248.3 nm laser based on 993.2 nm parametric light source

Abstract

The application belongs to the technical field of deep ultraviolet laser, and provides a 248.3 nm laser based on a 993.2 nm parametric light source. A 515 nm single-frequency pulsed laser is output by a pump laser light source, and a 1069.6 nm single-frequency continuous laser is output by a seed light source. The two lasers generate a 993.2 nm single-frequency pulsed signal light in a first-stage optical parametric amplification module, and the 993.2 nm single-frequency pulsed signal light is amplified in a second-stage optical parametric amplification module. The amplified 993.2 nm laser generates a 496.6 nm second harmonic wave through a frequency doubling module, and then outputs a 248.3 nm deep ultraviolet pulsed light through a four-frequency multiplication module. The 993.2 nm single-frequency pulsed light is generated and amplified through a nonlinear optical parametric process, so that the problem of high-gain band competition when the 993.2 nm laser is directly amplified through a ytterbium-doped gain medium can be avoided, and the output power, signal-to-noise ratio and spectral purity can be improved.

Description

Technical Field

[0001] This invention relates to the field of deep ultraviolet laser technology, and in particular to a 248.3nm laser based on a 993.2nm parametric light source. Background Technology

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

[0003] Ultraviolet (UV) laser technology plays a vital role in modern industry and scientific research due to its unique physical properties. This type of laser possesses characteristics such as short wavelength, high single-photon energy, small focused spot size, and ease of photochemical or photothermal interactions with materials, showing broad application prospects in fields such as photolithography, fiber grating writing, precision machining, high-resolution spectroscopy, and medicine. Deep-ultraviolet (DUV) lasers, as an important component of UV lasers, have received widespread attention for their technological development. Currently, the main technical routes for obtaining DUV lasers include direct generation using gas discharge lasers, harmonic conversion using solid-state lasers, and all-solid-state schemes based on nonlinear frequency conversion. These different technical routes each have their own characteristics, differing in output power, coherence, beam quality, and system complexity, providing diverse technical options for DUV laser applications.

[0004] In the process of generating deep ultraviolet lasers of specific wavelengths based on ytterbium-doped laser systems, the direct amplification of the target wavelength laser using conventional ytterbium-doped gain media faces the challenge of gain competition. Since the target wavelength is in the short-wavelength emission region of the ytterbium-doped gain medium, its effective net gain is relatively low, making it susceptible to competition from high-gain bands during power amplification. This competition effect can lead to problems such as parasitic oscillations at non-target wavelengths, enhanced spontaneous emission during amplification, and a reduced signal-to-noise ratio in the output signal, ultimately affecting the spectral purity and stability of the final deep ultraviolet laser output. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a 248.3nm laser based on a 993.2nm parametric light source. It generates and amplifies 993.2nm single-frequency pulsed light through a nonlinear optical parametric process, which avoids the problem of high-gain band competition when the 993.2nm laser is directly amplified through a ytterbium-doped gain medium. This is beneficial for improving output power, signal-to-noise ratio, and spectral purity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A 248.3nm laser based on a 993.2nm parametric light source includes: a pump laser source, a seed light source, a first-stage optical parametric amplification module, a second-stage optical parametric amplification module, a second-harmonic generation module, and a fourth-harmonic generation module; The pump laser source is used to output single-frequency pulsed linearly polarized light with a wavelength of 515nm; The seed light source is used to output single-frequency continuous linearly polarized light at 1069.6nm; The first-stage optical parametric amplification module is used to perform optical parametric amplification of the 515nm single-frequency pulse pump light and the 1069.6nm single-frequency continuous idler light to generate a 993.2nm single-frequency pulse signal light. The second-stage optical parametric amplification module is used to perform optical parametric amplification of the 515nm single-frequency pulse pump light and the 993.2nm single-frequency pulse light. The frequency doubling module is used to perform second harmonic conversion on the 993.2nm single-frequency pulse light amplified by the second-stage optical parametric amplification module to generate 496.6nm single-frequency pulse light; The quadruple harmonic generation module is used to perform second harmonic conversion on 496.6nm single-frequency pulse light to generate and output 248.3nm single-frequency deep ultraviolet pulse light.

[0007] In one optional implementation of the present invention, the pump laser source includes a 1030 nm single-frequency pulse laser and a 1030 nm laser frequency-second harmonic generation module arranged sequentially along the optical path. The 1030 nm single-frequency pulse laser is used to output 1030 nm single-frequency pulse laser. After the 1030 nm single-frequency pulse laser undergoes second harmonic conversion by the 1030 nm laser frequency-second harmonic generation module, it generates 515 nm single-frequency pulse pump light.

