A nonlinear optical crystal, preparation and application

Abstract

The present invention provides a nonlinear optical crystal, preparation and application. The chemical formula of the nonlinear optical crystal is NaM2PO8, wherein M=Nb, Ta, and it has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and has a space group of Pna21. The room temperature transmission spectrum shows that the nonlinear optical crystal has a wide transmission range (0.4-4.7μm), a transmittance of more than 60%, and almost completely covers the atmospheric window of 3-5μm, and has the advantages of stable physical and chemical properties, good mechanical properties, not easy to deliquesce, easy to cut, polish and preserve. In addition, the powder frequency doubling test results show that the nonlinear optical crystal has a large nonlinear optical effect and a large birefringence. For example, the powder frequency doubling effect of the NaNb2PO8 crystal is 5.3 times that of potassium dihydrogen phosphate, and the nonlinear coefficient d 23 =1.45pm / V,d 22 =0.66pm / V,d 14 =0.88pm / V, Δn=0.1169, and the powder frequency-harmonic effect of NaTa2PO8 crystal is 4.6 times that of potassium dihydrogen phosphate. Therefore, this nonlinear optical crystal is expected to be widely used in mid-infrared nonlinear optical crystal materials for high-power lasers.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal materials, and more specifically to a nonlinear optical crystal, its preparation and application. Background Art

[0002] Lasers in the 3-5μm mid-infrared region have a wide range of applications in industrial and civilian fields, such as laser communications, atmospheric sounding, laser medicine, lidar, laser guidance, and more. An efficient and convenient method for expanding existing infrared laser bands to obtain a wide range of tunable mid-infrared laser output is frequency conversion technology, including optical parametric amplification (OPA), optical parametric oscillator (OPO), difference frequency generation (DFG), and frequency doubling (SHG). The core of frequency conversion technology is infrared nonlinear optical crystals.

[0003] Over the past few decades, a number of high-performance infrared nonlinear optical crystals, including chalcogenides (AgGaX2 (X = S, Se), LiMX2 (M = Ga, In, X = S, Se)) and phosphides (ZnGeP2, CdSiP2), have been reported and commercialized due to their large nonlinear coefficients, wide transmission windows, and ease of growth. However, their low laser damage threshold due to their inherent band gap has seriously hindered their development in the field of high-power lasers. Oxides have attracted widespread attention due to their larger band gaps, high damage thresholds, good physical and chemical properties, and rich structural types, and are considered to be another major branch of the exploration of infrared nonlinear optical crystals.

[0004] Taking β-BaB2O4 (BBO), LiB3O5 (LBO), and KBe2BO3F2 (KBBF) crystals as examples, their UV cutoff edges are all below 200nm, and their applications span the visible, ultraviolet, and even deep ultraviolet regions. However, their infrared cutoff edges do not exceed 4μm. It is worth noting that some oxides, such as LiNbO3 (LN), KNbO3 (KN), KTiOPO4 (KTP), RbTiOPO4 (RTP), KTiOAsO4 (KTA), and RbTiOAsO4 (RTA), have been demonstrated to exhibit laser output in the mid-infrared region. However, each has certain drawbacks. For example, LN and KN crystals have low laser damage thresholds and are sensitive to photorefractive damage. In the KTP family, KTP and RTP have harmonic absorption at 3.5μm. RTA crystals maintain high transmittance in the wavelength range from 0.5μm to 3.6μm, and the transmittance drops sharply after 3.6μm.

[0005] Therefore, in order to solve the above problems, it is of great significance to seek a new mid-infrared nonlinear optical crystal material. Summary of the Invention

[0006] The first object of the present invention is to provide a nonlinear optical crystal having the advantages of a wide transmission range (0.4 to 4.6 μm), high transmittance, and a large nonlinear optical effect.

[0007] The second object of the present invention is to provide a method for preparing the above-mentioned nonlinear optical crystal.

[0008] The third object of the present invention is to provide a method for preparing the above-mentioned nonlinear optical crystal.

[0009] The fourth object of the present invention is to provide a method for preparing the above-mentioned nonlinear optical crystal.

[0010] A fifth object of the present invention is to provide an application of the above nonlinear optical crystal.

