213nm all-solid-state deep ultraviolet laser and application thereof

Abstract

The invention relates to a 213nm all-solid-state deep ultraviolet laser and application thereof, and belongs to the technical field of lasers. The laser comprises a laser diode, a pump light focusing system, a pump end mirror, a laser crystal, a deep ultraviolet output mirror, a sum frequency crystal, a frequency doubling crystal and a total reflection end mirror which are sequentially arranged along a light path, the pump end mirror, the deep ultraviolet output mirror and the total reflection end mirror form a V-shaped resonant cavity, and the laser crystal, the sum frequency crystal and the frequency doubling crystal are all cuboids. And birefringence main shafts of the laser crystal, the sum frequency crystal and the frequency doubling crystal are arranged in a staggered manner. Visible red light with the wavelength of 640 nm is adopted as fundamental frequency laser, only two-step frequency conversion is needed for output from the fundamental frequency laser to 213 nm, and the laser has the advantages of being simplified in process, small in size, easy to adjust, high in conversion efficiency, large in output power, low in manufacturing cost, stable in performance and the like.

Description

Technical Field

[0001] The invention relates to a 213nm all-solid-state deep ultraviolet laser and application thereof, belonging to the technical field of lasers. Background Art

[0002] In recent years, with the continuous development of nonlinear optical crystals in the deep ultraviolet field and the increasing maturity of various frequency conversion technologies, all-solid-state deep ultraviolet lasers have become one of the hot spots in the field of laser technology research. The emerging LD-pumped all-solid-state deep ultraviolet lasers have a series of advantages such as small size, long service life, high efficiency, good stability, good beam quality, and low cost, and are an important development direction of deep ultraviolet lasers. Among them, all-solid-state deep ultraviolet lasers with a wavelength of around 213nm play an important role in semiconductor defect detection, high-density storage of optical disks, fine processing of materials, and spectral analysis. For example, in the paper "IEEE JOURNAL OF QUANTUM ELECTRONICS, 26, 2284-2288, 1990", a 213nm deep ultraviolet laser was used to study the effects of corneal ablation and polymer synthesis; the paper "APPLIED OPTICS, 50, 876-885, 2011" reported a method of delivering 213nm laser to the tissue surface and applying 213nm laser to intraocular surgery; the paper "APPLIED SPECTROSCOPY, 69, 895-901, 2015" used a compact solid-state 213nm laser to measure nitrates and developed a deep ultraviolet Raman spectrometer; the paper "ELECTRONICS LETTERS, 57, 331-333, 2021" studied the photosensitivity of doped silica planes and demonstrated the use of 213nm lasers to write waveguides and Bragg gratings on doped silica planes.

[0003] The 213nm deep ultraviolet solid lasers currently on the market are mainly based on two frequency conversion technology routes. One is to sum the quadrupled frequency of the 1064nm laser with the fundamental frequency. For example, in the paper "Chinese Laser, 33, 1590-1592, 2006", KTP and BBO crystals are used to perform extracavity doubled and quadrupled frequency on the acousto-optically Q-switched 1064nm laser, respectively, and then BBO crystals are used to sum the quadrupled frequency with the remaining fundamental frequency wave to generate 213nm deep ultraviolet laser. The other is to frequency-sum the tripled and doubled frequencies of the 1064nm laser. For example, the paper "Journal of Chongqing Normal University (Natural Science Edition), 26, 82-84, 2009" concluded through theoretical analysis that this technical route is feasible in theory. No matter which of the above technical routes is used, starting from the 1064nm near-infrared laser, three steps of nonlinear optical frequency conversion are required to achieve 213nm laser output. There are disadvantages such as complex frequency conversion path, low optical conversion efficiency, difficult optimization design, many optical components required, high production cost, and poor system stability.