[0008] In one optional implementation of the present invention, the 515nm single-frequency pulse linearly polarized light is split into a first pump light and a second pump light by a first beam splitter. The first pump light is used for the first-stage optical parametric amplification process, and the second pump light is used for the second-stage optical parametric amplification process after being delayed by a delay adjustment module.

[0009] As a further limitation of the present invention, the delay module includes a first reflector, a second reflector and a third reflector arranged sequentially along the optical path. The delay module is used to make the second pump light and the 993.2nm single-frequency pulse light generated by the first-stage optical parametric amplification module coincide in time in the second-stage optical parametric amplification module.

[0010] In one optional implementation of the present invention, the first-stage optical parametric amplification module includes a first dichroic mirror and a first nonlinear crystal. The first dichroic mirror spatially combines the received first pump light with the 1069.6 nm single-frequency continuous idler light and outputs the combined light to the first nonlinear crystal. The first nonlinear crystal is used to realize the optical parametric amplification process between the 515 nm single-frequency pulse pump light, the 1069.6 nm single-frequency continuous idler light and the 993.2 nm single-frequency pulse signal light, thereby generating the 993.2 nm single-frequency pulse signal light.

[0011] As a further limitation of the present invention, the second-stage optical parametric amplification module includes a second dichroic mirror, a second nonlinear crystal, and a third dichroic mirror; The second dichroic mirror is used to spatially combine the received, delayed second pump light with the 993.2 nm single-frequency pulse light output from the first-stage optical parametric amplification module, and then output the combined light to the second nonlinear crystal. The second nonlinear crystal is used to realize the second-stage optical parametric amplification process, which amplifies the power of the 993.2 nm single-frequency pulse light. The third dichroic mirror is used to guide or separate the received amplified 993.2 nm single-frequency pulse light and output it to the frequency doubling module.

[0012] As a further limitation of the present invention, both the first nonlinear crystal and the second nonlinear crystal are nonlinear optical crystals that satisfy the optical parametric amplification phase matching condition between the 515 nm single-frequency pulse pump light, the 1069.6 nm single-frequency continuous idler light and the 993.2 nm single-frequency pulse signal light.

[0013] In one optional implementation of the present invention, the frequency doubling module includes a third nonlinear crystal and a fourth dichroic mirror arranged sequentially along the optical path. The third nonlinear crystal is used to perform second harmonic conversion on the 993.2 nm single-frequency pulse light amplified by the second-stage optical parametric amplification module to generate 496.6 nm single-frequency pulse light. The fourth dichroic mirror is used to separate or guide the 993.2 nm fundamental frequency light and the 496.6 nm frequency-doubled light, and outputs the 496.6 nm single-frequency pulse light to the fourth frequency-doubled module.

[0014] As a further limitation of the present invention, the fourth harmonic generation module includes a fourth nonlinear crystal and a fifth dichroic mirror arranged sequentially along the optical path. The fourth nonlinear crystal is used to perform second harmonic conversion on the received 496.6 nm single-frequency pulse light to generate 248.3 nm single-frequency deep ultraviolet pulse light. The fifth dichroic mirror is used to separate the 496.6 nm second harmonic light from the 248.3 nm deep ultraviolet light and output a 248.3 nm single-frequency deep ultraviolet laser.

[0015] As a further limitation of the present invention, the third nonlinear crystal is a nonlinear optical crystal that satisfies the phase matching condition of the second harmonic conversion from 993.2 nm to 496.6 nm, and the fourth nonlinear crystal is a deep ultraviolet nonlinear optical crystal that satisfies the phase matching condition of the second harmonic conversion from 496.6 nm to 248.3 nm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This invention employs a 515 nm single-frequency pulsed pump light and a 1069.6 nm single-frequency continuous idler light for optical parametric amplification to generate a 993.2 nm single-frequency pulsed signal light. Since the 1069.6 nm idler light is continuous, the first-stage optical parametric amplification process does not require external timing synchronization, resulting in a simple system structure and high stability. This invention generates and amplifies the 993.2 nm single-frequency pulsed light through optical parametric amplification, avoiding the gain competition, enhanced spontaneous emission, parasitic oscillations at non-target wavelengths, and decreased signal-to-noise ratio problems caused by gain competition in the high-gain band when directly using ytterbium-doped gain media to amplify 993.2 nm laser light. This facilitates obtaining high-power, narrow-linewidth, and high signal-to-noise ratio 993.2 nm single-frequency pulsed light, thereby providing a basis for subsequent frequency conversion to achieve high spectral purity and high stability. The present invention provides a basis for single-frequency deep ultraviolet pulsed light of nm; the pump laser source and seed source of the present invention can both adopt a modular structure, wherein the single-frequency pulsed pump light of 515nm is obtained by frequency doubling of Yb:YAG laser, and the single-frequency continuous idler light of 1069.6 nm can be obtained by ytterbium-doped fiber laser. The technology is mature and easy to realize system integration and engineering application.

