High repetition frequency deep ultraviolet pulse laser and design method thereof

Abstract

The invention provides a high repetition frequency deep ultraviolet pulse laser and a design method thereof. The laser comprises an optical fiber seed source, a multi-stage solid amplifier, a second acousto-optic modulator, a first frequency doubling system, a pre-compensation system, a second frequency doubling system and an output stability adjusting 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 which are arranged in front of the first BBO crystal and the second BBO crystal. And the output stability adjusting system is used for accurately controlling the temperature of the first frequency doubling system and the second frequency doubling system so as to maintain a phase matching condition. The obtained laser passes through a series of optical filters and light beam shaping devices, deep ultraviolet laser which is stable and good in monochromaticity is output, the device is suitable for the fields of precise photoetching, micromachining and scientific research, and efficient laser conversion efficiency and stable output performance are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of deep ultraviolet lasers, and in particular to a high repetition rate deep ultraviolet pulse laser and a design method thereof. Background Art

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

[0003] Deep ultraviolet lasers are a new type of laser technology, featuring high power and high energy density in the deep ultraviolet wavelength range (200-300nm). The development of this technology has brought important breakthroughs in many fields, including semiconductors, photolithography, biosciences, and materials processing. In the field of semiconductor testing, high-repetition-rate deep ultraviolet pulsed lasers play an important role. Deep ultraviolet pulsed lasers can be obtained through frequency doubling, but excessively high repetition rates reduce the peak pulse power of the laser, which in turn reduces the light-to-light conversion efficiency during the frequency doubling process.

[0004] Currently, while maintaining a high laser pulse repetition rate, a common approach to addressing this problem is to reduce the fundamental frequency spot size at the frequency-doubling crystal, thereby increasing the laser's power density and, consequently, the frequency-doubling conversion efficiency. However, this approach can lead to poor beam quality and spot energy distribution. Because BBO crystals have a small frequency-doubling acceptance angle and a large walk-off angle, previous methods have made it difficult to achieve a high-quality 266nm laser spot.

[0005] In view of this, the problem that existing deep ultraviolet lasers cannot simultaneously achieve high frequency doubling efficiency and good frequency doubling light beam quality has become a topic to be studied and solved by the present invention. Summary of the Invention

[0006] The purpose of the present invention is to provide a high repetition rate deep ultraviolet pulse laser and a design method thereof.

[0007] To achieve the above-mentioned object, the first aspect of the present invention provides a high repetition rate deep ultraviolet pulse laser.

[0008] The laser comprises an optical fiber seed source, a multi-stage solid 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 mirror group and a cylindrical mirror 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] Get the phase mismatch Δk x and the phase mismatch angle δθ x The relationship between the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane is determined. x The deflection angle with the optical axis oz is the phase mismatch angle δθ x , and calculate the phase mismatch Δk x , using the inherent properties of BBO crystals for specific wavelengths β θ Phase mismatch Δk x Simplify and get Δk x =β θ δθ x .

[0013] Establish the frequency doubling efficiency and phase mismatch angle δθ x When the phase mismatch angle δθ x The phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency with complete phase matching, the frequency doubling acceptance angle Δθ x is the frequency doubling efficiency relative to the phase mismatch angle δθ x The full width at half maximum is used to derive the SHG acceptance angle Δθ under the set SHG efficiency. x relation.

[0014] Calculate the BBO crystal's frequency doubling acceptance angle Δθ based on the BBO crystal's characteristics x .

[0015] The first BBO crystal and the second BBO crystal of the same length are rotated 180° and placed closely 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 size and opposite in direction.

[0016] The BBO crystal's doubled frequency acceptance angle Δθ is calculated based on the specific crystal characteristics and the length of the two BBO crystals combined. x To select and arrange the spherical mirror group and cylindrical mirror group in the pre-compensation system so that the divergence angle obtained after shaping by the pre-compensation system is smaller than the frequency doubling receiving angle Δθ x laser.

[0017] The output stabilization adjustment system is used to precisely control the temperature of the first frequency doubling system and the second frequency doubling system 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] A high repetition rate deep ultraviolet pulse laser is arranged including 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] Among them, when arranging the first frequency doubling system, the laser path is installed to set the convex lens M20, the concave lens M21, the convex lens M22, and the LBO crystal, and the cutting angle of the LBO crystal is accurately 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 of the second frequency doubling system;

[0022] When arranging the pre-compensation system and the second frequency doubling system, the following arrangement is adopted: Obtain the phase mismatch Δk x and the phase mismatch angle δθ x The relationship between the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane is determined. x The deflection angle with the optical axis oz is the phase mismatch angle δθ x , and calculate the phase mismatch Δk x , using the inherent properties of BBO crystals for specific wavelengths β θ Phase mismatch Δk x Simplify and get Δk x =β θ δθ x ;

[0023] Establish the frequency doubling efficiency and phase mismatch angle δθ x When the phase mismatch angle δθ x The phase mismatch Δk caused by x The frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, that is, the frequency doubling acceptance angle Δθ x is the frequency doubling efficiency relative to the phase mismatch angle δθ x The full width at half maximum is used to derive the SHG acceptance angle Δθ under the set SHG efficiency. x relation;

[0024] Calculate the BBO crystal's frequency doubling acceptance angle Δθ based on the BBO crystal's characteristics x , use the cylindrical lens group and spherical lens group of the pre-compensation system 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 Δθx ;

[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, where ρ1 and ρ2 are equal in magnitude and opposite in direction;

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

[0027] The relevant contents of the present invention are explained as follows:

