Barium tetraborate compound and barium tetraborate non-linear optical crystal, and preparation method and use thereof

Abstract

The present invention relates to a barium tetraborate compound and a barium tetraborate non-linear optical crystal, and a preparation method and use thereof, wherein the chemical formulae of the barium tetraborate compound and the non-linear optical crystal thereof are both BaB.sub.4O.sub.7, with a molecular weight of 292.58; the barium tetraborate non-linear optical crystal has a non-centrosymmetric structure, which belongs to a hexagonal system, and has a space group P6.sub.5 and lattice parameters of a=6.7233(6) , c=18.776(4) , V=735.01(17) .sup.3, and Z=6, wherein the powder frequency-doubled effect thereof is two times that of KDP (KH.sub.2PO.sub.4), and the ultraviolet cut-off edge is lower than 170 nm. The barium tetraborate compound is synthesized by a solid-phase reaction method; the barium tetraborate non-linear optical crystal is grown by a high-temperature molten solution method; and the crystal has a moderate mechanical hardness, is easy to cut, polish and store, and is widely applicable in the non-linear optics of a double-frequency doubling generator, an upper frequency converter, a lower frequency converter or an optical parameter oscillator etc.

Claims

1. A barium tetraborate compound, wherein the compound has a chemical formula of BaB.sub.4O.sub.7 and a molecular weight of 292.58, the compound has a non-centrosymmetric structure, belongs to a hexagonal crystal system, has a space group P6.sub.5, with lattice parameters of a=6.7233(6) , c=18.776(4) , V=735.01(17) .sup.3 and Z=6.

2. A barium tetraborate non-linear optical crystal, wherein the crystal has a chemical formula of BaB.sub.4O.sub.7 and a molecular weight of 292.58, the crystal is non-centrosymmetric, belongs to a hexagonal crystal system, has a space group P6.sub.5, with lattice parameters of a=6.7233(6) , c=18.776(4) , V=735.01(17) .sup.3 and Z=6.

3. A preparation method of the barium tetraborate non-linear optical crystal according to claim 2, wherein a high temperature solution method is utilized for the crystal growth, and the method comprises the following steps: a. a single-phase polycrystalline powder of the barium tetraborate prepared by a solid-phase reaction method is uniformly mixed with a flux to obtain a mixture; the mixture is heated to 720-820 C. at a rate of 1-50 C./h and held at this temperature for 1-100 hours to obtain a mixed melt liquid, which is then cooled to 650-750 C. to obtain a mixed melt liquid of barium tetraborate and flux; b. the mixed melt liquid obtained in Step (a) is slowly cooled to room temperature at a rate of 0.5-10 C./h, allowing for crystallization to obtain a seed crystal, or using a platinum wire suspension method during cooling to obtain a small crystal as barium tetraborate seed crystal; c. the seed crystal obtained in Step (b) is fixed to a seed crystal rod and descended from a top of a crystal growing furnace, the seed crystal is preheated for 5-60 minutes, and then descended underneath the mixed melt liquid of barium tetraborate and flux to allow for meltback, and mixed melt liquid held at a constant temperature for 5-60 minutes, and then cooled to 640-740 C.; d. the mixed melt liquid is cooled down at a rate of 0.1-5 C./day; the seed crystal rod is rotated at a rotation speed of 0-100 rpm to allow for crystal growth; when a monocrystal is grown to a desired size, the crystal is drawn out of a liquid surface, and cooled to room temperature at a rate of 1-100 C./h; the crystal is then taken out from the furnace to obtain the barium tetraborate non-linear optical crystal; in Step (a), a molar ratio of the barium tetraborate to the flux is 1:1-6; said flux is PbF.sub.2H.sub.3BO.sub.3, BaF.sub.2H.sub.3BO.sub.3, NaFH.sub.3BO.sub.3, PbOH.sub.3BO.sub.3 or PbOPbF.sub.2; in said flux PbF.sub.2H.sub.3BO.sub.3, BaF.sub.2H.sub.3BO.sub.3, NaFH.sub.3BO.sub.3 and PbOH.sub.3BO.sub.3, a molar ratio of PbF.sub.2, BaF.sub.2, NaF or PbO to H.sub.3BO.sub.3 is 1-6:1-4, and in said flux PbOPbF.sub.2, a molar ratio of PbO to PbF.sub.2 is 1-3:1-4.