[0004] The present invention is proposed to overcome the shortcomings of the existing three-step frequency conversion technology route for generating 213nm deep ultraviolet laser, simplify the frequency conversion path, and improve the conversion efficiency. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a 213nm all-solid-state deep ultraviolet laser and its application, which adopts visible red light with a wavelength of 640nm as the fundamental frequency laser. Only two steps of frequency conversion are required from the fundamental frequency light to the 213nm output. It has the advantages of simplified process, small size, easy adjustment, high conversion efficiency, large output power, low production cost and stable performance.

[0006] The technical solution of the present invention is as follows:

[0007] A 213nm all-solid-state deep ultraviolet laser comprises a laser diode, a pump light focusing system, a pump end mirror, a laser crystal, a deep ultraviolet output mirror, a sum frequency crystal, a frequency doubling crystal and a full reflection end mirror arranged in sequence along an optical path, wherein:

[0008] The pump end mirror, deep ultraviolet output mirror and all-reflecting end mirror form a V-shaped resonant cavity. The laser crystal, sum frequency crystal and frequency doubling crystal are all rectangular parallelepipeds. The birefringence principal axes of the laser crystal, sum frequency crystal and frequency doubling crystal are arranged in a staggered manner.

[0009] When light propagates in a crystal, it is decomposed into two linearly polarized lights, o light and e light, in a plane perpendicular to the optical path. These two linear polarization directions are called the principal axes of birefringence of the crystal. Figure 2 As shown, the o-ray and the e-ray are perpendicular to the side of the crystal.

[0010] The laser emitted by the laser diode is injected into the laser crystal through the pump light focusing system and the pump end mirror, realizing 640nm fundamental frequency laser oscillation in the V-shaped resonant cavity, generating 320nm laser after passing through the frequency doubling crystal, and then generating 213nm laser through the sum frequency crystal, which is output outside the cavity by the fully reflected end mirror.

[0011] Preferably, according to the present invention, the birefringence principal axis of the laser crystal is rotated relative to the birefringence principal axis of the frequency doubling crystal, and the rotation angle ψ is 18°-27°;

[0012] The birefringence principal axis of the frequency doubling crystal is rotated 90° relative to the birefringence principal axis of the sum frequency crystal.

[0013] Preferably, according to the present invention, the calculation process of the rotation angle ψ of the birefringence principal axis of the laser crystal relative to the birefringence principal axis of the frequency doubling crystal is as follows:

[0014] Assume that the fundamental frequency optical electric field intensity generated by the laser crystal is E, the electric field intensity in the vertical and horizontal directions are Ecosψ and Esinψ respectively, and the corresponding light intensity is E 2 cos 2 ψ and E 2 sin 2 ψ, assuming that the frequency doubling conversion efficiency of the frequency doubling crystal in the vertical direction is η, then ηE 2 cos 2 ψ is the intensity of the horizontally polarized frequency-doubled light;

[0015] For the sum frequency of sum frequency crystal, the best light intensity configuration is that the intensity of double frequency light is equal to twice the intensity of fundamental frequency light (under this condition, the ratio of the number of double frequency photons to the number of fundamental frequency photons is 1:1, and the sum frequency conversion efficiency is the highest), that is, ηE 2 cos 2 ψ=2E 2 sin 2 ψ, or tan 2 ψ=0.5η. Usually, due to design differences, the typical conversion efficiency η of intracavity frequency-doubled lasers from fundamental frequency to frequency doubling is between 20% and 50%. The rotation angle ψ is obtained from the above formula. ψ is between 18o and 27o. The specific angle can be set according to the actual value of η. When η is 20%, 30%, 40%, and 50%, ψ is 18o, 21o, 24o, and 27o, respectively.

[0016] According to the preferred embodiment of the present invention, the laser crystal is Pr:YLiF 4 (Pr:YLF), the two light-transmitting end faces of the laser crystal are coated with 444nm and 640nm anti-reflection films.

