A preparation method of a guanidinium tetrafluoroborate crystal quadruple frequency device

Abstract

The application relates to a preparation method of a four-fold frequency crystal guanidinium tetrafluoroborate device, which comprises the following steps: firstly, measuring a frequency doubling coefficient of the crystal by a Maker fringe method to obtain two non-zero effective frequency doubling coefficients; secondly, measuring main refractive indexes of the crystal at 11 wavelengths between 253 nm and 2325 nm by a minimum deviation angle method, and fitting a Sellmeier equation; thirdly, calculating a phase matching curve of the crystal I or II type by a computer program according to the Sellmeier equation, and combining the frequency doubling coefficient to determine a phase matching point of the crystal; fourthly, cutting the crystal according to the phase matching direction, polishing two light transmission surfaces, and coating a dielectric film to obtain the four-fold frequency crystal device; and the four-fold frequency crystal device is used for generating four-fold frequency laser output, the frequency doubling effect is 4.7 times that of KDP, and the four-fold frequency crystal device has good practical application value in the field of laser technology.

Description

Technical Field

[0001] This invention relates to a method for fabricating a guanidine tetrafluoroborate crystal fourth 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, fourth, and higher harmonics. They are a valuable source of visible, ultraviolet, and deep ultraviolet light radiation. In particular, the fourth harmonic at around 266 nm exhibits extremely superior characteristics in fields such as semiconductor detection, precision machining, micro-nano manufacturing, ultraviolet communication, molecular imaging, 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 fourth harmonic at approximately 266 nm is through frequency doubling and fourth harmonic devices to convert the laser radiation at approximately 1.064 μm. Currently, the main fourth harmonic devices used in commercial lasers are β-BaB₂O₄ (BBO) and CsLiB₆O₄. 10 (CLBO) are two types of inorganic borate crystal devices. However, both crystals have certain drawbacks. For example, BBO crystals exhibit severe nonlinear absorption and photorefractive effects, leading to unstable light output performance; CLBO crystals are highly hygroscopic, requiring moisture-proof measures during application and complicating system design. Therefore, finding a fourth-harmonic generation crystal with good physicochemical properties and excellent overall performance has become one of the most practically valuable directions for solving the needs of ultraviolet all-solid-state lasers in the approximately 266nm wavelength range required by advanced manufacturing and information industries.

[0004] Since the 1980s, guanidine tetrafluoroborate crystals (GFB) have been reported, 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 unit cell parameters of [missing information]. 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 its growth method and use.

[0006] In 1987, A. Kozak et al. studied the crystal structure of guanidine tetrafluoroborate (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 guanidine tetrafluoroborate crystals (S. Haussühl, 1989, Z. Kristallogr., 187, 153); and 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 no reports on fourth-harmonic devices fabricated using guanidine tetrafluoroborate crystals or their applications. Summary of the Invention

[0007] The purpose of this invention is to provide a method for fabricating a fourth harmonic device using a guanidine tetrafluoroborate crystal. This method is based on the refractive index of the guanidine tetrafluoroborate crystal at different wavelengths, and calculates the phase matching direction for laser-driven fourth harmonic conversion based on the refractive index data. After cutting the guanidine tetrafluoroborate crystal according to the phase matching direction of type I or II fourth harmonic conversion, the two light-transmitting surfaces are polished and coated with a dielectric film to obtain a type I or II fourth harmonic device. First, the frequency doubling coefficient of the crystal was measured using the Maker fringe method, yielding two non-zero effective frequency doubling coefficients. Then, the principal refractive index of the crystal at 11 wavelengths between 253 nm and 2325 nm was determined using the minimum deviation angle method, and the Sellmeier equation was fitted. Based on the Sellmeier equation, the type I or II phase-matching curve of the crystal was calculated using a computer program, and the phase-matching point of the crystal was determined by combining the frequency doubling coefficients. Next, the crystal was cut along the phase-matching direction, and the two light-transmitting surfaces were polished and coated with a dielectric film to obtain the crystal fourth-harmonic generation device. This crystal fourth-harmonic generation device is used to generate fourth-harmonic laser output, which has significant practical application value in the field of laser technology, achieving fourth-harmonic conversion of lasers around 1.064 μm, with a frequency doubling effect 4.7 times that of KDP.

