BISMUTH AND MAGNESIUM CO-DOPED LITHIUM NIOBATE CRYSTAL, PREPARATION METHOD THEREOF AND APPLICATION THEREOF

Abstract

A bismuth and magnesium co-doped lithium niobate crystal includes Li.sub.2CO.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3 and MgO, wherein the molar ratio of [Li] and [Nb] is 0.90-1.00, the molar percentage of Bi.sub.2O.sub.3 in the mixture is 0.25-0.80%, and the molar percentage of MgO in the mixture is 3.0-7.0%. The bismuth and magnesium co-doped lithium niobate crystal has enhanced photorefraction, improved photorefractive sensitivity, shortened holographic grating saturation writing time, and the photorefractive diffraction efficiency can reach up to 17%. The response time is only 170 ms, when the holographic storage experiment is carried out using 488 nm continuous laser. Therefore, this crystal can be used in the field of holographic imaging.

Claims

1. A bismuth and magnesium co-doped lithium niobate crystal, comprising: a mixture of Li.sub.2CO.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3 and MgO, wherein molar ratio of [Li] and [Nb] is 0.90-1.00, wherein molar percentage of Bi.sub.2O.sub.3 in the mixture is 0.25-0.80%, and wherein the molar percentage of MgO in the mixture is 3.0-7.0%.

2. The bismuth and magnesium co-doped lithium niobate crystal, according to claim 1, wherein purity of Li.sub.2CO.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O and MgO is 99.99%.

3. A method for preparing bismuth and magnesium co-doped lithium niobate crystal, the method comprising the following steps: mixing the powders of Li.sub.2CO.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3 and MgO by grinding with a planetary ball mill, wherein molar ratio of [Li] and [Nb] is 0.90-1.00, wherein molar percentage of Bi.sub.2O.sub.3 in the mixture is 0.25-0.80%, and wherein molar percentage of MgO in the mixture is 3.0-7.0%, keeping the mixture at a constant temperature of 850° C. to decompose Li.sub.2CO.sub.3; calcining at 1150° C. to make the mixed materials take place full solid phase reaction so as to form a powder of bismuth and magnesium co-doped lithium niobate; compacting the powder of bismuth and magnesium co-doped lithium niobate; placing into a platinum crucible; and heating with medium-frequency induction so as to form bismuth and magnesium co-doped lithium niobate crystal along a C-axis direction by Czochralski method.

4. The method for preparing the bismuth and magnesium co-doped lithium niobate crystal, according to claim 3, wherein the step of mixing the powders has a rotating speed of the ball mill of 250-320 r/min, and a grinding time of 2-3 hours, wherein the step of keeping the mixture at the constant temperature is 2-3 hours, and wherein the step of calcining is 6-10 hours.

5. A The method for preparing the bismuth and magnesium co-doped lithium niobate crystal, according to claim 3, wherein process parameters for the Czochralski method are: pulling rate of 0.5-1.0 mm/h, rotating speed of 6-10 r/min, temperature gradient in the melt of 0.5-2.0° C./mm, and temperature gradient above the melt of 0.5-2.0° C./mm.

6. A bismuth and magnesium co-doped lithium niobate crystal for application in at least one of a group consisting of: laser frequency conversion, parametric oscillation, Q-switch, electro-optical modulation, holographic storage, and holographic display.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0021] FIG. 1 is a schematic view of the diagram of change of the photorefractive diffraction efficiency of the lithium niobate crystals according to the present invention.

[0022] FIG. 2 is a schematic view of the diagram of change of the photorefractive response time of the lithium niobate crystals according to the present invention.

[0023] FIG. 3 is a schematic view of the diagram of the optical damage resistance experiment of the lithium niobate crystals according to the present invention: wherein, the legend (a) shows the original spot as control, the light intensity in the legends (a), (c) and (d) is 5.8×10.sup.6 mw/cm.sup.2; the light intensity in the legend (b) is 7.8×10.sup.2 mw/cm.sup.2.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The principles and features of the present invention will be described below in combination with the embodiments, the examples listed are only used to explain the present invention, but not to limit the scope of the present invention.

