High repetition rate deep ultraviolet pulse laser and method of designing the same

Abstract

The application provides a high-repetition-frequency deep-ultraviolet pulse laser and a design method thereof, and the laser comprises a fiber seed source, a multi-stage solid-state amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system and an output stabilization adjustment system. The second frequency doubling system comprises a first BBO crystal and a second BBO crystal. The pre-compensation system comprises a spherical mirror group and a cylindrical mirror group arranged in front of the first BBO crystal and the second BBO crystal. The output stabilization adjustment system is used for accurately controlling the temperature of the first frequency doubling system and the second frequency doubling system to maintain the phase matching condition. The laser obtained by the application is filtered and shaped by a series of filters and beam shaping devices, and the output is stable, monochromatic and good deep-ultraviolet laser, which is suitable for the fields of precision lithography, micro-processing and scientific research, and ensures the efficient laser conversion efficiency and stable output performance.

Description

Technical Field

[0001] This invention relates to the field of deep ultraviolet laser technology, specifically to a high repetition rate deep ultraviolet pulsed laser and its design method. Background Technology

[0002] The statements in this section are merely background information related to this application and do not necessarily constitute prior art.

[0003] Deep ultraviolet (DUV) lasers are a novel laser technology characterized by high power and high energy density in the deep ultraviolet band (200-300 nm). The development of this technology has brought significant breakthroughs to applications in many fields, including semiconductors, photolithography, bioscience, and materials processing. In the field of semiconductor detection, high-repetition-rate DUV pulsed lasers play a crucial role. DUV pulsed lasers can be obtained through frequency doubling, but excessively high repetition rates reduce the peak power of the laser pulse, which in turn lowers the optical-to-optical conversion efficiency during the frequency doubling process.

[0004] Currently, a common method to address this issue while maintaining a high repetition rate for laser pulses is to reduce the size of the fundamental frequency beam spot at the frequency doubling crystal, thereby increasing the laser power density and thus improving the frequency doubling conversion efficiency. However, this approach leads to a deterioration in beam quality and energy distribution. Because BBO crystals have a small frequency doubling acceptance angle and a large walk-off angle, previous methods have struggled to obtain high-quality 266nm laser beams.

[0005] In view of this, the problem that existing deep ultraviolet lasers cannot simultaneously achieve high frequency doubling efficiency and good beam quality has become the subject of this invention. Summary of the Invention

[0006] The purpose of this invention is to provide a high repetition rate deep ultraviolet pulsed laser and its design method.

[0007] To achieve the above objectives, a first aspect of the present invention provides a high repetition rate deep ultraviolet pulsed laser.

[0008] The laser includes an optical fiber seed source, a multi-stage solid-state amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system, and an output stabilization adjustment system.

[0009] The second frequency doubling system includes a first BBO crystal and a second BBO crystal.

[0010] The pre-compensation system includes a spherical lens group and a cylindrical lens group arranged in front of the first BBO crystal and the second BBO crystal.

[0011] The second frequency multiplication system and the pre-compensation system are arranged in the following manner:

[0012] Obtain the phase mismatch Δk x Phase mismatch angle δθ x The relationship was used to determine the wave vector k of the BBO crystal in the xoz plane of the e-optic vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x And calculate the phase mismatch Δk x Utilizing the inherent β property of BBO crystals for specific wavelengths θ For phase mismatch Δk x Simplify, and we get Δk x =β θ δθ x .

[0013] Establish frequency doubling efficiency and phase mismatch angle δθ x The relationship when the phase mismatch angle δθ x The resulting phase mismatch Δk x When the frequency doubling efficiency is reduced to 50% of the optical-to-optical conversion efficiency with perfect phase matching, i.e., the frequency doubling receiving angle Δθ x The frequency doubling efficiency is relative to the phase mismatch angle δθ x The full width at half maximum (FWHM) is used to derive the frequency doubling receiving angle Δθ under the given frequency doubling efficiency. x relation.

[0014] Calculate the harmonic reception angle Δθ of the BBO crystal based on its characteristics. x .

[0015] A first BBO crystal and a second BBO crystal of the same length are placed close together after being rotated 180°. The walk-off angle of the frequency-doubled light generated by the first BBO crystal is ρ1, and the walk-off angle generated by the second BBO crystal is ρ2. ρ1 and ρ2 are equal in magnitude but opposite in direction.

[0016] The harmonic reception angle Δθ of the BBO crystal is calculated based on specific crystal characteristics and the length of the combined two BBO crystals. x The spherical and cylindrical mirror groups in the pre-compensation system are selected and arranged so that the divergence angle obtained after shaping by the pre-compensation system is smaller than the harmonic reception angle Δθ. x The laser.

[0017] The output stabilization system is used to precisely control the temperature of the first and second frequency harmonic systems to maintain phase matching conditions.

[0018] A second aspect of the present invention provides a design method for a high repetition rate deep ultraviolet pulsed laser, the design method being used to design the high repetition rate deep ultraviolet pulsed laser as described in the first aspect of the present invention, the design method comprising the following steps:

[0019] The setup includes a high repetition rate deep ultraviolet pulsed laser comprising an optical fiber seed source, a multi-stage solid-state amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system, and an output stabilization adjustment system.

[0020] In the process of setting up the first frequency doubling system, a convex lens M20, a concave lens M21, a convex lens M22, and an LBO crystal are installed in the laser path. The cutting angle of the LBO crystal is precisely set according to the phase matching condition.

[0021] A concave lens M23, a convex lens M24, a cylindrical concave lens M25, and a cylindrical convex lens M26 are arranged in front of the first BBO crystal and the second BBO crystal in the second frequency doubling system.

[0022] When arranging the pre-compensation system and the second harmonic system, the following arrangement is adopted: to obtain the phase mismatch Δk x Phase mismatch angle δθ x The relationship was used to determine the wave vector k of the BBO crystal in the xoz plane of the e-optic vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x And calculate the phase mismatch Δk x Utilizing the inherent β property of BBO crystals for specific wavelengths θ For phase mismatch Δk x Simplify, and we get Δk x =β θ δθ x ;

[0023] Establish frequency doubling efficiency and phase mismatch angle δθ x The relationship when the phase mismatch angle δθ x The resulting phase mismatch Δk x This reduces the frequency doubling efficiency to 50% of the perfectly phase-matched optical-to-optical conversion efficiency, i.e., the frequency doubling receiver angle Δθ. x The frequency doubling efficiency is relative to the phase mismatch angle δθ x The full width at half maximum (FWHM) is used to derive the frequency doubling receiving angle Δθ under the given frequency doubling efficiency. x relation;

[0024] Calculate the harmonic reception angle Δθ of the BBO crystal based on its characteristics. x The cylindrical and spherical mirror groups of the pre-compensation system are used to shape the laser generated by the first frequency doubling system so that the divergence angle of the laser generated by the second frequency doubling system is less than Δθ.x ;

[0025] If a first BBO crystal and a second BBO crystal of the same length are rotated 180° and placed close together, the walk-off angle of the frequency-doubled light generated by the first BBO crystal is ρ1, and the walk-off angle generated by the second BBO crystal is ρ2. ρ1 and ρ2 are equal in magnitude but opposite in direction.