[0011] To achieve the first objective, the present invention provides a nonlinear optical crystal having a chemical formula of NaM2PO8, wherein M=Nb, Ta, a non-centrosymmetric structure, an orthorhombic crystal system, and a space group of Pna21;

[0012] When M=Nb, the unit cell parameters are α=90°, β=90°, γ=90°, Z=4,

[0013] When M=Ta, the unit cell parameters are α=90°, β=90°, γ=90°, Z=4,

[0014] According to a specific embodiment of the present invention, the size of the NaM2PO8 (M=Nb, Ta) crystal of the present invention is in the millimeter level. For example, the size of the NaNb2PO8 crystal is (15-20) mm×(13-20) mm×(8-15) mm, for example, 18 mm×16 mm×10 mm; the size of the NaTa2PO8 crystal is (10-16) mm×(9-15) mm×(8-16) mm, for example, 12 mm×13 mm×10 mm.

[0015] According to a specific embodiment of the present invention, the transmittance of the NaNb2PO8 crystal in the wavelength range of 0.4 to 4.7 μm is more than 60%, almost completely covering the atmospheric window of 3 to 5 μm, and has a large nonlinear optical effect and a large birefringence. For example, the powder frequency-harmonic effect of the NaNb2PO8 crystal is 5.3 times that of potassium dihydrogen phosphate, and the nonlinear coefficient d 23 =1.45pm / V,d 22 =0.66pm / V,d14 =0.88pm / V, Δn=0.1169, the powder frequency-harmonic effect of NaTa2PO8 crystal is 4.6 times that of potassium dihydrogen phosphate.

[0016] To achieve the second objective, the present invention provides a method for preparing the nonlinear optical crystal, comprising the following steps:

[0017] The sodium-containing compound, the M-containing compound and the B-containing compound are mixed into raw material powder in proportion, heated in a platinum crucible, pre-calcined, then cooled to room temperature, ground, calcined, and cooled to obtain NaM2PO8 powder;

[0018] The NaM2PO8 powder and flux are evenly mixed to obtain a crystal growth material, and then the crystal growth material is placed in a crystal growth furnace, heated to a molten state, stirred, first cooled to 780-950°C, and then cooled to room temperature for a second time to obtain NaM2PO8 crystals.

[0019] Among them, the pre-burning process is to remove water and carbon dioxide in the raw material powder in preparation for subsequent calcination. The preheating heating rate can be arbitrarily selected within the range of 30 to 50°C / h, such as 30°C / h, 35°C / h, 40°C / h, 45°C / h, and 50°C / h.

[0020] In the preparation process, polycrystalline NaM2PO8 powder is first synthesized through powder solid phase synthesis, and then single crystal NaM2PO8 crystals are prepared through the flux method.

[0021] Furthermore, the rate of the first cooling is 0.5-2°C / h, and the rate of the second cooling is 5-15°C.

[0022] Furthermore, the sodium-containing compound is sodium hydroxide, sodium carbonate, sodium bicarbonate or sodium sulfate with a purity of not less than 99.9%; the M-containing compound is tantalum oxide, tantalum oxalate, niobium oxide or niobium oxalate with a purity of not less than 99.9%; the P-containing compound is diammonium hydrogen phosphate or ammonium dihydrogen phosphate with a purity of not less than 99.9%.

[0023] Furthermore, the molar ratio of sodium:M:P in the raw material powder is 1:2:1.

[0024] Furthermore, the flux is sodium carbonate and ammonium dihydrogen phosphate; the molar ratio of the sodium carbonate to ammonium dihydrogen phosphate is 0.7-1.3:0.7-1.3.

[0025] Furthermore, the molar ratio of the raw material powder to the flux is 0.7-1.4:2-5.

[0026] Furthermore, when M is Nb, the crystal growth temperature is 850-950°C; when M is Ta, the crystal growth temperature is 780-900°C.

[0027] Furthermore, the heating rate of the pre-firing is 30-50°C / h; the pre-firing time is 8-24h; and the pre-firing temperature is 400-600°C.

[0028] Furthermore, when M is Nb, the calcination temperature rise rate is 30 to 50° C. / h; the calcination temperature is 950 to 1000° C.; and the calcination time is 8 to 24 hours.