[0017] Preferably, according to the present invention, two light-transmitting end faces of the frequency doubling crystal are plated with 640nm and 320nm anti-reflection films, the frequency doubling crystal converts the 640nm fundamental frequency light into 320nm frequency doubling light by a type I frequency doubling phase matching (o+o→e), and the frequency doubling crystal is processed along the type I frequency doubling phase matching direction;

[0018] When the frequency doubling crystal is BBO, the processing angle is θ=37.4o, φ=0o;

[0019] When the frequency doubling crystal is LBO, the processing angle is θ=90o, φ=53.3o;

[0020] When the frequency doubling crystal is BIBO, the processing angle is θ=132.1o, φ=90o;

[0021] When the frequency doubling crystal is ADP, the processing angle is θ=55.9o, φ=45o;

[0022] When the frequency doubling crystal is KDP, the processing angle is θ=55.4°, φ=0°.

[0023] The processing angle refers to the angle in the crystal space corresponding to the direction of light transmission through the crystal. The specific definition is as follows: a certain direction in the crystal space is represented by the angle (θ, φ), where θ is the angle between the direction and the crystal optical axis Z, and φ is the azimuth, which is the angle between the projection of the direction in the XY principal plane of the crystal and the X-axis. The processing angle is a commonly used expression for the crystal processing direction in this profession.

[0024] Preferably according to the present invention, the sum frequency crystal is BBO, and the two light-transmitting end faces of the sum frequency crystal are coated with 640nm, 320nm, and 213nm anti-reflection films (the anti-reflection films with three parameters correspond to the positions where 640nm and 320nm lasers convert 213nm sum frequency light, respectively), and are processed along the type I sum frequency phase matching direction, with a processing angle of θ=64.7o and φ=0o.

[0025] The sum frequency crystal converts 640nm and 320nm lasers into 213nm sum frequency light through type I phase matching (o+o→e).

[0026] Preferably according to the present invention, the laser diode emits blue light with a central wavelength of 444 nm, and its linear polarization direction is along the Z axis of the laser crystal, that is, the vibration direction of the e-light generated in the laser crystal, corresponding to the π polarization absorption peak of the laser crystal.

[0027] Preferably according to the present invention, the pump light focusing system is a lens group consisting of a single convex lens or multiple convex lenses, and the pump focal spot size after focusing on the laser crystal is close to the laser cavity mode size to achieve the most efficient pump light-laser mode matching.

[0028] Preferably according to the present invention, an acousto-optic modulator is arranged between the laser crystal and the deep ultraviolet output mirror. The acousto-optic modulator is an actively Q-switched optical element (such as an acousto-optic or electro-optic Q switch) or a passively Q-switched (such as a two-dimensional nano saturable absorber, a crystal with saturable absorption performance at 640nm) optical element to achieve 213nm deep ultraviolet pulsed laser output.

[0029] The application of the above 213nm all-solid-state deep ultraviolet laser is as follows:

[0030] (1) The laser emitted by the laser diode is injected into the laser crystal through the pump light focusing system and the pump end mirror. The laser crystal generates a 640nm linearly polarized fundamental frequency laser. The polarized fundamental frequency laser is decomposed into two mutually perpendicular linear polarized lights. Before and after entering the sum frequency crystal, no change occurs, and the sum frequency crystal has no effect.

[0031] (2) After the 640nm linearly polarized fundamental frequency laser enters the frequency doubling crystal, the ω ⊥ When the linearly polarized laser passes through the frequency doubling crystal to the all-reflecting end mirror and then returns and passes through the frequency doubling crystal, two type I frequency doubling phase matches occur, generating a 320nm linearly polarized laser along the e-light direction of the frequency doubling crystal, which enters the sum frequency crystal together with the polarized laser along the e-light direction of the frequency doubling crystal;

[0032] (3) Since the birefringence axis of the frequency doubling crystal is rotated 90 degrees relative to the birefringence axis of the sum frequency crystal, the horizontally polarized laser light emitted by the frequency doubling crystal is o-light relative to the sum frequency crystal. Type I sum frequency phase matching occurs in the sum frequency crystal, generating a 213nm linearly polarized laser light along the e-light direction of the sum frequency crystal, which is output by the deep ultraviolet output mirror.

