Lithium 2-hydroxyethanesulfonate second-order nonlinear optical crystal and preparation and application thereof

Abstract

The invention relates to a lithium 2-hydroxyethanesulfonate second-order nonlinear optical crystal and preparation and application thereof. The chemical formula of the crystal material is Li [SO3 (CH2) 2OH], the molecular weight is 132.06, the crystal material belongs to a monoclinic system, the space group is Cc, the cell parameters are alpha = gamma = 90 degrees, beta = 92.04-92.24 degrees, Z = 4, and the cell volume. The lithium 2-hydroxyethanesulfonate crystal has excellent optical performance. In the aspect of nonlinear optical performance, the powder frequency-doubled effect is remarkable: under 1064nm laser irradiation, the intensity is about 3 times of that of KH2PO4 (KDP); under the irradiation of 532 nm laser, the intensity is about 0.45 times of that of beta-BaB2O4 (BBO), and phase matching can be realized under the wavelength. In addition, the crystal has a moderate birefringence (0.06 at-546 nm) and a short ultraviolet absorption cut-off edge (lt; ), and has the characteristic of easy growth. Due to the characteristics, the crystal can effectively expand the wavelength range of a coherent light source through technologies such as second harmonic generation and optical parametric amplification, and has important application prospects in the fields of laser frequency conversion, photoelectric information storage and the like.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optical crystal materials technology, and relates to a second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate and its preparation and application. Background Technology

[0002] Coherent deep ultraviolet (DUV, λ < 200 nm) light sources have wide applications and are crucial in many fields, including laser frequency conversion, high-precision ranging, space communication, biomedicine, and national defense. Currently, the second harmonic generation (SHG) effect based on nonlinear optical (NLO) crystals is one of the most effective ways to generate coherent DUV radiation. Among the many NLO materials used as building blocks, [PO4] is a preferred choice. 3- and [SO4] 2- Non-π conjugated units, represented by [specific unit name], have attracted much attention due to their excellent deep-ultraviolet (DUL) transmittance resulting from their wide bandgap. However, these units typically suffer from polarizability anisotropy and weak hyperpolarizability, leading to insufficient macroscopic second-order nonlinear optical response and limiting their practical applications. To overcome this bottleneck, an effective strategy is to introduce heteroatoms or organic groups into these non-π conjugated units to construct heterotetrahedral structures, thereby enhancing structural anisotropy. However, this modification method easily causes an unfavorable redshift in the optical bandgap, weakening its width and thus impairing the material's transmittance in the DUL region. Therefore, achieving a strong second-harmonic response while maintaining a wide optical bandgap has become a core challenge in the field of DUL Vibration Non-Low-Earth Optical (NLO) materials. Against this backdrop, developing novel NLO crystals that combine deep-ultraviolet transmittance with efficient frequency doubling performance is particularly important. Summary of the Invention

[0003] The purpose of this invention is to provide a second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate, its preparation, and its applications. The unique advantage of this crystal lies in its sulfur-containing heterocoordinate tetrahedron [SO3(CH2)2OH]. - The group serves as the core building block and works synergistically with the alkali metal Li+ to ensure that the crystal has deep ultraviolet transmission capability. It also greatly enhances the macroscopic second-order nonlinear optical effect of the material, exhibiting moderate birefringence (0.06@546nm) and strong frequency doubling effect (3×KDP@1064nm, 0.45×BBO@532nm).

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] In one aspect, the present invention provides a second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate, with the chemical formula Li[SO3(CH2)2OH], a molecular weight of 132.06, belonging to the monoclinic crystal system, with space group Cc, and cell parameters of [missing information]. α=γ=90°, β=92.04~92.24°, Z=4, cell volume is

[0006] Furthermore, the unit cell parameters of the optical crystal are as follows: α = γ = 90°, β = 92.09–92.19°, Z = 4. More preferably, the cell parameters are... α = γ = 90°, β = 92.14–92.15°, Z = 4. Most preferably, the cell parameters are...

[0007] α=γ=90°, β=92.143°(2), Z=4.

[0008] The crystal structure of lithium 2-hydroxyethanesulfonate of the present invention is as follows: Figure 1 As shown. The optical functional unit cell of the crystal material is [SO3(CH2)2OH]. - The central S atom is coordinated with three O atoms and one CH2CH2OH moiety. The SO bond length in this structure is... SC bond length is Li + Through interaction with [SO3(CH2)2OH] - The Li-O bonds between the tetrahedra are interconnected, forming a three-dimensional crystal framework. [SO3(CH2)2OH] - The group greatly enhances the nonlinear optical properties of lithium 2-hydroxyethanesulfonate.

