High repetition rate 193nm laser based on LD pumped alexandrite crystal

Abstract

The present invention belongs to the field of laser technology, and provides a high repetition rate 193nm laser based on LD pumped alexandrite crystal, which includes an LD pump source, an alexandrite laser oscillator and a nonlinear frequency conversion module; the LD pump source is used to generate laser light and input it into the alexandrite laser oscillator; the alexandrite laser oscillator includes a first dichroic mirror, an alexandrite crystal, a first plano-convex lens, a birefringent filter, a Q-switched device, a first quarter wave plate and an output coupling mirror arranged in sequence along the optical path; the alexandrite laser oscillator is used to generate a fundamental frequency light source; the fundamental frequency light source is sequentially input into the nonlinear frequency conversion module through a first half wave plate and a second plano-convex lens to obtain a 193.4nm laser. The entire system is a fully solid-state structure, and has the characteristics of good pump source stability and high integration, short fundamental frequency light source wavelength, less nonlinear conversion times, high overall electro-optical conversion efficiency and low overall system cost.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to a high repetition rate 193nm laser based on LD pumped alexandrite crystal. Background Art

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

[0003] 193nm laser is located in the deep ultraviolet band (usually 100nm to 200nm), and plays an irreplaceable and important role in the fields of high-resolution spectroscopy, photochemistry, fiber grating preparation, precision laser processing, etc., especially in the manufacturing of semiconductor integrated circuits, etc., 193nm laser is a widely used and indispensable light source. At present, in the above-mentioned band, the ArF excimer gas laser has the largest market share; this gas laser directly produces deep ultraviolet laser output by combining inert gas and reactive gas under high pressure conditions. Its advantages are large output power (energy), and obvious disadvantages are that the working substance is highly toxic and needs to be replaced frequently, the system volume is large, maintenance is difficult, and the cost of use is high. In terms of laser parameters, the repetition frequency of gas lasers is low, the beam quality is poor, and it is difficult to apply in some detection aspects. Therefore, in order to solve the use difficulties encountered by ArF excimer gas lasers in the deep ultraviolet band, it is urgent to develop a deep ultraviolet light source with expandable repetition frequency, better beam quality, reliable and stable performance.

[0004] In recent years, all-solid-state 193nm lasers have gradually developed. They have the advantages of adjustable repetition frequency, good beam quality, good coherence, and small laser system size. They have begun to be used in fiber grating writing, semiconductor wafer defect detection, etc. The main methods for realizing solid-state 193nm lasers are:

[0005] (1) A 1547nm laser is selected as the fundamental frequency light source, which is generated by an erbium-doped optical fiber. The pump source is a laser semiconductor (LD). A nonlinear crystal is used to perform five nonlinear frequency conversion processes, namely, frequency doubling, frequency tripling, frequency sextuple, frequency septuple, and frequency octuple, to achieve 193nm laser output. However, this system requires a large number of nonlinear times and the overall electro-optical conversion efficiency is low.

[0006] (2) Select 1064nm laser as the fundamental frequency light source, which is generated by Nd:YAG laser and the pump source is LD. It goes through five nonlinear frequency conversion processes, including frequency doubling, optical parametric oscillation (OPO), frequency doubling again, sum frequency, and frequency summing again. The problem of low overall conversion efficiency also exists. In addition, after generating 532nm laser by frequency doubling 1064nm, the laser is divided into two paths, and the four-fold frequency doubling and OPO processes are performed respectively, and then the laser sum frequency is performed to generate 193nm laser. In addition to the large number of nonlinear frequency conversions, this scheme also has the problem of achieving spatial coupling and timing synchronization of the two laser beams before entering the nonlinear crystal, which makes the system bulky and increases the instability factors.

[0007] (3) Two laser beams, 1030nm laser (generated by Yb:YAG laser) and 1553nm laser (generated by erbium-doped fiber laser), are selected as the fundamental frequency light sources. The pump sources are both LDs. The 1030nm laser is frequency-doubled and quadrupled to generate 258nm laser, which is then frequency-summed twice with the 1553nm laser to generate 193nm laser. The problem with this scheme is that it requires a large number of nonlinear frequency conversions and the two laser beams are coupled in time and space, which is not conducive to the integration of the laser system and the improvement of the system's electro-optical conversion efficiency.