[0033] The beneficial effects of the present invention are:

[0034] 1. The previous 213nm all-solid-state laser technology uses near-infrared light with a wavelength of about 1μm as the fundamental frequency light. At least three steps of frequency conversion are required from the fundamental frequency to the 213nm output, and the conversion efficiency is low. In comparison, the present invention uses visible red light with a wavelength of 640nm as the fundamental frequency laser. From the fundamental frequency light to the 213nm output, only two steps of frequency conversion are required, namely, frequency doubling by a frequency doubling crystal and frequency summing by a frequency summing crystal. It has the advantages of simplified process, small size, easy adjustment, high conversion efficiency, large output power, low production cost, and stable performance.

[0035] 2. Previous laser diode pumped Pr:YLF 4Crystal cavity frequency conversion lasers all use a polarization configuration in which the birefringence principal axis of the laser crystal coincides with the birefringence principal axis of the nonlinear optical crystal, which cannot provide the polarization matching conditions required for cascade frequency conversion, and therefore cannot perform cascade frequency conversion and generate 213nm lasers. The present invention uses a special polarization configuration in which the birefringence principal axis of the laser crystal is deflected by a certain angle relative to the birefringence principal axis of the nonlinear optical crystal, which cleverly solves the above-mentioned problem and makes intracavity cascade frequency conversion of this type of laser possible. At the same time, the value of the optimal deflection angle of the laser crystal is given for different frequency doubling conversion efficiencies. The new 213nm all-solid-state deep ultraviolet laser light source provided by this technology will be important in many fields such as scientific research, medical treatment, and industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of the present invention;

[0037] Figure 2 is a schematic diagram of linear polarized light of the present invention, wherein: Figure 2 (a) is a schematic diagram of linear polarization light from a laser crystal; Figure 2 (b) is a schematic diagram of linear polarized light from a frequency-doubling crystal; Figure 2 (c) is a schematic diagram of linear polarization light from a sum frequency crystal;

[0038] Figure 3 This is a schematic diagram of the structure of Example 2 of the present invention.

[0039] Among them: 1. Laser diode, 2. Pump light focusing system, 3. Pump end mirror, 4. Laser crystal, 5. Deep ultraviolet output mirror, 6. Total reflection end mirror, 7. Frequency doubling crystal, 8. Sum frequency crystal, 9. Acousto-optic modulator. DETAILED DESCRIPTION

[0040] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0041] Embodiment 1:

[0042] like Figure 1-2 As shown, this embodiment provides a 213nm all-solid-state deep ultraviolet laser, including a laser diode 1, a pump light focusing system 2, a pump end mirror 3, a laser crystal 4, a deep ultraviolet output mirror 5, a sum frequency crystal 8, a frequency doubling crystal 7 and a full reflection end mirror 6 arranged in sequence along the optical path, wherein:

[0043] The pump end mirror 3, the deep ultraviolet output mirror 5 and the total reflection end mirror 6 form a V-shaped resonant cavity, the laser crystal 4, the sum frequency crystal 8 and the frequency doubling crystal 7 are all rectangular parallelepipeds, and the birefringence principal axes of the laser crystal 4, the sum frequency crystal 8 and the frequency doubling crystal 7 are arranged in a staggered manner;

[0044] When light propagates in a crystal, it is decomposed into two linearly polarized lights, o light and e light, in a plane perpendicular to the optical path. These two linear polarization directions are called the principal axes of birefringence of the crystal. Figure 2 As shown, the o-ray and the e-ray are perpendicular to the side of the crystal.

[0045] The laser emitted by the laser diode 1 is injected into the laser crystal 4 through the pump light focusing system 2 and the pump end mirror 3, realizing 640nm fundamental frequency laser oscillation in the V-shaped resonant cavity, generating 320nm laser after passing through the frequency doubling crystal 7, and then generating 213nm laser after passing through the sum frequency crystal 8, which is output outside the cavity through the fully reflected end mirror.