[0026] The output stabilization adjustment system is then used to precisely control the temperature of the phase-matched LBO and BBO crystals in the first and second frequency doubling systems. The optical angle of the phase-matched LBO and BBO crystals in the first and second frequency doubling systems is adjusted by the optical adjustment frame to maintain phase matching.

[0027] The relevant content of this invention is explained as follows:

[0028] 1. In the above-mentioned technical solution of the present invention, addressing the problem that existing deep ultraviolet lasers cannot simultaneously achieve high frequency doubling efficiency and good beam quality, a new high repetition rate deep ultraviolet pulsed laser and its design method have been innovatively developed. In this high repetition rate deep ultraviolet pulsed laser, a laser shaping scheme using spherical and cylindrical mirror groups and a double BBO crystal scheme, designed through theoretical calculations, achieves better beam quality and spot energy distribution. When the phase matching condition is met, the wave vectors of the fundamental frequency light and the frequency-doubled light propagating within the crystal are matched, reducing energy loss due to phase mismatch and allowing more fundamental frequency light energy to be converted into target frequency light. Reasonable cutting angles combined with phase matching can avoid or reduce beam walk-off effects. The method used in this invention is critical phase matching, which has advantages over non-critical phase matching in that it is simpler in structure, more reliable, and results in better spatial overlap of the beam during propagation within the crystal, and a higher divergence angle of the output laser. With superior beam morphology and stable phase matching conditions, this deep ultraviolet pulsed laser improves optical-to-optical conversion efficiency. Under high repetition rate conditions, it achieves a 266nm deep ultraviolet laser output with excellent beam quality and conversion efficiency. The use of two BBO crystals of the same length and a 180° rotation compensates for beam walk-off. Since ρ1 and ρ2 are equal in size and opposite in direction, and the two crystals are of the same length, the walk-off amounts generated by the two crystals compensate for each other, resulting in a good beam energy distribution. This solves the phase mismatch problem of the beam in the BBO crystal during the fourth harmonic process and the walk-off effect of the ultraviolet beam. Finally, the obtained laser passes through a series of filters and beam shaping devices to output a stable, monochromatic deep ultraviolet laser, suitable for precision lithography, micromachining, and scientific research, ensuring high laser conversion efficiency and stable output performance. The application of a design method for high repetition rate deep ultraviolet pulsed lasers provides strong support for the design of such lasers under different application requirements and scenarios. It helps to quickly and accurately design the required lasers, shorten the design and debugging cycles, and enhance product competitiveness.

[0029] 2. In the first aspect of the technical solution described above, the fiber seed source includes a laser diode, a wavelength division multiplexer, a high-reflectivity grating, a ytterbium-doped fiber, a saturable absorber, and a first acousto-optic modulator. After being driven, the laser diode emits continuous pump light, which enters the ytterbium-doped fiber through the wavelength division multiplexer and the high-reflectivity grating. The ytterbium-doped fiber absorbs the pump light energy, and a 1064nm laser is generated by a linear resonant cavity formed by the high-reflectivity grating, the ytterbium-doped fiber, and the saturable absorber mirror. After passing through the first acousto-optic modulator, the laser is amplified and output as a high-repetition-frequency pulsed laser with a wavelength of 1064nm through the ytterbium-doped fiber pumped by the semiconductor laser. Thus, the fiber seed source outputs a laser pulse with a wavelength of 1064nm and a power of approximately 50mW, so that the continuous pump light emitted by the laser diode after being driven circulates in the cavity with minimal loss, ultimately forming and maintaining a stable ultrashort pulse sequence before output, providing high-quality laser pulses for subsequent components of the deep ultraviolet pulsed laser. Furthermore, a photodetector (PD) can be installed inside the ring resonant cavity to monitor the laser characteristics inside or output in real time, thereby ensuring the stability of the laser pulse output from the fiber seed source.

[0030] 3. In the first aspect of the technical solution described above, the multi-stage solid-state amplifier includes a first-stage amplifier, a second-stage amplifier, a third-stage amplifier, and a fourth-stage amplifier;

[0031] The first-stage amplifier includes a first-stage pump source, a convex lens M1, a first laser crystal, a plane mirror M2, and a plane mirror M3;

[0032] The secondary amplifier includes a secondary pump source, a plane mirror M4, a convex lens M5, a second laser crystal, a concave lens M6, and a plane mirror M7;

[0033] The three-stage amplifier includes a three-stage pump source, a plane mirror M10, a convex lens M11, a third laser crystal, a concave lens M12, and a plane mirror M13;

[0034] The four-stage amplifier includes a four-stage pump source, a plane mirror M16, a convex lens M17, a fourth laser crystal, a concave lens M18, and a plane mirror M19.

[0035] The more specific application and arrangement of the multi-stage solid-state amplifiers described above will amplify the laser pulse with a wavelength of 1064nm and a power of approximately 50mW output from the fiber seed source through the multi-stage solid-state amplifiers, so that the 1064nm laser output by the multi-stage solid-state amplifiers has sufficiently high power and energy.

[0036] 4. In the first aspect of the above technical solution, in the multi-stage solid-state amplifier, the first laser crystal, the second laser crystal, the third laser crystal, and the fourth laser crystal all use Nd:YVO4 crystal as the gain medium and end-pumped to achieve high-efficiency amplification; the first-stage pump source, the second-stage pump source, the third-stage pump source, and the fourth-stage pump source all use 888nm LD lasers as pump sources; the convex lens M1 is a convex lens with a focal length of F=750; the surfaces of the plane mirrors M2, M3, M4, M7, M10, M13, and M16 are coated with a 1064nm high-reflection film; the convex lenses M5, M11, and M17 are convex lenses with a focal length of F=400 and an anti-reflection film with a 1064nm band on their surfaces; the concave lenses M6, M12, and M18 are concave lenses with a focal length of F=-75 and an anti-reflection film with a 1064nm band on their surfaces. This design, employing the more specific components of a multi-stage solid-state amplifier, enables ultra-high gain amplification while ensuring beam quality and stability, thus providing greater support for achieving high frequency doubling efficiency and good beam quality.

[0037] 5. In the above-mentioned first aspect of the technical solution, the second acousto-optic modulator includes an AOM beam splitting module. The AOM beam splitting module drives and controls the intensity and output direction of the incident laser to achieve beam splitting function and control the diffraction efficiency to above 80%, thereby ensuring maximum utilization of the amplified laser energy and ensuring that the 1064nm laser entering the first frequency doubling system after beam splitting is stable and of high quality.

[0038] 6. In the first aspect of the technical solution described above, the first frequency doubling system includes a convex lens M20, a concave lens M21, a convex lens M22, and an LBO crystal. The convex lens M20 is a convex lens with a focal length F=150 and a surface coated with a 1064nm anti-reflection film. The concave lens M21 is a concave lens with an F=-100 and a surface coated with a 1064nm anti-reflection film. The convex lens M22 is a convex lens with an F=125 and a surface coated with a 1064nm anti-reflection film. The cutting angle of the LBO crystal is precisely set to 90° and 11.3° according to the phase matching conditions. The 90° cutting angle corresponds to the optical axis direction of the LBO crystal, and the 11.3° cutting angle is an auxiliary phase matching angle that works in conjunction with the 90° angle. With this design, the split laser enters the LBO (lithium niobium phosphate) frequency doubling system. The LBO crystal with this specific phase matching design converts the 1064nm laser into a 532nm laser. In order to improve the frequency doubling conversion efficiency, the 532nm beam passes through a series of mirrors and shaping optical elements to focus it into the LBO crystal.