[0009] In a second aspect, the present invention provides a method for preparing a second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate, wherein a lithium source, a sulfur source and water are mixed and stirred continuously to obtain a clear and transparent solution, which is then left to stand in a low-temperature environment, and the colorless and transparent sheet-like target crystal is obtained by natural evaporation of the solvent.

[0010] Furthermore, the addition amounts of lithium source and sulfur source satisfy the following: the molar ratio of Li element to S element is (1~10):(1~10).

[0011] Furthermore, the lithium source is at least one selected from lithium carbonate, lithium chloride, and lithium nitrate. Preferably, the Li source is lithium chloride.

[0012] Furthermore, the sulfur source is at least one selected from sodium 2-hydroxyethanesulfonate and 2-hydroxyethanesulfonic acid. Preferably, the sulfur source is sodium 2-hydroxyethanesulfonate.

[0013] Furthermore, the solvent evaporates at a temperature of 0–10°C.

[0014] Furthermore, the solvent evaporation time should be no less than one week.

[0015] In a third aspect, the present invention provides an application of a second-order nonlinear optical crystal, lithium 2-hydroxyethanesulfonate, in laser frequency converters, optical parametric oscillators, optical parametric amplifiers, and photoelectric rectifiers.

[0016] Furthermore, when lithium 2-hydroxyethanesulfonate second-order nonlinear optical crystal material is used in laser frequency converters, it can output 532nm and 266nm lasers under 1064nm and 532nm laser irradiation.

[0017] This invention utilizes a substitution strategy with sulfur-containing heterocoordinated tetrahedra [SO3(CH2)2OH] - The group serves as the core building block and works synergistically with the alkali metal Li+ to ensure that the crystal has deep ultraviolet transmission capability while greatly enhancing the macroscopic second-order nonlinear optical effect of the material, exhibiting a large birefringence (0.06@546nm) and a strong frequency doubling effect (3×KDP@1064nm, 0.45×BBO@532nm).

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) This application provides a novel second-order nonlinear optical crystal, Li[SO3(CH2)2OH], which exhibits a large frequency doubling effect. Under 1064 nm laser irradiation, its frequency doubling intensity is approximately three times that of a KDP crystal, and under 532 nm laser irradiation, it is approximately 0.45 times that of a BBO crystal, enabling phase matching. Furthermore, this crystal material possesses high transmittance in the 190–800 nm spectral range, with an ultraviolet absorption cutoff wavelength less than 190 nm. Therefore, this crystal material has broad application prospects in the field of ultraviolet nonlinear optics.

[0020] (2) This application provides a method for preparing the nonlinear optical crystal Li[SO3(CH2)2OH], which uses a solution evaporation method to grow colorless, plate-like Li[SO3(CH2)2OH] crystals. The method is simple, the conditions are mild, and it is easy to grow millimeter-scale single crystals.

[0021] (3) The lithium 2-hydroxyethanesulfonate crystal material of the present invention can be applied to laser frequency converters and can be used to output laser beams as second harmonics. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the crystal structure of lithium 2-hydroxyethanesulfonate;

[0023] Figure 2The X-ray diffraction pattern of sample 1-1# obtained by fitting the crystal structure resolved by single-crystal X-ray diffraction is compared with the X-ray diffraction pattern obtained by grinding sample 1-1# into powder.

[0024] Figure 3 This is the ultraviolet-visible light transmission spectrum of sample 1#;

[0025] Figure 4 This is the infrared spectrum of sample 1#;

[0026] Figure 5 This is the thermogravimetric analysis chromatogram of sample 1#;

[0027] Figure 6 The diagram shows the second harmonic signal of sample 1# and KDP sample with dimensions in the range of 150-200 μm.

[0028] Figure 7 The diagram shows the second harmonic signal of sample 1# and BBO sample with dimensions in the range of 150-200 μm.

[0029] Figure 8 This is the second harmonic phase matching diagram of sample 1# at a wavelength of 1064nm.

[0030] Figure 9 This is the second harmonic phase matching diagram of sample 1# at a wavelength of 532nm.