[0028] 1. In the above technical solution of the present invention, in order to solve the problem that the existing deep ultraviolet laser cannot achieve high frequency doubling efficiency and good quality of the frequency doubling light beam at the same time, a new high repetition rate deep ultraviolet pulse laser and its design method are innovatively developed. In the high repetition rate deep ultraviolet pulse laser, the laser shaping scheme of the spherical mirror group and the cylindrical mirror group and the double BBO crystal scheme are designed after theoretical calculation to obtain better beam quality and spot energy distribution. When the phase matching conditions are met, the wave vectors of the fundamental frequency light and the frequency doubling light propagating in the crystal are matched, which reduces the energy loss caused by phase mismatch and allows more fundamental frequency light energy to be converted into target frequency light. Reasonable cutting angle and phase matching can avoid or reduce the beam walk-off effect. The method used in the present invention is critical phase matching. Compared with non-critical phase matching, the advantages are simpler structure and higher reliability, which makes the spatial overlap of the light beam good when propagating in the crystal, and the divergence angle of the output laser is The spot morphology is better, and the stable phase matching conditions are conducive to the stability of the laser output power; the deep ultraviolet pulsed laser improves the light-to-light conversion efficiency, and obtains a 266nm deep ultraviolet laser output with excellent beam quality and conversion efficiency under the premise of high repetition rate. The use of double BBO crystals of the same length and a 180° rotation position compensates for the walk-off phenomenon of the light spot. Since ρ1 and ρ2 are equal in size and opposite in direction, and the two crystals are of the same length, the walk-offs generated by the two crystals compensate each other to obtain a good spot energy distribution, solving the phase mismatch problem of the light beam in the BBO crystal during the quadruple frequency process and the walk-off effect of the ultraviolet light beam. Finally, the obtained laser passes through a series of filters and beam shaping devices to output stable, monochromatic deep ultraviolet laser, which is 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 powerful support 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 deep ultraviolet pulsed lasers, shorten their design and debugging cycles, and enhance product competitiveness.

[0029] 2. In the technical solution of the first aspect above, the optical fiber seed source includes a laser diode, a wavelength division multiplexer, a high-reflection grating, an ytterbium-doped optical 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 optical fiber through the wavelength division multiplexer and the high-reflection grating. The ytterbium-doped optical fiber absorbs the pump light energy. The high-reflection grating, the ytterbium-doped optical fiber, and the saturable absorber form a linear resonant cavity to generate 1064nm laser light. After passing through the first acousto-optic modulator, it is amplified by the ytterbium-doped optical fiber pumped by the semiconductor laser to output a high repetition frequency wavelength of 1064nm pulse laser. This optical fiber seed source outputs laser pulses 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 minimum loss, and finally forms and maintains a stable ultrashort pulse sequence and outputs it, providing high-quality laser pulses for subsequent components of the deep ultraviolet pulse laser. Furthermore, a photodetector PD can be set in the ring resonator to monitor the laser characteristics in the cavity or at the output in real time, so as to ensure the stability of the laser pulse output by the optical fiber seed source.

[0030] 3. In the above-mentioned first aspect of the technical solution, 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 reflector M2, and a plane reflector M3;

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

[0033] The three-stage amplifier includes a three-stage pump source, a plane reflector M10, a convex lens M11, a third laser crystal, a concave lens M12, and a plane reflector 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] Through the above more specific application and arrangement of the multi-stage solid-state amplifier, the laser pulse with a wavelength of 1064nm and a power of about 50mW output by the optical fiber seed source is amplified by the multi-stage solid-state amplifier, so that the power and energy of the 1064nm laser output by the multi-stage solid-state amplifier are high enough.

[0036] 4. In the above-mentioned first aspect of the 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 adopt an end-pumping method 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 LD lasers with a wavelength of 888nm 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 high-reflection film in the 1064nm band; the convex lenses M5, M11, and M17 are convex lenses with a focal length of F=400 and an anti-reflection film on the surface of the 1064nm band; the concave lenses M6, M12, and M18 are concave lenses with a focal length of F=-75 and an anti-reflection film on the surface of the 1064nm band. Thus, the design adopts the composition of the components of the above more specific multi-stage solid-state amplifier, which can achieve ultra-high gain amplification and ensure the beam quality and stability, thereby providing more support for the simultaneous realization of high frequency doubling efficiency and good frequency doubling light beam quality.

[0037] 5. In the above-mentioned first technical solution, the second acousto-optic modulator includes an AOM spectrometer module. The AOM spectrometer module realizes the spectrometer function by driving and controlling the intensity and emission direction of the incident laser and controls the diffraction efficiency to above 80%. This ensures maximum utilization of the amplified laser energy and ensures that the 1064nm laser entering the first frequency doubling system after spectrometry is stable and high-quality.

[0038] 6. In the technical solution of the first aspect above, the first frequency doubling system includes 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 surface coated with a 1064nm band anti-reflection film, the concave lens M21 is a concave lens with an F=-100 and a surface coated with a 1064nm band anti-reflection film, and the convex lens M22 is a convex lens with an F=125 and a surface coated with a 1064nm band anti-reflection film; the cutting angle of the LBO crystal is precisely 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, which cooperates 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. 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 above-mentioned technical solution of the first aspect, a concave lens M23, a convex lens M24, a cylindrical concave lens M25, and a cylindrical convex lens M26 are further provided in sequence in the incident direction of the first BBO crystal and the second BBO crystal, 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 surface coated with a 532nm band anti-reflection film, the convex lens M24 is a convex lens with an F=150 and a surface coated with a 532nm band 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 band anti-reflection film, and the cylindrical convex lens M26 is a cylindrical convex lens with a focal length of F=125 and a surface coated with a 532nm band anti-reflection film. This design allows the 532nm laser generated by the first frequency-doubling system to be further shaped before entering the second frequency-doubling system. Specifically, pre-compensation is achieved using F-100 plano-convex cylindrical lenses and F125 plano-concave cylindrical lenses to further shape the 532nm laser, preemptively compensating for the astigmatism caused by BBO. Specifically, the spherical lens group can be a circular one, and the cylindrical lens group can be a square one.