[0008] (4) 773.6 nm is selected as the fundamental frequency light source, which is generated by a titanium sapphire laser. The pump source is a green laser. A nonlinear crystal is used to perform three nonlinear frequency conversion processes, namely frequency doubling, tripling, and quadrupling, to achieve the target wavelength output. However, the pump source of the fundamental frequency light source is a green laser. The pump source is generated by Nd:YAG laser frequency doubling, which introduces an additional nonlinear frequency conversion process, reducing the overall electro-optical conversion efficiency of the system. In addition, the titanium sapphire crystal itself has a serious thermal effect and requires good temperature control measures to provide stability. The crystal can only be pumped in the blue-green band, which also makes the laser system bulky and increases the cost. Another solution based on titanium sapphire laser is to use two nonlinear frequency conversion processes, namely frequency doubling and quadrupling, to obtain the target wavelength laser in the nonlinear frequency conversion process. In addition to the problems of pump source and crystal temperature control, the quadrupling process requires the use of KBBF crystals, which have limited production capacity, are expensive, are easily damaged, and have poor long-term stability. Summary of the invention

[0009] In order to solve at least one technical problem existing in the above-mentioned background technology, the present invention provides a high repetition rate 193nm laser based on LD pumped alexandrite crystal, which has good pump source stability and high integration, short wavelength of fundamental frequency light source, fewer nonlinear frequency conversion processes, high overall electro-optical conversion efficiency of the system and low system cost.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] In one or more embodiments, a high repetition rate 193 nm laser based on LD pumped alexandrite crystal comprises: an LD pump source, an alexandrite laser oscillator and a nonlinear frequency conversion module;

[0012] The LD pump source is used to generate laser light and input into the alexandrite laser oscillator;

[0013] The alexandrite laser oscillator comprises a first dichroic mirror, an alexandrite crystal, a first plano-convex lens, a birefringent filter, a Q-switched device, a first quarter-wave plate and an output coupling mirror which are sequentially arranged along the optical path; the alexandrite laser oscillator is used to generate a fundamental frequency light source; the fundamental frequency light source is sequentially input into a nonlinear frequency conversion module through a first half-wave plate and a second plano-convex lens to obtain a 193.4nm laser.

[0014] As an implementation manner, the nonlinear frequency conversion module includes a frequency doubling nonlinear crystal, a frequency tripling nonlinear crystal, a frequency quadrupling nonlinear crystal and a beam splitter prism arranged along the optical path.

[0015] As an implementation mode, the laser output by the LD pump source passes through a collimating lens and a focusing lens in sequence and hits the alexandrite crystal.

[0016] As an implementation mode, the alexandrite crystal is cut along the crystal c-axis and the Brewster angle, the chromium ion doping concentration is 0.2-0.22at.%, and the crystal end face is coated with an anti-reflection film for 6XXnm and 700nm-800nm ​​bands.

[0017] In other embodiments, a high repetition rate 193nm laser based on LD pumped alexandrite crystal is provided, which includes: an LD pump source, an alexandrite regenerative amplifier and a nonlinear frequency conversion module;

[0018] The LD pump source is used to generate laser light and input it into the alexandrite regenerative amplifier;

[0019] The alexandrite regenerative amplifier comprises a second dichroic mirror, a resonant cavity, a second half-wave plate, a Faraday rotator, a second thin-film polarizer and an eighth reflector; the resonant cavity uses the first reflector and the seventh reflector as end mirrors, and an alexandrite crystal, a first thin-film polarizer and a Pockels cell are also arranged in the resonant cavity;

[0020] The seed light of the alexandrite regenerative amplifier passes through the second thin-film polarizer, the Faraday rotator, the second half-wave plate and the first thin-film polarizer in sequence to enter the resonant cavity, the seed light oscillates multiple times in the resonant cavity with the first reflector and the seventh reflector as end mirrors, and the seed light is amplified once each time it passes through the alexandrite crystal; when the high voltage at both ends of the Pockels cell is removed, the polarization state of the amplified seed light changes to s-polarization, and is reflected and output at the first thin-film polarizer; the amplified output laser then passes through the second half-wave plate, the Faraday rotator, the second thin-film polarizer and the eighth reflector in sequence for spatial collimation, and finally passes through the first half-wave plate and the second plano-convex lens in sequence to enter the nonlinear frequency conversion module to obtain a 193nm laser.