[0039] 7. In the first aspect of the technical solution described above, a concave lens M23, a convex lens M24, a cylindrical concave lens M25, and a cylindrical convex lens M26 are sequentially provided in the incident directions of the first BBO crystal and the second BBO crystal. The concave lens M23 and the convex lens M24 constitute the spherical lens group in the pre-compensation system, and the cylindrical concave lens M25 and the cylindrical convex lens M26 constitute the cylindrical lens group in the pre-compensation system. The concave lens M23 is a concave lens with a focal length of F=-50 and a surface coated with an anti-reflection film for the 532nm band. The convex lens M24 is a convex lens with an focal length of F=150 and a surface coated with an anti-reflection film for the 532nm band. The cylindrical concave lens M25 is a cylindrical concave lens with a focal length of F=-100 and a surface coated with an anti-reflection film for the 532nm band. The cylindrical convex lens M26 is a cylindrical convex lens with a focal length of F=125 and a surface coated with an anti-reflection film for the 532nm band. This design allows the 532nm laser generated from the first frequency doubling system to undergo further shaping before entering the second frequency doubling system. Specifically, a pre-compensation method is used, employing F-100 plano-convex cylindrical mirrors and F125 plano-concave cylindrical mirrors to further shape the 532nm laser, compensating for astigmatism caused by BBO in advance. Specifically, the spherical mirror group can be a circular spherical mirror group, and the cylindrical mirror group can be a square cylindrical mirror group.

[0040] 8. In the above-mentioned first aspect of the technical solution, the arrangement of the BBO crystals in the first BBO crystal and the second BBO crystal is as follows:

[0041] Determine the wave vector k of the BBO crystal in the xoz plane of the e-ray vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x ;

[0042] Then k x Phase mismatch Δk in the xoz plane x for: ;

[0043] in, The refractive index of the fundamental frequency light; θ is the refractive index of the frequency-doubled e-ray; m The phase matching angle;

[0044] When δθ x When the size is small, the formula Considering Δk as a fixed property of BBO crystals for a specific wavelength λ, x Simplify to obtain , where β θ Crystal characteristic parameters are used to obtain the phase mismatch Δk. x Phase mismatch angle δθ x Relationship;

[0045] When the phase mismatch angle δθ xThe resulting phase mismatch Δk x When the frequency doubling efficiency is reduced to 50% of the optical-to-optical conversion efficiency with perfect phase matching, Using the plane wave formula Derivation Substitute ,get Where L is the crystal length; let θ be... m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the xoz plane of the e-ray vibration plane is 47.6°. x For Δθ x =0.276mrad*cm, and the BBO crystal was cut at a type I phase matching angle of 47.7°;

[0046] Two BBO crystals, each 2.5 mm in length, are rotated 180° and placed tightly together. The walk-off angle of the frequency-doubled light generated by the first BBO crystal is ρ1, and the walk-off angle generated by the second BBO crystal is ρ2, where ρ1 and ρ2 are equal in magnitude but opposite in direction. The combined length of the first and second BBO crystals (both 2.5 mm in length) is 5 mm. Calculate the frequency-doubled reception angle Δθ of the 5 mm BBO crystal. x The value is 0.552 mrad. Based on the above calculations, spherical and cylindrical mirror groups with set curvature radii are used to control the emission angle of the 532nm laser incident on the BBO crystal at 0.5mrad, thereby avoiding the phase mismatch effect caused by excessive divergence angle during laser transmission in the crystal.

[0047] With this more specific calculation method, the frequency doubling receiving angle that needs to be injected into the BBO crystal can be obtained more quickly and accurately. It can also be used in conjunction with two BBO crystals that are rotated 180° and placed in close contact. In this way, the ideal 266 nm laser can be obtained. The use of dual BBO crystals and the 180° rotation can compensate for the beam drift phenomenon and obtain a good beam energy distribution.

[0048] 9. In the first aspect of the technical solution described above, the output stabilization adjustment system is used to precisely control the temperature of the phase-matched LBO crystal and BBO crystal in the first and second frequency doubling systems. An optical adjustment frame is used to adjust the optical angles of the phase-matched LBO crystal and BBO crystal in the first and second frequency doubling systems to maintain phase matching. The output stabilization adjustment system includes a heated metal base, an electrothermal ceramic plate, and a temperature feedback adjustment module. Both the LBO crystal and the BBO crystal are placed on the heated metal base. This method reliably and stably maintains the phase matching of the LBO crystal and BBO crystal during use, avoiding phase mismatch problems in the BBO crystal.

[0049] 10. In the above-mentioned second aspect of the technical solution, the second frequency multiplication system is arranged in the following manner:

[0050] Determine the wave vector k of the BBO crystal in the xoz plane of the e-ray vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x ;

[0051] Then k x Phase mismatch Δk in the xoz plane x for: When δθ x When the size is small, the formula Considering Δk as a fixed property of BBO crystals for a specific wavelength λ, x Simplify to obtain , where β θ Crystal characteristic parameters are used to obtain the phase mismatch Δk. x Phase mismatch angle δθ x Relationship;

[0052] When the phase mismatch angle δθ x The resulting phase mismatch Δk x When the frequency doubling efficiency is reduced to 50% of the optical-to-optical conversion efficiency with perfect phase matching, Using the plane wave formula Derivation Substitute ,get Where L is the crystal length; let θ be... m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the xoz plane of the e-ray vibration plane is 47.6°. x For Δθ x =0.276mrad*cm, and the BBO crystals were cut at a type I phase matching angle of 47.7°. The two BBO crystals were of equal length, each with dimensions of 4mm x 4mm x 2.5mm. Antireflection coatings of 532nm and 266nm were deposited on both ends of the BBO crystals. Specifically, the BBO crystal was 5mm long, with a frequency doubling reception angle of 0.552mrad. After shaping, this wafer assembly yielded a 532nm laser with a divergence angle of 0.5mrad.

[0053] 11. In this invention, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0054] 12. In this invention, the terms “center,” “upper,” “lower,” “bottom,” “inner,” “outer,” etc., indicate the orientation or positional relationship based on the orientation or positional assembly relationship shown in the drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0055] 13. In this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0056] 14. In addition, the term "and / or" in this application means that it includes three parallel options. For example, "A and / or B" includes option A, option B, or an option that satisfies both A and B.