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

[0041] Determine the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane x The deflection angle with 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, is the refractive index of fundamental frequency light; is the refractive index of the frequency-doubled light e; θ m is the phase matching angle;

[0044] When δθ x When it is smaller, the formula Considered as a fixed property of BBO crystal for a specific wavelength λ, Δk x Simplified to get , where β θ Crystal characteristic parameters, in order to obtain the phase mismatch Δk x and the phase mismatch angle δθ x relationship;

[0045] When the phase mismatch angle δθ xThe phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, ; Using the plane wave formula Derived , substitute ,get , where L is the crystal length; set θ m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the e-light vibration plane xoz plane x is Δθ x =0.276mrad*cm, and the BBO crystal is cut according to the type I phase matching angle of 47.7°;

[0046] The first and second BBO crystals, both 2.5 mm long, are rotated 180° and placed close together. The walk-off angle of the doubled frequency 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 and opposite in direction. The combined length of the first and second BBO crystals, both 2.5 mm long, is 5 mm. Calculate the doubled frequency acceptance angle Δθ of the 5 mm BBO crystal. x is 0.552 mrad; according to the above calculation, a spherical mirror group and a cylindrical mirror group with set curvature radius are used to control the emission angle of the 532nm laser entering the BBO crystal to 0.5 mrad, thereby avoiding the phase mismatch effect caused by the excessive divergence angle during the transmission of the laser in the crystal.

[0047] This more specific calculation method allows for a faster and more accurate way to obtain the frequency-doubled acceptance angle required to inject the laser beam into the BBO crystal. This, combined with the use of two BBO crystals rotated 180° and placed closely together, ultimately allows for the ideal 266 nm laser to be obtained. The use of dual BBO crystals and a 180° rotation compensates for the light spot walk-off phenomenon, resulting in a favorable light spot energy distribution.

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

[0049] 10. In the above-mentioned second technical solution, when arranging the second frequency doubling system, the following arrangement is adopted:

[0050] Determine the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane x The deflection angle with 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 it is smaller, the formula Considered as a fixed property of BBO crystal for a specific wavelength λ, Δk x Simplified to get , where β θ Crystal characteristic parameters, in order to obtain the phase mismatch Δk x and the phase mismatch angle δθ x relationship;

[0052] When the phase mismatch angle δθ x The phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, ; Using the plane wave formula Derived , substitute ,get , where L is the crystal length; set θ m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the e-light vibration plane xoz plane x is Δθ x =0.276mrad*cm, and the BBO crystal was cut with a Type I phase matching angle of 47.7°. The two BBO crystals were of equal length, each measuring 4mmx4mmx2.5mm. 532nm and 266nm antireflection coatings were applied to both ends of the BBO crystals. Specifically, the BBO crystals were 5mm long and had a SHG acceptance angle of 0.552mrad. After shaping, this wafer assembly produced a 532nm laser with a divergence angle of 0.5mrad.

[0053] 11. In this application, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," and the like are to be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; they may refer to mechanical connection, direct connection, or indirect connection through an intermediate medium; they may refer to internal communication between two elements or interaction between two elements, unless otherwise expressly limited. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0054] 12. In the present invention, the orientation or position relationship indicated by the terms "center", "upper", "lower", "bottom", "inside", "outside", etc. is based on the orientation or position assembly relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0055] 13. In this application, 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 the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0056] 14. In addition, the term "and / or" in this application means three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution in which both A and B are satisfied.