[0017] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] Figure 1 A schematic diagram of the optical path of a 248.3nm laser based on a 993.2nm parametric light source is provided as an exemplary embodiment of the present invention; The components include: 1. a 515 nm single-frequency pulsed laser source; 2. a 1030 nm single-frequency pulsed laser; 3. a 1030 nm laser frequency-secondation module; 4. a first beam splitter; 5. a first reflecting mirror; 6. a second reflecting mirror; 7. a third reflecting mirror; 8. a delay adjustment module; 9. a 1069.6 nm single-frequency continuous laser; 10. a first dichroic mirror; 11. a first nonlinear crystal; 12. a second dichroic mirror; 13. a second nonlinear crystal; 14. a third dichroic mirror; 15. a third nonlinear crystal; 16. a fourth dichroic mirror; 17. a fourth nonlinear crystal; and 18. a fifth dichroic mirror. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] Ultraviolet lasers possess characteristics such as short wavelength, high single-photon energy, small focused spot size, and ease of photochemical or photothermal interactions with materials, making them valuable for applications in photolithography, fiber grating writing, precision machining, high-resolution spectroscopy, medicine, and defense. The 248.3 nm deep ultraviolet laser is a typical output wavelength of KrF excimer lasers and has representative applications in photolithography, micro / nano fabrication, and fiber grating fabrication. For these applications, the linewidth, coherence, beam quality, and output stability of the 248.3 nm deep ultraviolet laser source directly affect exposure resolution, interference fringe quality, processing accuracy, and spectral resolution. Therefore, a 248.3 nm deep ultraviolet laser source with narrow linewidth, high coherence, good beam quality, and high stability is of great significance. Currently, the main technical routes for obtaining 248.3 nm deep ultraviolet laser sources include direct generation using KrF excimer lasers, third harmonic conversion of 745 nm lasers, and nonlinear frequency conversion based on multi-wavelength sum-frequency or difference-frequency conversion.

[0023] KrF excimer lasers are the most direct and mature technology for generating deep ultraviolet lasers around 248 nm, offering advantages such as high output energy and high average power, and have been widely used in fields such as deep ultraviolet lithography. However, these lasers typically rely on fluorine-containing gas discharge media and complex gas circulation and maintenance systems, resulting in large device size and high operating and maintenance costs. Furthermore, the output coherence, beam quality, and spectral stability of ordinary KrF excimer lasers are relatively limited, usually requiring additional linewidth narrowing, injection locking, or beam shaping measures to meet the requirements of high-precision lithography, fiber grating writing, and precision machining applications that demand narrow linewidth, high coherence, and good beam quality.

[0024] 248.3 nm deep ultraviolet laser can also be obtained by third harmonic conversion of a 745 nm laser. This route typically uses Ti:sapphire or alexandrite lasers as the fundamental frequency source, which has the advantages of good coherence, short pulse width, and good beam quality, making it suitable as the seed light for KrF excimer amplifiers. However, the 745 nm fundamental frequency source usually relies on Ti:sapphire or alexandrite lasers, and its high-energy pulse output often requires regenerative amplification or multi-pass amplification structures; at the same time, the 248 nm output power obtained after third harmonic conversion is usually limited, and if further improvement in output power is required, it is still necessary to combine it with a KrF excimer amplifier. Therefore, this route involves multiple stages such as tunable solid-state lasers, laser amplification, nonlinear third harmonic conversion, and excimer amplification, resulting in a complex system structure, large size, and high cost.

[0025] In addition, all-solid-state nonlinear frequency conversion methods can also be used to generate 248.3 nm deep ultraviolet lasers. For example, a 248 nm deep ultraviolet laser can be obtained from a 1064 nm single-frequency laser through frequency doubling, third harmonicization, optical parametric oscillation, and sum-frequency conversion. This type of all-solid-state approach has advantages such as good coherence, modular structure, and no need for a gaseous working medium. However, it usually involves multi-stage nonlinear frequency conversion and requires linewidth or frequency stabilization control of the output wavelength of the optical parametric oscillation. Furthermore, this type of system has high requirements for spatial overlap, time synchronization, and optical path stability of multi-wavelength beams. Besides the above-mentioned methods, using a 993.2 nm laser for fourth harmonic conversion is also a feasible approach to obtain 248.3 nm deep ultraviolet lasers.