[0057] Due to the application of the above-mentioned solution, the present invention has the following advantages and effects compared with the prior art:

[0058] 1. The above-mentioned solution of the present invention addresses the problem that existing deep ultraviolet lasers cannot simultaneously achieve high frequency doubling efficiency and good beam quality. It innovatively develops a new high-repetition-rate deep ultraviolet pulsed laser and its design method. In this high-repetition-rate deep ultraviolet pulsed laser, a laser shaping scheme using spherical and cylindrical mirror groups and a double BBO crystal scheme are designed based on theoretical calculations, resulting in better beam quality and beam energy distribution. When the phase matching condition is met, the wave vectors of the fundamental and frequency-doubled beams propagating within the crystal are matched, reducing energy loss due to phase mismatch and allowing more fundamental frequency energy to be converted into target frequency light. Reasonable divergence angle control and phase matching further improve the light-to-light conversion efficiency. Reasonable cutting angle combined with phase matching can avoid or reduce beam walk-off effects. The method used in this invention is critical phase matching, which has advantages over non-critical phase matching in that it has a simpler structure, higher reliability, and improves the spatial overlap of the beam propagating within the crystal. The laser output exhibits superior divergence angle and spot morphology, while stable phase matching conditions contribute to stable laser output power. This deep ultraviolet pulsed laser improves optical-to-optical conversion efficiency, achieving a 266nm deep ultraviolet laser output with excellent beam quality and conversion efficiency under high repetition rate conditions. The use of dual BBO crystals of equal length and a 180° rotation compensates for beam walk-off. Since ρ1 and ρ2 are equal in size and opposite in direction, and both crystals are of the same length, the walk-off amounts generated by the two crystals compensate for each other, resulting in a good beam energy distribution. This solves the phase mismatch problem in the BBO crystal during fourth harmonic generation and the walk-off effect of the ultraviolet beam. Finally, the obtained laser, after passing through a series of filters and beam shaping devices, outputs a stable, monochromatic deep ultraviolet laser suitable for precision lithography, micromachining, and scientific research, ensuring high laser conversion efficiency and stable output performance.

[0059] 2. The above-mentioned solution of the present invention, which is applied to the design method of a high repetition rate deep ultraviolet pulsed laser, provides strong assistance for the design of high repetition rate deep ultraviolet pulsed lasers under different application requirements and different scenario requirements. It helps to quickly and accurately design the required laser for deep ultraviolet pulsed lasers, and can also shorten the design cycle and debugging cycle, thereby improving product competitiveness. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the optical fiber seed source in an embodiment of the present invention;

[0061] Figure 2 This is a schematic diagram of a multi-stage solid-state amplifier in an embodiment of the present invention;

[0062] Figure 3 This is a schematic diagram of the first frequency multiplication system in an embodiment of the present invention;

[0063] Figure 4 This is a schematic diagram of the second frequency doubling system in an embodiment of the present invention;

[0064] Figure 5 A schematic diagram of the light spot morphology without using the pre-compensation system and the second frequency harmonic system in the embodiments of the present invention (I);

[0065] Figure 6 A schematic diagram of the light spot morphology without using the pre-compensation system and the second frequency harmonic system in the embodiments of the present invention (II);

[0066] Figure 7 A schematic diagram of the beam pattern using pre-compensation but without a dual-crystal scheme;

[0067] Figure 8 This is a schematic diagram of the light spot morphology using the pre-compensation system and the second frequency harmonic system in the embodiments of the present invention. Detailed Implementation

[0068] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0069] This invention addresses the problem of existing deep ultraviolet lasers being unable to simultaneously achieve high frequency doubling efficiency and good beam quality. It innovatively develops a new high-repetition-rate deep ultraviolet pulsed laser and its design method. The resulting laser, after passing through a series of filters and beam shaping devices, outputs a stable, monochromatic deep ultraviolet laser suitable for precision lithography, micromachining, and scientific research, ensuring high laser conversion efficiency and stable output performance.

[0070] Example 1, as Figure 1 As shown, Embodiment 1 of the present invention discloses a high repetition rate deep ultraviolet pulsed laser, the laser comprising an optical fiber seed source, a multi-stage solid-state amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system, and an output stabilization adjustment system.

[0071] The second frequency doubling system includes a first BBO crystal and a second BBO crystal.

[0072] The pre-compensation system includes a spherical lens group and a cylindrical lens group arranged in front of the first BBO crystal and the second BBO crystal.

[0073] The second frequency multiplication system and the pre-compensation system are arranged in the following manner:

[0074] Obtain the phase mismatch Δk x Phase mismatch angle δθ x The relationship was used to determine the wave vector k of the BBO crystal in the xoz plane of the e-optic vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x And calculate the phase mismatch Δk x Utilizing the inherent β property of BBO crystals for specific wavelengths θ For phase mismatch Δk x Simplify, and we get Δk x =β θ δθ x .

[0075] Establish frequency doubling efficiency and phase mismatch angle δθ x The relationship when the phase mismatch angle δθ x The resulting phase mismatch Δk x When the frequency doubling efficiency is reduced to 50% of the optical-to-optical conversion efficiency with perfect phase matching, i.e., the frequency doubling receiving angle Δθ x The frequency doubling efficiency is relative to the phase mismatch angle δθ x The full width at half maximum (FWHM) is used to derive the frequency doubling receiving angle Δθ under the given frequency doubling efficiency. x relation.

[0076] Calculate the harmonic reception angle Δθ of the BBO crystal based on its characteristics. x .

[0077] A first BBO crystal and a second BBO crystal of the same length are placed close together after being rotated 180°. The walk-off angle of the frequency-doubled light generated by the first BBO crystal is ρ1, and the walk-off angle generated by the second BBO crystal is ρ2. ρ1 and ρ2 are equal in magnitude but opposite in direction.

[0078] The harmonic reception angle Δθ of the BBO crystal is calculated based on specific crystal characteristics and the length of the combined two BBO crystals. x The spherical and cylindrical mirror groups in the pre-compensation system are selected and arranged so that the divergence angle obtained after shaping by the pre-compensation system is smaller than the harmonic reception angle Δθ. x The laser.

[0079] The output stabilization system is used to precisely control the temperature of the first and second frequency harmonic systems to maintain phase matching conditions.

[0080] Through the implementation of Embodiment 1 of this invention, a laser shaping scheme using spherical and cylindrical mirror groups and a double BBO crystal scheme were designed based on theoretical calculations, resulting in better beam quality and spot energy distribution. When the phase matching condition is met, the wave vectors of the fundamental and harmonic light propagating within the crystal are matched, reducing energy loss due to phase mismatch and allowing more fundamental light energy to be converted into target frequency light. Reasonable divergence angle control and phase matching result in higher light-to-light conversion efficiency. Reasonable cutting angle combined with phase matching can avoid or reduce beam walk-off effects. The method used in this invention is critical phase matching, which has advantages over non-critical phase matching in that the structure is simpler, the reliability is higher, the spatial overlap of the beam is better when propagating within the crystal, and the divergence angle and spot morphology of the output laser are better. Stable phase matching conditions are conducive to stable laser output power. Ultraviolet pulsed lasers improve optical-to-optical conversion efficiency, achieving a 266nm deep ultraviolet laser output with excellent beam quality and conversion efficiency under high repetition rate conditions. Using two BBO crystals of equal length and a 180° rotation compensates for beam walk-off. Since ρ1 and ρ2 are equal in size, opposite in direction, and of equal length, the walk-off amounts generated by the two crystals compensate for each other, resulting in a good beam energy distribution. This solves the phase mismatch problem and walk-off effect of the ultraviolet beam in the BBO crystal during fourth harmonic generation. Finally, the obtained laser, after passing through a series of filters and beam shaping devices, outputs a stable, monochromatic deep ultraviolet laser suitable for precision lithography, micromachining, and scientific research, ensuring high laser conversion efficiency and stable output performance.