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

[0058] 1. The above scheme of the present invention aims to solve the problem that the existing deep ultraviolet laser cannot achieve high frequency doubling efficiency and good quality of the frequency doubling light beam at the same time, and innovatively develops a new high repetition rate deep ultraviolet pulse laser and its design method. In the high repetition rate deep ultraviolet pulse laser, the laser shaping scheme of the spherical mirror group and the cylindrical mirror group and the double BBO crystal scheme are designed after theoretical calculation to obtain better beam quality and spot energy distribution. When the phase matching conditions are met, the wave vectors of the fundamental frequency light and the frequency doubling light propagating in the crystal are matched, which reduces the energy loss caused by phase mismatch and allows more fundamental frequency light energy to be converted into target frequency light. Reasonable divergence angle control and phase matching make the light-to-light conversion efficiency higher. Reasonable cutting angle combined with phase matching can avoid or reduce the beam walk-off effect. The method used in the present invention is critical phase matching. Compared with non-critical phase matching, the advantages are simpler structure and higher reliability, which makes the spatial overlap of the light beam when propagating in the crystal. The divergence angle and spot morphology of the output laser are better, and the stable phase matching condition is conducive to the stability of the laser output power. The deep ultraviolet pulsed laser improves the light-to-light conversion efficiency. Under the premise of high repetition rate, a 266nm deep ultraviolet laser output with excellent beam quality and conversion efficiency is obtained. The use of double BBO crystals of the same length and a 180° rotation position compensates for the walk-off phenomenon of the spot. Since ρ1 and ρ2 are equal in size and opposite in direction, and the two crystals are of the same length, the walk-offs generated by the two crystals compensate each other to obtain a good spot energy distribution, which solves the phase mismatch problem of the light beam in the BBO crystal during the quadruple frequency process of the BBO crystal 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 stable, monochromatic deep ultraviolet laser, which is 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 is aimed at the application of a design method for a high repetition rate deep ultraviolet pulse laser, which provides a strong support for the design of such high repetition rate deep ultraviolet pulse lasers under different application requirements and different scenario requirements, and helps to quickly and accurately design the required deep ultraviolet pulse lasers, and can also shorten the design cycle and debugging cycle, thereby improving product competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Schematic diagram of an optical fiber seed source according to an embodiment of the present invention; Figure 2 Schematic diagram of a multi-stage solid-state amplifier according to an embodiment of the present invention; Figure 3 is a schematic diagram of a first frequency doubling system according to an embodiment of the present invention; Figure 4is a schematic diagram of a second frequency doubling system according to an embodiment of the present invention; Figure 5 Schematic diagram of the light spot shape without using the pre-compensation system and the second frequency doubling system in the embodiment of the present invention (I); Figure 6 Schematic diagram of the light spot shape (II) without using the pre-compensation system and the second frequency doubling system in the embodiment of the present invention; Figure 7 Schematic diagram of the spot shape when pre-compensation is used but without the dual-crystal solution; Figure 8 FIG. 1 is a schematic diagram of the light spot shape using the pre-compensation system and the second frequency doubling system in an embodiment of the present invention. DETAILED DESCRIPTION

[0061] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0062] The present invention aims to address the problem that existing deep ultraviolet lasers cannot simultaneously achieve high frequency doubling efficiency and good frequency doubling light beam quality. Based on this, a new high repetition rate deep ultraviolet pulsed laser and its design method are innovatively developed. The laser finally obtained passes through a series of filters and beam shaping devices to output stable, monochromatic deep ultraviolet laser, which is suitable for precision lithography, micromachining and scientific research fields, ensuring high laser conversion efficiency and stable output performance.

[0063] Example 1, as Figure 1 As shown, embodiment 1 of the present invention discloses a high repetition rate deep ultraviolet pulse laser, which 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.

[0064] The second frequency doubling system includes a first BBO crystal and a second BBO crystal.

[0065] The pre-compensation system includes a spherical mirror group and a cylindrical mirror group arranged in front of the first BBO crystal and the second BBO crystal.

[0066] The second frequency multiplication system and the pre-compensation system are arranged in the following manner:

[0067] Get the phase mismatch Δk x and the phase mismatch angle δθ xThe relationship between the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane is determined. x The deflection angle with the optical axis oz is the phase mismatch angle δθ x , and calculate the phase mismatch Δk x , using the inherent properties of BBO crystals for specific wavelengths β θ Phase mismatch Δk x Simplify and get Δk x =β θ δθ x .

[0068] Establish the frequency doubling efficiency and phase mismatch angle δθ x When the phase mismatch angle δθ x The phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency with complete phase matching, the frequency doubling acceptance angle Δθ x is the frequency doubling efficiency relative to the phase mismatch angle δθ x The full width at half maximum is used to derive the SHG acceptance angle Δθ under the set SHG efficiency. x relation.

[0069] Calculate the BBO crystal's frequency doubling acceptance angle Δθ based on the BBO crystal's characteristics x .

[0070] The first BBO crystal and the second BBO crystal of the same length are rotated 180° and placed closely 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 size and opposite in direction.

[0071] The BBO crystal's doubled frequency acceptance angle Δθ is calculated based on the specific crystal characteristics and the length of the two BBO crystals combined. x To select and arrange the spherical mirror group and cylindrical mirror group in the pre-compensation system so that the divergence angle obtained after shaping by the pre-compensation system is smaller than the frequency doubling receiving angle Δθ x laser.

[0072] The output stabilization adjustment system is used to precisely control the temperature of the first frequency doubling system and the second frequency doubling system to maintain phase matching conditions.

[0073] Through the implementation of the first embodiment of the present invention, a laser shaping scheme of a spherical mirror group and a cylindrical mirror group and a double BBO crystal scheme are designed after theoretical calculation to obtain 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 in the crystal are matched, which reduces the energy loss caused by phase mismatch and allows more fundamental frequency light energy to be converted into target frequency light. Reasonable divergence angle control and phase matching make the light-to-light conversion efficiency higher. Reasonable cutting angle combined with phase matching can avoid or reduce the beam walk-off effect. The method used in the present invention is critical phase matching. Compared with non-critical phase matching, the advantages are simpler structure and higher reliability, which makes the spatial overlap of the light beam good when propagating in the crystal, and the divergence angle and spot morphology of the output laser are better. The stable phase matching condition is conducive to the stability of the laser output power. The ultraviolet pulsed laser improves the light-to-light conversion efficiency. Under the premise of high repetition rate, a 266nm deep ultraviolet laser output with excellent beam quality and conversion efficiency is obtained. The use of double BBO crystals of the same length and a 180° rotation compensates for the walk-off phenomenon of the light spot. Since ρ1 and ρ2 are equal in size and opposite in direction, and the two crystals are the same length, the walk-offs produced by the two crystals compensate each other, obtaining a good light spot energy distribution, solving the phase mismatch problem of the light beam in the BBO crystal during the quadruple frequency 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 stable, monochromatic deep ultraviolet laser, which is suitable for precision lithography, micromachining and scientific research, ensuring high laser conversion efficiency and stable output performance.

