Application of a methylene diboronic acid second-order nonlinear optical crystal material in the field of nonlinear optics

Abstract

The present invention relates to the application of a methylene diboric acid second-order nonlinear optical crystal material in the field of nonlinear optics. The chemical formula of the crystal material is CH6B2O4, the molecular weight is 103.68, it belongs to the tetragonal crystal system, its space group is I41md, the unit cell parameters are α=β=γ=90°, Z=4, and the unit cell volume is . The methylene diboric acid crystal material of the present invention has excellent optical properties. Under 1064nm laser irradiation, the powder frequency harmonic intensity is approximately 0.3 times that of potassium dihydrogen phosphate crystal, and phase matching can be achieved. In addition, the single crystal preparation method of the second-order nonlinear optical material is simple, and its ultraviolet absorption cutoff edge is less than 190nm. These advantages make it have important application potential in the fields of laser frequency conversion, optical information processing, holographic storage, and optical communication.

Description

Technical Field

[0001] The invention belongs to the technical field of nonlinear optical crystal materials and relates to the application of a methylene diboronic acid second-order nonlinear optical crystal material in the field of nonlinear optics. Background Art

[0002] Nonlinear optical (NLO) crystals are important optoelectronic information functional materials and a crucial material foundation for optoelectronic technology, particularly laser technology. Ultraviolet (UV) NLO crystals can utilize their frequency conversion properties to convert visible light and other wavelengths into UV lasers, possessing significant application value in fields such as medicine, communications, and scientific research. Currently, efforts to develop novel UV NLO materials are primarily focused on borate systems, such as β-BaB2O4 (β-BBO) and NH4B4O6F crystals. However, the dangling bonds of the [BO3] unit do not provide a wide deep UV transmittance range, and the small anisotropy of the [BO4] unit limits the birefringence of the crystal. Therefore, developing novel borate crystals that balance optical band gap and birefringence remains a significant challenge.

[0003] Although the molecular formula of CH6B2O4 is known (CAS No.: 13251-32-6), its crystal structure has not been determined, and its linear optical and nonlinear optical properties and applications in the field of nonlinear optics have not been reported. The existing CH6B2O4 synthesis method is to use C 13 H 26 The target product is obtained by post-treatment of the mother liquor after hydrolysis of B2O4 under acidic conditions (Hijazi AbuAli, et al. Organometallics. 2001, 20(18), 3962-3965), but there is no report on the preparation method of single crystals. Summary of the Invention

[0004] The purpose of the present invention is to provide a methylene diboronic acid second-order nonlinear optical crystal material for application in the field of nonlinear optics. The crystal exhibits a moderate frequency response (0.3×KH2PO4(KDP)), a moderate birefringence (0.074@546nm) and a short ultraviolet cutoff edge (<190nm).

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A methylene diboronic acid second-order nonlinear optical crystal material is used in the field of nonlinear optics. The chemical formula of the crystal material is CH6B2O4, the molecular weight is 103.68, it belongs to the tetragonal system, its space group is I41md, and the unit cell parameters are α=β=γ=90°,Z=4,the unit cell volume is

[0007] Furthermore, the chemical formula of the crystalline material is CH6B2O4, the molecular weight is 103.68, it belongs to the tetragonal system, its space group is I41md, and the unit cell parameters are α=β=γ=90°,Z=4。 Further preferably, the unit cell parameters are α=β=γ=90°,Z=4。 Most preferably, the unit cell parameters are α=β=γ=90°, Z=4.

[0008] The crystal structure of methylene diboronic acid of the present invention is as follows Figure 1 As shown in Figure 2, two [CBO2] trigonal planar units share carbon atoms to form a [CH2(B(OH)2)2] group. Each [CH2(B(OH)2)2] group forms a three-dimensional structure with four adjacent [CH2(B(OH)2)2] groups through hydrogen bonds.

[0009] Furthermore, the optical crystal material is composed of [CH2(B(OH)2)2] groups connected to each other through hydrogen bonds to form a three-dimensional framework structure.

[0010] Furthermore, the preparation process of the crystal material is specifically as follows:

[0011] C 13 H 26 B2O4 and water are mixed, and acid is added to form an initial mixed raw material. The mixture is then heated and refluxed until the solution becomes clear and transparent. After cooling, the solvent is naturally evaporated to obtain colorless and transparent millimeter-sized crystals, which are the target compound.

[0012] Furthermore, the heating reflux temperature is 115-125° C. and the time is 4-6 hours.

[0013] Furthermore, the temperature of the naturally evaporating solvent is 25-35° C., and the time is not less than 1 week.

[0014] Furthermore, the acid is hydrochloric acid, and its mass fraction is 36-38%.

[0015] Furthermore, C 13 H 26 The ratio of the added amounts of B2O4, acid and water is 20mmol:(20-30)mL:(100-150)mL.

[0016] More preferably, C 13 H 26 The ratio of added amounts of B2O4, acid and water is 20mmol:25mL:125mL.

[0017] Furthermore, the crystal material is used in laser frequency converters, frequency doubling generators, optical parametric oscillators, optical parametric amplifiers and photoelectric rectifiers.