[0081] In one embodiment of Embodiment 1 of the present invention, such as Figure 1 As shown, the fiber seed source includes a laser diode (LD), a wavelength division multiplexer (WDM), a high-reflectivity grating (HR), a ytterbium-doped fiber (YSF), a saturable absorber (SESAM), and a first acousto-optic modulator (ISO). After being driven, the laser diode emits continuous pump light, which enters the ytterbium-doped fiber through the WDM and HR. The ytterbium-doped fiber absorbs the pump light energy, and a 1064nm laser is generated by a linear resonant cavity formed by the HR, ytterbium-doped fiber, and saturable absorber mirror. After passing through the first acousto-optic modulator, the laser is amplified by the ytterbium-doped fiber pumped by the semiconductor laser and output as a high-repetition-frequency pulsed laser with a wavelength of 1064nm. Thus, the fiber seed source outputs a laser pulse with a wavelength of 1064nm and a power of approximately 50mW, allowing the continuous pump light emitted by the laser diode to circulate within the cavity with minimal loss, ultimately forming and maintaining a stable ultrashort pulse sequence before output, providing high-quality laser pulses for subsequent components of the deep ultraviolet pulsed laser. Furthermore, a photodetector (PD) can be placed inside the ring resonant cavity to monitor the laser characteristics inside or output in real time, thereby ensuring the stability of the laser pulse output from the fiber seed source.

[0082] In another embodiment of the first embodiment of the present invention, the multi-stage solid-state amplifier includes a first-stage amplifier, a second-stage amplifier, a third-stage amplifier, and a fourth-stage amplifier;

[0083] The first-stage amplifier includes a first-stage pump source, a convex lens M1, a first laser crystal, a plane mirror M2, and a plane mirror M3;

[0084] The secondary amplifier includes a secondary pump source, a plane mirror M4, a convex lens M5, a second laser crystal, a concave lens M6, and a plane mirror M7;

[0085] The three-stage amplifier includes a three-stage pump source, a plane mirror M10, a convex lens M11, a third laser crystal, a concave lens M12, and a plane mirror M13;

[0086] The four-stage amplifier includes a four-stage pump source, a plane mirror M16, a convex lens M17, a fourth laser crystal, a concave lens M18, and a plane mirror M19.

[0087] The more specific application and arrangement of the multi-stage solid-state amplifiers described above allows the laser pulse with a wavelength of 1064nm and a power of approximately 50mW output from the fiber seed source to be amplified by the multi-stage solid-state amplifiers, further improving the efficiency of optical-to-optical conversion. This ensures that the 1064nm laser output from the multi-stage solid-state amplifiers has sufficiently high power and energy.

[0088] More specifically, in the multi-stage solid-state amplifier, the first, second, third, and fourth laser crystals all use Nd:YVO4 crystals as gain media and employ end-pumping to achieve high-efficiency amplification; the first-stage, second-stage, third-stage, and fourth-stage pump sources all use 888nm LD lasers as pump sources; convex lens M1 is a convex lens with a focal length of F=750; plane mirrors M2, M3, M4, M7, M10, M13, and M16 have a 1064nm high-reflection coating on their surfaces; convex lenses M5, M11, and M17 are convex lenses with a focal length of F=400 and an anti-reflection coating with a 1064nm band on their surfaces; concave lenses M6, M12, and M18 are concave lenses with a focal length of F=-75 and an anti-reflection coating with a 1064nm band on their surfaces. This design, employing the more specific components of a multi-stage solid-state amplifier, enables ultra-high gain amplification while ensuring beam quality and stability, thus providing greater support for achieving high frequency doubling efficiency and good beam quality.

[0089] In one embodiment of the first embodiment of the present invention, the second acousto-optic modulator includes an AOM beam splitting module. The AOM beam splitting module controls the intensity and output direction of the incident laser to achieve beam splitting and control the diffraction efficiency to above 80%, thereby ensuring maximum utilization of the amplified laser energy and ensuring that the 1064nm laser entering the first frequency doubling system after beam splitting is stable and of high quality.

[0090] In another embodiment of the first embodiment of the present invention, the first frequency doubling system includes a convex lens M20, a concave lens M21, a convex lens M22, and an LBO crystal. The convex lens M20 is a convex lens with a focal length of F=150 and a surface coated with an anti-reflection film in the 1064nm band. The concave lens M21 is a concave lens with an f=-100 and a surface coated with an anti-reflection film in the 1064nm band. The convex lens M22 is a convex lens with an f=125 and a surface coated with an anti-reflection film in the 1064nm band. The cutting angle of the LBO crystal is precisely set to 90° and 11.3° according to the phase matching conditions. The 90° cutting angle corresponds to the optical axis direction of the LBO crystal, and the 11.3° cutting angle is an auxiliary phase matching angle that works in conjunction with the 90° angle. With this design, the split laser enters the LBO (lithium niobium phosphate) frequency doubling system. The LBO crystal with this specific phase matching design converts the 1064nm laser into a 532nm laser. In order to improve the frequency doubling conversion efficiency, the 532nm beam passes through a series of mirrors and shaping optical elements to focus it into the LBO crystal.

[0091] In another embodiment of the first embodiment of the present invention, a concave lens M23, a convex lens M24, a cylindrical concave lens M25, and a cylindrical convex lens M26 are sequentially arranged in the incident direction of the first BBO crystal and the second BBO crystal. The concave lens M23 and the convex lens M24 constitute the spherical lens group in the pre-compensation system, and the cylindrical concave lens M25 and the cylindrical convex lens M26 constitute the cylindrical lens group in the pre-compensation system. The concave lens M23 is a concave lens with a focal length of F=-50 and a surface coated with a 532nm anti-reflection film. The convex lens M24 is a convex lens with an focal length of F=150 and a surface coated with a 532nm anti-reflection film. The cylindrical concave lens M25 is a cylindrical concave lens with a focal length of F=-100 and a surface coated with a 532nm anti-reflection film. The cylindrical convex lens M26 is a cylindrical convex lens with a focal length of F=125 and a surface coated with a 532nm anti-reflection film. Therefore, this design specifically outlines further shaping of the 532nm laser before it enters the second frequency doubling system. Specifically, a pre-compensation method is employed, using F-100 plano-convex cylindrical mirrors and F125 plano-concave cylindrical mirrors to further shape the 532nm laser, compensating for astigmatism generated by the BBO (Browser-Based Astigmatism) in advance. Specifically, the spherical mirror group can be a circular spherical mirror group, and the cylindrical mirror group can be a square cylindrical mirror group.