[0074] In one implementation of the first embodiment of the present invention, Figure 1 As shown, the fiber seed source includes a laser diode (LD), a wavelength division multiplexer (WDM), a high-reflection grating (HR), an 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 wavelength division multiplexer and the high-reflection grating. The ytterbium-doped fiber absorbs the pump light energy. The high-reflection grating, the ytterbium-doped fiber, and the saturable absorber mirror form a linear resonant cavity to generate 1064nm laser light. After passing through the first acousto-optic modulator, it is amplified by the ytterbium-doped fiber pumped by the semiconductor laser to output a high repetition frequency wavelength of 1064nm pulse laser. This fiber seed source outputs laser pulses 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 minimum loss, and finally forms and maintains a stable ultrashort pulse sequence for output, providing high-quality laser pulses for subsequent components of the deep ultraviolet pulse laser. A photodetector (PD) can be set in the ring resonator to monitor the laser characteristics in the cavity or output in real time to ensure the stability of the laser pulse output by the fiber seed source.

[0075] In another embodiment of the first embodiment of the present invention, the multi-stage solid amplifier includes a first-stage amplifier, a second-stage amplifier, a third-stage amplifier, and a fourth-stage amplifier;

[0076] The first-stage amplifier includes a first-stage pump source, a convex lens M1, a first laser crystal, a plane reflector M2, and a plane reflector M3;

[0077] The secondary amplifier includes a secondary pump source, a plane reflector M4, a convex lens M5, a second laser crystal, a concave lens M6, and a plane reflector M7;

[0078] The three-stage amplifier includes a three-stage pump source, a plane reflector M10, a convex lens M11, a third laser crystal, a concave lens M12, and a plane reflector M13;

[0079] 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.

[0080] Through the application and arrangement of the more specific multi-stage solid-state amplifier above, the laser pulses with a wavelength of 1064nm and a power of about 50mW output by the optical fiber seed source are amplified by the multi-stage solid-state amplifier, which further improves the efficiency of optical-to-optical conversion, so that the power and energy of the 1064nm laser output by the multi-stage solid-state amplifier are sufficiently high.

[0081] More specifically, 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 adopt an end-pumping method 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 LD lasers with a wavelength of 888nm 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 high-reflection film in the 1064nm band; the convex lenses M5, M11, and M17 are convex lenses with a focal length of F=400 and an anti-reflection film on the surface of the 1064nm band; the concave lenses M6, M12, and M18 are concave lenses with a focal length of F=-75 and an anti-reflection film on the surface of the 1064nm band. Thus, the design adopts the composition of the components of the above more specific multi-stage solid-state amplifier, which can achieve ultra-high gain amplification and ensure the beam quality and stability, thereby providing more support for the simultaneous realization of high frequency doubling efficiency and good frequency doubling light beam quality.

[0082] In one embodiment of the first embodiment of the present invention, the second acousto-optic modulator includes an AOM spectrometer module. The AOM spectrometer module realizes the spectrometer function by driving and controlling the intensity and emission direction of the incident laser and controls the diffraction efficiency to above 80%. This ensures maximum utilization of the amplified laser energy and ensures that the 1064nm laser entering the first frequency doubling system after spectrometry is stable and high-quality.

[0083] 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, wherein the convex lens M20 is a convex lens with a focal length of F=150 and a surface coated with a 1064nm band anti-reflection film, the concave lens M21 is a concave lens with an F=-100 and a surface coated with a 1064nm band anti-reflection film, and the convex lens M22 is a convex lens with an F=125 and a surface coated with a 1064nm band anti-reflection film; the cutting angle of the LBO crystal is precisely 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, which cooperates 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. 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.

[0084] 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 provided in the incident direction of the first BBO crystal and the second BBO crystal, 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 surface coated with a 532nm band anti-reflection film, the convex lens M24 is a convex lens with F=150 and a surface coated with a 532nm band 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 band anti-reflection film, and the cylindrical convex lens M26 is a cylindrical convex lens with a focal length of F=125 and a surface coated with a 532nm band anti-reflection film. This design specifically provides for further shaping of the 532nm laser before it enters the second harmonic generation system. Specifically, a pre-compensation approach is employed using F-100 plano-convex cylindrical lenses and F125 plano-concave cylindrical lenses to further shape the 532nm laser and pre-compensate for the astigmatism generated by BBO. Specifically, the spherical lens group can be a circular one, and the cylindrical lens group can be a square one.

[0085] In one implementation manner of Example 1 of the present invention, in the arrangement of the BBO crystals in the first BBO crystal and the second BBO crystal:

[0086] Determine the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane x The deflection angle with the optical axis oz is the phase mismatch angle δθ x ;

[0087] Then k x Phase mismatch Δk in the xoz plane x for: ;

[0088] in is the refractive index of fundamental frequency light; is the refractive index of the frequency-doubled light e; θ m is the phase matching angle;

[0089] When δθ x When it is smaller, the formula Considered as a fixed property of BBO crystal for a specific wavelength λ, Δk x Simplified to get , where β θ Crystal characteristic parameters, in order to obtain the phase mismatch Δk x and the phase mismatch angle δθ x relationship;

[0090] When the phase mismatch angle δθ x The phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, ; Using the plane wave formula Derived , substitute ,get , where L is the crystal length; set θ m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the e-light vibration plane xoz plane x is Δθ x =0.276mrad*cm, and the BBO crystal is cut according to the type I phase matching angle of 47.7°;

[0091] The first BBO crystal and the second BBO crystal of the same length are rotated 180° and placed closely together so that the optical axes of the two crystals form an angle of 2 times the phase mismatch angle δθ x , so that the energy propagation direction of the doubled frequency light generated by the first BBO crystal has a walk-off angle of ρ1 with respect to the fundamental frequency light, and the walk-off angle generated by the second BBO crystal is ρ2, where ρ1 and ρ2 are equal in magnitude and opposite in direction;

[0092] According to the above calculations, a spherical mirror group and a cylindrical mirror group with set curvature radius are used to control the emission angle of the 532nm laser incident on the BBO crystal to be 0.5mrad.

