Miniaturized high-efficiency frequency-stabilized 355nm ultraviolet pulse laser

Abstract

The invention discloses a miniaturized high-efficiency frequency-stabilized 355nm ultraviolet pulse laser, and belongs to the technical field of lasers. Comprising a seed laser module, a laser frequency stabilization module, a laser amplification module, a beam shaping module and a frequency tripling module. After frequency stabilization control is carried out on seed laser, a large-energy pumping source is generated through laser amplification, flat-topped light beams are formed after the light beams pass through a light beam shaping module, and high-efficiency 355 nm ultraviolet pulse laser output is achieved in combination with a nonlinear crystal frequency conversion technology. The device has the advantages of miniaturization, high conversion efficiency, high frequency stability, strong anti-interference capability and the like, can be used for an atmospheric component detection laser radar light source, and can meet the application requirements of airborne, satellite-borne and other complex environments.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically to a miniaturized, high-efficiency, frequency-stabilized 355nm all-solid-state ultraviolet pulsed laser. Through the coordinated design of a seed laser module, a frequency stabilization module, an amplifier module, a beam shaping module, and a frequency tripler module, this laser achieves efficient and stable output of 355nm ultraviolet pulsed laser light, while also balancing miniaturization and anti-interference capabilities. It is suitable for use as a light source for atmospheric composition detection lidars, meeting the requirements of complex airborne and satellite-based applications. Background Art

[0002] Ultraviolet lasers are widely used in many fields, such as laser marking, laser cleaning, material surface treatment, medical diagnosis, scientific experiments, etc. Especially in the field of precision machining and micromachining, ultraviolet lasers can provide excellent processing effects due to their short wavelength and high energy density. However, existing ultraviolet laser technology still has many limitations:

[0003] Patent CN116780335A discloses an all-semiconductor ultraviolet laser with high beam quality and a wide wavelength range. The laser includes an edge-emitting semiconductor excitation light source, a surface-emitting semiconductor gain medium, and a fundamental frequency oscillation and frequency conversion component. The surface-emitting semiconductor gain medium, the fundamental frequency oscillation, and the frequency conversion component form a resonant cavity, and the final output is ultraviolet laser. However, due to the power limitation of the fundamental frequency oscillation, the conversion efficiency and output power of the final output ultraviolet laser cannot be further improved. Patent CN112260042A discloses an ultraviolet pulsed laser that uses a Class II phase-matched frequency-doubling crystal to perform extracavity secondary sum frequency generation on polarized light with perpendicular polarization directions, ultimately outputting ultraviolet pulsed laser light. However, during the sum frequency generation process, the polarized light in one of the polarization directions is directly output as useless light, limiting the overall conversion efficiency of fundamental frequency light to ultraviolet light. Patent CN118448971B discloses a high-power nanosecond ultraviolet laser that uses double-ended pumping to increase pump power to achieve higher-power ultraviolet laser output. However, this method simply increases the pump power to increase the output power of the ultraviolet laser, without further improving the overall conversion efficiency of the pump light to ultraviolet laser light. The discrete pump and complex resonant cavity structure design make the overall laser bulky and cannot be miniaturized. Therefore, there is an urgent need for a new ultraviolet laser technology that can effectively improve the conversion efficiency of ultraviolet lasers, reduce the size and weight of the equipment, and at the same time perform frequency stabilization control on the laser so that the output ultraviolet laser has high frequency stability. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention proposes a miniaturized, high-efficiency, frequency-stabilized 355nm all-solid-state ultraviolet pulse laser, which aims to solve the problems of low conversion efficiency, bulky size, and insufficient frequency stability of existing ultraviolet lasers, and provide a miniaturized, lightweight, high-conversion-efficiency, and high-frequency-stability ultraviolet light source.

[0005] The technical solution of the present invention is:

[0006] A miniaturized, high-efficiency, frequency-stabilized 355nm all-solid-state ultraviolet pulsed laser includes the following modules connected in this order: A seed laser module (A) is used to generate a 1064nm single-frequency pulse seed laser, comprising an 808nm semiconductor laser (1), an NPRO ring laser (2) pumped by the 808nm semiconductor laser (1), an isolator (3), an asymmetric beam splitter (4), a first focusing mirror (5), an optical wedge (6), a first reflecting mirror (7), and a polarization beam splitter prism (8), wherein the asymmetric beam splitter (4) splits the seed light into a monitoring path beam and a main path beam, and the main path beam is extracted through the polarization beam splitter prism (8) to output P-polarized light; A laser frequency stabilization module (B) receives the monitoring path light beam and includes a fiber polarization beam splitter (9), a fiber polarization beam combiner (10), a high-speed photodetector (11), a data collector (12), a data processor (13) and a driver (14), and is used for real-time separation of TE / TM modes, generation of polarization beat frequency signals, and adjustment of the frequency of the NPRO ring laser through dynamic feedback control; A laser amplification module (C) receives the main P-polarized light and comprises a right-angle prism (15), a first amplifying crystal (16), a first dichroic mirror (17), a second reflecting mirror (18), a second focusing mirror (19), a second amplifying crystal (20), a second dichroic mirror (21), an 878nm semiconductor laser (22), a collimating mirror (23), a beam splitter (24), a third focusing mirror (25), a third reflecting mirror (26) and a fourth focusing mirror (27). The fundamental frequency optical power is increased by combining single-pass and double-pass amplification, and pump light is multiplexed to split the beam and pump the two-stage crystal. A beam shaping module (D) receives the amplified laser light and includes a first shaping lens (28), a fourth reflecting mirror (29), a second shaping lens (30) and a third shaping lens (31), and converts the Gaussian beam into a flat-top beam through aspheric collaborative correction; The triple frequency module (E) receives the flat-top beam and comprises a half-wave plate (32), a frequency doubling crystal (33), a sum frequency crystal (34) and a third dichroic mirror (35), and outputs a 355nm ultraviolet pulse laser through step-by-step frequency conversion and walk-off compensation. The specific structure is as follows:

[0007] The seed laser module includes an 808nm semiconductor laser, an NPRO ring laser, an isolator, an asymmetric beam splitter, a first focusing mirror, an optical wedge, a first reflector, and a polarization beam splitter prism. The 808nm semiconductor laser is used as pump light to pump the NPRO ring laser. The NPRO ring laser generates a 1064nm single-frequency pulse seed laser, which is isolated from the return light by the isolator. The asymmetric beam splitter splits the seed light. The monitoring path light beam enters the laser frequency stabilization module. The main path light beam passes through the first focusing mirror, the optical wedge, and the first reflector in the transmission direction of the seed laser, and finally passes through the polarization beam splitter prism to extract the laser component with the polarization state of P polarization and then enters the laser amplification module.

[0008] The laser frequency stabilization module includes a fiber polarization beam splitter, a fiber polarization beam combiner, a high-speed photoelectric detector, a data collector, a data processor, and a driver. The fiber polarization beam splitter separates the monitoring path light beam received from the asymmetric beam splitter into two light beams with mutually perpendicular polarization modes, which are respectively transmitted through polarization-maintaining optical fibers into the fiber polarization beam combiner for combined output. The output end of the fiber polarization beam combiner is connected to the input end of the high-speed photoelectric detector, the output end of the high-speed photoelectric detector is connected to the input end of the data collector, the output end of the data collector is connected to the input end of the data processor, providing a digital signal for the data processor, the output end of the data processor is connected to the input end of the driver, and the two output ends of the driver are connected to the NPRO ring laser, providing a feedback control signal for the NPRO ring laser.

[0009] The laser amplification module is composed of a right-angle prism, a first amplifying crystal, a first dichroic mirror, a second reflecting mirror, a second focusing mirror, a second amplifying crystal, a second dichroic mirror, an 878nm semiconductor laser, a collimating mirror, a beam splitter, a third focusing mirror, a third reflecting mirror, and a fourth focusing mirror. The 1064nm single-frequency pulse seed laser is reflected by the first reflecting surface of the right-angle prism into the first amplifying crystal for amplification, passes through the crystal once and is incident on the first dichroic mirror for reflection, enters the first amplifying crystal again for amplification, passes through the crystal twice and is incident on the second reflecting surface of the right-angle prism for reflection, and then passes through the second reflecting mirror, the second focusing mirror, and the fourth focusing mirror in sequence. The 878nm semiconductor laser generates 878nm pump light, which is collimated and output by the collimating mirror and incident on the beam splitter for splitting. A portion of the pump light is transmitted and output to the third focusing mirror for focusing to adjust the size and position of the pump light spot. After passing through the first dichroic mirror, the pump light enters the first amplifying crystal for pumping and providing gain. The other portion of the pump light is reflected by the beam splitter and incident on the third reflecting mirror. After reflection, it is focused by the fourth focusing mirror to adjust the size and position of the light spot. After incident on the second dichroic mirror, the pump light is transmitted and output, and enters the second amplifying crystal for pumping and providing gain.