[0092] In one embodiment of the first embodiment of the present invention, the arrangement of the BBO crystals in the first BBO crystal and the second BBO crystal is as follows:

[0093] Determine the wave vector k of the BBO crystal in the xoz plane of the e-ray vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x ;

[0094] Then k x Phase mismatch Δk in the xoz plane x for: ;

[0095] in The refractive index of the fundamental frequency light; θ is the refractive index of the frequency-doubled e-ray; m The phase matching angle;

[0096] When δθ x When the size is small, the formula Considering Δk as a fixed property of BBO crystals for a specific wavelength λ, x Simplify to obtain , where β θ Crystal characteristic parameters are used to obtain the phase mismatch Δk. x Phase mismatch angle δθ x Relationship;

[0097] When the phase mismatch angle δθ x The resulting phase mismatch Δk x When the frequency doubling efficiency is reduced to 50% of the optical-to-optical conversion efficiency with perfect phase matching, Using the plane wave formula Derivation Substitute ,get Where L is the crystal length; let θ be... m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the xoz plane of the e-ray vibration plane is 47.6°. x For Δθ x =0.276mrad*cm, and the BBO crystal was cut at a type I phase matching angle of 47.7°;

[0098] Two BBO crystals of the same length were rotated 180° and placed close together, so that the optical axes of the two crystals formed a phase mismatch angle δθ, which was twice the angle between their optical axes. x This results in the energy propagation direction of the frequency-doubled light generated in the first BBO crystal having a walk-off angle of ρ1 with respect to the fundamental frequency light, and a walk-off angle of ρ2 generated by the second BBO crystal, where ρ1 and ρ2 are equal in magnitude but opposite in direction.

[0099] Based on the above calculations, spherical and cylindrical mirror groups with set curvature radii are used to control the emission angle of the 532nm laser incident on the BBO crystal at 0.5mrad.

[0100] With this more specific calculation method, the frequency doubling receiving angle that needs to be injected into the BBO crystal can be obtained more quickly and accurately. It can also be used in conjunction with two BBO crystals that are rotated 180° and placed in close contact. In this way, the ideal 266 nm laser can be obtained. The use of dual BBO crystals and the 180° rotation can compensate for the beam drift phenomenon and obtain a good beam energy distribution.

[0101] In another embodiment of the first embodiment of the present invention, the output stabilization adjustment system is used to precisely control the temperature of the phase-matched LBO crystal and BBO crystal in the first and second frequency doubling systems. An optical adjustment frame is used to adjust the optical angles of the phase-matched LBO crystal and BBO crystal in the first and second frequency doubling systems to maintain phase matching. The output stabilization adjustment system includes a heated metal base, an electrothermal ceramic plate, and a temperature feedback adjustment module. Both the LBO crystal and the BBO crystal are placed on the heated metal base. This method reliably and stably maintains the phase matching of the LBO crystal and BBO crystal during use, avoiding phase mismatch problems in the BBO crystal.

[0102] In another embodiment of the first embodiment of the present invention, the second frequency doubling system is arranged in the following manner:

[0103] Determine the wave vector k of the BBO crystal in the xoz plane of the e-ray vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x ;

[0104] Then k x Phase mismatch Δk in the xoz plane x for: When δθ x When the size is small, the formula Considering Δk as a fixed property of BBO crystals for a specific wavelength λ, x Simplify to obtain , where β θ Crystal characteristic parameters are used to obtain the phase mismatch Δk. x Phase mismatch angle δθ x Relationship;

[0105] When the phase mismatch angle δθ x The resulting phase mismatch Δk xWhen the frequency doubling efficiency is reduced to 50% of the optical-to-optical conversion efficiency with perfect phase matching, Using the plane wave formula Derivation Substitute ,get Where L is the crystal length; let θ be... m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the xoz plane of the e-ray vibration plane is 47.6°. x For Δθ x =0.276mrad*cm, and the BBO crystals were cut at a type I phase matching angle of 47.7°. The two BBO crystals were of equal length (2.5mm each), with specific dimensions of 4mm x 4mm x 2.5mm. Anti-reflection coatings of 532nm and 266nm were deposited on both ends of the BBO crystals. Specifically, the BBO crystal was 5mm long, with a frequency doubling reception angle of 0.552mrad. After shaping, this wafer assembly yielded a 532nm laser with a divergence angle of 0.5mrad.

[0106] Example 2: This invention proposes a design method for a high repetition rate deep ultraviolet pulsed laser. The design method is used to design the high repetition rate deep ultraviolet pulsed laser as described in the first aspect of this invention. The design method includes the following steps:

[0107] The setup includes a high repetition rate deep ultraviolet pulsed laser comprising an optical fiber seed source, a multi-stage solid-state amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system, and an output stabilization adjustment system.

[0108] In the process of setting up the first frequency doubling system, a convex lens M20, a concave lens M21, a convex lens M22, and an LBO crystal are installed along the laser path. The cutting angle of the LBO crystal is precisely set according to the phase matching conditions.

[0109] A concave lens M23, a convex lens M24, a cylindrical concave lens M25, and a cylindrical convex lens M26 are arranged in front of the first BBO crystal and the second BBO crystal in the second frequency doubling system.

[0110] The second frequency harmonic system shall be arranged in the following manner:

[0111] Determine the wave vector k of the BBO crystal in the xoz plane of the e-ray vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x ;

[0112] Then k x Phase mismatch Δk in the xoz plane x for: When δθ x When the size is small, the formula Considering Δk as a fixed property of BBO crystals for a specific wavelength λ, x Simplify to obtain , where β θ These are crystal characteristic parameters, used to obtain the phase mismatch Δk. x Phase mismatch angle δθ x Relationship;

[0113] When the phase mismatch angle δθ x The resulting phase mismatch Δk x When the frequency doubling efficiency is reduced to 50% of the optical-to-optical conversion efficiency with perfect phase matching, Using the plane wave formula Derivation Substitute ,get Where L is the crystal length; let θ be... m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the xoz plane of the e-ray vibration plane is 47.6°. x For Δθ x =0.276mrad*cm, and the BBO crystals were cut at a type I phase matching angle of 47.7°. The two BBO crystals were of equal length, each with dimensions of 4mm x 4mm x 2.5mm. Antireflection coatings of 532nm and 266nm were deposited on both ends of the BBO crystals. Specifically, the length of the BBO crystal was 5mm, and its frequency doubling reception angle was 0.552mrad. After shaping, this wafer set yielded a 532nm laser with a divergence angle of 0.5mrad.

[0114] Based on the above calculations, a circular plano-convex spherical mirror with a radius of curvature of F-50 and a circular plano-concave spherical mirror with a radius of curvature of F150 are used to control the emission angle of the 532nm laser incident on the BBO crystal at 0.5mrad. Furthermore, since the frequency-harmonic light generated after the fundamental frequency light passes through the BBO crystal produces significant astigmatism, this invention employs a pre-compensation method using a square plano-convex cylindrical mirror of F-100 and a square plano-concave cylindrical mirror of F125 to further shape the 532nm laser, compensating for the astigmatism generated by the BBO in advance.

[0115] Through the implementation of Embodiment 2 of the present invention, the application of a design method for a high repetition rate deep ultraviolet pulsed laser provides strong assistance for the design of high repetition rate deep ultraviolet pulsed lasers under different application requirements and scenario requirements. It helps to quickly and accurately design the required laser for deep ultraviolet pulsed lasers, and can also shorten the design cycle and debugging cycle, thereby improving product competitiveness.