[0008] The method for preparing a guanidine tetrafluoroborate crystal fourth 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 the propagation in the corresponding XZ and YZ planes, the formula for the effective frequency doubling coefficient of the GFB crystal cut according to the phase matching angle is as follows:

[0018]

[0019]

[0020]

[0021]

[0022] d. The principal refractive index of guanidine tetrafluoroborate 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 guanidine tetrafluoroborate crystal, and λ is the incident wavelength in μm.

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

[0027] This invention discloses a method for preparing a guanidine tetrafluoroborate crystal fourth harmonic device. The guanidine tetrafluoroborate crystal used in this method has the chemical formula [C(NH₂)₃]BF₄, a molecular weight of 146.89, belongs to the trigonal crystal system, has a space group of R₃m, and its cell parameters are as follows: Z = 3,

[0028] The guanidine tetrafluoroborate crystal fourth-harmonic device obtained by the method described in this invention is used to generate fourth-harmonic laser output. The generation of fourth-harmonic laser output is as follows:

[0029] Using Nd-doped YAG, YLF, YAP, LuVO4, YVO4, or GdVO4 lasers as the light source, and employing 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 frequency-doubled light generated by the frequency doubling device directly enters the aforementioned guanidine tetrafluoroborate crystal fourth-harmonic generation device, thereby producing fourth-harmonic laser output. The guanidine tetrafluoroborate crystal fourth-harmonic generation device is either a type I or type II guanidine tetrafluoroborate crystal fourth-harmonic generation device.

[0030] The fourth-harmonic laser generated by the guanidine tetrafluoroborate crystal fourth-harmonic device is a fourth-harmonic laser with a wavelength of about 266nm, and is output after being filtered by a filter or split by a beam splitter prism.

[0031] The guanidine tetrafluoroborate crystal fourth harmonic device of this invention is relatively easy to prepare, does not easily deliquesce, and does not require additional moisture-proof devices. In addition, the guanidine tetrafluoroborate crystal has a frequency doubling effect comparable to that of BBO crystal, good mechanical properties, is not easily broken, and is easy to process and store. It can achieve high-power fourth harmonic output, making the realization of fourth harmonic lasers simpler, simplifying the laser preparation process, reducing manufacturing costs, and facilitating the application of fourth harmonic lasers. Attached Figure Description

[0032] Figure 1 The refractive index dispersion curve of the guanidine tetrafluoroborate crystal fourth harmonic device of the present invention;

[0033] Figure 2 A photograph of the prism used for testing the refractive index of the guanidine tetrafluoroborate crystal fourth harmonic device of the present invention;

[0034] Figure 3 These are the Type I and Type II phase matching curves of the guanidine tetrafluoroborate crystal fourth harmonic device of the present invention;

[0035] Figure 4 This is a schematic diagram of the fourth-harmonic laser output using the guanidine tetrafluoroborate crystal fourth-harmonic device obtained in this invention; where 1 is the laser, 2 is the frequency doubling device, 3 is the filter, 4 is the fourth-harmonic device, 5 is the beam splitter, and 6 is the filter.

[0036] Figure 5 This is a diagram of the guanidine tetrafluoroborate crystal fourth harmonic device of the present invention. Detailed Implementation

[0037] Example 1

[0038] 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:

[0039] d 22 =±4.03×d 36 (KDP);

[0040] d 15 =±1.95×d 36 (KDP);

[0041] Where d 36 (KDP) = 0.39 pm / V;

[0042] b. Based on Kleinman symmetry, the formulas for the effective harmonic coefficients of Type I and Type II are obtained as follows:

[0043]

[0044]

[0045] 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;

[0046] c. Based on the propagation in the corresponding XZ and YZ planes, the formula for the effective frequency doubling coefficient of the GFB crystal cut according to the phase matching angle is as follows:

[0047]

[0048]

[0049]

[0050]

[0051] d. The principal refractive index of guanidine tetrafluoroborate 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.