[0026] A 993.2 nm laser can be converted into 496.6 nm and 248.3 nm deep ultraviolet lasers through two-stage second harmonic conversion. Alternatively, a 248.3 nm deep ultraviolet laser can be obtained by combining second harmonic generation with a cascaded fundamental frequency beam. Therefore, obtaining a high-power, narrow-linewidth, and high signal-to-noise ratio 993.2 nm single-frequency pulsed laser is a crucial foundation for achieving all-solid-state generation of 248.3 nm deep ultraviolet lasers. However, 993.2 nm falls within the short-wavelength emission region of ytterbium-doped gain media, resulting in relatively low effective net gain. Directly amplifying its power using conventional ytterbium-doped fiber or crystal amplification structures is susceptible to gain competition from the high-gain band, potentially introducing problems such as amplified spontaneous emission, parasitic oscillations, and a decrease in signal-to-noise ratio.

[0027] In view of the problems existing in the existing solutions, the present invention proposes a 248.3nm laser based on a 993.2nm parametric light source. The 993.2nm single-frequency pulse light is generated through an optical parametric amplification process of 515nm single-frequency pulse pump light and 1069.6nm single-frequency continuous idler light. The 248.3nm deep ultraviolet laser output is obtained by further frequency conversion. This avoids the gain competition and noise amplification problems caused by directly using ytterbium-doped gain medium to amplify 993.2nm laser, while realizing a compact structure, high spectral purity and high stability 248.3nm deep ultraviolet laser output.

[0028] like Figure 1 As shown, the laser source includes a 515 nm single-frequency pulsed laser source 1, a 1069.6 nm single-frequency continuous laser 9, a two-stage optical parametric amplification module, a second-harmonic generation module, and a fourth-harmonic generation module. The 515 nm single-frequency pulsed laser source 1 is used to provide pump light for the two-stage optical parametric amplification module, and its output wavelength is 515 nm single-frequency pulsed linearly polarized light.

[0029] In this embodiment, the 515 nm single-frequency pulsed laser source 1 includes a 1030 nm single-frequency pulsed laser 2 and a 1030 nm laser frequency-second harmonic generation module 3. The 1030 nm single-frequency pulsed light output from the 1030 nm single-frequency pulsed laser 2 is frequency-doubled by the 1030 nm laser frequency-second harmonic generation module 3 to generate 515 nm single-frequency pulsed pump light. More specifically, the 1030 nm single-frequency pulsed laser 2 outputs 1030 nm single-frequency pulsed laser light, which undergoes second harmonic conversion by the 1030 nm laser frequency-second harmonic generation module 3 to generate 515 nm single-frequency pulsed pump light. The 515 nm single-frequency pulsed pump light is split into a first pump light and a second pump light by a first beam splitter 4. The first pump light is used for the first-stage optical parametric amplification process, and the second pump light is used for the second-stage optical parametric amplification process.

[0030] In this embodiment, the 1069.6 nm single-frequency continuous laser 9 is used to provide seed light for the first-stage optical parametric amplification process, and its output wavelength is 1069.6 nm single-frequency continuous linearly polarized light. Since the 1069.6 nm single-frequency continuous seed light exists continuously in time, it does not need to be externally synchronized with the 515 nm single-frequency pulse pump light during the first-stage optical parametric amplification process.

[0031] A two-stage optical parametric amplification module is used to generate and amplify 993.2 nm single-frequency pulse light. The first-stage module amplifies a 515 nm single-frequency pulse pump light and a 1069.6 nm single-frequency continuous idler light in a first nonlinear crystal 11 to generate a 993.2 nm single-frequency pulse signal light. The second-stage module amplifies a second 515 nm single-frequency pulse pump light and a 993.2 nm single-frequency pulse light in a second nonlinear crystal 13 to increase the output power of the 993.2 nm single-frequency pulse light.

[0032] More specifically, the first pump light is spatially combined with the 1069.6 nm single-frequency continuous idler light output from the 1069.6 nm single-frequency continuous laser 9 via the first dichroic mirror 10, and both are incident on the first nonlinear crystal 11. The first nonlinear crystal 11 is used to realize the optical parametric amplification process between the 515 nm single-frequency pulse pump light, the 1069.6 nm single-frequency continuous idler light, and the 993.2 nm single-frequency pulse signal light, thereby generating the 993.2 nm single-frequency pulse signal light. Since the 1069.6 nm idler light is continuous light, it does not need to be externally synchronized with the 515 nm pump pulse during the first-stage optical parametric amplification process.