[0021] As an implementation mode, the resonant cavity further includes a second reflector, a second dichroic mirror, a third reflector, a fourth reflector, a fifth reflector, a sixth reflector and a second quarter wave plate;

[0022] The polarization state of the seed light entering the resonant cavity is s polarization. It passes through the Pockels cell and the second quarter-wave plate, is reflected by the seventh reflector, and passes through the second quarter-wave plate and the Pockels cell again. The polarization state of the laser changes to p polarization. At this time, a quarter-wave voltage is applied to both ends of the Pockels cell. The seed light is transmitted through the first thin-film polarizer, and passes through the sixth reflector, the fifth reflector, the fourth reflector, the third reflector, the alexandrite crystal, the second dichroic mirror, the second reflector and the first reflector in turn, and then returns to the seventh reflector along the same route. At this time, the polarization state of the laser is still p polarization.

[0023] As an implementation mode, the second dichroic mirror is a plane mirror, which has high transmittance to 638nm laser, with a transmittance greater than 95%, and high reflectivity to 700nm-800nm ​​laser, with a reflectivity greater than 99.9%;

[0024] The first reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%;

[0025] The second reflector is a plano-concave mirror with a curvature radius of 800mm, which is highly reflective to lasers in the 700nm-800nm ​​band, with a reflectivity greater than 99.9%;

[0026] The third reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%;

[0027] The fourth reflector is a plano-concave mirror with a curvature radius of 500 mm, which is highly reflective to lasers in the 700nm-800nm ​​band and has a reflectivity greater than 99.9%;

[0028] The fifth reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%;

[0029] The sixth reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%;

[0030] The seventh reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%;

[0031] The eighth reflector is a plane mirror, which has high reflection to the laser in the wavelength band of 700nm-800nm, and the reflectivity is greater than 99.9%.

[0032] As an embodiment, the first thin-film polarizer has an extinction ratio greater than 500:1 and is inserted at a Brewster angle with respect to the direction of laser transmission in the cavity;

[0033] The extinction ratio of the second thin-film polarizer is greater than 500:1, and it forms a Brewster angle with the transmission direction of the seed light.

[0034] As an implementation manner, the central wavelength of the seed light is 773.6 nm.

[0035] As an implementation manner, the nonlinear frequency conversion module includes a frequency doubling nonlinear crystal, a frequency tripling nonlinear crystal, a frequency quadrupling nonlinear crystal and a beam splitter prism arranged along the optical path.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The fundamental frequency light source used in the present invention is generated by an alexandrite laser. The alexandrite crystal is a laser crystal with excellent performance, which can achieve tunable output of laser in the 700nm-800nm ​​band. The crystal has a high damage threshold, high thermal conductivity, and is suitable for high-power pumping, which is beneficial to improving the power of the fundamental frequency light source and thus the power of the 193nm laser. In addition, the laser output by the alexandrite laser is linearly polarized, which can be directly adjusted by a wave plate to meet the requirements of nonlinear crystal phase matching.

[0038] (2) The fundamental frequency light source used in the present invention is about 773.6nm, and a laser output of about 193.4nm can be obtained through at most three nonlinear processes. Compared with the fundamental frequency light source in the 1μm and 1.5μm bands, there are fewer nonlinear frequency conversion processes and the overall conversion efficiency is higher.

[0039] (3) The laser described in the present invention is an all-solid-state laser. Compared with the traditional excimer gas laser, it has obvious advantages in parameters such as beam quality and laser repetition frequency. In particular, the repetition frequency is mainly controlled by the Pockels cell and can reach the kHz or even MHz level. In addition, the all-solid-state laser is smaller, more portable, more robust, and easier to maintain.

[0040] (4) Compared with the titanium sapphire laser solution which is also a solid-state laser, the LD pump source used in the laser of the present invention has high electro-optical conversion efficiency, good long-term stability, and lower quantum loss in the laser generation process. In addition, the crystal thermal management device used in the present invention is simple, which can achieve further integration and simplification of the system.

[0041] (5) In the nonlinear frequency conversion module, the polarization characteristics of the fundamental frequency light source and the new wavelength laser generated during the frequency conversion process are fully utilized, the three crystals used are designed with different cutting angles, and the cascade frequency multiplication method is adopted to avoid the introduction of other devices, greatly reducing the volume of the entire frequency conversion module, which is beneficial to the system integration and miniaturization. In addition, the nonlinear crystals used are LBO and BBO, and the manufacturing technology is quite mature, which effectively controls the cost.

[0042] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0044] Figure 1 1 is a schematic diagram of the structure of a high repetition rate 193nm laser based on LD pumped alexandrite crystal according to Example 1 of the present invention;

[0045] Figure 2 Schematic diagram of the structure of a high repetition rate 193nm laser based on LD pumped alexandrite crystal according to Example 2 of the present invention;

[0046] Figure 3 These are the light spots of the fundamental frequency light, the doubled frequency light, the tripled frequency light, and the quadrupled frequency light obtained in Example 2 of the present invention.

