213nm all-solid-state deep ultraviolet laser

Abstract

The utility model relates to a 213nm all-solid-state deep ultraviolet laser, 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. According to the utility model, the visible red light with the wavelength of 640nm is adopted as the fundamental frequency laser, the output from the fundamental frequency laser to 213nm only needs two-step frequency conversion, and the laser has the advantages of simplified process, small volume, easy adjustment, high conversion efficiency, large output power, low manufacturing cost, stable performance and the like.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of 213nm full solid-state deep ultraviolet laser, belong to laser technical field. BACKGROUND

[0002] In recent years, with the continuous development of nonlinear optical crystal in the field of deep ultraviolet and the increasing maturity of various frequency conversion technologies, full solid-state deep ultraviolet laser has become one of the hotspots in the field of laser technology research. The emerging LD pumped full solid-state deep ultraviolet laser has a series of advantages such as small size, long service life, high efficiency, good stability, good beam quality and low cost, and is an important development direction of deep ultraviolet laser. Among them, the full solid-state deep ultraviolet laser with a wavelength near 213nm plays an important role in the fields of semiconductor defect detection, high-density storage of optical discs, fine processing of materials and spectral analysis. For example, in the paper "IEEE JOURNAL OF QUANTUM ELECTRONICS, 26, 2284-2288, 1990", 213nm deep ultraviolet laser is used to study corneal ablation and polymer synthesis effect; the paper "APPLIED OPTICS, 50, 876-885, 2011" reports a method of delivering 213nm laser to the surface of tissue, and applies 213nm laser to intraocular surgery; the paper "APPLIED SPECTROSCOPY, 69, 895-901, 2015" uses a compact solid-state 213nm laser to measure nitrate, and develops a deep ultraviolet Raman spectrometer; the paper "ELECTRONICS LETTERS, 57, 331-333, 2021" studies the photosensitivity of doped silica plane, and demonstrates the writing of waveguide and Bragg grating on the plane of doped silica by 213nm laser.

[0003] The 213nm deep ultraviolet solid laser in the current market is mainly based on two frequency conversion technical routes, one is the sum frequency of the fourth frequency of 1064nm laser and the base frequency, such as the paper "China Laser, 33, 1590-1592, 2006", which uses KTP and BBO crystals to perform cavity-outside second frequency conversion and fourth frequency conversion on the acoustic-optical Q-switched 1064nm laser respectively, and then uses the BBO crystal to perform sum frequency conversion on the fourth frequency and the remaining base frequency wave to generate 213nm deep ultraviolet laser. The other is the sum frequency of the third frequency of 1064nm laser and the second frequency, such as the paper "Chongqing Normal University Journal (Natural Science Edition), 26, 82-84, 2009", which is theoretically feasible through theoretical analysis. No matter which of the above technical routes, starting from the near-infrared laser of 1064nm, three steps of nonlinear optical frequency conversion are needed to realize the output of 213nm laser, and there are disadvantages such as complex frequency conversion path, low optical conversion efficiency, difficult optimization design, many required optical elements, high manufacturing cost, and poor system stability.

[0004] In order to overcome the shortcomings of the existing three-step frequency conversion technology for generating 213nm deep ultraviolet laser, simplify the frequency conversion path, and improve the conversion efficiency, the utility model is provided. SUMMARY

[0005] In view of the shortcomings of the prior art, the utility model provides a kind of 213nm full solid state deep ultraviolet laser, and visible red light with wavelength of 640nm is used as base frequency laser, and only two steps of frequency conversion are needed from base frequency light to 213nm output, with the advantages of process simplification, small size, easy adjustment, high conversion efficiency, high output power, low manufacturing cost and stable performance.

[0006] The technical scheme of the utility model is as follows:

[0007] A kind of 213nm full solid state deep ultraviolet laser, including laser diode, pump light focusing system, pump end mirror, laser crystal, deep ultraviolet output mirror, sum frequency crystal, frequency doubling crystal and full reflection end mirror arranged in sequence along optical path, wherein,

[0008] Pump end mirror, deep ultraviolet output mirror and full reflection end mirror form V-shaped resonant cavity, laser crystal, sum frequency crystal and frequency doubling crystal are all cuboids, and the birefringent principal axis of laser crystal, sum frequency crystal and frequency doubling crystal is arranged in staggered manner;

[0009] When light propagates in the crystal, it is decomposed into o light and e light two vibration directions perpendicular to each other in the plane perpendicular to the optical path, and the two perpendicular linear polarization directions are called the birefringent principal axis of the crystal, as shown in the accompanying drawings. Figure 2 O light and e light are perpendicular to the side surface 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. The laser oscillates at a fundamental frequency of 640nm in the V-shaped resonant cavity. After passing through the frequency doubling crystal, a 320nm laser is generated. Then, after passing through the sum frequency crystal, a 213nm laser is generated. Finally, the laser is output out of the cavity by the total reflection end mirror.