[0033] The second pump light, guided by the delay adjustment module 8 composed of the first reflector 5, the second reflector 6, and the third reflector 7, enters the second-stage optical parametric amplification module. The delay adjustment module 8 is used to adjust the propagation optical path of the second pump light, ensuring that the second pump light and the 993.2 nm single-frequency pulse light generated by the first nonlinear crystal 11 coincide in time within the second nonlinear crystal 13. The delay adjustment module 8 can be composed of one or more reflectors, which can be mounted on a movable translation stage. Changing the position of the reflectors adjusts the optical path of the 515 nm second pump light.

[0034] The second pump light, after time-delay adjustment, is spatially combined with the 993.2 nm single-frequency pulse light output from the first-stage optical parametric amplification module via the second dichroic mirror 12, and both are incident on the second nonlinear crystal 13. The second nonlinear crystal 13 is used to realize the second-stage optical parametric amplification process, amplifying the power of the 993.2 nm single-frequency pulse light. The amplified 993.2 nm single-frequency pulse light is then guided or separated by the third dichroic mirror 14 before entering the subsequent frequency second harmonic module.

[0035] The second harmonic generation module performs a second harmonic conversion on the 993.2 nm single-frequency pulse light output from the two-stage optical parametric amplification module to generate a 496.6 nm single-frequency pulse light. The fourth harmonic generation module performs a second harmonic conversion on the 496.6 nm single-frequency pulse light to generate and output a 248.3 nm single-frequency deep ultraviolet pulse light. Specifically, the fourth harmonic generation module is a deep ultraviolet frequency conversion module used to achieve the fourth harmonic output of the 993.2 nm fundamental frequency light. It obtains the 248.3 nm deep ultraviolet light by performing a second harmonic conversion on the 496.6 nm second harmonic light again.

[0036] More specifically, the frequency-second harmonic generation module includes a third nonlinear crystal 15 and a fourth dichroic mirror 16. The third nonlinear crystal 15 is used to perform second harmonic conversion on the amplified 993.2 nm single-frequency pulse light to generate 496.6 nm single-frequency pulse light. The fourth dichroic mirror 16 is used to separate or guide the 993.2 nm fundamental frequency light and the 496.6 nm harmonic light, allowing the 496.6 nm single-frequency pulse light to enter the frequency-fourth harmonic generation module. The frequency-fourth harmonic generation module includes a fourth nonlinear crystal 17 and a fifth dichroic mirror 18; the fourth nonlinear crystal 17 is used to perform second harmonic conversion on the 496.6 nm single-frequency pulse light to generate 248.3 nm single-frequency deep ultraviolet pulse light, and the fifth dichroic mirror 18 is used to separate the 496.6 nm second harmonic light and the 248.3 nm deep ultraviolet light, and output 248.3 nm single-frequency deep ultraviolet laser.

[0037] In this embodiment, a 515 nm single-frequency pulse pump light is generated and amplified into a 993.2 nm single-frequency pulse light through a two-stage optical parametric amplification module. This pulse light is then sequentially doubled and quadrupled to generate a 248.3 nm single-frequency deep ultraviolet pulse light. This structure utilizes optical parametric amplification to obtain the 993.2 nm single-frequency pulse light, avoiding the gain competition problems caused by high-gain bands, enhanced spontaneous emission, and parasitic oscillations at non-target wavelengths that occur when directly using ytterbium-doped gain media to amplify 993.2 nm laser light. Furthermore, the entire light source employs an all-solid-state nonlinear frequency conversion structure, offering advantages such as compact structure, high spectral purity, good stability, and ease of modular integration.

[0038] In this embodiment, the first beam splitter 4 has a first surface and a second surface, and the working incident angle of the first beam splitter 4 is 45°. The first surface is a beam-splitting functional surface, coated with a partially reflective beam-splitting film optimized for a 515 nm wavelength, a 45° working incident angle, and a preset beam-splitting ratio, or coated with a polarizing beam-splitting film optimized for a 515 nm wavelength, a 45° working incident angle, and a polarization state, used to split the 515 nm single-frequency pulse pump light into a first pump light and a second pump light. The second surface is coated with an anti-reflection optical film optimized for a 515 nm wavelength to reduce the reflection loss of transmitted light at the second surface. The preset beam-splitting ratio can be set according to the pump energy required by the first-stage optical parametric amplification module and the second-stage optical parametric amplification module; when a polarizing beam-splitting film is used, the energy ratio of the first pump light and the second pump light can be adjusted by adjusting the polarization state of the incident 515 nm pump light.