[0047] Among them, 1. LD pump source; 2. collimating lens; 3. focusing lens; 4. first dichroic mirror; 5. emerald crystal; 6. first plano-convex lens; 7. birefringent filter; 8. Q-switched device; 9. first quarter wave plate; 10. output coupling mirror; 11. first half wave plate; 12. second plano-convex lens; 13. fundamental frequency light source; 14. frequency doubling nonlinear crystal; 15. mixed light of fundamental frequency light and frequency doubling light; 16. triple frequency nonlinear crystal; 17. mixed light of fundamental frequency light, frequency doubling light and frequency tripling light; 18. quadruple frequency nonlinear crystal; 19. fundamental frequency light A mixture of frequency light, frequency-doubled light, frequency-tripled light and frequency-quadrupled light; 20. a beam splitter; 21. a 193nm laser; 22. a second dichroic mirror; 23. a first reflector; 24. a second reflector; 25. a third reflector; 26. a fourth reflector; 27. a fifth reflector; 28. a sixth reflector; 29. ​​a first thin-film polarizer; 30. a Pockels cell; 31. a second quarter-wave plate; 32. a seventh reflector; 33. a second half-wave plate; 34. a Faraday rotator; 35. a second thin-film polarizer; 36. an eighth reflector; 37. a seed light. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0049] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0050] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0051] In the present invention, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention, and do not specifically refer to any part or element in the present invention and should not be understood as limitations on the present invention.

[0052] In the present invention, terms such as "fixed connection", "connected", "connection", etc. should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meanings of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

[0053] Example 1

[0054] like Figure 1 As shown, a high repetition rate 193nm laser based on LD pumped alexandrite crystal according to an embodiment of the present invention comprises: an LD pump source 1, an alexandrite laser oscillator and a nonlinear frequency conversion module;

[0055] The LD pump source 1 is used to generate laser light and input it into the alexandrite laser oscillator;

[0056] The alexandrite laser oscillator includes a first dichroic mirror 4, an alexandrite crystal 5, a first plano-convex lens 6, a birefringent filter 7, a Q-switched device 8, a first quarter-wave plate 9 and an output coupling mirror 10 which are sequentially arranged along the optical path; the alexandrite laser oscillator is used to generate a fundamental frequency light source 13; the fundamental frequency light source 13 is sequentially input into a nonlinear frequency conversion module through a first half-wave plate 11 and a second plano-convex lens 12 to obtain a 193.4nm laser.

[0057] In the embodiment of the present invention, the central wavelength of the LD pump source is 6XXnm, and the alexandrite crystal is pumped; the fiber-coupled output has a numerical aperture of 0.22, and the fiber core diameter is one of 105μm, 200μm, 400μm, and 600μm.

[0058] For example, the central wavelength of the LD pump source 1 is 638 nm, the fiber-coupled output, the numerical aperture is 0.22, the fiber core diameter is 400 μm, and the maximum output power is 45 W; the laser output by the LD pump source 1 passes through the collimating lens 2 and the focusing lens 3 in sequence and hits the alexandrite crystal 5.

[0059] The alexandrite laser oscillator generates a Q-switched pulse laser, and the birefringent filter 7 is rotated to tune the central wavelength of the laser oscillator to about 773.6 nm; the birefringent filter 7 is made of quartz material, and has a thickness of 0.5 mm to 8 mm, or is a combination of multiple birefringent filters with equal thicknesses, inserted at a Brewster angle with respect to the laser transmission direction in the cavity; the birefringent filter 7 is a combination of three birefringent filters with thicknesses of 0.5 mm, 1 mm, and 2 mm;

[0060] The fundamental frequency light source 12 is polarized by the first half wave plate 11 and then enters the nonlinear frequency conversion module through the second plano-convex lens 12 .

[0061] The cutting method of the alexandrite crystal is one of cutting along the crystal c-axis and cutting at the Brewster angle, the chromium ion doping concentration is 0.2-0.22at.%, and the crystal end face is plated with an anti-reflection film for the 6XXnm and 700nm-800nm ​​bands. For example, the alexandrite crystal 5 has a doping concentration of 0.22at.%, and a size of 3×3×10mm 3 , cutting along the c-axis.

[0062] The collimating lens 2 is composed of at least two lenses, which are highly transparent to 6XXnm lasers with a transmittance greater than 99%. According to different requirements for mode matching between the pump light and the laser in the cavity, the corresponding lens focal length combination is selected to achieve mode matching between the pump light and the laser in the cavity.