[0029] Furthermore, when M is Ta, the heating rate of the calcination is 30 to 50° C. / h; the calcination temperature is 900 to 950° C.; and the calcination time is 8 to 24 hours.

[0030] To achieve the third objective, the present invention further provides a method for preparing the nonlinear optical crystal, comprising the following steps:

[0031] The sodium-containing compound, the M-containing compound and the P-containing compound are mixed into raw material powder in proportion, heated in a platinum crucible, pre-calcined, then cooled to room temperature, ground, calcined, and cooled to obtain NaM2PO8 powder;

[0032] NaM2PO8 powder and flux are evenly mixed to obtain a crystal growth material, which is then placed in a crystal growth furnace, heated to a molten state, stirred, cooled to the crystal growth temperature in one stage, and then a seed rod is placed in it. Subsequently, a second stage of cooling is performed while the seed rod is rotated. After the crystal growth is completed, the seed rod is lifted and the crystal attached to the seed rod is lifted off the liquid surface. The NaM2PO8 crystal is obtained by cooling to room temperature in three stages.

[0033] Furthermore, the sodium-containing compound is sodium hydroxide, sodium carbonate, sodium bicarbonate or sodium sulfate with a purity of not less than 99.9%; the M-containing compound is tantalum oxide, tantalum oxalate, niobium oxide or niobium oxalate with a purity of not less than 99.9%; the P-containing compound is diammonium hydrogen phosphate or ammonium dihydrogen phosphate with a purity of not less than 99.9%.

[0034] Furthermore, the molar ratio of sodium:M:P in the raw material powder is 1:2:1.

[0035] Furthermore, the flux is sodium carbonate and ammonium dihydrogen phosphate; the molar ratio of the sodium carbonate to ammonium dihydrogen phosphate is 0.7-1.3:0.7-1.3.

[0036] Furthermore, the molar ratio of the raw material powder to the flux is 0.7-1.4:2-5.

[0037] Furthermore, when M is Nb, the crystal growth temperature is 850-950°C; when M is Ta, the crystal growth temperature is 780-900°C.

[0038] Furthermore, the second stage cooling rate is 0.01-2°C / d; the rotation speed of the seed rod is 20-30rd / min; the crystal growth cycle is 10-30 days; and the third stage cooling rate is 5-15°C / h.

[0039] To achieve the fourth objective, the present invention provides a method for preparing the nonlinear optical crystal, comprising the following steps:

[0040] The sodium-containing compound, the M-containing compound and the P-containing compound are mixed into raw material powder in proportion, mixed with a flux, heated to a molten state in a platinum crucible, and cooled to room temperature to obtain a crystal growth material;

[0041] The crystal growth material is placed in a crystal growth furnace, heated to a molten state, stirred, cooled to the crystal growth temperature in one stage, and then a seed rod is placed in it. Then, a second stage of cooling is performed while the seed rod is rotated. After the crystal growth is completed, the seed rod is lifted and the crystal attached to the seed rod is lifted off the liquid surface. The NaM2PO8 crystal is obtained by cooling to room temperature in three stages.

[0042] Furthermore, the sodium-containing compound is sodium hydroxide, sodium carbonate, sodium bicarbonate or sodium sulfate with a purity of not less than 99.9%; the M-containing compound is tantalum oxide, tantalum oxalate, niobium oxide or niobium oxalate with a purity of not less than 99.9%; the P-containing compound is diammonium hydrogen phosphate or ammonium dihydrogen phosphate with a purity of not less than 99.9%; and the flux is sodium carbonate and ammonium dihydrogen phosphate.

[0043] Furthermore, the molar ratio of sodium:M:P in the raw material powder is 1:2:1.

[0044] Furthermore, the molar ratio of the sodium carbonate to the ammonium dihydrogen phosphate is 0.7-1.3:0.7-1.3.

[0045] Furthermore, the molar ratio of the raw material powder to the flux is 0.7-1.4:2-5.

[0046] Furthermore, when M is Nb, the crystal growth temperature is 850-950°C; when M is Ta, the crystal growth temperature is 780-900°C.

