A method for preparing a large aperture ultraviolet tripler device

Abstract

The present application relates to a kind of preparation methods of large aperture ultraviolet third harmonic generator, the method is first using Maker stripe method to measure the frequency doubling coefficient of guanidinium tetrafluoroborate crystal, obtain 2 non-zero effective frequency doubling coefficient;Again, the minimum deflection angle method is used to determine the principal refractive index of guanidinium tetrafluoroborate crystal from 253nm-2325nm between 11 wavelengths, fitting Sellmeier equation;According to Sellmeier equation, the computer program is calculated, and the phase matching curve of the guanidinium tetrafluoroborate crystal type I or type I is calculated, then the phase matching point of the guanidinium tetrafluoroborate crystal is determined by combining frequency doubling coefficient;Then, according to the phase matching direction, guanidinium tetrafluoroborate crystal is cut, and two light transmitting surfaces are polished and coated with dielectric film to obtain the guanidinium tetrafluoroborate crystal third harmonic generator;The large aperture ultraviolet third harmonic generator of the guanidinium tetrafluoroborate crystal is used to generate high-power third harmonic laser output, and has good practical application value in the field of laser technology, especially in high-power laser device.

Description

Technical Field

[0001] This invention relates to a method for fabricating a large-aperture ultraviolet third harmonic device, belonging to the field of laser and nonlinear optics technology. Background Technology

[0002] Solid-state lasers using Nd(neodymium) ion-doped laser crystals as the working medium can efficiently convert laser radiation around 1.064 μm into second, third, and higher harmonics, making them a valuable source of visible, ultraviolet, and deep ultraviolet radiation. In particular, the third harmonic around 355 nm exhibits extremely superior characteristics in fields such as precision machining, micro-nano manufacturing, laser marking, high-energy lasers, and scientific research, and is receiving widespread attention and urgent demand.

[0003] Optical devices capable of laser frequency doubling based on nonlinear optical crystals are called laser frequency doubling devices. The optimal approach to obtaining the third harmonic at approximately 355 nm is through frequency doubling and third harmonic devices to convert the laser radiation at approximately 1.064 μm. Currently, commercially available third harmonic devices mainly include KH₂PO₄ / KD₂PO₄ (KDP / DKDP), LiB₃O₅ (LBO), β-BaB₂O₄ (BBO), and CsLiB₆O₅. 10 Several inorganic crystal devices, such as CLBO, exist. However, each of these crystals has its own drawbacks. For example, KDP / DKDP crystals have a relatively small frequency doubling effect, LBO crystals are prone to deliquescence, BBO crystals exhibit severe nonlinear absorption and photorefractive effects, and CLBO crystals are highly hygroscopic, requiring moisture-proof measures during application. Furthermore, high-energy laser systems require large-aperture devices, and existing DKDP crystals, while exhibiting small effects, are expensive. Therefore, finding large-aperture ultraviolet third-harmonic generation devices with good physicochemical properties and excellent overall performance has become one of the most practically valuable directions for solving the problem of ultraviolet all-solid-state lasers in the approximately 355nm wavelength band required by advanced manufacturing and information industries.

[0004] Since the 1980s, guanidine tetrafluoroborate crystals have been reported, with the molecular formula CH6BF4N3 or C(NH2)3BF4, abbreviated as GFB crystals, a molecular weight of 146.90, belonging to the trigonal crystal system, space group R3m, and unit cell parameters of... α=90.00°, β=90.00°, γ=120.00°, Z=3,

[0005] Chinese invention patent No. 202011568533.1 and patent application No. 202211670253.0 disclose the growth method and application of GFB crystals.

[0006] In 1987, A. Kozak et al. studied the crystal structure of GFB (A. Kozak, et al., 1987, J. Phys. C: Solid State Phys., 20, 5433); in 1989, S. Haussühl studied the thermoelectric, dielectric, piezoelectric, and elastic properties of GFB crystals (S. Haussühl, 1989, Z. Kristallogr., 187, 153); in 2018, S. Nandhini et al. conducted research on its structure, optics, mechanics, electricity, and nonlinear optics (S. Nandhini, et al., 2018, Optics and Laser Technology, 105, 249). There are currently no reports on third-harmonic devices fabricated using GFB crystals or their applications. Summary of the Invention