[0039] In this embodiment, the first reflector 5, the second reflector 6, and the third reflector 7 are all used to guide the 515 nm second pump light. Each reflector has a reflective surface coated with a thin optical film highly reflective to 515 nm. The working incident angle of each reflector is 45°. Preferably, the second reflector 6 and the third reflector 7 are disposed in the delay adjustment module 8 to achieve fine adjustment of the optical path of the second pump light.

[0040] In this embodiment, the first dichroic mirror 10, the second dichroic mirror 12, and the third dichroic mirror 14 all have a first surface and a second surface, and the working incident angle of the dichroic mirrors is 45°. The first surface may be coated with an optical thin film with high reflectivity and anti-reflection function matching the corresponding beam combining, reflection, or beam splitting function, and the second surface may be coated with an anti-reflection optical thin film matching the transmission wavelength. Specifically, the first surface of the first dichroic mirror 10 is highly reflective of 515 nm light, highly transmittant of 1069.6 nm light, and highly transmittant of 993.2 nm light; the first surface of the second dichroic mirror 12 is highly reflective of 515 nm light, highly transmittant of 1069.6 nm light, and highly transmittant of 993.2 nm light; the first surface of the third dichroic mirror 14 is highly transmittant of 515 nm light, highly transmittant of 1069.6 nm light, and highly reflective of 993.2 nm light.

[0041] In this embodiment, the first nonlinear crystal 11 and the second nonlinear crystal 13 are nonlinear optical crystals that satisfy the optical parametric amplification phase matching condition between 515 nm, 1069.6 nm, and 993.2 nm. The first nonlinear crystal 11 and the second nonlinear crystal 13 can be selected from one or more of LBO (LiB3O5, lithium triborate), BBO (β-BaB2O4, β-phase barium metaborate), BIBO (BiB3O6, bismuth triborate), KTP (KTiOPO4, potassium titanyl phosphate), or periodically polarized nonlinear crystals.

[0042] Preferably, the first nonlinear crystal 11 and the second nonlinear crystal 13 are BBO or LBO crystals. The BBO crystal can use angular phase matching, with a typical phase matching cut angle of θ = 23.4° and φ = 30°, where 515 nm is the e-ray, 1069.6 nm is the o-ray, and 993.2 nm is the o-ray. The LBO crystal can use angular or temperature phase matching, with a typical phase matching cut angle of θ = 90° and φ = 13.7°, where 515 nm is the e-ray, 1069.6 nm is the o-ray, and 993.2 nm is the o-ray. It should be noted that the above cut angles are only preferred embodiments; the actual cut angle can be determined based on the phase matching type, operating temperature, polarization direction, and the results calculated using the Sellmeier equation. Both end faces of the first nonlinear crystal 11 and the second nonlinear crystal 13 are coated with optical thin films that enhance the light transmittance at 515 nm, 993.2 nm, and 1069.6 nm.

[0043] In this embodiment, the third nonlinear crystal 15 is a nonlinear optical crystal that satisfies the phase matching condition for the second harmonic conversion from 993.2 nm to 496.6 nm. The third nonlinear crystal 15 can be LBO, BBO, BiBO, or CLBO (CsLiB6O). 10 One of them is lithium cesium hexaborate.

[0044] Preferably, the third nonlinear crystal 15 can be a BBO or LBO crystal; wherein, the BBO crystal can be used with angular phase matching, and the phase matching cut angle of the BBO crystal can be θ=24°, φ=30°, in which case 993.2 nm is all o-ray and 496.6 nm is e-ray; the LBO crystal can be used with angular phase matching or temperature phase matching, and the phase matching cut angle of the LBO crystal can be θ=90°, φ=16.2°, in which case 993.2 nm is all o-ray and 496.6 nm is e-ray. Both end faces of the third nonlinear crystal 15 are coated with optical thin films that enhance the light transmittance of 993.2 nm and 496.6 nm.

[0045] The fourth dichroic mirror 16 may have a first surface and a second surface, and the working incident angle of the dichroic mirror is 45°. The first surface is coated with an optical thin film with high reflectivity and anti-reflection function for separating the 993.2 nm fundamental frequency light and the 496.6 nm second-harmonic light, and the second surface is coated with an anti-reflection optical thin film that matches the transmission wavelength. Specifically, the first surface of the fourth dichroic mirror 16 is highly reflective of 496.6 nm light and highly transmittant of 993.2 nm light.