4. The preparation method of the barium tetraborate non-linear optical crystal according to claim 3, wherein the barium tetraborate in Step (a) is substituted by a barium-containing compound, and said barium-containing compound is BaCO.sub.3, Ba(OH).sub.2, BaO, Ba(NO.sub.3).sub.2 or Ba(HCO.sub.3).sub.2.

5. The preparation method of the barium tetraborate non-linear optical crystal according to claim 3, the seed crystal in Step (c) is fixed to the seed crystal rod in any orientation.

6. A use of the barium tetraborate non-linear optical crystal according to claim 2, wherein the crystal is used to prepare a frequency doubling generator, an upper frequency converter, a lower frequency converter or an optical parametric oscillator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an X-ray diffraction pattern of the barium tetraborate compound of the present invention, which is the phase characteristic profile analysis of the barium tetraborate compound. Each compound has a unique XRD profile. After the barium tetraborate compound of the present invention is subjected to qualitative analysis, the peak intensity of the XRD profile shown in FIG. 1 corresponds to the total number of electrons in atoms, the greater number of electrons, the stronger peak intensity; the diffraction angle of the XRD profile corresponds to the distance between atomic layers, large distance between atomic layers corresponding to low angle while small distance corresponding to high angle.

(2) FIG. 2 is a diagram of working principle of the barium tetraborate crystal non-linear optical device of the present invention, wherein 1 is a laser generator, 2 is a convex lens, 3 is the barium tetraborate non-linear optical crystal, 4 is a beam splitter prism and 5 is a filter, and is refracted light frequency, equal to incident light frequency or 2 times as much as incident light frequency.

EXAMPLES

(3) The present invention will be described in details hereinafter in combination of the accompanying drawings.

Example 1

(4) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
BaCO.sub.3+4H.sub.3BO.sub.3.fwdarw.BaB.sub.4O.sub.7+CO.sub.2+6H.sub.2O

(5) BaCO.sub.3 and H.sub.3BO.sub.3 were placed in a mortar at a molar ratio of 1:4, and then mixed and ground carefully. The mixture was charged into a 100 mm100 mm open-mouth corundum crucible which was then loaded into a muffle furnace. The muffle furnace was heated to 500 C. slowly, held at this temperature for 24 hours and cooled to room temperature. The mixture was taken out and ground carefully, and then compacted and placed back to the muffle furnace, which was heating to 780 C. and held at this temperature for 72 hours. The single-phase polycrystalline powder of the completely sintered barium tetraborate compound was obtained after grinding and then taken out. The product was subjected to X-ray assay to get a X-ray profile in correspondence with the X-ray profile of the barium tetraborate in a monocrystal structure.

(6) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux PbF.sub.2H.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:PbF.sub.2H.sub.3BO.sub.31:1. The mixture was charged into a 60 mm60 mm open-mouth platinum crucible. The platinum crucible was heated to 800 C., held at this temperature for 1 hour, and then cooled to 740 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was PbF.sub.2:H.sub.3BO.sub.3=1:2.

(7) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 0.5 C./h, allowing for crystallization to obtain a small crystal as the barium tetraborate seed crystal.

(8) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 5 minutes, and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 5 minutes and then quickly cooled to 730 C.

(9) The mixed melt liquid was slowly cooled down at a rate of 5 C./day. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 1 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 24 mm18 mm15 mm.

(10) The barium-containing compound can be substituted by Ba(OH).sub.2, BaO, Ba(NO.sub.3).sub.2 or Ba(HCO.sub.3).sub.2, while boric acid can be substituted by boron trioxide.

Example 2

(11) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
Ba(OH).sub.2+4H.sub.3BO.sub.3.fwdarw.BaB.sub.4O.sub.7+7H.sub.2O
and the specific operation as described in Example 1.