[0093] This more specific calculation method allows for a faster and more accurate way to obtain the frequency-doubled acceptance angle required to inject the laser beam into the BBO crystal. This, combined with the use of two BBO crystals rotated 180° and placed closely together, ultimately allows for the ideal 266 nm laser to be obtained. The use of dual BBO crystals and a 180° rotation compensates for the light spot walk-off phenomenon, resulting in a favorable light spot energy distribution.

[0094] In another embodiment of the first embodiment of the present invention, the output stabilization and adjustment system is used to precisely control the temperature of the phase-matched LBO and BBO crystals in the first and second frequency doubling systems. An optical adjustment mount is used to adjust the optical angles of the phase-matched LBO and BBO crystals in the first and second frequency doubling systems to maintain phase matching. The output stabilization and adjustment system comprises a heated metal base, an electrothermal ceramic plate, and a temperature feedback adjustment module, with the LBO and BBO crystals both placed on the heated metal base. This approach reliably and stably maintains phase matching between the LBO and BBO crystals during use, avoiding phase mismatch issues in the BBO crystals.

[0095] In another implementation of the first embodiment of the present invention, the second frequency doubling system is arranged in the following manner:

[0096] Determine the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane x The deflection angle with the optical axis oz is the phase mismatch angle δθ x ;

[0097] Then k x Phase mismatch Δk in the xoz plane x for: ; When δθ x When it is smaller, the formula Considered as a fixed property of BBO crystal for a specific wavelength λ, Δk x Simplified to get , where β θ Crystal characteristic parameters, in order to obtain the phase mismatch Δk x and the phase mismatch angle δθ x relationship;

[0098] When the phase mismatch angle δθ x The phase mismatch Δk caused by xWhen the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, ; Using the plane wave formula Derived , substitute ,get , where L is the crystal length; set θ m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the e-light vibration plane xoz plane x is Δθ x =0.276mrad*cm, and the BBO crystal was cut with a Type I phase matching angle of 47.7°. The two BBO crystals were of equal length (2.5mm each), with specific dimensions of 4mmx4mmx2.5mm. 532nm and 266nm antireflection coatings were applied to both ends of the BBO crystals. Specifically, the BBO crystal length was 5mm, and its SHG acceptance angle was 0.552mrad. After shaping, this wafer assembly produced a 532nm laser with a divergence angle of 0.5mrad.

[0099] Embodiment 2: Embodiment 2 of the present invention provides 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 the present invention. The design method comprises the following steps:

[0100] The high repetition rate deep ultraviolet pulse laser is arranged including an optical fiber seed source, a multi-stage solid 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.

[0101] When arranging the first frequency doubling system, the laser path is installed to set the convex lens M20, the concave lens M21, the convex lens M22, and the LBO crystal, and the cutting angle of the LBO crystal is accurately set according to the phase matching condition.

[0102] 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.

[0103] When arranging the second frequency doubling system, the following arrangement is adopted: When arranging the second frequency doubling system, the following arrangement is adopted:

[0104] Determine the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane x The deflection angle with the optical axis oz is the phase mismatch angle δθ x ;

[0105] Then k x Phase mismatch Δk in the xoz plane x for: ; When δθ x When it is smaller, the formula Considered as a fixed property of BBO crystal for a specific wavelength λ, Δk x Simplified to get , where β θ is the crystal characteristic parameter, and the phase mismatch Δk is obtained from it x and the phase mismatch angle δθ x relationship;

[0106] When the phase mismatch angle δθ x The phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, ; Using the plane wave formula Derived , substitute ,get , where L is the crystal length; set θ m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the e-light vibration plane xoz plane x is Δθ x =0.276mrad*cm, and the BBO crystal was cut with a Type I phase matching angle of 47.7°. The two BBO crystals were of equal length, each measuring 4mmx4mmx2.5mm. 532nm and 266nm antireflection coatings were applied to both ends of the BBO crystals. Specifically, the BBO crystals were 5mm long and had a SHG acceptance angle of 0.552mrad. After shaping, this wafer assembly produced a 532nm laser with a divergence angle of 0.5mrad.

[0107] Based on the above calculations, a circular plano-convex spherical mirror with a curvature radius of F-50 and a circular plano-concave spherical mirror with a curvature radius of F150 are used to control the emission angle of the 532nm laser incident on the BBO crystal to 0.5 mrad. Furthermore, because the frequency-doubled light generated by the fundamental frequency light passing through the BBO crystal can produce significant astigmatism, the present invention uses a pre-compensation method using a square plano-convex cylindrical mirror with a radius of F-100 and a square plano-concave cylindrical mirror with a radius of F125 to further shape the 532nm laser light and preemptively compensate for the astigmatism generated by the BBO.