[0047] Furthermore, the second stage cooling rate is 0.01-2°C / d; the rotation speed of the seed rod is 20-30rd / min; the crystal growth cycle is 10-30 days; and the third stage cooling rate is 5-15°C / h.

[0048] To achieve the fifth purpose, the present invention provides an application of the above nonlinear optical crystal in a laser frequency conversion device, a piezoelectric device, a ferroelectric crystal, a pyroelectric crystal or a laser matrix material.

[0049] According to a specific embodiment, the laser frequency conversion device is selected from one of a frequency doubling device, a sum frequency device or a difference frequency device, and the piezoelectric device is selected from one of a piezoelectric oscillator, a filter, a piezoelectric transducer, a piezoelectric pressure sensor, an electroacoustic transducer or an ultrasonic sensor.

[0050] The beneficial effects of the present invention are as follows:

[0051] The present invention provides a nonlinear optical crystal, preparation and application. The chemical formula of the nonlinear optical crystal is NaM2PO8, wherein M=Nb, Ta, and it has a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and has a space group of Pna21. The room temperature transmission spectrum shows that the nonlinear optical crystal has a wide transmission range (0.4-4.7μm), a transmittance of more than 60%, and almost completely covers the atmospheric window of 3-5μm. The transmission range is comparable to that of commercial LN (0.4-5μm), KN (0.4-4.5μm), KTP (0.35-4.5μm), and RTA (0.35-5.2μm), and has the advantages of stable physical and chemical properties, good mechanical properties, not easy to deliquesce, easy to cut, polish and preserve. In addition, the powder frequency doubling test results show that the nonlinear optical crystal has a large nonlinear optical effect and a large birefringence. For example, the powder frequency doubling effect of the NaNb2PO8 crystal is 5.3 times that of potassium dihydrogen phosphate, and the nonlinear coefficient d 23 =1.45pm / V,d 22 =0.66pm / V,d 14 =0.88pm / V, Δn=0.1169, and the powder frequency-harmonic effect of NaTa2PO8 crystal is 4.6 times that of potassium dihydrogen phosphate. Therefore, this nonlinear optical crystal is expected to be widely used in mid-infrared nonlinear optical crystal materials for high-power lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0053] Figure 1 The powder X-ray diffraction spectrum (PXRD) of the NaNb2PO8 powder prepared in Example 1 is shown.

[0054] Figure 2 A schematic structural diagram of the NaNb2PO8 crystal prepared in Example 1 is shown.

[0055] Figure 3 The powder X-ray diffraction spectrum (PXRD) of the NaTa2PO8 powder prepared in Example 2 is shown.

[0056] Figure 4 A schematic structural diagram of the NaTa2PO8 crystal prepared in Example 2 is shown.

[0057] Figure 5 The room temperature transmission spectrum of the NaNb2PO8 crystal prepared in Example 1 is shown.

[0058] Figure 6 A schematic diagram of an optical system of the NaM2BO8 crystal prepared by the present invention as a nonlinear optical device is shown.

[0059] Figure 7 The laser intensity test graphs of the nonlinear optical crystals prepared in Example 1 and Example 2 are shown.

[0060] Among them, Figure 6 In the figure, a is the laser, b is the lens, c is the crystal, d is the prism, e is the doubled frequency light, and f is the fundamental frequency light. DETAILED DESCRIPTION

[0061] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0062] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0063] Example 1

[0064] This example is to prepare and test the single crystal data parameters of NaNb2PO8 crystal. The sample used for preparation is about 2g:

[0065] 0.305 g of Na2CO3, 1.532 g of Nb2O5 and 0.663 g of NH4H2PO4 were mixed in a mortar and ground thoroughly, then placed in a platinum crucible and placed in a muffle furnace; the temperature was raised to 500°C at a rate of 50°C / h for pre-calcination, and the mixture was stirred at a constant temperature for 12 hours and then cooled. After cooling, the sample was taken out and ground and mixed again, and the mixture was placed in a muffle furnace and raised to 980°C at the same temperature rate for calcination and stirred at a constant temperature for 12 hours. After cooling to room temperature, NaNb2PO8 powder was obtained;

[0066] Then put 1.069g of NaNb2PO8 polycrystalline powder, 0.924g of Na2CO3 flux and 1.003g of NH4H2PO4 flux into a mortar, mix them, grind them thoroughly, and obtain crystal growth material. In a platinum crucible;

[0067] The crucible containing the mixed material was then placed in a crystal growth furnace and heated to 1150°C until it was completely melted. The temperature was then lowered at a rate of 1°C / hour to 750°C, and then to room temperature at a rate of 10°C / hour, yielding a colorless, flake-like single crystal. Structural analysis of the resulting crystal confirmed it to be the target NaNb2PO8 crystal.