(12) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux BaF.sub.2H.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:BaF.sub.2H.sub.3BO.sub.3=1:2. The mixture was charged into a 80 mm80 mm open-mouth platinum crucible. The platinum crucible was heated to 820 C., held at this temperature for 20 hours, and then cooled to 750 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was BaF.sub.2:H.sub.3BO.sub.3=1:4.

(13) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 10 C./h. The platinum wire suspension method was used during cooling to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(14) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 60 minutes, and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 30 minutes and then quickly cooled to 740 C.

(15) The mixed melt liquid was slowly cooled down at a rate of 0.1 C./day. The seed crystal rod was rotated at a rotation speed of 30 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 100 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 35 mm24 mm20 mm.

(16) The barium-containing compound can be substituted by BaCO.sub.3, BaO, Ba(NO.sub.3).sub.2 or Ba(HCO.sub.3).sub.2, while boric acid can be substituted by boron trioxide.

Example 3

(17) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
BaO+4H.sub.3BO.sub.3.fwdarw.BaB.sub.4O.sub.7+6H.sub.2O
and the specific operation as described in Example 1.

(18) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux NaFH.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:NaFH.sub.3BO.sub.3=1:3. The mixture was charged into a 100 mm100 mm open-mouth platinum crucible. The platinum crucible was heated to 750 C., held at this temperature for 50 hours, and then cooled to 700 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was NaF:H.sub.3BO.sub.3=4:1.

(19) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 3 C./h, allowing for crystallization to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(20) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 30 minutes and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 60 minutes and then quickly cooled to 690 C.

(21) The mixed melt liquid was slowly cooled down at a rate of 2 C./day. The seed crystal rod was rotated at a rotation speed of 100 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 10 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 27 mm24 mm13 mm.

(22) The barium-containing compound can be substituted by BaCO.sub.3, Ba(OH).sub.2, Ba(NO.sub.3).sub.2 or Ba(HCO.sub.3).sub.2, while boric acid can be substituted by boron trioxide.

Example 4

(23) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
2Ba(NO.sub.3).sub.2+8H.sub.3BO.sub.3.fwdarw.2BaB.sub.4O.sub.7+4NO.sub.2+O.sub.2+12H.sub.2O
and the specific operation as described in Example 1.

(24) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux PbOH.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:PbOH.sub.3BO.sub.3=1:3. The mixture was charged into a 100 mm100 mm open-mouth platinum crucible. The platinum crucible was heated to 750 C., held at this temperature for 50 hours, and then cooled to 700 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was PbO:H.sub.3BO.sub.3=3:2.

(25) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 7 C./h. The platinum wire suspension method was used during cooling to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(26) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 35 minutes, and then descended underneath the surface of the mixed melt liquid of the barium tetraborate and flux. The mixed melt liquid was held at the temperature for 60 minutes and then quickly cooled to 690 C.

(27) The mixed melt liquid was slowly cooled down at a rate of 5 C./day. The seed crystal rod was rotated at a rotation speed of 100 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 50 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 19 mm15 mm8 mm.

(28) The barium-containing compound can be substituted by BaCO.sub.3, Ba(OH).sub.2, BaO or Ba(HCO.sub.3).sub.2, while boric acid can be substituted by boron trioxide.

Example 5

(29) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
Ba(HCO.sub.3).sub.2+4H.sub.3BO.sub.3.fwdarw.BaB.sub.4O.sub.7+2CO.sub.2+7H.sub.2O
and the specific operation as described in Example 1.

(30) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux PbOPbF.sub.2 at a molar ratio of BaB.sub.4O.sub.7:PbOPbF.sub.2=1:6. The mixture was charged into a 80 mm80 mm open-mouth platinum crucible. The platinum crucible was heated to 720 C., held at this temperature for 70 hours, and then cooled to 650 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was PbO:PbF.sub.2=3:1.