[0108] Through the implementation of the second embodiment of the present invention, the application of a design method for a high repetition rate deep ultraviolet pulse laser provides a powerful aid for the design of such high repetition rate deep ultraviolet pulse lasers under different application requirements and different scenario requirements, which helps to quickly and accurately design the required deep ultraviolet pulse laser, and can also shorten the design cycle and debugging cycle, thereby improving product competitiveness.

[0109] In addition, in the implementation of the high repetition rate deep ultraviolet pulse laser in the first and second embodiments of the present invention, the laser signal image acquisition spot morphology under different conditions was carried out for the special setting of the double BBO crystal in the pre-compensation system and the second frequency doubling system. Figure 5 、 Figure 6 As shown, the spot circularity is 45.7%, which is of poor quality. The spot shape using pre-compensation but not using the dual crystal solution is as follows Figure 7 As shown in the figure, the roundness is 85%, which is an improvement compared to before using pre-compensation. However, the spot shape is obviously distorted due to walk-off. Figure 8 As shown in the figure, the spot circularity is 92.4%, which improves the spot shape distortion caused by walk-off.

[0110] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A high repetition rate deep ultraviolet pulsed laser, characterized by: 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; The second frequency doubling system includes a first BBO crystal and a second BBO crystal; The pre-compensation system includes a spherical mirror group and a cylindrical mirror group arranged in front of the first BBO crystal and the second BBO crystal; The second frequency multiplication system and the pre-compensation system are arranged in the following manner: Obtain the phase mismatch amount and phase mismatch angle δθ x The relationship between the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane is determined. x The deflection angle with the optical axis oz is the phase mismatch angle δθ x , and calculate the phase mismatch Δk x , using the inherent properties of BBO crystals for specific wavelengths β θ Phase mismatch Δk x Simplify and get Δk x =β θ δθ x ; Establish the relationship between the frequency doubling efficiency and the phase mismatch angle. When the phase mismatch caused by the phase mismatch angle reduces the frequency doubling efficiency to 50% of the optical-optical conversion efficiency of complete phase matching, the frequency doubling acceptance angle is the frequency doubling efficiency relative to the phase mismatch angle δθ. x The full width at half maximum is used to derive the relationship between the SHG acceptance angle under the set SHG efficiency; Calculate the frequency doubling acceptance angle of BBO crystal based on BBO crystal characteristics; 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, where ρ1 and ρ2 are equal in magnitude and opposite in direction. The spherical mirror group and cylindrical mirror group in the pre-compensation system are selected and arranged according to the specific crystal characteristics and the BBO crystal's double frequency acceptance angle calculated by the length of the two BBO crystals combined, so that the laser with a divergence angle smaller than the double frequency acceptance angle is obtained after shaping by the pre-compensation system; The output stabilization adjustment system is used to precisely control the temperature of the first frequency doubling system and the second frequency doubling system to maintain phase matching conditions.

2. The high repetition rate deep ultraviolet pulse laser according to claim 1, characterized in that: The optical fiber seed source comprises a laser diode, a wavelength division multiplexer, a high-reflection grating, an ytterbium-doped optical 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 optical fiber through the wavelength division multiplexer and the high-reflection grating. The ytterbium-doped optical fiber absorbs the pump light energy. The high-reflection grating, the ytterbium-doped optical fiber, and the saturable absorber form a linear resonant cavity to generate a 1064nm pulse laser. After passing through the first acousto-optic modulator, it is amplified by the ytterbium-doped optical fiber pumped by a semiconductor laser, and outputs a pulse laser with a high repetition frequency and a wavelength of 1064nm.

3. The high repetition rate deep ultraviolet pulse laser according to claim 1, characterized in that: The multi-stage solid amplifier includes a first-stage amplifier, a second-stage amplifier, a third-stage amplifier and a fourth-stage amplifier; The first-stage amplifier includes a first-stage pump source, a convex lens M1, a first laser crystal, a plane reflector M2, and a plane reflector M3; The secondary amplifier includes a secondary pump source, a plane reflector M4, a convex lens M5, a second laser crystal, a concave lens M6, and a plane reflector M7; The three-stage amplifier includes a three-stage pump source, a plane reflector M10, a convex lens M11, a third laser crystal, a concave lens M12, and a plane reflector M13; 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.

4. The high repetition rate deep ultraviolet pulse laser according to claim 3, characterized in that: 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 adopt an end-pumping method 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 LD lasers with a wavelength of 888nm as pump sources; the convex lens M1 is a convex lens with a focal length of F=750; the surfaces of the plane reflectors M2, M3, M4, M7, M10, M13, and M16 are coated with a high-reflection film in the 1064nm band; the convex lenses M5, M11, and M17 are convex lenses with a focal length of F=400 and an anti-reflection film on the surface of the 1064nm band; and the concave lenses M6, M12, and M18 are concave lenses with a focal length of F=-75 and an anti-reflection film on the surface of the 1064nm band.

5. The high repetition rate deep ultraviolet pulse laser according to claim 1, characterized in that: The second acousto-optic modulator includes an AOM spectrometer module, which controls the intensity and emission direction of the incident laser by driving to achieve the spectrometer function and control the diffraction efficiency to above 80%.

6. The high repetition rate deep ultraviolet pulse laser according to claim 1, characterized in that: The first frequency doubling system includes 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 surface coated with a 1064nm band anti-reflection film, the concave lens M21 is a concave lens with an F=-100 and a surface coated with a 1064nm band anti-reflection film, and the convex lens M22 is a convex lens with an F=125 and a surface coated with a 1064nm band anti-reflection film; the cutting angle of the LBO crystal is precisely 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, which cooperates with the 90° angle.