[0007] The present invention aims to provide a large-aperture ultraviolet third-harmonic generation device and its fabrication method. The method first uses the Maker fringe method to measure the frequency doubling coefficient of a guanidine tetrafluoroborate crystal, obtaining two non-zero effective frequency doubling coefficients. Then, the principal refractive index of the guanidine tetrafluoroborate crystal at 11 wavelengths between 253 nm and 2325 nm is determined using the minimum deviation angle method, and the Sellmeier equation is fitted. Based on the Sellmeier equation, a computer program calculates the type I or type II phase-matching curve of the guanidine tetrafluoroborate crystal, and the phase-matching point of the guanidine tetrafluoroborate crystal is determined by combining the frequency doubling coefficients. Then, the guanidine tetrafluoroborate crystal is cut according to the phase-matching direction, and the two light-transmitting surfaces are polished and coated with a dielectric film to obtain the guanidine tetrafluoroborate crystal third-harmonic generation device. This large-aperture ultraviolet third-harmonic generation device of the guanidine tetrafluoroborate crystal is used to generate high-power third-harmonic laser output, and has good practical application value in the field of laser technology, especially in high-power laser devices, successfully achieving third-harmonic conversion of lasers around 1.064 μm.

[0008] The method for fabricating a large-aperture ultraviolet third harmonic device according to the present invention comprises the following steps:

[0009] a. The harmonic doubling coefficients of guanidine tetrafluoroborate crystal at standard Type I phase matching in the 1.064 μm band were measured using the Mark fringe method, yielding two non-zero effective harmonic doubling coefficients:

[0010] d 22 =±4.03×d 36 (KDP);

[0011] d 15 =±1.95×d 36 (KDP);

[0012] Where d 36 (KDP) = 0.39 pm / V;

[0013] b. Based on Kleinman symmetry, the formulas for the effective harmonic coefficients of Type I and Type II are obtained as follows:

[0014]

[0015]

[0016] Where θ is the polar angle, the angle between the light propagation direction k and the Z-axis; φ is the azimuth angle, the angle between the projection of k onto the XY plane and the Z-axis;

[0017] c. Based on its propagation in the corresponding XZ and YZ planes, the effective frequency doubling coefficient formula for a GFB crystal cut according to the phase-matching angle can be expressed as follows:

[0018]

[0019]

[0020]

[0021]

[0022] d. The principal refractive index of the GFB crystal at 11 wavelengths between 253 nm and 2325 nm was determined using the minimum deviation angle method, and the Sellmeier equation was obtained by fitting the results.

[0023]

[0024]

[0025] Where, n o n e λ is the principal axis refractive index of the GFB crystal, and λ is the incident wavelength in μm.

[0026] e. Using the Sellmeier equation from step d, the type I or type II phase matching curves of the guanidine tetrafluoroborate crystal are calculated by a computer program. Then, the phase matching point with higher conversion efficiency of the guanidine tetrafluoroborate crystal is determined by combining the frequency doubling coefficients measured in steps a, b, and c. The guanidine tetrafluoroborate crystal is then cut according to the phase matching direction, and the two light-transmitting surfaces are polished and coated with a dielectric film to obtain a large-aperture guanidine tetrafluoroborate crystal ultraviolet third harmonic device.

[0027] This invention discloses a method for fabricating a large-aperture ultraviolet third harmonic device. The method involves guanidine tetrafluoroborate crystal with the molecular formula CH6BF4N3 or C(NH2)3BF4, a molecular weight of 146.90, belonging to the trigonal crystal system, space group R3m, and cell parameters of... α=90.00°, β=90.00°, γ=120.00°, Z=3,

[0028] The large-aperture ultraviolet third harmonic device provided by this invention is a guanidine tetrafluoroborate (GFB) crystal third harmonic device prepared by cutting a guanidine tetrafluoroborate (GFB) crystal according to a type I or type II third harmonic phase matching direction, polishing the two light-transmitting surfaces and depositing a dielectric film; the guanidine tetrafluoroborate (GFB) crystal third harmonic device is a type I guanidine tetrafluoroborate (GFB) crystal third harmonic device or a type II guanidine tetrafluoroborate (GFB) crystal third harmonic device.