[0046] The birefringence principal axis of the laser crystal 4 is rotated relative to the birefringence principal axis of the frequency doubling crystal 7, and the rotation angle ψ is 24°;

[0047] The birefringence principal axis of the frequency doubling crystal 7 is rotated 90 degrees relative to the birefringence principal axis of the sum frequency crystal 8 .

[0048] Laser crystal 4 is Pr:YLiF 4 (Pr:YLF), the two light-transmitting end faces of the laser crystal 4 are coated with 444nm and 640nm anti-reflection films.

[0049] The two light-transmitting end faces of the frequency doubling crystal 7 are plated with 640nm and 320nm anti-reflection films. The frequency doubling crystal 7 converts the 640nm fundamental frequency light into the 320nm frequency doubling light by the type I frequency doubling phase matching (o+o→e). The frequency doubling crystal 7 is processed along the type I frequency doubling phase matching direction;

[0050] When the frequency doubling crystal 7 is BBO, the processing angle is θ=37.4°, φ=0°;

[0051] When the frequency doubling crystal 7 is LBO, the processing angle is θ=90°, φ=53.3°;

[0052] When the frequency doubling crystal 7 is BIBO, the processing angle is θ=132.1o, φ=90o;

[0053] When the frequency doubling crystal 7 is ADP, the processing angle is θ=55.9°, φ=45°;

[0054] When the frequency doubling crystal 7 is KDP, the processing angle is θ=55.4°, φ=0°.

[0055] The processing angle refers to the angle in the crystal space corresponding to the direction of light transmission through the crystal. The specific definition is as follows: a certain direction in the crystal space is represented by the angle (θ, φ), where θ is the angle between the direction and the crystal optical axis Z, and φ is the azimuth, which is the angle between the projection of the direction in the XY principal plane of the crystal and the X-axis. The processing angle is a commonly used expression for the crystal processing direction in this profession.

[0056] The sum frequency crystal 8 is BBO, and the two light-transmitting end faces of the sum frequency crystal 8 are coated with 640nm, 320nm, and 213nm anti-reflection films (the three parameters of the anti-reflection films correspond to the positions of 640nm and 320nm lasers converting 213nm sum frequency light respectively), and are processed along the type I sum frequency phase matching direction, with a processing angle of θ=64.7o and φ=0o.

[0057] The sum frequency crystal 8 converts 640nm and 320nm lasers into 213nm sum frequency light through type I phase matching (o+o→e).

[0058] Laser diode 1 emits blue light with a central wavelength of 444 nm, and the linear polarization direction is along the Z axis of the laser crystal, that is, the vibration direction of the e-light generated in the laser crystal, corresponding to the π polarization absorption peak of the laser crystal.

[0059] The pump light focusing system 2 is a single convex lens. The pump focal spot size after focusing on the laser crystal is close to the laser cavity mode size to achieve the most efficient pump light-laser mode matching.

[0060] The light-transmitting surface of the pump end mirror facing away from the resonant cavity is coated with a 444nm high-transmittance dielectric film, and the light-transmitting surface facing the resonant cavity is coated with a 444nm high-transmittance, 640nm high-reflection dielectric film; the light-transmitting surface of the deep ultraviolet output mirror facing the resonant cavity is coated with a 213nm high-transmittance, 640nm high-reflection dielectric film, and the light-transmitting surface facing away from the resonant cavity is coated with a 213nm high-transmittance dielectric film; the light-transmitting surface of the fully-reflective end mirror facing the resonant cavity is coated with a 640nm, 320nm high-reflection dielectric film.