[0010] The beam shaping module is composed of a first shaping lens, a fourth reflector, a second shaping lens, and a third shaping lens. The first shaping lens, the fourth reflector, the second shaping lens, and the third shaping lens are arranged in sequence along the transmission direction of the amplified laser.

[0011] The triple frequency module includes a half-wave plate, a frequency doubling crystal, a sum frequency crystal, and a third dichroic mirror. The shaped 1064nm fundamental frequency laser is incident on the half-wave plate to adjust the polarization state to S polarization and then is incident on the frequency doubling crystal. A portion of the 1064nm fundamental frequency laser is subjected to nonlinear frequency conversion to generate a 532nm frequency doubling laser. The remaining 1064nm fundamental frequency laser and the 532nm frequency doubling laser are incident on the sum frequency crystal to generate a 355nm ultraviolet pulse laser by sum frequency. After being split by the third dichroic mirror, the remaining 1064nm fundamental frequency laser and the remaining 532nm frequency doubling laser are transmitted and output, and the 355nm ultraviolet pulse laser is reflected and output.

[0012] Furthermore, the miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulsed laser is characterized in that the half-wave plate is a 1064nm half-wave plate, and the surface is coated with a 1064nm 0° anti-reflection film; the polarization beam splitter is a 1064nm polarization beam splitter, and its extinction ratio is greater than 1000:1; the half-wave plate is a 1064nm half-wave plate, and the surface is coated with a 1064nm 0° anti-reflection film.

[0013] Furthermore, the miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser is characterized in that the focal length of the first focusing mirror is f=100mm; the focal length of the second focusing mirror is f=200mm; the focal length of the collimating mirror is f=8mm; the focal length of the third focusing mirror is f=25mm; and the focal length of the fourth focusing mirror is f=25mm.

[0014] Furthermore, the miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulsed laser is characterized in that the first reflecting mirror is coated with a 45° 1064nm high-reflection film; the first dichroic mirror is coated with a 0° 1064nm high-reflection film and an 878nm anti-reflection film; the second reflecting mirror is coated with a 45° 1064nm high-reflection film; the second dichroic mirror is coated with a 45° 1064nm high-reflection film and an 878nm anti-reflection film; the beam splitter is coated with a 50% transmittance dielectric film at 878nm; the third reflecting mirror is coated with a 45° 878nm high-reflection film; the fourth reflecting mirror is coated with a 45° 1064nm high-reflection film; and the third dichroic mirror is coated with a 45° 355nm high-reflection film, a 532nm anti-reflection film, and a 1064nm anti-reflection film.

[0015] Furthermore, the miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulsed laser is characterized in that the first amplifying crystal and the second amplifying crystal are Nd:YVO4 crystals; the frequency doubling crystal is a type I phase-matched LBO crystal; the sum frequency crystal is a type II phase-matched LBO crystal; and the frequency doubling crystal and the sum frequency crystal are placed for walk-off compensation.

[0016] Furthermore, the miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulsed laser is characterized in that the laser frequency stabilization module adopts a polarization-birefringence coupled self-feedback digital design, the asymmetric beam splitter has a splitting ratio of 9.5:1, the seed laser is coupled into the fiber polarization beam splitter through a polarization-maintaining fiber to separate the TE mode and TM mode with mutually perpendicular polarizations, and then the two beams are respectively coupled into the fiber polarization combiner through polarization-maintaining fibers; the fiber polarization combiner rotates the polarization direction of one polarized light by 90°, and then the two combined beams are input into the high-speed photodetector to generate a polarization beat frequency signal; the signal processing process first performs high-speed sampling by the data collector, and then goes through the five steps of the data processor: digital phase detection, real-time processing of error signals, generation of preliminary feedback voltage, dynamic learning of the spectral characteristics of environmental disturbances, online optimization of feedback voltage parameters, and finally, the driver generates a piezoelectric ceramic drive signal and a temperature adjustment drive signal as feedback control signals input to the NPRO ring laser.

[0017] Furthermore, the miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser is characterized in that the first shaping lens, the second shaping lens, and the third shaping lens are all aspheric lenses, forming a three-lens compact flat-top beam shaping system, the first shaping lens has a focal length of f = 40 mm, a conic coefficient of k1 = -0.95, and an aspheric coefficient of A4 = +1.2×10 -6 (mm -3 ), A6=-3.0×10 -9 (mm -5 ), collimated Gaussian beam, used for pre-correcting spherical aberration; the focal length of the second shaping lens is f = -30mm, the conic coefficient is k2 = -1.10, and the aspheric coefficient is A4 = -2.8×10 -6 (mm -3 ), A6=+1.5×10 -9 (mm -5 ), controls the intermediate light field to offset field curvature and coma; the third shaping lens has a focal length of f = 50 mm, a conic coefficient of k3 = -0.98, and an aspheric coefficient of A4 = -1.5×10 -6 (mm -3 ), A6=+2.2×10 -9 (mm -5 ), perform Fourier transform on the light field, and generate a flat-top spot through phase modulation; the distance between the first shaping lens and the second shaping lens is d1 = 40 mm, and the distance between the second shaping lens and the third shaping lens is d2 = 80 mm.