[0052]

[0053]

[0054] Where, n o n e λ is the principal axis refractive index of the guanidine tetrafluoroborate crystal, and λ is the incident wavelength in μm.

[0055] e. Using the Sellmeier equation in step d, the type I phase matching curve of the guanidine tetrafluoroborate crystal is calculated by a computer program. Then, combined with the doubling coefficient, the fourth harmonic phase matching point (θ = 39.1°, φ = 90°) with high conversion efficiency is determined. The guanidine tetrafluoroborate crystal is then cut according to this phase matching direction, and its two light-transmitting surfaces are polished. Finally, a dielectric film is deposited to fabricate the type I fourth harmonic device of the guanidine tetrafluoroborate crystal.

[0056] According to the appendix Figure 4 As shown, the guanidine tetrafluoroborate crystal type I fourth harmonic generation device is placed at position 4. 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 is incident with infrared laser light in the 1.064μm band. The frequency-doubled light generated by the frequency doubling device 2 passes through a filter and directly enters the guanidine tetrafluoroborate crystal fourth harmonic generation device 4 for fourth harmonic conversion, thereby generating a fourth harmonic laser output with a power of 0.5W. The fourth harmonic output wavelength is 266nm, and the conversion efficiency reaches 5.1%. The generated fourth harmonic laser with a wavelength of 266nm can be filtered by a beam splitter prism 5 or a filter 6 before being output.

[0057] The phase matching direction during the cutting of the guanidine tetrafluoroborate crystal is a type I direction. The light-transmitting surface of the type I fourth harmonic device of the guanidine tetrafluoroborate crystal is square with a cross-sectional size of 4mm × 5mm and a thickness of 6mm in the light-transmitting direction.

[0058] Example 2

[0059] In this embodiment, the method step ad is performed according to embodiment 1;

[0060] e. Using the Sellmeier equation and a computer program, the type II phase matching curve of the guanidine tetrafluoroborate crystal is calculated. Then, combined with the doubling coefficient, the fourth harmonic phase matching point (θ = 52.7°, φ = 0°) with high conversion efficiency is determined. The guanidine tetrafluoroborate crystal is then cut according to this phase matching direction, and its two light-transmitting surfaces are polished. Finally, a dielectric film is deposited to fabricate the type II fourth harmonic device of the guanidine tetrafluoroborate crystal.

[0061] According to the appendix Figure 4As shown, the guanidine tetrafluoroborate crystal type II fourth harmonic generation device is placed at position 4. 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 generated by the frequency doubling device 2 passes through a filter and then directly enters the guanidine tetrafluoroborate crystal fourth harmonic generation device 4 for fourth harmonic conversion, thereby generating a fourth harmonic laser output with a power of 1W. The fourth harmonic output wavelength is 266nm, and the conversion efficiency reaches 8%. The generated fourth harmonic laser with a wavelength of 266nm can be filtered by a beam splitter prism 5 or a filter 6 before being output.

[0062] The phase matching direction during the cutting of the guanidine tetrafluoroborate crystal is a type II direction. The light-transmitting surface of the type II fourth harmonic device of the guanidine tetrafluoroborate crystal is square with a cross-sectional size of 5mm×5mm and a thickness of 8mm in the light-transmitting direction.

[0063] Example 3

[0064] In this embodiment, the method step ad is performed according to embodiment 1;

[0065] e. Using the Sellmeier equation and a computer program, the type I phase matching curve of the guanidine tetrafluoroborate crystal is calculated. Then, combined with the doubling coefficient, the fourth harmonic phase matching point (θ = 39.1°, φ = 90°) with high conversion efficiency is determined. The guanidine tetrafluoroborate crystal is then cut according to this phase matching direction, and its two light-transmitting surfaces are polished. Finally, a dielectric film is deposited to fabricate the type I fourth harmonic device of the guanidine tetrafluoroborate crystal.