[0011] According to a preferred embodiment of 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] According to a preferred embodiment of this invention, the calculation process for 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] Assuming the fundamental frequency photoelectric field intensity generated by the laser crystal is E, and the electric field intensities in the vertical and horizontal directions are Ecosψ and Esinψ, respectively, with corresponding light intensities of E and E, respectively. 2 cos 2 ψ and E 2 sin 2 ψ, assuming the frequency doubling crystal has a frequency doubling conversion efficiency of η in the vertical direction, then ηE is generated. 2 cos 2 The intensity of the horizontally polarized frequency-doubled light of ψ;

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

[0016] According to the preferred embodiment of this invention, the laser crystal is Pr:YLiF4 (Pr:YLF), and the two light-transmitting end faces of the laser crystal are coated with 444nm and 640nm anti-reflection films.

[0017] According to the utility model, the two light transmission end faces of the frequency doubling crystal are coated with 640nm and 320nm anti-reflection films, the frequency doubling crystal converts 640nm fundamental frequency light into 320nm frequency-doubled light through a type I frequency doubling phase matching (o+o→e) mode, 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, and φ=0o.

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

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

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

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

[0023] The processing angle refers to the angle in the crystal space corresponding to the light transmission direction of the crystal, and is specifically defined as follows: the angle (θ, φ) represents a certain direction in the crystal space, wherein θ is the included angle between the direction and the optical main axis Z of the crystal, and φ is the azimuth angle, which is the included angle between the projection of the direction in the XY main plane of the crystal and the X axis; the processing angle is a commonly used expression about the processing direction of the crystal in the field.

[0024] According to the utility model, the sum frequency crystal is BBO, the two light transmission end faces of the sum frequency crystal are coated with 640nm, 320nm and 213nm anti-reflection films (the anti-reflection films of the three parameters correspond to the positions of 640nm, 320nm laser converting 213nm sum frequency light), the sum frequency crystal is processed along the type I sum frequency phase matching direction, and the processing angle is θ=64.7o and φ=0o.

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

[0026] According to the utility model, the laser diode emits blue light with a center wavelength of 444nm, the linear polarization direction is along the Z axis of the laser crystal, that is, the e light vibration direction generated in the laser crystal, and the linear polarization direction corresponds to the π polarization absorption peak of the laser crystal.

[0027] According to the utility model, the pump light focusing system is a single convex lens or a lens group composed of multiple convex lenses, the pump focal spot size after focusing on the laser crystal is close to the laser cavity mode size, so that the most efficient pump light-laser mode matching is realized.

[0028] According to a preferred embodiment of the present invention, an acousto-optic modulator is disposed 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 optical element (such as a two-dimensional nano saturable absorber or a crystal with saturable absorption performance at 640 nm) to achieve 213 nm deep ultraviolet pulsed laser output.

[0029] The application of the aforementioned 213nm all-solid-state deep ultraviolet laser follows these steps:

[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 linearly polarized lights. Before and after entering the sum frequency crystal, no change occurs, and the sum frequency crystal does not play a role.

[0031] (2) After the 640nm linearly polarized fundamental frequency laser enters the frequency doubling crystal, the ω along the o-beam direction of the frequency doubling crystal... ⊥ As the linearly polarized laser passes through the frequency doubling crystal to reach the total reflection 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-beam direction of the frequency doubling crystal, which enters the sum frequency crystal together with the polarized laser along the e-beam direction of the frequency doubling crystal.

[0032] (3) Since the birefringence principal axis of the frequency doubling crystal is rotated by 90° relative to the birefringence principal axis of the sum frequency crystal, the horizontally polarized laser emitted from 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 along the e-light direction of the sum frequency crystal, which is output by the deep ultraviolet output mirror.