[0068] Example 2

[0069] This example is to prepare and test the single crystal data parameters of NaTa2PO8 crystal. The sample used for preparation is about 2g:

[0070] 0.174 g Na2CO3, 1.449 g Ta2O5 and 0.377 g NH4H2PO4 were mixed in a mortar and ground thoroughly, then placed in a platinum crucible and placed in a muffle furnace; the temperature was raised to 500°C at a rate of 50°C / h for pre-calcination, and the mixture was stirred at a constant temperature for 12 hours and then cooled. After cooling, the sample was taken out and ground and mixed again, and the mixture was placed in a muffle furnace and raised to 940°C at the same temperature rate for calcination and stirred at a constant temperature for 12 hours. After cooling to room temperature, NaTa2PO8 powder was obtained;

[0071] Then put 1.723g of NaTa2PO8 polycrystalline powder, 0.825g of Na2CO3 flux and 1.114g of NH4H2PO4 flux into a mortar, mix them, grind them thoroughly, and obtain crystal growth material. In a platinum crucible;

[0072] The crucible containing the mixed material was then placed in a crystal growth furnace and heated to 1130°C until it was completely melted. The temperature was then lowered at a rate of 1°C / hour to 730°C, and then to room temperature at a rate of 10°C / hour, yielding a colorless, flaky single crystal. Structural analysis of the resulting crystal confirmed it to be the target NaTa2PO8 crystal.

[0073] Example 3

[0074] The flux is Na2CO3 and NH4H2PO4. Weigh 155.86g Na2CO3, 390.90g Nb2O5, 253.66g NH4H2PO4, put them into a mortar and grind them together. Melt in a platinum crucible to obtain a mixed melt, and cool to room temperature after the melting is completed to obtain a crystal growth material;

[0075] A crucible containing the crystal growth material was placed in a crystal growth furnace, heated to 1150°C, and stirred at a constant temperature for 24 hours to completely melt it; when the temperature was cooled to 904°C in the first stage, a seed rod was placed and extended into the melt; the temperature was cooled in a second stage at a rate of 0.5°C / d, while the seed rod was rotated at a speed of 20rd / min. After the crystal growth was completed (growth cycle: 28 days), the seed rod was lifted and the crystal attached to the seed rod was lifted off the liquid surface, and then the temperature was cooled to room temperature in a third stage at a rate of 10°C / h to obtain NaNb2PO8 crystals with a size of 18mm×16mm×10mm.

[0076] Example 4

[0077] 37.19 g of Na2CO3, 186.53 g of Nb2O5 and 80.72 g of NH4H2PO4 were mixed in a mortar and ground thoroughly. The mixture was then placed in a platinum crucible and placed in a muffle furnace. The mixture was heated to 500°C at a rate of 50°C / h for pre-calcination, stirred at a constant temperature for 12 hours, and then cooled. After cooling, the sample was taken out and ground and mixed again. The mixture was placed in a muffle furnace and heated to 980°C at the same rate for calcination, stirred at a constant temperature for 12 hours, and cooled to room temperature to obtain NaNb2PO8 powder.

[0078] Put 216.34g of NaNb2PO8 polycrystalline powder, 187.04g of Na2CO3 flux and 202.99g of NH4H2PO4 flux into a mortar and grind them. Melt in a platinum crucible to obtain a mixed melt, which is then cooled to room temperature to obtain a crystal growth material;

[0079] The crucible containing the crystal growth material is placed in a crystal growth furnace, heated to 1150°C, and stirred at a constant temperature for 24 hours to completely melt it; when the temperature is cooled to 913.3°C in the first stage, a seed rod is placed and inserted into the melt; the temperature is cooled in the second stage at a rate of 0.5°C / d, while the seed rod is rotated at a speed of 26rd / min. After the crystal growth is completed (the growth cycle is 26 days), the seed rod is lifted, and the crystal attached to the seed rod is lifted off the liquid surface, and then the temperature is cooled to room temperature in the third stage at a rate of 10°C / h to obtain a 16mm×14mm×10mm Ba3Sc2(BO3)4 crystal.