[0029] The present invention discloses a method for fabricating a large-aperture ultraviolet third-harmonic generation device. The application of the large-aperture ultraviolet third-harmonic generation device obtained by this method is to generate third-harmonic laser output, wherein the generation of third-harmonic laser output is as follows:

[0030] Using Nd-doped YAG, YLF, YAP, LuVO4, YVO4, or GdVO4 lasers as the light source, and using type I GTP-KTP, type I KTP, type I KTA, type I LBO, type I BBO, or type I CLBO as the frequency doubling device, the infrared laser emitted by the Nd-based laser is directly fed into the guanidine tetrafluoroborate (GFB) crystal third frequency harmonic device by the frequency doubling device to generate a third frequency harmonic laser output; the guanidine tetrafluoroborate (GFB) crystal third frequency harmonic device is a type I or type II GFB crystal third frequency harmonic device.

[0031] The generated third-harmonic laser is a third-harmonic laser with a wavelength of about 355nm, and is output after being filtered by a filter or split by a beam splitter.

[0032] The large-aperture ultraviolet third-harmonic generation device provided by this invention is prepared based on a large-size guanidine tetrafluoroborate (GFB) crystal grown by an aqueous solution method. It is not prone to deliquescence and does not require additional moisture-proof devices. In addition, the frequency doubling effect of guanidine tetrafluoroborate (GFB) crystal is comparable to that of BBO crystal, with good mechanical properties, not easily broken, easy to process and store, and can achieve high-power third-harmonic output, making the realization of third-harmonic lasers simpler, simplifying the laser fabrication process, reducing manufacturing costs, and facilitating the application of third-harmonic lasers. Attached Figure Description

[0033] Figure 1 The refractive index dispersion curve of the third harmonic device of this invention;

[0034] Figure 2 Photograph of the prism used for testing the refractive index of the third harmonic device of this invention;

[0035] Figure 3 These are the Type I and Type II phase matching curves of the third harmonic device of this invention;

[0036] Figure 4 This is a schematic diagram of the third-harmonic laser output by the third-harmonic device of the present invention; wherein 1 is a laser, 2 is a frequency doubling device, 3 is a third-harmonic device, 4 is a beam splitter, and 5 is a filter.

[0037] Figure 5 This invention relates to a large-aperture ultraviolet third harmonic device fabricated using GFB crystals. Detailed Implementation

[0038] Example 1

[0039] a. The doubling coefficients of guanidine tetrafluoroborate (GFB) crystal at standard Type I phase matching in the 1.064 μm band were measured using the Mark fringe method, yielding two non-zero effective doubling coefficients:

[0040] d 22 =±4.03×d 36 (KDP);

[0041] d 15 =±1.95×d 36 (KDP);

[0042] Where d 36 (KDP) = 0.39 pm / V;

[0043] b. Based on Kleinman symmetry, the formulas for the effective harmonic coefficients of Type I and Type II are obtained as follows:

[0044]

[0045]

[0046] Where θ is the polar angle, the angle between the light propagation direction k and the Z-axis; φ is the azimuth angle, the angle between the projection of k onto the XY plane and the Z-axis;

[0047] c. Based on its propagation in the corresponding XZ and YZ planes, the effective frequency doubling coefficient formula for a guanidine tetrafluoroborate (GFB) crystal cut at a phase-matching angle can be expressed as follows:

[0048]

[0049]

[0050]

[0051]

[0052] d. The principal refractive index of the GFB crystal at 11 wavelengths between 253 nm and 2325 nm was determined using the minimum deviation angle method, and the Sellmeier equation was obtained by fitting the results.

[0053]

[0054]

[0055] Where, n o n e λ is the principal axis refractive index of the GFB crystal, and λ is the incident wavelength in μm.

[0056] e. Using guanidine tetrafluoroborate (GFB) crystal, the Sellmeier equation is used to calculate the type I phase matching curve of the guanidine tetrafluoroborate (GFB) crystal through a computer program. Then, combined with the doubling coefficient, the third harmonic phase matching point (θ = 25.6°, φ = 90°) with high conversion efficiency is determined. Then, the guanidine tetrafluoroborate (GFB) crystal is cut according to this phase matching direction, and its two light-transmitting surfaces are polished. After that, a dielectric film is deposited to make a type I third harmonic device of large-aperture GFB crystal.