[0116] Furthermore, in the implementation of the high repetition rate deep ultraviolet pulsed laser in Embodiments 1 and 2 of this invention, the special settings of the double BBO crystals in the pre-compensation system and the second frequency doubling system were used to acquire laser signal image spot morphology under different conditions. The spot morphology without using the pre-compensation system and the second frequency doubling system in the embodiments of this invention is as follows: Figure 5 , Figure 6 As shown, the spot roundness is 45.7%, indicating poor quality; the spot morphology using pre-compensation but without a dual-crystal scheme is as follows. Figure 7 As shown, the roundness is 85%, which is an improvement compared to before using pre-compensation. However, obvious distortion of the beam pattern due to beam drift can be seen in the beam pattern. The beam pattern of the system using the pre-compensation system and the second harmonic system in this embodiment is as follows: Figure 8 As shown, its spot roundness is 92.4%, which improves the spot shape distortion caused by the departure of the light.

[0117] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high repetition rate deep ultraviolet pulse laser, characterized in that: the laser comprises a fiber seed source, a multi-stage solid-state amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system, and an output stabilization adjustment system; the fiber seed source comprises a laser diode, a wavelength division multiplexer, a high-reflection grating, a ytterbium-doped fiber, a saturable absorber, and a first acousto-optic modulator; the laser diode emits continuous pumping light after being driven, the continuous pumping light enters the ytterbium-doped fiber through the wavelength division multiplexer and the high-reflection grating, the ytterbium-doped fiber absorbs the pumping light energy, a linear resonant cavity is formed by the high-reflection grating, the ytterbium-doped fiber, and the saturable absorber to generate 1064 nm pulse laser, the pulse laser is amplified by a ytterbium-doped fiber pumped by a semiconductor laser after passing through the first acousto-optic modulator, and then high repetition rate pulse laser with a wavelength of 1064 nm is output; the second frequency doubling system comprises a first BBO crystal and a second BBO crystal; the pre-compensation system comprises a spherical lens group and a cylindrical lens group arranged in front of the first BBO crystal and the second BBO crystal; the second frequency doubling system and the pre-compensation system are arranged in the following manner: the frequency doubling acceptance angle of the BBO crystal is calculated according to the characteristics of the BBO crystal; the first BBO crystal and the second BBO crystal with the same length are placed in close contact with a rotation of 180°, the walk-off angle of the frequency-doubled light generated by the first BBO crystal is ρ1, and the walk-off angle generated by the second BBO crystal is ρ2, wherein ρ1 and ρ2 are equal in size and opposite in direction; the spherical lens group and the cylindrical lens group in the pre-compensation system are selected according to the frequency doubling acceptance angle of the BBO crystal calculated according to the specific crystal characteristics and the length of the two BBO crystal combinations, so that the laser with a divergence angle less than the frequency doubling acceptance angle is obtained after being shaped by the pre-compensation system; the output stabilization adjustment system is used to accurately control the temperature of the first frequency doubling system and the second frequency doubling system to maintain the phase matching condition; the multi-stage solid-state amplifier comprises a first-stage amplifier, a second-stage amplifier, a third-stage amplifier, and a fourth-stage amplifier; the first-stage amplifier comprises a first-stage pump source, a convex lens M1, a first laser crystal, a plane mirror M2, and a plane mirror M3; the second-stage amplifier comprises a second-stage pump source, a plane mirror M4, a convex lens M5, a second laser crystal, a concave lens M6, and a plane mirror M7; the third-stage amplifier comprises a third-stage pump source, a plane mirror M10, a convex lens M11, a third laser crystal, a concave lens M12, and a plane mirror M13; and the fourth-stage amplifier comprises a fourth-stage pump source, a plane mirror M16, a convex lens M17, a fourth laser crystal, a concave lens M18, and a plane mirror M19. ​ ​ ​ ​ ​ Obtain the phase mismatch amount and phase mismatch angle δθ x The relationship was used to determine the wave vector k of the BBO crystal in the xoz plane of the e-optic vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x And calculate the phase mismatch Δk x Utilizing the inherent β property of BBO crystals for specific wavelengths θ For phase mismatch Δk x Simplify, and we get Δk x =β θ δθ x ; The relationship between the frequency doubling efficiency and the phase mismatch angle is established. When the phase mismatch caused by the phase mismatch angle reduces the frequency doubling efficiency to 50% of the light- light conversion efficiency of the complete phase matching, the frequency doubling acceptance angle is the full width at half maximum of the frequency doubling efficiency relative to the phase mismatch angle δθ x The frequency doubling acceptance angle relationship under the set frequency doubling efficiency is derived. ​ ​ ​ ​ 2. The high repetition rate deep-ultraviolet pulse laser of claim 1, wherein: ​ ​ ​ ​ ​ 3. The high repetition rate deep-ultraviolet pulse laser of claim 2, wherein: In the multi-stage solid-state amplifier, the first laser crystal, the second laser crystal, the third laser crystal and the fourth laser crystal all adopt a Nd:YVO4 crystal as a gain medium, and an end-pumping mode is adopted to realize high-efficiency amplification; the first pump source, the second pump source, the third pump source and the fourth pump source all adopt a wavelength of 888nm LD laser as a pump source; the convex lens M1 is a convex lens with a focal length of F=750; the surfaces of the plane mirrors M2, M3, M4, M7, M10, M13 and M16 are coated with a 1064nm waveband high-reflection film; the convex lenses M5, M11 and M17 are convex lenses with a focal length of F=400 and a 1064nm waveband anti-reflection film on the surfaces; and the concave lenses M6, M12 and M18 are concave lenses with a focal length of F=-75 and a 1064nm waveband anti-reflection film on the surfaces.

4. The high-repetition-rate deep-ultraviolet pulse laser of claim 1, wherein: The second acousto-optic modulator comprises an AOM light splitting module, which controls the intensity and the outgoing direction of the incident laser by driving, realizes light splitting function and controls the diffraction efficiency to be above 80%.

5. The high repetition rate deep-ultraviolet pulse laser of claim 1, wherein: In the first frequency doubling system, there are a convex lens M20, a concave lens M21, a convex lens M22 and an LBO crystal, wherein the convex lens M20 is a convex lens with a focal length of F=150 and a 1064nm waveband anti-reflection film on the surface, the concave lens M21 is a concave lens with F=-100 and a 1064nm waveband anti-reflection film on the surface, and the convex lens M22 is a convex lens with F=125 and a 1064nm waveband anti-reflection film on the surface; the cutting angle of the LBO crystal is accurately set to 90° and 11.3° according to the phase matching condition, the 90° cutting angle corresponds to the optical axis direction of the LBO crystal, and the 11.3° cutting angle is an auxiliary phase matching angle cooperating with the 90° angle.

6. The high repetition rate deep-ultraviolet pulse laser of claim 1, wherein: In the incident direction of the first BBO crystal and the second BBO crystal, there are in sequence a concave lens M23, a convex lens M24, a cylindrical concave lens M25 and a cylindrical convex lens M26, wherein the concave lens M23 and the convex lens M24 constitute a spherical lens group in the pre-compensation system, and the cylindrical concave lens M25 and the cylindrical convex lens M26 constitute a cylindrical lens group in the pre-compensation system, wherein the concave lens M23 is a concave lens with a focal length of F=-50 and a 532nm waveband anti-reflection film on the surface, the convex lens M24 is a convex lens with F=150 and a 532nm waveband anti-reflection film on the surface, the cylindrical concave lens M25 is a cylindrical concave lens with a focal length of F=-100 and a 532nm waveband anti-reflection film on the surface, and the cylindrical convex lens M26 is a cylindrical convex lens with a focal length of F=125 and a 532nm waveband anti-reflection film on the surface.