[0063] Preferably, the focal length of the collimating lens 2 is 50 mm;

[0064] The focal length of the focusing lens 3 is 50 mm;

[0065] The first dichroic mirror 4 is a plane mirror, which has high transmittance to 638nm laser with a transmittance greater than 95%, and high reflectivity to 700nm-800nm ​​laser with a reflectivity greater than 99.9%.

[0066] The Q-switching device 8 is one of a BBO Pockels cell, a KD*P Pockels cell, and an acousto-optic modulator;

[0067] The output coupling mirror 10 is coated with a partial reflection film for the 700nm-800nm ​​band, and the reflectivity is 95% to 99%.

[0068] The focal length of the second plano-convex lens 12 is 500 mm.

[0069] In this embodiment, the nonlinear frequency conversion module includes a frequency doubling nonlinear crystal 14 , a frequency tripling nonlinear crystal 16 , a frequency quadrupling nonlinear crystal 18 and a beam splitter prism 20 arranged along the optical path.

[0070] The fundamental frequency light source 13 is o light relative to the frequency doubling nonlinear crystal 14. After passing through the frequency doubling nonlinear crystal 14, the crystal is type I phase matching (ooe), and the doubled frequency light is generated, and a mixed light 15 of the fundamental frequency light and the doubled frequency light is obtained, wherein the doubled frequency light is e light. After passing through the tripled frequency nonlinear crystal 16, the crystal is type II phase matching (oeo), and the tripled frequency light is generated, and a mixed light 17 of the fundamental frequency light, the doubled frequency light and the tripled frequency light is obtained, wherein the tripled frequency light is o light. After passing through the quadruple frequency nonlinear crystal 18, the crystal is type I phase matching (ooe), and the quadruple frequency light is generated, and a mixed light 19 of the fundamental frequency light, the doubled frequency light, the tripled frequency light and the quadruple frequency light is obtained. After passing through the beam splitter prism 20, a 193.4 nm laser 21 is obtained.

[0071] Preferably, the frequency-doubling nonlinear crystal 14 is LBO, the phase matching mode is type I phase matching, the cutting angle is θ=90°, φ=34.4°, and it is coated with an anti-reflection film for the 700nm-800nm ​​band and the 350nm-400nm band, and the transmittance is greater than 95%;

[0072] The triple frequency nonlinear crystal 16 is BBO, the phase matching mode is type II phase matching, the cutting angle is θ=46.4°, φ=30°, and it is coated with anti-reflection films for the 700nm-800nm, 350nm-400nm, and 230nm-270nm bands, and the transmittance is greater than 95%;

[0073] The quadrupled frequency nonlinear crystal 18 is BBO, the phase matching mode is type I phase matching, the cutting angle is θ=70.9°, and it is coated with anti-reflection films for the 700nm-800nm, 350nm-400nm, and 230nm-270nm bands, with a transmittance greater than 95%, and a transmittance greater than 90% in the 190nm-200nm band;

[0074] The material of the beam splitter prism 20 can be selected as CaF2.

[0075] The nonlinear frequency conversion module is integrated with three nonlinear crystals and a beam splitter prism. It makes full use of the polarization state characteristics of the previous laser and designs different phase matching methods for each crystal, so that no other devices for adjusting the polarization state of the laser need to be introduced into the module. In addition, since the nonlinear frequency conversion process only occurs three times and the lasers at each stage are collinear, there is no need to introduce additional devices to adjust the laser spot size and spatial optical path. Therefore, the module can be integrated in a small volume, greatly saving space and cost.

[0076] In other embodiments, a heat sink (ie, a supporting device) is designed for the crystal of the nonlinear frequency conversion module, and the length of the crystal is designed so that the structure composed of three crystals can function in a very small volume.

[0077] Example 2

[0078] like Figure 2 As shown, this embodiment also provides a high repetition rate 193nm laser based on LD pumped alexandrite crystal, which includes: an LD pump source 1, an alexandrite regenerative amplifier and a nonlinear frequency conversion module;

[0079] The LD pump source 1 is used to generate laser light and input it into the alexandrite regenerative amplifier;

[0080] The alexandrite regenerative amplifier comprises a second dichroic mirror 22, a resonant cavity, a second half-wave plate 31, a Faraday rotator, a second thin-film polarizer 34 and an eighth reflector 36; the resonant cavity has the first reflector 23 and the seventh reflector 32 as end mirrors, and an alexandrite crystal, a first thin-film polarizer and a Pockels cell are also arranged in the resonant cavity;