[0031] Figure 10 This is a birefringence test result of sample 1-1# at a wavelength of 546nm. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0033] In the following embodiments, unless otherwise specified, the raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0034] Example 1:

[0035] Preparation of samples 1# to 8#

[0036] Lithium source, sulfur source and water are mixed in a certain proportion to form raw materials, which are placed in a polytetrafluoroethylene liner. After continuous stirring to obtain a clear and transparent solution, the solution is left to stand in a low temperature environment and the solvent is allowed to evaporate naturally to obtain colorless and transparent flaky Li[SO3(CH2)2OH] crystals.

[0037] The relationship between the types and proportions of raw materials, volatilization temperature, volatilization time and sample number in the initial mixture is shown in Table 1.

[0038] Table 1. Correspondence between samples and raw materials and synthesis conditions.

[0039]

[0040]

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

[0042] The structural analysis and phase analysis of samples 1# to 8# were performed using single-crystal X-ray diffraction and powder X-ray diffraction techniques, respectively.

[0043] Single-crystal X-ray diffraction measurements were performed on a Bruker D8 VENTURE CMOS X-ray single-crystal diffractometer (Germany). Data collection was conducted at 100 K, using graphite-monochromatic Mo Kα rays as the diffraction source. The scanning mode was ω; the data underwent absorption correction processing using the Multi-Scan method. Structural analysis was performed using the Olex2 package; the positions of heavy atoms were determined using a direct method, and the coordinates of the remaining atoms were obtained using difference Fourier synthesis; F-based... 2 The full matrix least squares method is used to refine the coordinates and anisotropic thermal parameters of all atoms.

[0044] Single-crystal X-ray diffraction results showed that samples 1# to 8# had the same chemical formula and crystal structure, with the chemical formula Li[SO3(CH2)2OH], a molecular weight of 132.06, belonging to the monoclinic crystal system, with space group Cc and cell parameters of [missing information]. α=γ=90°, β=92.04~92.24°, Z=4.

[0045] Taking sample 1# as a typical example, its crystal structure data is as follows: α=γ=90°, β=92.143°(2), Z=4. The crystal structure of Li[SO3(CH2)2OH] is as follows: Figure 1 As shown.

[0046] Powder X-ray diffraction tests were performed on a Bruker D8 X-ray powder diffractometer from Bruker GmbH, Germany. The test conditions were a fixed target, a monochromatic Cu-Kα light source, and a wavelength of [missing information]. The voltage and current are 40kV / 20A, the slits DivSlit / RecSlit / SctSlit are 2.00deg / 0.3mm / 2.00deg respectively, the scanning range is 10~70°, and the scanning step size 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, while the peak intensities are slightly different.

[0048] Taking sample 1# as a typical example, such as Figure 2 As shown, the peak positions of the fitted X-ray diffraction pattern obtained from the single-crystal X-ray diffraction analysis are consistent with those of the X-ray diffraction pattern obtained after grinding sample #1 into powder. This indicates that the obtained sample has high purity.

[0049] Ultraviolet-Visible Light Transmission Spectroscopy Test

[0050] The UV-Vis transmittance spectrum of sample 1# was measured using an Agilent Technologies Cary 5000 UV-Vis-NIR spectrophotometer. The results are as follows: Figure 3 As shown, the ultraviolet absorption cutoff edge of this compound is less than 190 nm.

[0051] Infrared spectroscopy test

[0052] The infrared spectroscopy of sample 1# was performed using a Nicoleti S10 Fourier transform infrared spectrometer from Thermo Fisher Scientific, Inc., USA. The results are as follows: Figure 4 As shown, in the infrared spectrum (746 cm⁻¹) -1 1031cm -1 1142cm -1 1340cm -1 2898cm -1 The characteristic absorption peaks confirmed the presence of [SO3(CH2)2OH] in the crystal. - The presence of functional groups.

[0053] Thermogravimetric test

[0054] Thermogravimetric analysis (TGA) of sample #1 was performed on a Netzsch STA 409PC thermogravimetric analyzer from Netzsch GmbH, Germany. The results are as follows: Figure 5 As shown, the thermal decomposition temperature of this compound is 274℃.