[0080] Example 5

[0081] Weigh 117.77g Na2CO3, 490.99g Ta2O5, 191.72g NH4H2PO4 into a mortar, mix and grind, and add Melt in a platinum crucible to obtain a mixed melt, and cool to room temperature after the melting is completed to obtain a crystal growth material;

[0082] A crucible containing the crystal growth material was placed in a crystal growth furnace, heated to 1030°C, and stirred at a constant temperature for 24 hours to completely melt it; when the temperature was cooled to 887.6°C in the first stage, a seed rod was placed and extended into the melt; the temperature was cooled in a second stage at a rate of 0.5°C / d, while the seed rod was rotated at a speed of 20rd / min. After the crystal growth was completed (growth cycle: 28 days), the seed rod was lifted and the crystal attached to the seed rod was lifted off the liquid surface, and then the temperature was cooled to room temperature in a third stage at a rate of 10°C / h to obtain NaTa2PO8 crystals with a size of 12mm×13mm×10mm.

[0083] Example 6

[0084] 26.50 g of Na2CO3, 220.95 g of Ta2O5 and 57.52 g of NH4H2PO4 were mixed in a mortar and ground thoroughly. The mixture was then placed in a platinum crucible and placed in a muffle furnace. The mixture was heated to 500°C at a rate of 50°C / h for pre-calcination, stirred at a constant temperature for 12 hours, and then cooled. After cooling, the sample was taken out and ground and mixed again. The mixture was placed in a muffle furnace and heated to 940°C at the same rate for calcination, stirred at a constant temperature for 12 hours, and cooled to room temperature to obtain NaTa2PO8 powder.

[0085] 271.88g NaTa2PO8 polycrystalline powder, 158.99g Na2CO3 flux and 172.55g NH4H2PO4 flux were mixed and ground in a mortar, and then added in batches. Melt in a platinum crucible to obtain a mixed melt, which is then cooled to room temperature to obtain a crystal growth material;

[0086] The crucible containing the crystal growth material is placed in a crystal growth furnace, heated to 1040°C, and stirred at a constant temperature for 24 hours to completely melt it; when the temperature is cooled to 893°C in the first stage, a seed rod is placed and extended into the melt; the temperature is cooled in the second stage at a rate of 0.5°C / d, while the seed rod is rotated at a speed of 26rd / min. After the crystal growth is completed (the growth cycle is 26 days), the seed rod is lifted and the crystal attached to the seed rod is lifted off the liquid surface, and then the temperature is cooled to room temperature in the third stage at a rate of 10°C / h to obtain a 10mm×12mm×9mm NaTa2PO8 crystal.

[0087] Experimental Example 1

[0088] The NaNb2PO8 powder obtained in Example 1 was subjected to powder X-ray diffraction test, and the results are shown in FIG. Figure 1 The obtained spectrum is basically consistent with the standard XRD spectrum, which is a polycrystalline powder, proving that the polycrystalline powder of the target NaNb2PO8 has been prepared.

[0089] The NaNb2PO8 crystal prepared in Example 1 was then structurally characterized. The test conditions were: a Mercury CCD single crystal diffractometer, a Mo target, a Kα radiation source (λ = 0.07107 nm), a test temperature of 293 K, and structural elucidation using Shelxtl software. The resulting crystallographic data are shown in Table 1.

[0090] Table 1 is the crystallographic data of NaNb2PO8 crystals prepared in Example 1

[0091]

[0092]

[0093] Experimental Example 2

[0094] The NaTa2PO8 powder obtained in Example 2 was subjected to powder X-ray diffraction test, and the results are shown in FIG. Figure 2 The obtained spectrum is basically consistent with the standard XRD spectrum, which is a polycrystalline powder, proving that the polycrystalline powder of the target NaTa2PO8 has been prepared.