[0061] The application of the above 213nm all-solid-state deep ultraviolet laser is as follows:

[0062] (1) The laser (444nm blue light) emitted by the laser diode is injected into the laser crystal through the pump light focusing system and the pump end mirror. The laser crystal generates a 640nm linearly polarized fundamental frequency laser with its polarization along Figure 2 After the deflection ψ in (a), the polarized fundamental frequency laser is decomposed into ω ⊥ ,ω / / Two mutually perpendicular linear polarized lights do not undergo any changes before and after entering the sum frequency crystal, and the sum frequency crystal has no effect;

[0063] (2) After the 640nm linearly polarized fundamental frequency laser enters the frequency doubling crystal, the ω along the o direction (vertical direction) of the frequency doubling crystal ⊥ When the linearly polarized laser passes through the frequency doubling crystal to the all-reflecting end mirror and then returns and passes through the frequency doubling crystal, two type I frequency doubling phase matches (o+o→e) occur, generating a 320nm linearly polarized laser (2ω) along the e-light direction (horizontal direction) of the frequency doubling crystal. / / ), and ω along the e-light direction of the frequency doubling crystal / / The polarized lasers enter the sum frequency crystal together;

[0064] (3) Since the birefringence axis of the frequency doubling crystal is rotated 90 degrees relative to the birefringence axis of the sum frequency crystal, the horizontally polarized ω emitted by the frequency doubling crystal / / , 2ω / / The laser is o-light relative to the sum frequency crystal. Type I sum frequency phase matching (o+o=e) occurs in the sum frequency crystal, generating a 213nm linearly polarized laser (3ω) along the e-light direction (vertical direction) of the sum frequency crystal. ⊥ ), output by the deep ultraviolet output mirror.

[0065] Embodiment 2:

[0066] like Figure 3 As shown, this embodiment provides a 213nm all-solid-state deep ultraviolet laser, the structure of which is as shown in Example 1, except that an acousto-optic modulator 9 is arranged between the laser crystal 4 and the deep ultraviolet output mirror 5, and the acousto-optic modulator 9 is an acousto-optic Q-switch AO, which changes the operation mode of the laser from continuous to pulse, and can achieve high peak power and short pulse width 213nm deep ultraviolet laser output, which meets the special application requirements of biological tissue cutting, organic material marking, optical waveguide and grating engraving, etc.

[0067] 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 213nm all-solid-state deep ultraviolet laser, characterized in that: It includes a laser diode, a pump light focusing system, a pump end mirror, a laser crystal, a deep ultraviolet output mirror, a sum frequency crystal, a frequency doubling crystal and a total reflection end mirror which are arranged in sequence along the optical path, wherein: The pump end mirror, deep ultraviolet output mirror and all-reflecting end mirror form a V-shaped resonant cavity. The laser crystal, sum frequency crystal and frequency doubling crystal are all rectangular parallelepipeds. The birefringence principal axes of the laser crystal, sum frequency crystal and frequency doubling crystal are arranged in a staggered manner. When light propagates in a crystal, it is decomposed into two linearly polarized lights, o light and e light, with mutually perpendicular vibration directions in the plane perpendicular to the light path. These two mutually perpendicular linear polarization directions are called the principal axes of birefringence of the crystal. o light and e light are perpendicular to the side of the crystal.

2. The 213 nm all-solid-state deep ultraviolet laser according to claim 1, characterized in that: The birefringence principal axis of the laser crystal is rotated relative to the birefringence principal axis of the frequency doubling crystal, and the rotation angle ψ is 18o-27o; The birefringence principal axis of the frequency doubling crystal is rotated 90° relative to the birefringence principal axis of the sum frequency crystal.