[0055] Frequency doubling test experiment and results

[0056] The frequency doubling test experiment for sample #1 is as follows: A Q-switched Nd:YAG solid-state laser with a wavelength of 1064 nm was used as the fundamental frequency light to irradiate the test crystal powder. The generated second harmonic intensity was detected by an Ocean Optics Maya2000Pro spectrometer. The crystal sample, standard sample KDP, and standard sample BBO crystals were ground separately and sieved with standard sieves to separate crystals of different particle sizes, with particle size ranges of 26–50, 50–74, 74–105, 105–150, and 150–200 μm, respectively. The variation of the frequency doubling signal with particle size was observed to determine whether phase matching could be achieved. Under the same test conditions, the second harmonic intensity generated by the sample was compared with that of the standard sample KDP and standard sample BBO crystals to obtain the relative magnitude of the sample's frequency doubling effect. Using the same test method, the test crystal powder was irradiated with a fundamental frequency light with a wavelength of 532 nm, and the generated second harmonic intensity was detected by an Ocean Optics Maya2000 Pro spectrometer. Observe the variation of the harmonic signal with particle size to determine whether phase matching can be achieved. Under the same test conditions, compare the second harmonic intensity generated by the sample and the standard sample BBO to obtain the relative magnitude of the harmonic effect of the sample.

[0057] Test results show that the Li[SO3(CH2)2OH] crystal exhibits a significant powder frequency doubling effect; under 1064 nm laser irradiation, the frequency doubling signal intensity is three times that of the KDP crystal (e.g., Figure 6 This crystalline material can achieve phase matching under 1064nm laser irradiation (e.g., Figure 7 Under 532nm laser irradiation, the frequency doubling signal intensity is 0.45 times that of the BBO crystal (e.g., Figure 8 This crystalline material can achieve phase matching under 532nm laser irradiation (e.g., Figure 9 ).

[0058] Crystal birefringence test

[0059] The birefringence properties of crystal sample 1# were measured using a ZEISS AXIO Scope 5 polarizing microscope equipped with a Berek compensator. The light source wavelength was 546 nm. The birefringence was calculated using the following formula:

[0060] ΔR(retardation)=|n e -n o |×T=Δn×T

[0061] In the formula, ΔR represents the optical path difference, Δn represents birefringence, and T represents the crystal thickness. The compensated positive and negative rotations provide a relative delay.

[0062] The results are as follows Figure 10 As shown, Figure 10 Image a shows a Li[SO3(CH2)2OH] crystal after complete extinction achieved using a Berek compensator. The optical path difference (R) is 8.07 μm, and the measured single crystal thickness (T) is 134.54 μm. Figure 10 b). The crystal plane identified by single-crystal XRD analysis is (001)( Figure 10 c). The refractive index difference of the (001) crystal plane at 546 nm was calculated to be 0.06.

[0063] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any 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 invention should be within the protection scope of the present invention.

Claims

1. A second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate, characterized in that, Its chemical formula is Li[SO3(CH2)2OH], its molecular weight is 132.06, it belongs to the monoclinic crystal system, its space group is Cc, and its unit cell parameters are... α=γ=90°, β=92.04~92.24°, Z=4, cell volume is 2. The second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate according to claim 1, characterized in that, The cell parameters of the optical crystal are: α=γ=90°, β=92.09~92.19°, Z=4.

3. The method for preparing a second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate as described in claim 1 or 2, wherein: a lithium source, a sulfur source and water are mixed, and a clear and transparent solution is obtained by continuous stirring. The solution is then left to stand in a low-temperature environment, and a colorless and transparent sheet-like target crystal is obtained by natural evaporation of the solvent.

4. The method for preparing the second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate according to claim 3, characterized in that, The addition amounts of lithium source and sulfur source satisfy the following: the molar ratio of Li element to S element is (1~10):(1~10).

5. The method for preparing the second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate according to claim 3, characterized in that, The lithium source is at least one of lithium carbonate, lithium chloride, and lithium nitrate.

6. The method for preparing the second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate according to claim 3, characterized in that, The S source is at least one of sodium 2-hydroxyethanesulfonate and 2-hydroxyethanesulfonic acid.

7. The method for preparing the second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate according to claim 3, characterized in that, The solvent evaporates at a temperature of 0–15°C.

8. The method for preparing the second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate according to claim 3, characterized in that, The solvent should be allowed to evaporate for at least one week.

9. The application of a second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate as described in claim 1 or 2 in laser frequency converters, optical parametric oscillators, optical parametric amplifiers, and photoelectric rectifiers.

10. The application of the second-order nonlinear optical crystal of lithium 2-hydroxyethanesulfonate according to claim 9, characterized in that, When lithium 2-hydroxyethanesulfonate, a second-order nonlinear optical crystal material, is used in a laser frequency converter, it can output 532nm and 266nm lasers under 1064nm and 532nm laser irradiation, respectively.

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