[0081] The seed light 37 of the alexandrite regenerative amplifier passes through the second thin-film polarizer 35, the Faraday rotator 34, the second half-wave plate 33 and the first thin-film polarizer 29 in sequence to enter the resonant cavity. The seed light oscillates multiple times in the resonant cavity 37 with the first reflector 23 and the seventh reflector 32 as end mirrors, and the seed light is amplified each time it passes through the alexandrite crystal 5. When the high voltage at both ends of the Pockels cell 30 is removed, the polarization state of the amplified seed light becomes s-polarization, and is reflected and output at the first thin-film polarizer 29. The amplified output laser then passes through the second half-wave plate 33, the Faraday rotator 34, the second thin-film polarizer 35 and the eighth reflector 36 in sequence for spatial collimation, and finally passes through the first half-wave plate 11 and the second plano-convex lens 12 in sequence to enter the nonlinear frequency conversion module to obtain a 193nm laser 21.

[0082] The resonant cavity further includes a second reflector 24, a second dichroic mirror 25, a third reflector 25, a fourth reflector 26, a fifth reflector 27, a sixth reflector 28 and a second quarter-wave plate 31; the polarization state of the seed light entering the resonant cavity is s polarization, passes through the Pockels cell 30 and the second quarter-wave plate 31, is reflected by the seventh reflector 32, and passes through the second quarter-wave plate 31 and the Pockels cell 30 again, and the polarization state of the laser changes to p polarization. At this time, a quarter-wave voltage is applied to both ends of the Pockels cell 30, and the seed light is transmitted through the first thin-film polarizer 29, and passes through the sixth reflector 28, the fifth reflector 27, the fourth reflector 26, the third reflector 25, the emerald crystal 5, the second dichroic mirror 22, the second reflector 24 and the first reflector 23 in sequence, and then returns to the seventh reflector 32 along the original route. At this time, the polarization state of the laser is still p polarization.

[0083] Specifically, the working process of the alexandrite regenerative amplifier is:

[0084] The seed light 37 of the alexandrite regenerative amplifier passes through the second thin-film polarizer 35, the Faraday rotator 34, the second half-wave plate 33, and the first thin-film polarizer 29 to enter the resonant cavity of the alexandrite regenerative amplifier. At this time, the polarization state of the seed light is s polarization. It passes through the Pockels cell 30 and the second quarter-wave plate 31, is reflected by the seventh reflector 32, and passes through the quarter-wave plate 31 and the Pockels cell 30 again. The laser polarization state changes to p polarization. At this time, a quarter-wave voltage is applied to both ends of the Pockels cell 30, and the seed light is transmitted through the first thin-film polarizer 29, and passes through the seventh reflector 32 in sequence. After passing through the sixth reflector 28, the fifth reflector 27, the fourth reflector 26, the third reflector 25, the alexandrite crystal 5, the second dichroic mirror 22, the second reflector 24, the first reflector 23, and then returning to the seventh reflector 32, the polarization state of the laser is still p-polarized, and the seed light oscillates multiple times in the resonant cavity with the first reflector 23 and the seventh reflector 32 as end mirrors, and the seed light is amplified once each time it passes through the alexandrite crystal 5; the high voltage at both ends of the Pockels cell is removed, and the polarization state of the amplified seed light becomes s-polarized, and is reflected and outputted at the first thin-film polarizer 29. The amplified output laser then passes through the second half-wave plate 33, the Faraday rotator 34, the second thin-film polarizer 35 and the eighth reflector 36 in sequence for spatial collimation, and finally passes through the first half-wave plate 11 and the second plano-convex lens 12 in sequence to enter the nonlinear frequency conversion module to obtain a 193nm laser 21.

[0085] Specifically, the second dichroic mirror 22 is a plane mirror, which has high transmittance to 638nm laser, with a transmittance greater than 95%, and high reflectivity to 700nm-800nm ​​laser, with a reflectivity greater than 99.9%;

[0086] The first reflector 23 is a plane mirror, which has high reflectivity to lasers in the 700nm-800nm ​​band, and a reflectivity greater than 99.9%;

[0087] The second reflector 24 is a plano-concave mirror with a curvature radius of 800 mm, and is highly reflective to lasers in the 700nm-800nm ​​band, with a reflectivity greater than 99.9%;

[0088] The third reflector 25 is a plane mirror, which has high reflectivity to lasers in the 700nm-800nm ​​band, and a reflectivity greater than 99.9%;