[0018] The present invention has the following advantages:

[0019] 1. Using a semiconductor laser to pump the NPRO ring laser as a seed laser has high frequency stability and fast frequency tuning speed. By controlling the 1064nm seed laser, a good 355nm ultraviolet pulsed laser single-frequency output can be achieved.

[0020] 2. The frequency stabilization module adopts a polarization-birefringence coupled self-feedback digital design, which has strong anti-interference and can dynamically optimize parameters. Compared with the traditional Fabry-Perot cavity, it does not require an external cavity and utilizes the inherent characteristics of NPRO, with a compact structure.

[0021] 3. A multi-stage amplification system is used, and a combination of single-pass amplification and double-pass amplification is used to amplify the 1064nm seed laser to improve the conversion efficiency of the pump light. The two-stage amplification modules share a pump source, and the two-stage amplification modules are pumped separately by splitting, which improves the energy utilization efficiency and greatly reduces the size of the overall laser.

[0022] 4. A flat-top beam shaper is designed using three aspheric lenses. Parameters such as lens focal length, spacing, lens surface conic coefficient, and lens surface aspheric coefficient are designed. The optical path is compressed by a negative lens and combined with aspheric collaborative correction to achieve the unity of compactness and high performance.

[0023] 5. The Gaussian spot is subjected to flat-top beam shaping, which improves the spatial uniformity of the beam, solves the problem of decreased nonlinear conversion efficiency due to beam unevenness, and improves the nonlinear conversion efficiency in the frequency tripling process.

[0024] 6. The present invention has the advantages of miniaturization, high conversion efficiency, high frequency stability, and strong anti-interference ability. It can be used as a laser radar light source for atmospheric composition detection and can meet the application requirements of complex environments such as airborne and satellite-borne. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a structural schematic diagram of a miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser of the present invention.

[0026] Figure 2 This is a schematic diagram of the walk-off compensation structure of the frequency doubling crystal and the sum frequency crystal. DETAILED DESCRIPTION

[0027] The following is combined with Figure 1 , Attachment Figure 2 , a complete description of the specific technical solutions in the embodiments of the present invention is given. The technical solutions and parameters described in the embodiments of the present invention are only part of the present invention. All other embodiments based on the embodiments of the present invention are within the scope of protection of the present invention without making creative improvements and inventions.

[0028] A miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser comprises five parts: a seed laser module A, a laser frequency stabilization module B, a laser amplification module C, a beam shaping module D, and a frequency tripling module E.

[0029] In this embodiment, the seed laser module A includes an 808nm semiconductor laser 1, an NPRO ring laser 2, an isolator 3, an asymmetric beam splitter 4, a first focusing mirror 5, an optical wedge 6, a first reflector 7, and a polarization beam splitter prism 8. The 808nm semiconductor laser 1 is used as pump light to pump the NPRO ring laser 2 to generate a 1064nm single-frequency pulse seed laser. The isolator 3 suppresses the interference of the return light. The asymmetric beam splitter 4 splits the seed light. The monitoring path light beam enters the laser frequency stabilization module B. The main path light beam passes through the first focusing mirror 5, the optical wedge 6, the first reflector 7 in the transmission direction of the seed laser, and finally passes through the polarization beam splitter prism 8 to extract the polarization state as the P-polarized laser component and enter the laser amplification module C.

[0030] The 808nm semiconductor laser 1 has a pigtail core diameter of 105μm and a numerical aperture of 0.22. The isolator 3 is a 1064nm isolator. The asymmetric beam splitter 4 has a fractional ratio of 9.5:1. The first focusing mirror 5 is a plano-convex lens with a focal length of f=100mm, plane incidence, and a surface coated with a 1064nm anti-reflection coating. The surface of the optical wedge 6 is coated with a 1064nm anti-reflection coating. The first reflector 7 is coated with a 1064nm 45° high-reflection coating. The polarization beam splitter 8 is a 1064nm polarization beam splitter with an extinction ratio greater than 1000:1.