[0057] According to the appendix Figure 4 As shown, the guanidine tetrafluoroborate (GFB) crystal type I third frequency harmonic device is placed at position 3. At room temperature, a Q-switched Nd:YAG laser 1 is used as the light source, and a type II LBO is used as the frequency harmonic device 2. The laser is incident with infrared laser light in the 1.064μm band. The frequency-doubled light and the fundamental light generated by the frequency harmonic device 2 directly enter the guanidine tetrafluoroborate (GFB) crystal third frequency harmonic device 3 for third frequency harmonic conversion, thereby generating a third frequency harmonic laser output with a power of 8W and a third frequency harmonic output wavelength of 355nm. The generated third frequency harmonic laser with a wavelength of 355nm can be filtered by a beam splitter prism 4 or a filter 5 before being output.

[0058] The phase matching direction of the guanidine tetrafluoroborate (GFB) crystal during cutting is a type I direction. The light-transmitting surface of the guanidine tetrafluoroborate (GFB) crystal ultraviolet third harmonic device is square, with a cross-sectional size of 10mm × 10mm and a thickness of 1mm in the light-transmitting direction.

[0059] Example 2

[0060] In this embodiment, the method steps ad are performed in accordance with those in Embodiment 1;

[0061] e. Using guanidine tetrafluoroborate (GFB) crystal, the Sellmeier equation is used to calculate the type II phase matching curve of the guanidine tetrafluoroborate (GFB) crystal through a computer program. Then, combined with the doubling coefficient, the third harmonic phase matching point with high conversion efficiency (θ = 43.8°, φ = 0°) is determined. Then, the large-size guanidine tetrafluoroborate (GFB) crystal is cut according to this phase matching direction, and its two light-transmitting surfaces are polished. After that, a dielectric film is deposited to make a type II third harmonic device of large-aperture GFB crystal.

[0062] According to the appendix Figure 4 As shown, the GFB crystal type II third frequency harmonic device is placed at position 3. At room temperature, a Q-switched Nd:YAG laser 1 is used as the light source, and a type II LBO is used as the frequency harmonic device 2. The laser is incident with infrared laser light in the 1.064μm band. The frequency-doubled light and the fundamental light generated by the frequency harmonic device 2 directly enter the guanidine tetrafluoroborate (GFB) crystal third frequency harmonic device 3 for third frequency harmonic conversion, thereby generating a third frequency harmonic laser output with a power of 10W and a third frequency harmonic output wavelength of 355nm. The generated third frequency harmonic laser with a wavelength of 355nm can be filtered by a beam splitter prism 4 or a filter 5 before being output.

[0063] The phase matching direction of the guanidine tetrafluoroborate (GFB) crystal during cutting is a type II direction. The light-transmitting surface of the guanidine tetrafluoroborate (GFB) crystal ultraviolet third harmonic device is square, with a cross-sectional size of 20mm×20mm and a thickness of 5mm in the light-transmitting direction.

[0064] Example 3

[0065] In this embodiment, the method steps ad are performed in accordance with those in Embodiment 1;

[0066] e. Using guanidine tetrafluoroborate (GFB) crystal, the Sellmeier equation is used to calculate the type II phase matching curve of the guanidine tetrafluoroborate (GFB) crystal through a computer program. Then, combined with the doubling coefficient, the third harmonic phase matching point (θ = 30.7°, φ = 0°) with high conversion efficiency is determined. Then, the large-size guanidine tetrafluoroborate (GFB) crystal is cut according to this phase matching direction, and its two light-transmitting surfaces are polished. After that, a dielectric film is deposited to make a type II third harmonic device of large-aperture GFB crystal.

[0067] According to the appendix Figure 4As shown, the guanidine tetrafluoroborate (GFB) crystal type II third harmonic device is placed at position 3. At room temperature, a Q-switched Nd:YAG laser 1 is used as the light source, and a type II LBO is used as the frequency doubling device 2. The laser emits infrared laser light in the 1.064μm band. The frequency-doubled light and the fundamental light generated by the frequency doubling device 2 directly enter the guanidine tetrafluoroborate (GFB) crystal third harmonic device 3 for third harmonic conversion, thereby generating a third harmonic laser output with a power of 15W and a third harmonic output wavelength of 355nm. The generated third harmonic laser with a wavelength of 355nm can be filtered by a beam splitter prism 4 or a filter 5 before being output.

[0068] The phase matching direction of the guanidine tetrafluoroborate (GFB) crystal during cutting is a type II direction. The light-transmitting surface of the guanidine tetrafluoroborate (GFB) crystal ultraviolet third harmonic device is square, with a cross-sectional size of 30mm×30mm and a thickness of 7mm in the light-transmitting direction.