7. The high repetition rate deep ultraviolet pulse laser according to claim 1, characterized in that: 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 direction of the first BBO crystal and the second BBO crystal. 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. 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 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.

8. The high repetition rate deep ultraviolet pulse laser according to claim 1, characterized in that: In the arrangement of the BBO crystals in the first BBO crystal and the second BBO crystal: Determine the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane x The deflection angle with the optical axis oz is the phase mismatch angle δθ x ; Then k x Phase mismatch Δk in the xoz plane x for: ;in, is the refractive index of fundamental frequency light; is the refractive index of the frequency-doubled light e; θ m is the phase matching angle; When δθ x When it is smaller, the formula Considered as a fixed property of BBO crystal for a specific wavelength λ, Δk x Simplified to get , where β θ Crystal characteristic parameters, in order to obtain the phase mismatch Δk x and the phase mismatch angle δθ x relationship; When the phase mismatch angle δθ x The phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, ; Using the plane wave formula Derived , substitute ,get , where L is the crystal length; set θ m =47.6°, then the frequency-doubled acceptance angle Δθ of the BBO crystal per centimeter in the e-light vibration plane xoz plane x is Δθ x =0.276mrad*cm, and the BBO crystal is cut according to the type I phase matching angle of 47.7°; The first and second BBO crystals, both 2.5 mm long, are rotated 180° and placed close together. The walk-off angle of the doubled frequency 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 and opposite in direction. The combined length of the first and second BBO crystals, both 2.5 mm long, is 5 mm. Calculate the doubled frequency acceptance angle Δθ of the 5 mm BBO crystal. x 0.552 mrad; According to the above calculations, a spherical mirror group and a cylindrical mirror group with set curvature radius are used to control the emission angle of the 532nm laser incident on the BBO crystal to be 0.5mrad.

9. The high repetition rate deep ultraviolet pulse laser according to claim 8, characterized in that: The output stabilization adjustment system is used to precisely control the temperature of the phase-matched LBO crystal and BBO crystal in the first frequency doubling system and the second frequency doubling system. The optical adjustment frame is used to adjust the optical angle of the phase-matched LBO crystal and BBO crystal in the first frequency doubling system and the second frequency doubling system to maintain phase matching adjustment. The output stabilization adjustment system includes a heated metal base, an electrothermal ceramic plate and a temperature feedback adjustment module. The LBO crystal and the BBO crystal are both placed on the heated metal base.

10. A design method for a high repetition rate deep ultraviolet pulsed laser, characterized in that: The design method is used to design a high repetition rate deep ultraviolet pulse laser according to any one of claims 1 to 9, and the design method comprises the following steps: A high repetition rate deep ultraviolet pulse laser is arranged including 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; Among them, when arranging the first frequency doubling system, the laser path is installed to set the convex lens M20, the concave lens M21, the convex lens M22, and the LBO crystal, 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 frequency doubling system, the following arrangement is adopted: Obtain the phase mismatch Δk x and the phase mismatch angle δθ x The relationship between the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane is determined. x The deflection angle with the optical axis oz is the phase mismatch angle δθ x , and calculate the phase mismatch Δk x , using the inherent properties of BBO crystals for specific wavelengths β θ Phase mismatch Δk x Simplify and get Δk x =β θ δθ x ; Establish the frequency doubling efficiency and phase mismatch angle δθ x When the phase mismatch angle δθ x The phase mismatch Δk caused by x The frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, that is, the frequency doubling acceptance angle Δθ x is the frequency doubling efficiency relative to the phase mismatch angle δθ x The full width at half maximum is used to derive the SHG acceptance angle Δθ under the set SHG efficiency. x relation; Calculate the BBO crystal's frequency doubling acceptance angle Δθ based on the BBO crystal's characteristics x , use the cylindrical lens group and spherical lens group of the pre-compensation system 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 ; 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, where ρ1 and ρ2 are equal in magnitude and opposite in direction; The output stabilization adjustment system is then used to precisely control 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 adjustment frame is used to adjust the optical angle of the phase-matched LBO crystal and BBO crystal in the first frequency doubling system and the second frequency doubling system to maintain phase matching adjustment.

11. The method for designing a high repetition rate deep ultraviolet pulsed laser according to claim 10, characterized in that: When arranging the second frequency doubling system, use the following arrangement: Determine the wave vector k of the BBO crystal in the xoz plane of the e-light vibration plane x The deflection angle with the optical axis oz is the phase mismatch angle δθ x ; Then k x Phase mismatch Δk in the xoz plane x for: ; When δθ x When it is smaller, the formula Considered as a fixed property of BBO crystal for a specific wavelength λ, Δk x Simplified to get , where β θ Crystal characteristic parameters, in order to obtain the phase mismatch Δk x and the phase mismatch angle δθ x relationship; When the phase mismatch angle δθ x The phase mismatch Δk caused by x When the frequency doubling efficiency is reduced to 50% of the optical-optical conversion efficiency of complete phase matching, ; Using the plane wave formula Derived , substitute ,get , where L is the crystal length; set θ m =47.6°, then the acceptance angle Δθ of the BBO crystal per centimeter in the e-light vibration plane xoz plane x is Δθ x =0.276mrad*cm, and the BBO crystal is cut according to the type I phase matching angle of 47.7°. The lengths of the two BBO crystals are equal, and their dimensions are both 4mmx4mmx2.5mm. 532nm and 266nm antireflection films are coated on both end faces of the BBO crystal.

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