(31) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 8 C./h, allowing for crystallization to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(32) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 50 minutes and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 40 minutes and then quickly cooled to 640 C.

(33) The mixed melt liquid was slowly cooled down at a rate of 1.5 C./day. The seed crystal rod was rotated at a rotation speed of 40 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 70 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 34 mm28 mm19 mm.

(34) The barium-containing compound can be substituted by BaCO.sub.3, Ba(OH).sub.2, BaO or Ba(NO.sub.3).sub.2, while boric acid can be substituted by boron trioxide.

Example 6

(35) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
BaCO.sub.3+2B.sub.2O.sub.3.fwdarw.BaB.sub.4O.sub.7+CO.sub.2
and the specific operation as described in Example 1.

(36) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux PbF.sub.2H.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:PbF.sub.2H.sub.3BO.sub.3=1:5. The mixture was charged into a 60 mm60 mm open-mouth platinum crucible. The platinum crucible was heated to 780 C., held at this temperature for 60 hours, and then cooled to 730 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was PbF.sub.2:H.sub.3BO.sub.3=1:4.

(37) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 5.5 C./h. The platinum wire suspension method was used during cooling to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(38) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 40 minutes, and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 20 minutes and then quickly cooled to 720 C.

(39) The mixed melt liquid was slowly cooled down at a rate of 0.1 C./day. The seed crystal rod was rotated at a rotation speed of 30 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 20 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 38 mm27 mm24 mm.

(40) The barium-containing compound can be substituted by Ba(HCO.sub.3).sub.2, Ba(OH).sub.2, BaO or Ba(NO.sub.3).sub.2, while boron trioxide can be substituted by boric acid.

Example 7

(41) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
Ba(OH).sub.2+2B.sub.2O.sub.3.fwdarw.BaB.sub.4O.sub.7+H.sub.2O
and the specific operation as described in Example 1.

(42) The barium tetraborateBaB.sub.4O.sub.7 compound synthesized was mixed with a flux PbF.sub.2H.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:PbF.sub.2H.sub.3BO.sub.3=1:5. The mixture was charged into a 70 mm70 mm open-mouth platinum crucible. The platinum crucible was heated to 770 C., held at this temperature for 90 hours, and then cooled to 710 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was PbF.sub.2:H.sub.3BO.sub.3=2:3.

(43) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 3.5 C./h, allowing for crystallization to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(44) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 10 minutes and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 40 minutes and then quickly cooled to 700 C.

(45) The mixed melt liquid was slowly cooled down at a rate of 10 C./day. The seed crystal rod was rotated at a rotation speed of 5 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 5 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 15 mm13 mm8 mm.

(46) The barium-containing compound can be substituted by Ba(HCO.sub.3).sub.2, BaCO.sub.3, BaO or Ba(NO.sub.3).sub.2, while boron trioxide can be substituted by boric acid.

Example 8

(47) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
BaO+2B.sub.2O.sub.3.fwdarw.BaB.sub.4O.sub.7
and the specific operation as described in Example 1.

(48) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux NaFH.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:NaFH.sub.3BO.sub.3=2:5. The mixture was charged into a 50 mm50 mm open-mouth platinum crucible. The platinum crucible was heated to 800 C., held at this temperature for 20 hours, and then cooled to 740 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was NaFH.sub.3BO.sub.3=4:3.

(49) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 7 C./h. The platinum wire suspension method was used during cooling to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(50) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 25 minutes, and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at this temperature for 30 minutes and then quickly cooled to 730 C.

(51) The mixed melt liquid was cooled down at a rate of 1.5 C./day. The seed crystal rod was rotated at a rotation speed of 55 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 35 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 22 mm17 mm11 mm.

(52) The barium-containing compound can be substituted by Ba(HCO.sub.3).sub.2, BaCO.sub.3, Ba(OH).sub.2 or Ba(NO.sub.3).sub.2, while boron trioxide can be substituted by boric acid.

Example 9

(53) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
2Ba(NO.sub.3).sub.2+4B.sub.2O.sub.3.fwdarw.2BaB.sub.4O.sub.7+4NO.sub.2+O.sub.2
and the specific operation as described in Example 1.