[0095] The NaTa2PO8 crystal prepared in Example 2 was then subjected to structural characterization. The test conditions were: a Mercury CCD single crystal diffractometer, a Mo target, a Kα radiation source (λ = 0.07107 nm), a test temperature of 293 K, and structural elucidation using Shelxtl software. The resulting crystallographic data are shown in Table 2.

[0096] Table 2 is the crystallographic data of NaNb2PO8 crystals prepared in Example 2

[0097]

[0098] Experimental Example 3

[0099] The NaNb2PO8 crystal prepared in Example 3 was cut in a directional manner to obtain a crystal device with a cross-sectional size of 4×4 mm and a length of 6 mm in the light-transmitting direction; the light-transmitting surfaces at both ends of the crystal device were precisely polished and coated. Figure 6 As shown in the optical path system diagram, the infrared light with a wavelength of 1064nm generated by laser a is converged by lens b and incident on crystal c. It then passes through dispersion prism d to obtain frequency-doubled light e and unconverted fundamental frequency light f.

[0100] Experimental Example 4

[0101] The NaTa2PO8 crystal prepared in Example 5 was cut in a directional manner to obtain a crystal device with a cross-sectional size of 4×4 mm and a length of 6 mm in the light-transmitting direction; the light-transmitting surfaces at both ends of the crystal device were precisely polished and coated. Figure 6As shown in the optical path system diagram, the infrared light with a wavelength of 1064nm generated by laser a is converged by lens b and incident on crystal c. It then passes through dispersion prism d to obtain frequency-doubled light e and unconverted fundamental frequency light f.

[0102] Experimental Example 5

[0103] The NaNb2PO8 crystal prepared in Example 3 was placed on an Agilent Cary 7000 UV-vis-NIR spectrometer to test the optical transmission curve in the range of 200nm to 2500nm; and placed on an Excalibur 3100 Fourier transform infrared spectrometer to test the optical transmission curve in the range of 2500nm to 15μm. Figure 5 From the spectral transmission curve, it can be seen that NaNb2PO8 has a wide transmission range (0.4-4.7μm), the ultraviolet cutoff edge is 354nm, and the infrared cutoff edge is 4.7μm.

[0104] Experimental Example 6

[0105] The laser intensity of the NaNb2PO8 crystals prepared in Example 1 was tested according to different particle sizes. The standard sample used KDP (potassium dihydrogen phosphate) crystals of the same particle size range. The incident light source was a 1064nm neodymium ion laser source. The test results are shown in Figure 2. Figure 7 The results show that the laser intensity of the crystal at the largest particle size in the test range is 5.3 times that of KDP at the same particle size, which is verified by theoretical calculations (d 23 =1.45pm / V;d 22 =0.66pm / V;d 14 =0.88pm / V, Δn=0.1169), indicating that the crystal has a large nonlinear optical effect.

[0106] Example 7

[0107] The laser intensity of the NaTa2PO8 crystals prepared in Example 2 was tested according to different particle sizes. The standard sample used KDP (potassium dihydrogen phosphate) crystals of the same particle size range. The incident light source was a 1064nm neodymium ion laser source. The test results are shown in Figure 2. Figure 7 As shown in the figure, the laser intensity of the crystal at the largest particle size in the tested range is 4.7 times that of KDP at the same particle size, indicating that the crystal has a large nonlinear optical effect.

[0108] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A nonlinear optical crystal, characterized in that: The chemical formula is NaM2PO8, where M=Nb,Ta. It is a non-centrosymmetric structure, belongs to the orthorhombic crystal system, and the space group is Pna2 1; When M=Nb, the unit cell parameters are a= 17.9192 (14)Å, b=6.6270(6)Å, c=5.3605(5)Å, α=90°, β=90°, γ=90°, Z=4, V = 636.56(10)Å 3 ; When M=Ta, the unit cell parameters are a= 17.9364(12)Å, b=6.6428(4)Å, c=5.3508(3)Å, α=90°, β=90°, γ=90°, Z=4, V = 637.55(7)Å 3 .