[0031] In this example, the laser frequency stabilization module B includes a fiber polarization beam splitter 9, a fiber polarization beam combiner 10, a high-speed photodetector 11, a data collector 12, a data processor 13, and a driver 14. The fiber polarization beam splitter 9 separates the monitoring path light beam received from the asymmetric beam splitter 4 into two light beams with mutually perpendicular polarization modes, which are respectively transmitted through polarization-maintaining optical fibers into the fiber polarization beam combiner 10 for combined output. The output end of the fiber polarization beam combiner 10 is connected to the input end of the high-speed photodetector 11, the output end of the high-speed photodetector 11 is connected to the input end of the data collector 12, the output end of the data collector 12 is connected to the input end of the data processor 13, providing a digital signal to the data processor 13, the output end of the data processor 13 is connected to the input end of the driver 14, and the two output ends of the driver 14 are connected to the NPRO ring laser 2 to provide a feedback control signal to the NPRO ring laser 2.

[0032] The laser frequency stabilization module B adopts a polarization-birefringence coupled self-feedback digital design. The monitoring path laser is coupled into the optical fiber polarization beam splitter 9 through a polarization-maintaining optical fiber to separate the TE mode and TM mode with polarizations perpendicular to each other, and then the two beams of light are respectively coupled into the optical fiber polarization combiner 10 through polarization-maintaining optical fibers; the optical fiber polarization combiner 10 rotates the polarization direction of one of the polarized lights by 90°, and then the two combined beams are input into the high-speed photodetector 11 to generate a polarization beat signal; the signal processing process first performs high-speed sampling by the data collector 12, and then goes through the five steps of the data processor 13: digital phase detection, real-time processing of error signals, generation of preliminary feedback voltage, dynamic learning of the spectrum characteristics of environmental disturbances, online optimization of feedback voltage parameters, and finally, the driver 14 generates a piezoelectric ceramic drive signal and a temperature adjustment drive signal as feedback control signals input into the NPRO ring laser 2.

[0033] In this example, the laser amplification module C is composed of a right-angle prism 15, a first amplifying crystal 16, a first dichroic mirror 17, a second reflecting mirror 18, a second focusing mirror 19, a second amplifying crystal 20, a second dichroic mirror 21, an 878nm semiconductor laser 22, a collimating mirror 23, a beam splitter 24, a third focusing mirror 25, a third reflecting mirror 26, and a fourth focusing mirror 27. The 1064nm single-frequency pulse seed laser is reflected by the first reflecting surface of the right-angle prism 15 and enters the first amplifying crystal 16 for amplification. After passing through the crystal once, it is incident on the first dichroic mirror 17 for reflection, and then enters the first amplifying crystal 16 again for amplification. After passing through the crystal twice, it is incident on the second reflecting surface of the right-angle prism 15 for reflection, and then passes through the second reflecting mirror 27 in sequence. The 878nm semiconductor laser 22 generates 878nm pump light, which is collimated by the collimating mirror 23 and incident on the beam splitter 24 for splitting. A portion of the pump light is transmitted and output to the third focusing mirror 25 for focusing to adjust the size and position of the pump light spot. After passing through the first dichroic mirror 17, it enters the first amplifying crystal 16 for pumping and providing gain. The other portion of the pump light is reflected by the beam splitter 24 and incident on the third reflecting mirror 26. After reflection, it is focused by the fourth focusing mirror 27 to adjust the size and position of the light spot. After entering the second dichroic mirror 21, it is transmitted and output and enters the second amplifying crystal 20 for pumping and providing gain.

[0034] The first and second reflecting surfaces of the right-angle prism 15 are coated with a 1064nm 45° high-reflection film. The first amplifying crystal 16 is a Nd:YVO4 crystal with a dopant atomic fraction of 0.35% and a size of 3mm×3mm×16mm. The two end faces of the crystal are cut with a 5° bevel and coated with a 1064nm anti-reflection film and an 878nm anti-reflection film. The surface of the first dichroic mirror 17 is coated with a 1064nm high-reflection film and an 878nm anti-reflection film. The surface of the second reflector 18 is coated with a 1064nm 45° high-reflection film. The second focusing lens 19 is a plano-convex lens with a focal length of f=200mm, plane incidence, and a surface coated with a 1064nm anti-reflection film. The second amplifying crystal 20 is a Nd:YVO4 crystal with a dopant atomic fraction of 0.35% and a size of 3mm×3mm×1 6mm, the two end faces of the crystal are cut with a 5° bevel and coated with a 1064nm anti-reflection film and an 878nm anti-reflection film; the surface of the second dichroic mirror 21 is coated with a 1064nm high-reflection film and an 878nm anti-reflection film; the fiber core diameter of the 878nm semiconductor laser 22 is 200μm, the numerical aperture is 0.22, the collimator 23 is a plano-convex lens, with plane incidence, a focal length of f=8mm, and a surface coated with an 878nm anti-reflection film; the surface of the beam splitter 29 is coated with an 878nm semi-transparent and semi-reflective film; the third focusing mirror 25 is a plano-convex lens with a focal length of f=25mm, convex incidence, and a surface coated with an 878nm anti-reflection film; the surface of the third reflector 26 is coated with an 878nm high-reflection film; the fourth focusing mirror 27 is a plano-convex lens with a focal length of f=25mm, convex incidence, and a surface coated with an 878nm anti-reflection film.