[0069] Example 4

[0070] In this embodiment, the method steps ad are performed in accordance with those in Embodiment 1;

[0071] e. Using a guanidine tetrafluoroborate (GFB) crystal, the Sellmeier equation is used to calculate the type I phase matching curve of the guanidine tetrafluoroborate (GFB) crystal through a computer program. Then, combined with the doubling coefficient, the third harmonic phase matching point (θ = 25.6°, φ = 90°) with high conversion efficiency is determined. Then, the large-size guanidine tetrafluoroborate (GFB) crystal is cut according to this phase matching direction, and its two light-transmitting surfaces are polished. After that, a dielectric film is deposited to make a type I third harmonic device of a large-diameter guanidine tetrafluoroborate (GFB) crystal.

[0072] According to the appendix Figure 4 As shown, the guanidine tetrafluoroborate (GFB) crystal type I third frequency harmonic device is placed at position 3. At room temperature, a Q-switched Nd:YAG laser 1 is used as the light source, and a type II LBO is used as the frequency harmonic device 2. The laser is incident with infrared laser light in the 1.064μm band. The frequency-doubled light and the fundamental light generated by the frequency harmonic device 2 directly enter the guanidine tetrafluoroborate (GFB) crystal third frequency harmonic device 3 for third frequency harmonic conversion, thereby generating a third frequency harmonic laser output with a power of 20W and a third frequency harmonic output wavelength of 355nm. The generated third frequency harmonic laser with a wavelength of 355nm can be filtered by a beam splitter prism 4 or a filter 5 before being output.

[0073] The phase matching direction of the guanidine tetrafluoroborate (GFB) crystal during cutting is a type I direction. The light-transmitting surface of the guanidine tetrafluoroborate (GFB) crystal ultraviolet third harmonic device is square, with a cross-sectional size of 50mm×50mm and a thickness of 10mm in the light-transmitting direction.

[0074] Those skilled in the art can easily fabricate other ultraviolet third harmonic devices using GFB crystals using similar methods, and these cannot exceed the concept and scope of this invention.

Claims

1. A method of fabricating a large aperture UV frequency tripler device, characterized by Follow these steps: a. The harmonic doubling coefficients of guanidine tetrafluoroborate crystal at standard Type I phase matching in the 1.064 μm band were measured using the Mark fringe method, yielding two non-zero effective harmonic doubling coefficients: d 22 = ±4.03 x d 36 (KDP) d 15 = ±1.95 x d 36 (KDP) where d 36 (KDP) = 0.39 pm / V; b. Based on Kleinman symmetry, the formulas for the effective harmonic coefficients of Type I and Type II are obtained as follows: = d ooe = d 15 sinθ-d 22 cosθsin3φ = d oee = d 22 cos 2 θcos3φ Where θ is the polar angle, the angle between the light propagation direction k and the Z-axis; φ is the azimuth angle, the angle between the projection of k onto the XY plane and the Z-axis; c. Based on its propagation in the corresponding XZ and YZ planes, the effective frequency doubling coefficient formula for a GFB crystal cut according to the phase-matching angle can be expressed as follows: = d 15 sinθ PM (φ = 0 o ) = d 15 sinθ PM + d 22 cosθ PM (φ = 90 o ) = d 22 cos 2 θ PM (φ = 0 o ) = 0 (φ = 90 o ) d. The principal refractive index of the GFB crystal at 11 wavelengths between 253 nm and 2325 nm was determined using the minimum deviation angle method, and the Sellmeier equation was obtained by fitting the results. wherein n o , n e is the principal refractive index of the GFB crystal, and λ is the incident wavelength in units of μm. e. Using the Sellmeier equation from step d, the type I or type II phase matching curves of the guanidine tetrafluoroborate crystal are calculated by a computer program. Then, the phase matching point with higher conversion efficiency of the guanidine tetrafluoroborate crystal is determined by combining the frequency doubling coefficients measured in steps a, b, and c. The guanidine tetrafluoroborate crystal is then cut according to the phase matching direction, wherein the phase matching direction during the cutting of the guanidine tetrafluoroborate crystal is the type II direction. The two light-transmitting surfaces are polished and coated with a dielectric film to obtain a large-diameter guanidine tetrafluoroborate crystal ultraviolet third harmonic device.

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