[0089] The fourth reflector 26 is a plano-concave mirror with a curvature radius of 500 mm, and is highly reflective to lasers in the 700nm-800nm ​​band, with a reflectivity greater than 99.9%;

[0090] The fifth reflector 27 is a plane mirror, which has high reflectivity to lasers in the 700nm-800nm ​​band, and a reflectivity greater than 99.9%;

[0091] The sixth reflector 28 is a plane mirror, which has high reflectivity to lasers in the 700nm-800nm ​​band, and a reflectivity greater than 99.9%;

[0092] The seventh reflector 32 is a plane mirror, which has high reflectivity to lasers in the 700nm-800nm ​​band, and a reflectivity greater than 99.9%;

[0093] The eighth reflector 36 is a plane mirror, which has high reflectivity to laser beams in the wavelength range of 700nm-800nm, and a reflectivity greater than 99.9%.

[0094] Wherein, the first thin film polarizer 29 has an extinction ratio greater than 500:1 and is inserted at a Brewster angle with respect to the direction of laser transmission in the cavity;

[0095] The extinction ratio of the second thin-film polarizer 25 is greater than 500:1, and forms a Brewster angle with the transmission direction of the seed light.

[0096] The Pockels cell 30 is a BBO Pockels cell with a clear aperture of 4 mm and a quarter-wave operating voltage of about 3.2 kV;

[0097] The clear aperture of the Faraday rotator 34 is 5 mm;

[0098] The central wavelength of the seed light 7 is 773.6 nm, and the pulse width is 7.8 ns. The seed light 7 can be one of a femtosecond laser, a picosecond laser, and a nanosecond laser, and can realize the output of a 193 nm laser of different pulse types.

[0099] In this embodiment, the nonlinear frequency conversion module includes a frequency doubling nonlinear crystal 14 , a frequency tripling nonlinear crystal 16 , a frequency quadrupling nonlinear crystal 18 and a beam splitter prism 20 arranged along the optical path.

[0100] The fundamental frequency light source 13 is o light relative to the frequency doubling nonlinear crystal 14. After passing through the frequency doubling nonlinear crystal 14, the crystal is type I phase matching (ooe), and the doubled frequency light is generated, and a mixed light 15 of the fundamental frequency light and the doubled frequency light is obtained, wherein the doubled frequency light is e light. After passing through the tripled frequency nonlinear crystal 16, the crystal is type II phase matching (oeo), and the tripled frequency light is generated, and a mixed light 17 of the fundamental frequency light, the doubled frequency light and the tripled frequency light is obtained, wherein the tripled frequency light is o light. After passing through the quadruple frequency nonlinear crystal 18, the crystal is type I phase matching (ooe), and the quadruple frequency light is generated, and a mixed light 19 of the fundamental frequency light, the doubled frequency light, the tripled frequency light and the quadruple frequency light is obtained. After passing through the beam splitter prism 20, a 193.4 nm laser 21 is obtained.

[0101] Preferably, the frequency-doubling nonlinear crystal 14 is LBO, the phase matching mode is type I phase matching, the cutting angle is θ=90°, φ=34.4°, and it is coated with an anti-reflection film for the 700nm-800nm ​​band and the 350nm-400nm band, and the transmittance is greater than 95%;

[0102] The triple frequency nonlinear crystal 16 is BBO, the phase matching mode is type II phase matching, the cutting angle is θ=46.4°, φ=30°, and it is coated with anti-reflection films for the 700nm-800nm, 350nm-400nm, and 230nm-270nm bands, and the transmittance is greater than 95%;

[0103] The quadrupled frequency nonlinear crystal 18 is BBO, the phase matching mode is type I phase matching, the cutting angle is θ=70.9°, and it is coated with anti-reflection films for the 700nm-800nm, 350nm-400nm, and 230nm-270nm bands, with a transmittance greater than 95%, and a transmittance greater than 90% in the 190nm-200nm band;

[0104] The material of the beam splitter prism 20 can be selected from CaF2.

[0105] Figure 3 This is the spatial spot of the laser output obtained in this embodiment. After the mixed light 19 of the fundamental frequency light, the doubled frequency light, the tripled frequency light and the quadruple frequency light is split by the beam splitter prism, four separated wavelengths of laser light are obtained on the white paper. Figure 3 The four light spots in the middle correspond to the fundamental frequency light, the doubled frequency light, the tripled frequency light and the quadruple frequency light from right to left, that is, the leftmost light spot is the 193.4 nm laser obtained in this embodiment.