[0033] The beneficial effects of this utility model are as follows:

[0034] 1. Previous 213nm all-solid-state laser technologies all used near-infrared light with a wavelength of around 1μm as the fundamental frequency light. At least three frequency conversion steps are required from the fundamental frequency to the 213nm output, resulting in low conversion efficiency. In contrast, this 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 frequency conversion steps are required: frequency doubling with a frequency doubling crystal and summing with a frequency doubling crystal. This has the advantages of simplified process, small size, easy adjustment, high conversion efficiency, high output power, low manufacturing cost, and stable performance.

[0035] 2. Previous laser diode-pumped Pr:YLF4 crystal intracavity frequency-converting lasers all adopted a polarization configuration in which the principal axes of the laser crystal's birefringence and the nonlinear optical crystal's birefringence coincided. This could not provide the polarization matching conditions required for cascade frequency conversion, thus preventing cascade frequency conversion and the generation of 213nm laser. This invention adopts a special polarization configuration in which the principal axis of the laser crystal's birefringence is deflected by a certain angle relative to the principal axis of the nonlinear optical crystal, cleverly solving the above problem and making intracavity cascade frequency conversion possible for this type of laser. At the same time, the optimal deflection angle of the laser crystal is given for different frequency doubling conversion efficiencies. The novel 213nm all-solid-state deep ultraviolet laser source provided by this technology will have important applications in scientific research, medicine, industry and other fields. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of this utility model;

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

[0038] Figure 3 This is a structural schematic diagram of Embodiment 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 Implementation

[0040] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0041] Example 1:

[0042] like Figures 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 total reflection end mirror 6 arranged sequentially along the optical path.

[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 cuboids. 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 the light propagates in the crystal, it is decomposed into o light and e light which are two linearly polarized lights with perpendicular vibration directions in the plane perpendicular to the optical path, and the two perpendicular linearly polarized directions are called the birefringent principal axes of the crystal, as shown in Fig. 1, wherein the o light and the e light are perpendicular to the side surface of the crystal. Figure 2

[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, and the 640 nm fundamental frequency laser oscillation is realized in the V-type resonant cavity, the 320 nm laser is generated after the frequency doubling crystal 7, and the 213 nm laser is generated after the sum frequency crystal 8, and then the laser is output outside the cavity by the total reflection end mirror.

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

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

[0048] The laser crystal 4 is Pr:YLiF4 (Pr:YLF), and the two light transmitting end surfaces of the laser crystal 4 are coated with 444 nm and 640 nm anti-reflection films.

[0049] The two light transmitting end surfaces of the frequency doubling crystal 7 are coated with 640 nm and 320 nm anti-reflection films, the frequency doubling crystal 7 converts the 640 nm fundamental frequency light into 320 nm frequency doubled light through the type I frequency doubling phase matching (o+o→e) mode, and 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° and φ=0°.

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

[0052] When the frequency doubling crystal 7 is BIBO, the processing angle is θ=132.1° and φ=90°.

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

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

[0055] The processing angle refers to the angle in the crystal space corresponding to the light transmitting direction of the crystal, and is specifically defined as follows: an angle (θ, φ) is used to represent a certain direction in the crystal space, wherein θ is the included angle between the direction and the optical principal axis Z of the crystal, φ is the azimuth angle, which is the included angle between the projection of the direction in the XY principal plane of the crystal and the X axis, and the processing angle is a commonly used expression about the processing direction of the crystal in the profession.

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

[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 center wavelength of 444nm. The linear polarization direction is along the Z-axis of the laser crystal, which is the vibration direction of the e-light generated in the laser crystal and corresponds to the π-polarization absorption peak of the laser crystal.

[0059] The pump light focusing system 2 is a single convex lens. The size of the pump spot after focusing onto the laser crystal is similar to the size of the laser cavity mode, so as to achieve the most efficient pump light-laser mode matching.

[0060] The application of the aforementioned 213nm all-solid-state deep ultraviolet laser follows these steps:

[0061] (1) The laser light emitted by the laser diode (444nm blue light) is injected into the laser crystal through the pump focusing system and the pump end mirror. The laser crystal generates a 640nm linearly polarized fundamental frequency laser, whose polarization is along... Figure 2 In (a), the direction after deflection ψ is decomposed into polarization fundamental frequency laser ω. ⊥ ω / / Two mutually perpendicular linearly polarized beams do not change before and after entering the sum-frequency crystal, so the sum-frequency crystal has no effect.