3. The 213 nm all-solid-state deep ultraviolet laser according to claim 2, characterized in that: The calculation process of the rotation angle ψ of the birefringence principal axis of the laser crystal relative to the birefringence principal axis of the frequency doubling crystal is as follows: Assume that the fundamental frequency optical electric field intensity generated by the laser crystal is E, the electric field intensity in the vertical and horizontal directions are Ecosψ and Esinψ respectively, and the corresponding light intensity is E 2 cos 2 ψ and E 2 sin 2 ψ, assuming that the frequency doubling conversion efficiency of the frequency doubling crystal in the vertical direction is η, then ηE 2 cos 2 ψ is the intensity of the horizontally polarized frequency-doubled light; For the sum frequency of sum frequency crystal, the best light intensity configuration is that the intensity of double frequency light is equal to twice the intensity of fundamental frequency light, that is, ηE 2 cos 2 ψ=2E 2 sin 2 ψ, or tan 2 ψ=0.5η, the typical conversion efficiency η from the fundamental frequency to the double frequency is between 20% and 50%, and the rotation angle ψ is obtained from the above formula.

4. The 213 nm all-solid-state deep ultraviolet laser according to claim 3, characterized in that: The laser crystal is Pr:YLiF4, and the two light-transmitting end faces of the laser crystal are coated with anti-reflection films.

5. The 213 nm all-solid-state deep ultraviolet laser according to claim 4, characterized in that: The two light-transmitting end faces of the frequency doubling crystal are coated with anti-reflection coating, and the frequency doubling crystal is processed along the direction of type I frequency doubling phase matching; When the frequency doubling crystal is BBO, the processing angle is θ=37.4o, φ=0o; When the frequency doubling crystal is LBO, the processing angle is θ=90o, φ=53.3o; When the frequency doubling crystal is BIBO, the processing angle is θ=132.1o, φ=90o; When the frequency doubling crystal is ADP, the processing angle is θ=55.9o, φ=45o; When the frequency doubling crystal is KDP, the processing angle is θ=55.4°, φ=0°.

6. The 213 nm all-solid-state deep ultraviolet laser according to claim 5, characterized in that: The sum frequency crystal is BBO, and the two light-transmitting end faces of the sum frequency crystal are plated with anti-reflection films and processed along the type I sum frequency phase matching direction, with a processing angle of θ=64.7o and φ=0o.

7. The 213 nm all-solid-state deep ultraviolet laser according to claim 6, characterized in that: The laser diode emits blue light with a central wavelength of 444nm, and the linear polarization direction is along the Z axis of the laser crystal, that is, the vibration direction of the e-light generated in the laser crystal.

8. The 213 nm all-solid-state deep ultraviolet laser according to claim 7, characterized in that: The pump light focusing system is a lens group consisting of a single convex lens or a plurality of convex lenses.

9. The 213 nm all-solid-state deep ultraviolet laser according to claim 8, characterized in that: An acousto-optic modulator is arranged between the laser crystal and the deep ultraviolet output mirror.

10. The use of the 213 nm all-solid-state deep ultraviolet laser as claimed in claim 8, characterized in that: Here are the steps: (1) The laser emitted by the laser diode is injected into the laser crystal through the pump light focusing system and the pump end mirror. The laser crystal generates a 640nm linearly polarized fundamental frequency laser. The polarized fundamental frequency laser is decomposed into two mutually perpendicular linear polarized lights. Before and after entering the sum frequency crystal, no change occurs, and the sum frequency crystal has no effect. (2) After the 640nm linearly polarized fundamental frequency laser enters the frequency doubling crystal, the ω ⊥ When the linearly polarized laser passes through the frequency doubling crystal to the all-reflecting end mirror and then returns and passes through the frequency doubling crystal, two type I frequency doubling phase matches occur, generating a 320nm linearly polarized laser along the e-light direction of the frequency doubling crystal, which enters the sum frequency crystal together with the polarized laser along the e-light direction of the frequency doubling crystal; (3) Since the birefringence axis of the frequency doubling crystal is rotated 90 degrees relative to the birefringence axis of the sum frequency crystal, the horizontally polarized laser light emitted by the frequency doubling crystal is o-light relative to the sum frequency crystal. Type I sum frequency phase matching occurs in the sum frequency crystal, generating a 213nm linearly polarized laser light along the e-light direction of the sum frequency crystal, which is output by the deep ultraviolet output mirror.

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