[0018] Furthermore, when the crystal material is used in a laser frequency converter, it can achieve frequency-doubled output under 1064nm laser irradiation.

[0019] Specifically, under 1064nm laser irradiation, the crystal can output 532nm green light, its powder frequency doubling intensity is about 0.3 times that of KDP crystal, and phase matching can be achieved.

[0020] Based on the hydrolysis reaction of an ester, this invention uses a solution volatilization method to synthesize a deep UV-transmitting second-order nonlinear optical crystal material, methylene diboronic acid. This crystal material exhibits excellent linear and nonlinear optical properties, including a moderate frequency response (0.3×KDP), a moderate birefringence (0.074@546nm), and a short UV absorption cutoff edge (<190nm).

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) This application provides a second-order nonlinear optical crystal, methylene diboronic acid. This crystal material has a large frequency-doubled effect, approximately 0.3 times the frequency-doubled intensity of a KDP crystal under 1064nm laser irradiation, and is capable of phase matching. In addition, the crystal material has an ultraviolet absorption cutoff wavelength of less than 190nm and a wide optical band gap. Therefore, this crystal material has broad application prospects in the field of nonlinear optics.

[0023] (2) This application provides a method for preparing methylenediboric acid single crystals. After the hydrolysis reaction of the ester, colorless and transparent methylenediboric acid crystals are successfully obtained by solution volatilization. This method is simple, requires mild conditions, and can grow millimeter-scale single crystals with high optical quality and purity, which is conducive to large-scale industrial production.

[0024] (3) The methylene diboric acid crystal material provided by the present invention can be applied to a laser frequency converter, which can convert a laser beam into a double frequency harmonic output. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the crystal structure of methylenediboronic acid;

[0026] Figure 2 This is a photo of millimeter-scale crystals of methylenediboronic acid;

[0027] Figure 3Comparison of X-ray diffraction patterns; (a) is the simulated X-ray diffraction pattern of sample 1# based on the crystal structure analyzed based on single crystal X-ray diffraction data; (b) is the pattern obtained by X-ray diffraction testing after sample 1# was ground into powder;

[0028] Figure 4 is the UV-visible light transmission spectrum of sample 1#;

[0029] Figure 5 is the infrared spectrum of sample 1#;

[0030] Figure 6 This is the birefringence test chart of sample 1#;

[0031] Figure 7 This is the second harmonic signal diagram of sample 1# and KDP sample with size ranging from 200 to 280 μm;

[0032] Figure 8 This is the second harmonic phase matching diagram of sample 1# in the 1064nm band. DETAILED DESCRIPTION

[0033] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0034] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0035] Example 1:

[0036] Preparation of samples 1# to 8#

[0037] C 13 H 26 B2O4, water and acid (using hydrochloric acid with a mass fraction of about 37%) are mixed into raw materials in a certain proportion, placed in a three-necked flask, and heated while stirring in a condensation reflux device until a clear and transparent solution is obtained. After cooling, transfer to a beaker and slowly evaporate at room temperature to obtain colorless and transparent methylenediboric acid crystals.

[0038] The relationship between the type and ratio of raw materials in the initial mixture, heating temperature, heating time, volatilization temperature, volatilization time and sample number is shown in Table 1.

[0039] Table 1 Correspondence between samples, raw materials and synthesis conditions

[0040]

[0041] Crystal structure analysis of samples 1# to 8#

[0042] Single crystal X-ray diffraction and powder X-ray diffraction methods were used to perform structural analysis and phase analysis on samples 1# to 8#, respectively.

[0043] Single crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single crystal diffractometer from Germany. The data collection temperature was 298.15 K, and the diffraction light source was graphite monochromatized Mo Kα rays. The scanning mode was ω; the data were processed for absorption correction using the Multi-Scan method. The structure was solved using the Olex2 program package; the positions of heavy atoms were determined by direct method, and the coordinates of the remaining atoms were obtained by difference Fourier synthesis method; the F-based 2 The coordinates of all atoms and anisotropic thermal parameters were refined using the full-matrix least-squares method.

[0044] Single crystal X-ray diffraction results show that samples 1# to 8# have the same chemical formula and crystal structure, the chemical formula is CH6B2O4, the molecular weight is 103.68, and they belong to the tetragonal system. Their space group is I41md and the unit cell parameters are α=β=γ=90°, Z=4.

[0045] Taking sample 1# as a typical representative, its crystal structure data is α=β=γ=90°,Z=4,the crystal structure is as follows Figure 1 shown.

[0046] The powder X-ray diffraction test was carried out on a Bruker D8 X-ray powder diffractometer from Bruker, Germany. The test conditions were a fixed target monochromatic light source Cu Kα, a wavelength of The voltage and current are 40 kV / 20 A, the slits DivSlit / RecSlit / SctSlit are 2.00 deg / 0.3 mm / 2.00 deg respectively, the scanning range is 10-70°, and the scanning step is 0.02°.

[0047] The powder X-ray diffraction test results show that the peak positions of samples 1# to 8# are basically the same.