2. A method for preparing a nonlinear optical crystal according to claim 1, characterized in that: The steps include: The sodium-containing compound, the M-containing compound and the P-containing compound are mixed into raw material powder in proportion, heated in a platinum crucible, pre-calcined, cooled to room temperature, ground, calcined, and cooled to obtain NaM2BO8 powder; NaM2PO8 powder and flux are mixed evenly to obtain a crystal growth material, and then the crystal growth material is placed in a crystal growth furnace, heated to a molten state, stirred, cooled to 780~950℃ once, and then cooled to room temperature for a second time to obtain NaM2PO8 crystals.

3. The preparation method according to claim 2, characterized in that The rate of the first cooling is 0.5-2°C / h, and the rate of the second cooling is 5-15°C / h.

4. A method for preparing a nonlinear optical crystal according to claim 1, characterized in that: The steps include: The sodium-containing compound, the M-containing compound and the P-containing compound are mixed into raw material powder in proportion, heated in a platinum crucible, pre-calcined, then cooled to room temperature, ground, calcined, and cooled to obtain NaM2PO8 powder; NaM2PO8 powder and flux are evenly mixed to obtain a crystal growth material, which is then placed in a crystal growth furnace, heated to a molten state, stirred, cooled to the crystal growth temperature in one stage, and then a seed rod is placed in it. Subsequently, a second stage of cooling is performed while the seed rod is rotated. After the crystal growth is completed, the seed rod is lifted and the crystal attached to the seed rod is lifted off the liquid surface. The NaM2PO8 crystal is obtained by cooling to room temperature in three stages.

5. A method for preparing a nonlinear optical crystal according to claim 1, characterized in that: The steps include: The sodium-containing compound, the M-containing compound and the P-containing compound are mixed into raw material powder in proportion, mixed with a flux, heated to a molten state in a platinum crucible, and cooled to room temperature to obtain a crystal growth material; The crystal growth material is placed in a crystal growth furnace, heated to a molten state, stirred, cooled to the crystal growth temperature in one stage, and then a seed rod is placed in it. Then, a second stage of cooling is performed while the seed rod is rotated. After the crystal growth is completed, the seed rod is lifted and the crystal attached to the seed rod is lifted off the liquid surface. The NaM2PO8 crystal is obtained by cooling to room temperature in three stages.

6. The preparation method according to any one of claims 2 to 5, characterized in that The sodium-containing compound is sodium hydroxide, sodium carbonate, sodium bicarbonate or sodium sulfate with a purity of not less than 99.9%; the M-containing compound is tantalum oxide, tantalum oxalate, niobium oxide or niobium oxalate with a purity of not less than 99.9%; the P-containing compound is diammonium hydrogen phosphate or ammonium dihydrogen phosphate with a purity of not less than 99.9%; the flux is sodium carbonate and ammonium dihydrogen phosphate; the molar ratio of sodium:M:P in the raw material powder is 1:2:1; the molar ratio of sodium carbonate and ammonium dihydrogen phosphate is 0.7-1.3:0.7-1.3; and the molar ratio of the raw material powder to the flux is 0.7-1.4:2-5.

7. The preparation method according to any one of claims 2 to 4, characterized in that The heating rate of the pre-sintering is 30-50°C / h; the pre-sintering time is 8-24h; the pre-sintering temperature is 400-600°C; when M is Nb, the heating rate of the sintering is 30-50°C / h; the sintering temperature is 950-1000°C; the sintering time is 8-24h; When M is Ta, the heating rate of the calcination is 30-50° C. / h; the calcination temperature is 900-950° C.; and the calcination time is 8-24 hours.

8. The preparation method according to claim 4 or 5, characterized in that When M is Nb, the crystal growth temperature is 850-950°C; when M is Ta, the crystal growth temperature is 780-900°C.

9. The preparation method according to claim 4 or 5, characterized in that The second-stage cooling rate is 0.01-2°C / d; the rotation speed of the seed rod is 20-30 rd / min; the crystal growth cycle is 10-30 days; and the third-stage cooling rate is 5-15°C / h.

10. Use of the nonlinear optical crystal according to claim 1 in a laser frequency conversion device, a piezoelectric device, a ferroelectric crystal, a pyroelectric crystal or a laser matrix material.

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