[0046] In this embodiment, the fourth nonlinear crystal 17 is a deep ultraviolet nonlinear optical crystal that satisfies the phase matching condition for the second harmonic conversion from 496.6 nm to 248.3 nm. The fourth nonlinear crystal 17 can be selected from CLBO, BBO, and KBBF.

[0047] Preferably, the fourth nonlinear crystal 17 can be a CLBO or BBO crystal; wherein, the CLBO crystal can adopt angular phase matching or temperature phase matching. When the CLBO crystal is at a temperature of 300 K, the first-order phase matching cut angle of the CLBO crystal can be θ=71.4° and φ=45°, at which time 496.6 nm is o-ray and 248.3 nm is e-ray; the BBO crystal can adopt angular phase matching. The first-order phase matching cut angle of the BBO crystal can be θ=53° and φ=30°, at which time 496.6 nm is o-ray and 248.3 nm is e-ray.

[0048] Both ends of the fourth nonlinear crystal 17 can be coated with anti-reflection optical films optimized for wavelengths of 496.6 nm and 248.3 nm. The fifth dichroic mirror 18 has a first surface and a second surface. The first surface is coated with an optical film that provides high reflection and anti-reflection for separating 496.6 nm second harmonic light and 248.3 nm deep ultraviolet light, while the second surface is coated with an anti-reflection optical film that matches the transmission wavelength. Specifically, the first surface of the fifth dichroic mirror 18 is highly reflective of 248.3 nm light and highly transmittant of 496.6 nm light.

[0049] In this embodiment, when the fourth nonlinear crystal 17 is a CLBO crystal, the CLBO crystal can be placed in a sealed or dry environment and can be used in conjunction with a crystal heating device to reduce the impact of crystal moisture absorption on the deep ultraviolet frequency conversion efficiency and long-term stability. When the first nonlinear crystal 11, the second nonlinear crystal 13, the third nonlinear crystal 15, or the fourth nonlinear crystal 17 adopts a temperature phase matching method, the corresponding nonlinear crystal can be placed in a temperature-controlled crystal furnace to improve phase matching stability.

[0050] In some alternative embodiments, the 248.3 nm deep ultraviolet laser can also be obtained by combining second harmonic generation with cascaded sum-frequency generation. Specifically, the 993.2 nm fundamental frequency light is first converted to 496.6 nm light through second harmonic conversion. The 496.6 nm light is then summed with the remaining 993.2 nm fundamental frequency light to generate 331.1 nm light. The 331.1 nm light is then summed with the remaining 993.2 nm fundamental frequency light to generate the 248.3 nm deep ultraviolet laser.

[0051] In some alternative embodiments, the splitting ratio of the first beam splitter 4, and the crystal types, cutting angles, lengths, temperatures, and focusing conditions of the first nonlinear crystal 11, the second nonlinear crystal 13, the third nonlinear crystal 15, and the fourth nonlinear crystal 17 can be optimized according to the pump light power, pulse width, repetition frequency, output power requirements, and phase matching conditions. In other embodiments, 248.3 nm output can also be achieved by sequentially performing frequency doubling, third harmonicization, and fourth harmonicization on the 993.2 nm fundamental frequency light, but its structure is more complex than this embodiment, and it places higher demands on the optical element coating design and optical path adjustment.

[0052] In some alternative embodiments, the ytterbium-doped laser system includes a ytterbium-doped pulsed laser for generating a 515 nm single-frequency pulsed pump light, and a ytterbium-doped fiber laser for generating a 1069.6 nm single-frequency continuous idler seed light. The 515 nm single-frequency pulsed pump light can be obtained by second harmonic conversion of near-infrared single-frequency pulsed light output from a ytterbium-doped laser, including but not limited to Yb:YAG, Yb:KGW, Yb:YLF, or a ytterbium-doped fiber laser; the 1069.6 nm single-frequency continuous idler seed light can be output from a ytterbium-doped fiber laser, a ytterbium-doped fiber DBR laser, or a ytterbium-doped fiber DFB laser.

[0053] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A 248.3nm laser based on a 993.2nm parametric light source, Its features are, include: Pump laser source, seed source, first-stage optical parametric amplification module, second-stage optical parametric amplification module, second-harmonic generation module and fourth-harmonic generation module; The pump laser source is used to output single-frequency pulsed linearly polarized light with a wavelength of 515nm; The seed light source is used to output single-frequency continuous linearly polarized light at 1069.6nm; The first-stage optical parametric amplification module is used to perform optical parametric amplification of the 515nm single-frequency pulse pump light and the 1069.6nm single-frequency continuous idler light to generate a 993.2nm single-frequency pulse signal light. The second-stage optical parametric amplification module is used to perform optical parametric amplification of the 515nm single-frequency pulse pump light and the 993.2nm single-frequency pulse light. The frequency doubling module is used to perform second harmonic conversion on the 993.2nm single-frequency pulse light amplified by the second-stage optical parametric amplification module to generate 496.6nm single-frequency pulse light; The quadruple harmonic generation module is used to perform second harmonic conversion on 496.6nm single-frequency pulse light to generate and output 248.3nm single-frequency deep ultraviolet pulse light.

2. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 1, characterized in that, The pump laser source includes a 1030 nm single-frequency pulse laser and a 1030 nm laser frequency-second harmonic generation module arranged sequentially along the optical path. The 1030 nm single-frequency pulse laser is used to output 1030 nm single-frequency pulse laser. After the 1030 nm single-frequency pulse laser undergoes second harmonic conversion by the 1030 nm laser frequency-second harmonic generation module, it generates 515 nm single-frequency pulse pump light.

3. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 1, characterized in that, The 515nm single-frequency pulse linearly polarized light is split into a first pump light and a second pump light by the first beam splitter. The first pump light is used for the first-stage optical parametric amplification process, and the second pump light is used for the second-stage optical parametric amplification process after being delayed by the delay adjustment module.

4. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 3, characterized in that, The delay module includes a first mirror, a second mirror, and a third mirror arranged sequentially along the optical path. The delay module is used to make the second pump light and the 993.2 nm single-frequency pulse light generated by the first-stage optical parametric amplification module coincide in time in the second-stage optical parametric amplification module.

5. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 1, characterized in that, The first-stage optical parametric amplification module includes a first dichroic mirror and a first nonlinear crystal. The first dichroic mirror spatially combines the received first pump light with the 1069.6 nm single-frequency continuous idler light and outputs the combined light to the first nonlinear crystal. The first nonlinear crystal is used to realize the optical parametric amplification process between the 515 nm single-frequency pulse pump light, the 1069.6 nm single-frequency continuous idler light and the 993.2 nm single-frequency pulse signal light, thereby generating the 993.2 nm single-frequency pulse signal light.

6. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 5, characterized in that, The second-stage optical parametric amplification module includes a second dichroic mirror, a second nonlinear crystal, and a third dichroic mirror; The second dichroic mirror is used to spatially combine the received, delayed second pump light with the 993.2 nm single-frequency pulse light output from the first-stage optical parametric amplification module, and then output the combined light to the second nonlinear crystal. The second nonlinear crystal is used to realize the second-stage optical parametric amplification process, which amplifies the power of the 993.2 nm single-frequency pulse light. The third dichroic mirror is used to guide or separate the received amplified 993.2 nm single-frequency pulse light and output it to the frequency doubling module.

7. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 6, characterized in that, Both the first and second nonlinear crystals are nonlinear optical crystals that satisfy the optical parametric amplification phase matching condition between the 515 nm single-frequency pulse pump light, the 1069.6 nm single-frequency continuous idler light, and the 993.2 nm single-frequency pulse signal light.

8. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 1, characterized in that, The frequency doubling module includes a third nonlinear crystal and a fourth dichroic mirror arranged sequentially along the optical path. The third nonlinear crystal is used to perform second harmonic conversion on the 993.2 nm single-frequency pulse light amplified by the second-stage optical parametric amplification module to generate 496.6 nm single-frequency pulse light. The fourth dichroic mirror is used to separate or guide the 993.2 nm fundamental frequency light and the 496.6 nm frequency-doubled light, and outputs the 496.6 nm single-frequency pulse light to the fourth frequency-doubled module.

9. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 8, characterized in that, The quadruple harmonic generation module includes a fourth nonlinear crystal and a fifth dichroic mirror arranged sequentially along the optical path. The fourth nonlinear crystal is used to perform second harmonic conversion on the received 496.6 nm single-frequency pulse light to generate 248.3 nm single-frequency deep ultraviolet pulse light. The fifth dichroic mirror is used to separate the 496.6 nm second harmonic light from the 248.3 nm deep ultraviolet light and output a 248.3 nm single-frequency deep ultraviolet laser.

10. The 248.3nm laser based on a 993.2nm parametric light source as described in claim 9, characterized in that, The third nonlinear crystal is a nonlinear optical crystal that satisfies the phase matching condition of the second harmonic conversion from 993.2 nm to 496.6 nm, and the fourth nonlinear crystal is a deep ultraviolet nonlinear optical crystal that satisfies the phase matching condition of the second harmonic conversion from 496.6 nm to 248.3 nm.

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