[0035] In this example, the beam shaping module D is composed of a first shaping lens 28, a fourth reflector 29, a second shaping lens 30, and a third shaping lens 31. Along the transmission direction of the amplified laser, the first shaping lens 28, the fourth reflector 29, the second shaping lens 30, and the third shaping lens 31 are arranged in order.

[0036] The focal length of the first shaping lens 28 is f=40 mm, the conic coefficient is k1=-0.95, and the aspheric coefficient is A4=+1.2×10 -6 (mm -3 ), A6=-3.0×10 -9 (mm -5 ), collimated Gaussian beam, used for pre-correction of spherical aberration; the surface of the fourth reflector 29 is coated with a 1064nm 45° high-reflection film; the second shaping lens 30 has a focal length of f = -30mm, a conic coefficient of k2 = -1.10, and an aspheric coefficient of A4 = -2.8×10 -6 (mm -3 ), A6=+1.5×10-9 (mm -5 ), controls the intermediate light field to offset field curvature and coma; the third shaping lens 31 has a focal length of f = 50 mm, a conic coefficient of k3 = -0.98, and an aspheric coefficient of A4 = -1.5×10 -6 (mm -3 ), A6=+2.2×10 -9 (mm -5 ), used to perform Fourier transform on the light field and generate a flat-top spot through phase modulation; the distance between the first shaping lens 29 and the second shaping lens 30 is d1 = 40 mm, and the distance between the second shaping lens 30 and the third shaping lens 31 is d2 = 80 mm.

[0037] In this example, the triple frequency module E includes a half-wave plate 32, a frequency doubling crystal 33, a sum frequency crystal 34, and a third dichroic mirror 35. The shaped 1064nm fundamental frequency laser is incident on the half-wave plate 32 and adjusted to an S polarization state before being incident on the frequency doubling crystal 33. A portion of the 1064nm fundamental frequency laser undergoes nonlinear frequency conversion to generate a 532nm frequency doubling laser. The remaining 1064nm fundamental frequency laser and the 532nm frequency doubling laser are incident on the sum frequency crystal 34 and frequency-doubled to generate a 355nm ultraviolet pulse laser. After being split by the third dichroic mirror 35, the remaining 1064nm fundamental frequency laser and the remaining 532nm frequency doubling laser are transmitted and output, and the 355nm ultraviolet pulse laser is reflected and output.

[0038] The half-wave plate 32 is a 1064nm half-wave plate with a 1064nm anti-reflection film on its surface; the frequency doubling crystal 33 is an LBO crystal with a crystal size of 3mm×3mm×18mm. The crystal adopts type I critical phase matching and a cutting angle of θ=90°. The crystal end faces are coated with 1064nm and 532nm antireflection films; the sum frequency crystal 34 is an LBO crystal with a crystal size of 3mm×3mm×20mm. The crystal adopts type II critical phase matching and the cutting angle is θ=42.6°. The crystal end faces are coated with 1064nm, 532nm and 355nm antireflection films; the third dichroic mirror 35 is coated with a 45° 355nm high reflection film, a 532nm antireflection film and a 1064nm antireflection film.

[0039] In the triple frequency module of this embodiment, the frequency doubling crystal 33 and the sum frequency crystal 34 are placed for walk-off compensation, as shown in FIG. Figure 2 shown.

[0040] The embodiments described above are only preferred specific implementation methods of the present invention, and the scope of protection of the present invention is not limited thereto. Any simple change or equivalent replacement of the technical solution that can be obviously obtained by any technician familiar with the field within the technical scope disclosed in the present invention, or various other corresponding changes and deformations made based on the technical concept of the present invention all fall within the scope of protection of the present invention.