[0048] Take sample 1# as a typical example. Figure 3 As shown in the figure, according to the crystal structure obtained by single crystal X-ray diffraction analysis, the fitted X-ray diffraction pattern is consistent with the X-ray diffraction pattern measured after sample 1# is ground into powder in terms of peak position and peak intensity, indicating that the obtained sample has a high purity.

[0049] UV-visible light transmission spectrum test

[0050] The UV-visible light transmission spectrum of sample 1# was tested on a Cary 5000 UV-visible-near-infrared spectrophotometer from Agilent Technologies, USA. Figure 4 As shown, the compound has no absorption in the range of 190 to 800 nm. It has a short UV absorption cutoff edge (<190 nm) and an optical band gap greater than 6.52 eV. This wide optical band gap facilitates the generation of second harmonic UV light from fundamental frequency light passing through the crystal.

[0051] Infrared spectrum test

[0052] The infrared spectrum test of sample 1# was conducted on a Nicolet iS10 Fourier infrared spectrometer from Thermo Fisher Scientific Inc., USA. Figure 5 As shown, 1150, 1286, 1370, 3180 cm-1 in the infrared spectrum -1 The characteristic absorption peak at proves the existence of the unit [CH2(B(OH)2)2].

[0053] Birefringence test

[0054] The birefringence of sample 1# was measured using a Zeiss Axioscope A1 polarizing microscope equipped with a Berek compensator. The wavelength of the light source was 546nm. The birefringence can be calculated using the formula:

[0055] ΔR=Δn×T (3)

[0056] ΔR represents the optical path difference, Δn represents the birefringence, and T is the thickness of the crystal. The test results are as follows Figure 6 As shown, the crystal optical path difference is 3.166 μm, the crystal thickness is 42.784 μm, and the birefringence measurement value is calculated to be 0.074.

[0057] Frequency doubling test experiment and results

[0058] The SHG test experiment for sample 1# was conducted as follows: a Q-switched Nd:YAG solid-state laser with a wavelength of 1064 nm was used as the fundamental frequency to illuminate the crystal powder under test. The generated second harmonics were detected using a spectrometer, and the harmonic intensity was displayed using an oscilloscope. The crystal sample and a control KDP crystal were ground separately and sieved using a standard sieve to produce crystals of varying particle sizes: 50-74 μm, 74-105 μm, 105-150 μm, 150-200 μm, and 200-280 μm. The SHG signal intensity was observed as a function of particle size to determine whether phase matching was achieved. Under the same test conditions, the second harmonic intensities generated by the sample and the KDP sample were compared to determine the relative magnitude of the SHG effect.

[0059] The test results show that the methylene diboronic acid crystal has a large frequency doubling effect. Under 1064nm wavelength laser irradiation, the frequency doubling signal intensity is 0.3 times that of the control sample KDP crystal (such as Figure 7 ), phase matching can be achieved (such as Figure 8 ).

[0060] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. An application of a methylene diboronic acid second-order nonlinear optical crystal material in the field of nonlinear optics, characterized in that: The chemical formula of the crystalline material is CH6B2O4, the molecular weight is 103.68, it belongs to the tetragonal system, and its space group is I 41 md , the unit cell parameters are a = b = 10.79~10.97 Å, c = 4.09~4.28 Å, α = β = γ = 90°, Z = 4, the unit cell volume is V = 484.8~501.2 Å 3 .

2. The use of a methylene diboronic acid second-order nonlinear optical crystal material according to claim 1, characterized in that: The preparation process of the crystal material is specifically as follows: C 13 H 26 B2O4 and water are mixed, and acid is added to form an initial mixed raw material. The mixture is then heated and refluxed until the solution becomes clear and transparent. After cooling, the solvent is naturally evaporated to obtain colorless and transparent millimeter-sized crystals, which are the target compound; The reflux temperature is 115~125 o C, time is 4 to 6 hours; The temperature of the natural volatile solvent is 25~35 o C, duration of not less than 1 week; The acid is hydrochloric acid, and its mass fraction is 36-38%; C 13 H 26 The ratio of added B2O4, acid and water is 20 mmol: (20~30) mL: (100~150) mL.

3. The use of a methylene diboronic acid second-order nonlinear optical crystal material according to claim 2, characterized in that: C 13 H 26 The ratio of added amounts of B2O4, acid, and water was 20 mmol: 25 mL: 125 mL.

4. The use of a methylene diboronic acid second-order nonlinear optical crystal material according to claim 1, characterized in that: The crystal material is used in laser frequency converters, frequency doubling generators, optical parametric oscillators, optical parametric amplifiers and photoelectric rectifiers.

5. The use of a methylene diboronic acid second-order nonlinear optical crystal material according to claim 1, characterized in that: When the crystal material is used in a laser frequency converter, it can achieve frequency-doubled output under 1064 nm laser irradiation.

6. The use of a methylene diboronic acid second-order nonlinear optical crystal material according to claim 1, characterized in that: The optical crystal material is composed of [CH2(B(OH)2)2] groups connected to each other through hydrogen bonds to form a three-dimensional framework structure.

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