[0062] (2) After the 640nm linearly polarized fundamental frequency laser enters the frequency doubling crystal, the ω along the o-beam direction (perpendicular direction) of the frequency doubling crystal... ⊥ As the linearly polarized laser passes through the frequency-doubling crystal to the total reflection end mirror, and then returns and passes through the frequency-doubling crystal again, two type I frequency-doubling phase matches occur (o + o → e), generating a 320nm linearly polarized laser (2ω) along the e-beam direction (horizontal direction) of the frequency-doubling crystal. / / ), and ω along the e-beam direction of the frequency doubling crystal / / Polarized laser light enters the sum-frequency crystal along with the laser beam;

[0063] (3) Since the principal axis of the birefringence of the frequency doubling crystal is rotated by 90° relative to the principal axis of the sum-frequency crystal, the horizontally polarized ω emitted from the frequency doubling crystal... / / 2ω / / The laser is o light relative to the sum frequency crystal, and the I type sum frequency phase matching (o+o=e) occurs in the sum frequency crystal to generate 213nm linearly polarized laser (3ω ⊥ ) along the e light direction (vertical direction) of the sum frequency crystal.

[0064] Embodiment 2

[0065] As shown in Figure 3 , the embodiment provides a 213nm all-solid-state deep ultraviolet laser, and the structure is shown in Embodiment 1, and the difference is that an acousto-optic modulator 9 is arranged between the laser crystal 4 and the deep ultraviolet output mirror 5, and the operation mode of the laser is changed from continuous to pulse, so that the 213nm deep ultraviolet laser output with high peak power and short pulse width can be realized, and special application requirements such as biological tissue cutting, organic material marking, optical waveguide and grating carving and the like can be met.

[0066] The above only describes preferred embodiments of the utility model and is not used for limiting the utility model, and for the person skilled in the art, the utility model can have various changes and changes. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. A 213 nm all-solid-state deep-ultraviolet laser, characterized by, The laser diode, the pump light focusing system, the pump end mirror, the laser crystal, the deep ultraviolet output mirror, the sum frequency crystal, the frequency doubling crystal and the full reflection end mirror are sequentially arranged along an optical path, wherein The pump end mirror, the deep ultraviolet output mirror and the full reflection end mirror form a V-shaped resonant cavity, the laser crystal, the sum frequency crystal and the frequency doubling crystal are cuboids, and the birefringent principal axes of the laser crystal, the sum frequency crystal and the frequency doubling crystal are arranged in a staggered manner; When the light propagates in the crystal, the light is decomposed into o light and e light which are two linearly polarized lights with perpendicular vibration directions in a plane perpendicular to the optical path, and the two linearly polarized directions are called the birefringent principal axes of the crystal, and the o light and the e light are perpendicular to the side surface of the crystal.

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

3. The 213 nm all-solid-state deep-ultraviolet laser as claimed in claim 2, characterized in that, The laser crystal is Pr:YLiF4, and the two light transmission end faces of the laser crystal are coated with an antireflection film.

4. The 213 nm all-solid-state deep-ultraviolet laser as claimed in claim 3, characterized in that, The two light transmission end faces of the frequency doubling crystal are coated with an antireflection film, and the frequency doubling crystal is processed along a type I frequency doubling phase matching direction. When the frequency doubling crystal is BBO, the processing angle is θ=37.4° and φ=0°. When the frequency doubling crystal is LBO, the processing angle is θ=90° and φ=53.3°. When the frequency doubling crystal is BIBO, the processing angle is θ=132.1° and φ=90°. When the frequency doubling crystal is ADP, the processing angle is θ=55.9° and φ=45°. When the frequency doubling crystal is KDP, the processing angle is θ=55.4° and φ=0°.

5. The 213 nm all-solid-state deep-ultraviolet laser as claimed in claim 4, characterized in that, The sum frequency crystal is BBO, the two light transmission end faces of the sum frequency crystal are coated with an antireflection film, and the sum frequency crystal is processed along a type I sum frequency phase matching direction with a processing angle of θ=64.7° and φ=0°.

6. The 213 nm all-solid-state deep-ultraviolet laser as claimed in claim 5, characterized in that, The laser diode emits blue light with a center wavelength of 444 nm, and the linear polarization direction is along the Z axis of the laser crystal, i.e., the e light vibration direction in the laser crystal.

7. The 213 nm all-solid-state deep-ultraviolet laser as claimed in claim 6, characterized in that, The pump light focusing system is a single convex lens or a lens group composed of multiple convex lenses.

8. The 213 nm all-solid-state deep-ultraviolet laser as claimed in claim 7, characterized by, An acousto-optic modulator is arranged between the laser crystal and the deep ultraviolet output mirror.

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