(54) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux PbOH.sub.3BO.sub.3 at a molar ratio of BaB.sub.4O.sub.7:PbOH.sub.3BO.sub.3=1:1. The mixture was charged into a 90 mm90 mm open-mouth platinum crucible. The platinum crucible was heated to 750 C., held at this temperature for 70 hours, and then cooled to 690 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was PbOH.sub.3BO.sub.3=5:4.

(55) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 7.5 C./h, allowing for crystallization to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(56) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 45 minutes and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 20 minutes and then quickly cooled to 680 C.

(57) The mixed melt liquid was slowly cooled down at a rate of 2.5 C./day. The seed crystal rod was rotated at a rotation speed of 80 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 60 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 38 mm26 mm19 mm.

(58) The barium-containing compound can be substituted by Ba(HCO.sub.3).sub.2, BaCO.sub.3, Ba(OH).sub.2 or BaO, while boron trioxide can be substituted by boric acid.

Example 10

(59) The BaB.sub.4O.sub.7 compound was prepared according to the reaction equation:
Ba(HCO.sub.3).sub.2+2B.sub.2O.sub.3.fwdarw.BaB.sub.4O.sub.7+2CO.sub.2+H.sub.2O
and the specific operation as described in Example 1.

(60) The barium tetraborate BaB.sub.4O.sub.7 compound synthesized was mixed with a flux PbOPbF.sub.2 at a molar ratio of BaB.sub.4O.sub.7:PbOPbF.sub.2=1:3. The mixture was charged into a 60 mm60 mm open-mouth platinum crucible. The platinum crucible was heated to 780 C., held at this temperature for 30 hours, and then cooled to 720 C. to obtain a mixed melt liquid of barium tetraborate and flux, wherein the molar ratio of the flux was PbOPbF.sub.2=1:4.

(61) The mixed melt liquid obtained was slowly cooled to room temperature at a rate of 8 C./h. The platinum wire suspension method was used during cooling to obtain a small crystal as the barium tetraborate BaB.sub.4O.sub.7 seed crystal.

(62) The seed crystal obtained was fixed to a seed crystal rod in any orientation and descended from the top of a crystal growing furnace. The seed crystal was preheated for 15 minutes and then descended underneath the surface of the mixed melt liquid of barium tetraborate and flux. The mixed melt liquid was held at the temperature for 50 minutes and then quickly cooled to 710 C.

(63) The mixed melt liquid was slowly cooled down at a rate of 0.5 C./day. The seed crystal rod was rotated at a rotation speed of 5 rpm to allow for crystal growth. When the monocrystal stopped growing, the crystal was drawn out of the liquid surface, and cooled to room temperature at a rate of 10 C./h. The crystal was then taken out from the furnace to obtain a barium tetraborate BaB.sub.4O.sub.7 non-linear optical crystal at a size of 18 mm12 mm9 mm.

(64) The barium-containing compound can be substituted by Ba(NO.sub.3).sub.2, BaCO.sub.3, Ba(OH).sub.2 or BaO, while boron trioxide can be substituted by boric acid.

Example 11

(65) Any one of the crystals obtained in Examples 1-10 was arranged at the position (3) as shown in FIG. 2. At room temperature, when a Q-switched Nd:YAG laser generator, setting at 1,064 nm, was used as light source, it was observed that clear frequency-doubled green light in 532 nm was output, the output intensity of which was equivalent to twice of that of KDP. As shown in FIG. 2, Q-switched Nd:YAG laser generator 1 emitted an infrared light at a wavelength of 1,064 nm, which then entered the BaB.sub.4O.sub.7 non-linear optical crystal after passing through the convex lens 2, and then a frequency-doubled green light at a wavelength of 532 nm was generated. The output light beam from dispersion prism 4 comprised both the infrared light at a wavelength of 1,064 nm and the green light at wavelength of 532 nm. After filtration by filter 5, the frequency-doubled light at a wavelength of 532 nm was obtained.