7. The high repetition rate deep-ultraviolet pulse laser of claim 1, wherein: In the arrangement of the BBO crystals in the first BBO crystal and the second BBO crystal: The wave vector k of the BBO crystal in the xoz plane of the e light oscillation surface is determined x The deflection angle of the pass light axis oz is the phase mismatch angle δθ x ; then k x the phase mismatch amount Δk in the xoz plane x is: ; wherein, is the base frequency light o light refractive index; is the frequency-doubled light e light refractive index; θ m is the phase matching angle; When δθ x is small, the formula is considered as a fixed property of the BBO crystal for a specific wavelength λ, and Δk x is simplified to where β θ is a crystal-specific parameter, and Δk x is obtained as a function of the phase mismatch angle δθ x . When the phase mismatch angle δθ x The phase mismatch amount Δk x When the frequency doubling efficiency is reduced to 50% of the light-light conversion efficiency of the complete phase matching, 2δθ x = Δθ x ; using the plane wave formula Derivation of , substitution of , obtains , wherein L is the crystal length; set θ m = 47.6°, then the frequency doubling acceptance angle Δθ x of the BBO crystal per centimeter in the e light vibration plane xoz is Δθ x = 0.276 mrad*cm, and the BBO crystal is cut at the I-type phase matching angle 47.7°; The first BBO crystal and the second BBO crystal each having a length of 2.5 mm are closely placed with a rotation of 180°, and then the walk-off angle of the frequency-doubled light generated from the first BBO crystal is p1, and the walk-off angle generated by the second BBO crystal is p2, wherein p1 and p2 are equal in size and opposite in direction; wherein the first BBO crystal and the second BBO crystal each having a length of 2.5 mm are combined to have a length of 5 mm, and the frequency-doubled receiving angle of the 5-mm BBO crystal is calculated as Δθ x 0.552 mrad; According to the above calculation, the spherical lens group and the cylindrical lens group with the set curvature radius are adopted, so that the 532nm laser emission angle into the BBO crystal is controlled to be 0.5mrad.

8. The high repetition rate deep-ultraviolet pulse laser of claim 7, wherein: The output stabilization adjustment system is used for precisely controlling the temperature of the phase-matched LBO crystal and BBO crystal in the first frequency doubling system and the second frequency doubling system, and the optical angle of the phase-matched LBO crystal and BBO crystal in the first frequency doubling system and the second frequency doubling system is adjusted by the optical adjustment frame to maintain the phase matching adjustment, wherein the output stabilization adjustment system comprises a heating metal base, an electrothermal ceramic sheet and a temperature feedback adjustment module, and the LBO crystal and the BBO crystal are both arranged on the heating metal base.

9. A design method for a high repetition rate deep ultraviolet pulsed laser, characterized in that, The design method is used for designing the high repetition rate deep ultraviolet pulse laser according to any one of claims 1 to 8, and the design method comprises the following steps: The high repetition rate deep ultraviolet pulse laser comprises a fiber seed source, a multi-stage solid-state amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system and an output stabilization adjustment system. When the first frequency doubling system is arranged, a convex lens M20, a concave lens M21, a convex lens M22 and the LBO crystal are installed, and the cutting angle of the LBO crystal is accurately set according to the phase matching condition; A concave lens M23, a convex lens M24, a cylindrical concave lens M25 and a cylindrical convex lens M26 are arranged in front of the first BBO crystal and the second BBO crystal of the second frequency doubling system; When arranging the pre-compensation system and the second harmonic system, the following arrangement is adopted: to obtain the phase mismatch Δk x Phase mismatch angle δθ x The relationship was used to determine the wave vector k of the BBO crystal in the xoz plane of the e-optic vibration plane. x The deflection angle relative to the optical axis oz is the phase mismatch angle δθ. x And calculate the phase mismatch Δk x Utilizing the inherent β property of BBO crystals for specific wavelengths θ For phase mismatch Δk x Simplify, and we get Δk x =β θ δθ x ; Establish frequency doubling efficiency and phase mismatch angle δθ x The relationship when the phase mismatch angle δθ x The resulting phase mismatch Δk x This reduces the frequency doubling efficiency to 50% of the perfectly phase-matched optical-to-optical conversion efficiency, i.e., the frequency doubling receiver angle Δθ. x The frequency doubling efficiency is relative to the phase mismatch angle δθ x The full width at half maximum (FWHM) is used to derive the frequency doubling receiving angle Δθ under the given frequency doubling efficiency. x relation; The receiving angle Δθ of the BBO crystal is calculated according to the characteristics of the BBO crystal x The first frequency doubling system is shaped by using a cylindrical lens group and a spherical lens group of a pre-compensation system, so that the divergence angle of the laser generated by the second frequency doubling system is less than Δθ x ​ The first BBO crystal and the second BBO crystal with the same length are tightly placed in a rotation of 180°, and the walk-off angle of the frequency-doubled light generated in the first BBO crystal is ρ1, and the walk-off angle generated by the second BBO crystal is ρ2, wherein ρ1 and ρ2 are equal in size and opposite in direction; The output stabilization adjustment system is used for precisely controlling the temperature of the phase-matched LBO crystal and BBO crystal in the first frequency doubling system and the second frequency doubling system, and the optical angle of the phase-matched LBO crystal and BBO crystal in the first frequency doubling system and the second frequency doubling system is adjusted by the optical adjustment frame to maintain the phase matching adjustment.

10. The method of designing a high repetition rate deep-ultraviolet pulse laser of claim 9, wherein: When the second frequency doubling system is arranged, the following arrangement is adopted: The wave vector k of the BBO crystal in the xoz plane of the e light oscillation surface is determined x The deflection angle of the pass light axis oz is the phase mismatch angle δθ x ; then k x the phase mismatch amount Δk in the xoz plane x is: ; when δθ x is small, the formula is considered as a fixed property of the BBO crystal for a specific wavelength λ, Δk x is simplified to , where β θ is a crystal characteristic parameter, and the phase mismatch amount Δk x is obtained by this x relationship with the phase mismatch angle δθ When the phase mismatch angle δθ x The phase mismatch amount Δk x When the frequency doubling efficiency is reduced to 50% of the light-light conversion efficiency of the complete phase matching, 2δθ x = Δθ x ; using the plane wave formula Derivation of , into , get , where L is the length of the crystal; set θ m = 47.6°, then the acceptance angle Δθ x of the BBO crystal per centimeter in the e light vibration plane xoz is Δθ x = 0.276 mrad*cm, and the BBO crystal is cut at the I type phase matching angle 47.7°, the lengths of the two BBO crystals are equal, the sizes are both 4mmx4mmx2.5mm, and the 532nm and 266nm antireflection films are plated on the two end surfaces of the BBO crystal.

Images