Claims

1. A miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulsed laser, characterized in that: Includes the following modules connected in this way: A seed laser module (A) is used to generate a 1064nm single-frequency pulse seed laser, comprising an 808nm semiconductor laser (1), an NPRO ring laser (2) pumped by the 808nm semiconductor laser (1), an isolator (3), an asymmetric beam splitter (4), a first focusing mirror (5), an optical wedge (6), a first reflecting mirror (7), and a polarization beam splitter prism (8), wherein the asymmetric beam splitter (4) splits the seed light into a monitoring path beam and a main path beam, and the main path beam is extracted through the polarization beam splitter prism (8) to output P-polarized light; A laser frequency stabilization module (B) receives the monitoring path light beam and includes a fiber polarization beam splitter (9), a fiber polarization beam combiner (10), a high-speed photodetector (11), a data collector (12), a data processor (13) and a driver (14), and is used for real-time separation of TE / TM modes, generation of polarization beat frequency signals, and adjustment of the frequency of the NPRO ring laser through dynamic feedback control; A laser amplification module (C) receives the main P-polarized light and comprises a right-angle prism (15), a first amplifying crystal (16), a first dichroic mirror (17), a second reflecting mirror (18), a second focusing mirror (19), a second amplifying crystal (20), a second dichroic mirror (21), an 878nm semiconductor laser (22), a collimating mirror (23), a beam splitter (24), a third focusing mirror (25), a third reflecting mirror (26) and a fourth focusing mirror (27). The fundamental frequency optical power is increased by combining single-pass and double-pass amplification, and pump light is multiplexed to split the beam and pump the two-stage crystal. A beam shaping module (D) receives the amplified laser light and includes a first shaping lens (28), a fourth reflecting mirror (29), a second shaping lens (30) and a third shaping lens (31), and converts the Gaussian beam into a flat-top beam through aspheric collaborative correction; The triple frequency module (E) receives the flat-top beam and comprises a half-wave plate (32), a frequency doubling crystal (33), a sum frequency crystal (34) and a third dichroic mirror (35), and outputs a 355nm ultraviolet pulse laser through step-by-step frequency conversion and walk-off compensation.

2. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The 808nm semiconductor laser (1) is used as pump light to pump the NPRO ring laser (2). The NPRO ring laser (2) generates a 1064nm single-frequency pulse seed laser, which is isolated from the return light by the isolator (3). The asymmetric beam splitter (4) splits the seed light. The monitoring path light beam enters the laser frequency stabilization module (B). The main path light beam passes through the first focusing mirror (5), the optical wedge (6), and the first reflecting mirror (7) in the transmission direction of the seed laser. Finally, it passes through the polarization splitting prism (8) to extract the laser component with the polarization state of P polarization and then enters the laser amplification module (C).

3. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The optical fiber polarization beam splitter (9) separates the monitoring path light beam received from the asymmetric beam splitter (4) into two light beams with mutually perpendicular polarization modes, and transmits the two light beams through polarization-maintaining optical fibers to enter the optical fiber polarization beam combiner (10) for beam combining and output. The output end of the optical fiber polarization beam combiner (10) is connected to the input end of the high-speed photodetector (11), the output end of the high-speed photodetector (11) is connected to the input end of the data collector (12), the output end of the data collector (12) is connected to the input end of the data processor (13), and provides a digital signal to the data processor (13). The output end of the data processor (13) is connected to the input end of the driver (14), and the two output ends of the driver (14) are connected to the NPRO ring laser (2), and provide a feedback control signal to the NPRO ring laser (2).

4. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The 1064nm single-frequency pulse seed laser is reflected by the first reflection surface of the right-angle prism (15) and enters the first magnifying crystal (16) for amplification, passes through the crystal once and is incident on the first dichroic mirror (17) for reflection, enters the first magnifying crystal (16) again for amplification, passes through the crystal twice and is incident on the second reflection surface of the right-angle prism (15) for reflection, then passes through the second reflection mirror (18), the second focusing mirror (19), the second magnifying crystal (20) in sequence, and finally is reflected by the second dichroic mirror (21) and output into the beam shaping module (D). The 878nm semiconductor laser The device (22) generates 878nm pump light, which is collimated and output through the collimating mirror (23) and incident on the spectrometer (24) for splitting. A part of the pump light is transmitted and output to the third focusing mirror (25) for focusing and adjusting the size and position of the pump light spot. After passing through the first dichroic mirror (17), the pump light enters the first amplifying crystal (16) for pumping and providing gain. The other part of the pump light is reflected by the spectrometer (24) and incident on the third reflecting mirror (26). After reflection, the pump light is focused by the fourth focusing mirror (27) and the size and position of the light spot are adjusted. After entering the second dichroic mirror (21), the pump light is transmitted and output, and enters the second amplifying crystal (20) for pumping and providing gain.

5. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The shaped 1064nm fundamental frequency laser is incident on the half-wave plate (32) to adjust the polarization state to S polarization and then incident on the frequency doubling crystal (33). A part of the 1064nm fundamental frequency laser generates 532nm frequency doubling laser after nonlinear frequency conversion. The remaining 1064nm fundamental frequency laser and 532nm frequency doubling laser are incident on the sum frequency crystal (34) to sum-frequency generate 355nm ultraviolet pulse laser. After being split by the third dichroic mirror (35), the remaining 1064nm fundamental frequency laser and the remaining 532nm frequency doubling laser are transmitted and output, and the 355nm ultraviolet pulse laser is reflected and output.

6. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The asymmetric beam splitter (4) has a splitting ratio of 9:1 to 10:1; the polarization beam splitting prism (8) has an extinction ratio of ≥1000:1; and the 1064 nm seed laser line width output by the NPRO ring laser (2) is ≤1 MHz.

7. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The surface of the optical wedge (6) is coated with a 1064nm 0° anti-reflection film; the polarization beam splitter (8) is a 1064nm polarization beam splitter; and the half-wave plate (32) is a 1064nm half-wave plate, the surface of which is coated with a 1064nm 0° anti-reflection film.

8. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: In the laser frequency stabilization module, the optical fiber polarization beam splitter (9) and the optical fiber polarization beam combiner (10) are connected via polarization-maintaining optical fiber, wherein the polarization direction of a beam of light is rotated 90° before being combined; the data processor (13) extracts an error signal via digital phase detection, optimizes feedback parameters in combination with a dynamic spectrum learning algorithm, generates a piezoelectric ceramic drive signal and a temperature adjustment signal, and controls the frequency drift of the NPRO ring laser (2), with a frequency stabilization accuracy better than ±1 MHz.

9. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The laser frequency stabilization module (B) adopts a polarization-birefringence coupled self-feedback digital design, the asymmetric beam splitter (4) has a splitting ratio of 9.5:1, the seed laser is coupled into the optical fiber polarization beam splitter (9) through a polarization-maintaining optical fiber to separate the TE mode and the TM mode with polarizations perpendicular to each other, and then the two beams are coupled into the optical fiber polarization combiner (10) through polarization-maintaining optical fibers respectively; the optical fiber polarization combiner (10) rotates the polarization direction of one polarized light by 90 degrees, and then the two beams are combined and input into the high-speed photodetector (11) to generate a polarization beat frequency signal; the signal processing process first performs high-speed sampling by the data collector (12), and then goes through the five steps of the data processor (13): digital phase detection, real-time processing of error signals, generation of preliminary feedback voltage, dynamic learning of the spectrum characteristics of environmental disturbances, online optimization of feedback voltage parameters, and finally generates a piezoelectric ceramic drive signal and a temperature adjustment drive signal through the driver (14) as feedback control signals and inputs them into the NPRO ring laser (2).

10. The miniaturized, high-efficiency, frequency-stabilized 355nm ultraviolet pulse laser according to claim 1, characterized in that: The first shaping lens (28), the second shaping lens (30), and the third shaping lens (31) are all aspheric lenses, forming a three-lens compact flat-top beam shaping system. The first shaping lens (28) has a focal length of f = 40 mm, a conic coefficient of k1 = -0.95, and an aspheric coefficient of A4 = +1.2×10 -6 (mm -3 ), A6=-3.0×10 -9 (mm -5 ), a collimated Gaussian beam is used to pre-correct spherical aberration; the second shaping lens (30) has a focal length of f = -30 mm, a conic coefficient of k2 = -1.10, and an aspheric coefficient of A4 = -2.8×10 -6 (mm -3 ), A6=+1.5×10 -9 (mm -5 ), controls the intermediate light field, and is used to offset field curvature and coma; the third shaping lens (31) has a focal length of f = 50 mm, a conic coefficient of k3 = -0.98, and an aspheric coefficient of A4 = -1.5×10 -6 (mm -3 ), A6=+2.2×10 -9 (mm -5 ), Fourier transform is performed on the light field, and a flat-top spot is generated by phase modulation; the distance between the first shaping lens (28) and the second shaping lens (30) is d1 = 40 mm, and the distance between the second shaping lens (30) and the third shaping lens (31) is d2 = 80 mm.

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