[0106] The embodiment of the present invention can amplify high-performance, low-power 773.6nm laser, thereby achieving an increase in the power of the fundamental frequency light source.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high repetition rate 193nm laser based on LD pumped alexandrite crystal, characterized in that: include: LD pump source, alexandrite regenerative amplifier and nonlinear frequency conversion module; The LD pump source is used to generate laser light and input it into the alexandrite regenerative amplifier; The alexandrite regenerative amplifier comprises a second dichroic mirror, a resonant cavity, a second half-wave plate, a Faraday rotator, a second thin-film polarizer and an eighth reflector; the resonant cavity uses the first reflector and the seventh reflector as end mirrors, and an alexandrite crystal, a first thin-film polarizer and a Pockels cell are also arranged in the resonant cavity; The seed light of the alexandrite regenerative amplifier passes through the second thin-film polarizer, the Faraday rotator, the second half-wave plate and the first thin-film polarizer in sequence to enter the resonant cavity, the seed light oscillates multiple times in the resonant cavity with the first reflector and the seventh reflector as end mirrors, and the seed light is amplified once each time it passes through the alexandrite crystal; when the high voltage at both ends of the Pockels cell is removed, the polarization state of the amplified seed light changes to s-polarization, and is reflected and output at the first thin-film polarizer; the amplified output laser then passes through the second half-wave plate, the Faraday rotator, the second thin-film polarizer and the eighth reflector in sequence for spatial collimation, and finally passes through the first half-wave plate and the second plano-convex lens in sequence to enter the nonlinear frequency conversion module to obtain 193nm laser; The resonant cavity further includes a second reflector, a second dichroic mirror, a third reflector, a fourth reflector, a fifth reflector, a sixth reflector, and a second quarter wave plate; The polarization state of the seed light entering the resonant cavity is s polarization. It passes through the Pockels cell and the second quarter-wave plate, is reflected by the seventh reflector, and passes through the second quarter-wave plate and the Pockels cell again. The polarization state of the laser changes to p polarization. At this time, a quarter-wave voltage is applied to both ends of the Pockels cell. The seed light is transmitted through the first thin-film polarizer, and passes through the sixth reflector, the fifth reflector, the fourth reflector, the third reflector, the alexandrite crystal, the second dichroic mirror, the second reflector and the first reflector in turn, and then returns to the seventh reflector along the same route. At this time, the polarization state of the laser is still p polarization.

2. The high repetition rate 193nm laser based on LD pumped alexandrite crystal as claimed in claim 1, characterized in that: The second dichroic mirror is a plane mirror, which has high transmittance to 638nm laser, with a transmittance greater than 95%, and high reflection to 700nm-800nm ​​laser, with a reflectivity greater than 99.9%; The first reflector is a plane mirror, which has high reflection to the laser in the 700nm-800nm ​​band, and the reflectivity is greater than 99.9%; The second reflector is a plano-concave mirror with a curvature radius of 800mm. It has high reflection for 700nm-800nm ​​laser and a reflectivity greater than 99.9%; The third reflector is a plane mirror, which has high reflection to the laser in the 700nm-800nm ​​band, and the reflectivity is greater than 99.9%; The fourth reflector is a plano-concave mirror with a curvature radius of 500 mm. It is highly reflective to lasers in the 700nm-800nm ​​band, with a reflectivity greater than 99.9%; The fifth reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%; The sixth reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%; The seventh reflector is a plane mirror, which has high reflection to the laser in the wavelength range of 700nm-800nm, and the reflectivity is greater than 99.9%; The eighth reflector is a plane mirror, which has high reflectivity to lasers in the 700nm-800nm ​​band, and a reflectivity greater than 99.9%.

3. The high repetition rate 193nm laser based on LD pumped alexandrite crystal as claimed in claim 1, characterized in that: The first thin-film polarizer has an extinction ratio greater than 500:1 and is inserted at a Brewster angle with respect to the laser transmission direction in the cavity; The extinction ratio of the second thin-film polarizer is greater than 500:1, and it forms a Brewster angle with the transmission direction of the seed light.

4. The high repetition rate 193nm laser based on LD pumped alexandrite crystal as claimed in claim 1, characterized in that: The central wavelength of the seed light is 773.6nm.

5. The high repetition rate 193nm laser based on LD pumped alexandrite crystal as claimed in claim 1, characterized in that: The nonlinear frequency conversion module comprises a frequency doubling nonlinear crystal, a frequency tripling nonlinear crystal, a frequency quadrupling nonlinear crystal and a beam splitter prism arranged along the optical path.

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