[0066] According to the appendix Figure 4 As shown, the guanidine tetrafluoroborate crystal type I fourth harmonic generation device is placed at position 4. 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 is incident with infrared laser light in the 1.064μm band. The frequency-doubled light generated by the frequency doubling device 2 passes through a filter and directly enters the guanidine tetrafluoroborate crystal fourth harmonic generation device 4 for fourth harmonic conversion, thereby generating a fourth harmonic laser output with a power of 2W. The fourth harmonic output wavelength is 266nm, and the conversion efficiency reaches 10%. The generated fourth harmonic laser with a wavelength of 266nm can be filtered by a beam splitter prism 5 or a filter 6 before being output.

[0067] The phase matching direction during the cutting of the guanidine tetrafluoroborate crystal is a type I direction. The light-transmitting surface of the type I fourth harmonic device of the guanidine tetrafluoroborate crystal is square with a cross-sectional size of 5mm × 5mm and a thickness of 12mm in the light-transmitting direction.

[0068] Example 4

[0069] In this embodiment, the method step ad is performed according to embodiment 1;

[0070] e. Using the Sellmeier equation and a computer program, the type II phase matching curve of the guanidine tetrafluoroborate crystal is calculated. Then, combined with the doubling coefficient, the fourth harmonic phase matching point (θ = 52.7°, φ = 0°) with high conversion efficiency is determined. The guanidine tetrafluoroborate crystal is then cut according to this phase matching direction, and its two light-transmitting surfaces are polished. Finally, a dielectric film is deposited to fabricate the type II fourth harmonic device of the guanidine tetrafluoroborate crystal.

[0071] According to the appendix Figure 4 As shown, the guanidine tetrafluoroborate crystal type II fourth harmonic device is placed at position 4. 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 is incident with infrared laser light in the 1.064μm band. The frequency-doubled light generated by the frequency doubling device 2 passes through a filter and directly enters the guanidine tetrafluoroborate crystal fourth harmonic device 4 for fourth harmonic conversion, thereby generating a fourth harmonic laser output with a power of 1.5W. The fourth harmonic output wavelength is 266nm, and the conversion efficiency reaches 9%. The generated fourth harmonic laser with a wavelength of 266nm can be filtered by a beam splitter prism 5 or a filter 6 before being output.

[0072] The phase matching direction during the cutting of the guanidine tetrafluoroborate crystal is a type II direction. The light-transmitting surface of the type II fourth harmonic device of the guanidine tetrafluoroborate crystal is square with a cross-sectional size of 5mm×5mm and a thickness of 10mm in the light-transmitting direction.

[0073] Those skilled in the art can easily prepare other fourth-frequency devices using guanidine tetrafluoroborate crystals using similar methods, and these are all within the scope and concept of this invention.

Claims

1. A method for fabricating a guanidine tetrafluoroborate crystal fourth harmonic device, characterized in that... 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 N±4.03×d 36 (KDP) d 15 N±1.95×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: 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 the propagation in the corresponding XZ and YZ planes, the formula for the effective frequency doubling coefficient of the GFB crystal cut according to the phase matching angle is as follows: d. The principal refractive index of guanidine tetrafluoroborate 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. Where n o n e λ is the principal axis refractive index of the guanidine tetrafluoroborate crystal, and λ is the incident wavelength in μm. e. Using the Sellmeier equation from step d, the phase matching curves of type I or II of the guanidine tetrafluoroborate crystal are calculated by a computer program. Then, the phase matching points with higher conversion efficiency of the guanidine tetrafluoroborate crystal are determined by combining the doubling coefficients measured in step a. The guanidine tetrafluoroborate crystal is then cut according to the phase matching direction, and the two light-transmitting surfaces are polished and coated with dielectric films to obtain the guanidine tetrafluoroborate crystal fourth-harmonic device.

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