the power and spot size of the 355nm laser.

[0039] The beam quality control module 4 is a 355nm beam quality control optical path, which consists of a 355nm spatial light modulator. By detecting the phase distribution of the ultraviolet laser in real time, it uses algorithms such as deep learning to transform the phase distribution loaded on the spatial light modulator in real time, thereby achieving beam quality control of the ultraviolet laser and realizing high beam quality picosecond ultraviolet laser output.

[0040] In this embodiment, the fundamental frequency light source module 1 stabilizes the output phase and energy, providing stable incident conditions for nonlinear frequency conversion. Cascaded fiber power amplification and sequential second harmonic and sum-frequency conversion significantly improve the output power and conversion efficiency in the ultraviolet band. Cascaded amplification increases pulse energy while maintaining mode quality, keeping pulse morphology and spectrum controllable. Simultaneously, the sequential conversion path of second harmonic and sum-frequency conversion reduces the impact of group velocity mismatch and phase mismatch on efficiency. Under good wavefront and mode quality conditions, the coupling efficiency and stability of the nonlinear process are improved. Color separation and collimation reduce crosstalk and thermal load accumulation. The beam quality control module 4 performs real-time wavefront detection and phase compensation for the ultraviolet pulse light, effectively suppressing aberrations introduced by amplification, harmonics, and thermal effects, making the beam approximately diffraction-limited, and allowing for repeated acquisition of small focal spots and high peak intensity.

[0041] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "connected" or "linked" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0042] 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 principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-beam-quality, high-power picosecond ultraviolet laser, characterized in that, It includes a fundamental frequency light source module (1), an optical fiber power amplification module (2), a frequency conversion module (3), and a beam quality control module (4), wherein, The baseband light source module (1) is connected to the fiber power amplifier module (2), and the baseband light source module (1) is used to generate stable baseband pulse light; The fiber power amplifier module (2) is coupled to the frequency conversion module (3). The fiber power amplifier module (2) is used to cascade amplify the fundamental frequency pulse light to obtain high-power fundamental frequency pulse light. The frequency conversion module (3) is coupled to the beam quality control module (4). The frequency conversion module (3) is used to sequentially perform second harmonic and sum-frequency conversion on the high-power fundamental frequency pulse light to obtain second harmonic pulse light and ultraviolet pulse light. By performing color separation and collimation on the high-power fundamental frequency pulse, the second harmonic pulse light and the ultraviolet pulse light, the frequency conversion module (3) outputs only the ultraviolet pulse light. The beam quality control module (4) is used to receive the ultraviolet pulse light emitted by the frequency conversion module (3) and perform wavefront detection and phase compensation on the ultraviolet pulse light to shape the ultraviolet pulse light.

2. The high beam quality, high power picosecond ultraviolet laser as described in claim 1, characterized in that, The fundamental frequency light source module (1) includes a semiconductor saturable absorber mirror (11), a wavelength division multiplexer (12), a semiconductor single-mode pump laser (13), a first polarization-maintaining fiber (14), a chirped fiber Bragg grating (15), and a first polarization-maintaining fiber isolator (16) connected in sequence. The output end of the wavelength division multiplexer (12) is coupled to the semiconductor saturable absorber mirror (11). The first input end of the wavelength division multiplexer (12) is connected to the semiconductor single-mode pump laser (13). The second input end of the wavelength division multiplexer (12) is connected to one end of the chirped fiber Bragg grating (15) through the first polarization-maintaining fiber (14). The first polarization-maintaining fiber isolator (16) is connected to the other end of the chirped fiber Bragg grating (15) and the fiber power amplifier module (2).

3. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 2, characterized in that, The fiber optic power amplifier module (2) includes a first power amplifier unit (21) and a second power amplifier unit (22). The first power amplifier unit (21) is connected to the baseband light source module (1) and the second power amplifier unit (22) respectively, and the second power amplifier unit (22) is coupled to the frequency conversion module (3).

4. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 3, characterized in that, The first power amplification unit (21) includes a first signal pump combiner (211), a first multimode semiconductor pump laser (212), a second polarization-maintaining fiber (213), and a second polarization-maintaining fiber isolator (214). The first input end of the first signal pump combiner (211) is connected to the fundamental frequency light source module (1), the second input end of the first signal pump combiner (211) is connected to the first multimode semiconductor pump laser (212), the output end of the first signal pump combiner (211) is connected to one end of the second polarization-maintaining fiber isolator (214) through the second polarization-maintaining fiber (213), and the other end of the second polarization-maintaining fiber isolator (214) is connected to the second power amplification unit (22).

5. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 4, characterized in that, The second power amplification unit (22) includes a mode field adapter (221), a second signal pump combiner (222), a second multimode semiconductor pump laser (223), a third polarization-maintaining fiber (224), a cladding power stripper (225), and a fiber collimator (226). One end of the mode field adapter (221) is connected to the first power amplification unit (21), and the other end of the mode field adapter (221) is connected to the first input end of the second signal pump combiner (222). The second input end of the second signal pump combiner (222) is connected to the second multimode semiconductor pump laser (223). The output end of the second signal pump combiner (222) is connected to the cladding power stripper (225) through the third polarization-maintaining fiber (224). One end of the fiber collimator (226) is connected to the cladding power stripper (225), and the other end of the fiber collimator (226) is coupled to the frequency conversion module (3).

6. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 1, characterized in that, The frequency conversion module (3) includes a first focusing lens (31), a second-harmonic crystal (32), a second focusing lens (33), a third-harmonic crystal (34), a first dichroic mirror (35), a second dichroic mirror (36), and a collimating lens (37). The first focusing lens (31), the second-harmonic crystal (32), the second focusing lens (33), the third-harmonic crystal (34), and the first dichroic mirror (35) are located on the same optical axis, and the second dichroic mirror (36) and the collimating lens (37) are located on the same optical axis.

7. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 6, characterized in that, The principal plane of the second harmonic crystal (32) is the XY plane, and the crystal angles of the second harmonic crystal (32) are θ=90° and φ=0°. The principal plane of the third harmonic crystal (34) is the YZ plane, and the crystal angles of the third harmonic crystal (34) are θ=45° and φ=90°.

8. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 6, characterized in that, The incident and exit surfaces of the second harmonic crystal (32) are coated with antireflection films in the 1064nm and 532nm bands, and the incident and exit surfaces of the third harmonic crystal (34) are coated with antireflection films in the 1064nm, 532nm and 355nm bands.

9. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 6, characterized in that, Both the second harmonic crystal (32) and the third harmonic crystal (34) are LBO crystals.

10. A high-beam-quality, high-power picosecond ultraviolet laser as described in claim 5, characterized in that, The first polarization-maintaining fiber (14) is a single-clad ytterbium-doped fiber, the second polarization-maintaining fiber (213) is a 10 / 125 polarization-maintaining double-clad ytterbium-doped fiber, and the third polarization-maintaining fiber (224) is a 25 / 250 polarization-maintaining double-clad ytterbium-doped fiber.

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