Embodiment 1

[0025] A bismuth and magnesium co-doped lithium niobate crystal, which is prepared by the following steps:

[0026] 1) Li.sub.2CO.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3 and MgO with purity of 99.99% are weighed for formulating, wherein the molar ratio of [Li] and [Nb] is 0.90, the molar percentage of Bi.sub.2O.sub.3 in the mixture is 0.25%, the molar percentage of MgO in the mixture is 3.0%, the mixture is mixed by grinding sufficiently with a planetary ball mill at 250 r/min for 2 hours, then it is kept at a constant temperature of 850° C. for 2 hours to decompose Li.sub.2CO.sub.3 sufficiently, calcined at 1150° C. for 6 hours to make the mixed materials take place full solid phase reaction, such that the powder of bismuth and magnesium co-doped lithium niobate can be obtained;

[0027] 2) The powder prepared from the step is compacted, put into a platinum crucible and heated with medium-frequency induction, then the bismuth and magnesium co-doped lithium niobate crystal is grown along the C-axis direction following the procedures of seeding, pulling neck, diameter enlarging, diameter equaling and ending by Czochralski method; process parameters are: pulling rate of 1.0 mm/h, rotating speed of 6 r/min, temperature gradient in the melt of 0.5-2.0° C./mm, and temperature gradient above the melt of 0.5-2.0° C./mm.

[0028] The crystal obtained by Czochralski method is annealed at 1190° C. for single domain, orientation, cutting and polishing process, to be made 3 mm and 1 mm-thickness plates and optical grade polished in the y-direction. The photorefractive experiment of lithium niobate crystal.

[0029] Employ the continuous laser of 532 nm or 488 nm at 400 mw/cm.sup.2 to carry out the photorefractive experiment of lithium niobate crystal, the test results (as shown in FIG. 1 and FIG. 2) indicated that: the holographic diffraction efficiencies are 0.87% and 3.45%, respectively. The photorefractive response times are 8 s and 5 s, respectively; and the photorefractive sensitivities are 0.094 cm.sup.2/J and 0.097 cm.sup.2/J, respectively. Compared to the congruent lithium niobate(CLN)crystal, the crystal of the present invention had advantages of enhanced photorefraction, shortened response time, and improved sensitivity. Meanwhile, the spot distortion method is used to carry out the optical damage resistance ability test of lithium niobate crystal, the results (as shown in FIG. 3 (b) indicated that: the optical damage resistance threshold of the crystal is 7.8×10.sup.2 W/cm.sup.2.

Embodiment 2

[0030] A bismuth and magnesium co-doped lithium niobate crystal, which is prepared by the following steps:

[0031] 1) Li.sub.2CO.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3 and MgO with purity of 99.99% are weighed for formulating, wherein the molar ratio of [Li] and [Nb] is 0.94, the molar percentage of Bi.sub.2O.sub.3 in the mixture is 0.5%, and the molar percentage of MgO in the mixture is 5.0%, the mixture is mixed by grinding sufficiently with a planetary ball mill at 320 r/min for 3 hours, then it is kept at 850° C. for 3 hours to decompose Li.sub.2CO.sub.3 sufficiently, calcined at 1150° C. for 10 hours to make the mixed materials take place full solid phase reaction, such that the powder of bismuth and magnesium co-doped lithium niobate can be obtained.

[0032] 2) The powder of the bismuth and magnesium co-doped lithium niobate prepared from the step 1) is compacted, put into a platinum crucible and heated with medium-frequency induction, then the bismuth and magnesium co-doped lithium niobate crystal is grown along the C-axis direction following the procedures of seeding, pulling neck, diameter enlarging, diameter equaling and ending by Czochralski method. Process parameters are: pulling rate of 1.0 mm/h, rotating speed of 8 r/min, temperature gradient in the melt of 0.5-2.0° C./mm, and temperature gradient above the melt of 0.5-2.0° C./mm.

[0033] 3) The bismuth and magnesium co-doped lithium niobate crystal obtained from the step 2) is annealed at 1190° C. for single domain, orientation, cutting and polishing process, to be made into 3 mm and 1 mm-thickness plates and optical grade polished in the y-direction. The photorefractive experiment of lithium niobate crystal is carried out with continuous laser of 532 nm or 488 nm at 400 mw/cm.sup.2, the test results (as shown in FIG. 1 and FIG. 2) indicated that: the holographic diffraction efficiencies are 5.01% and 17.24%, respectively; the response times are 1.8 s and 1 s, respectively; and the photorefractive sensitivities are 1.04 cm.sup.2/J and 3.46 cm.sup.2/J, respectively. Compared to the iron-doped lithium niobate crystal, the photorefractive response time of the crystal of the present invention is shortened by one order of magnitude, and the photorefractive sensitivity is improved by two orders of magnitude. The results of the optical damage resistance ability test (as shown in FIG. 3 (c)) indicated that: the optical damage resistance threshold of the crystal is 5.8×10.sup.6 W/cm.sup.2, thus this crystal can be used for application in the field of high light intensity and density of holographic storage.

Embodiment 3

[0034] A bismuth and magnesium co-doped lithium niobate crystal, which is prepared by the following steps:

[0035] 1) Li.sub.2CO.sub.3, Nb.sub.2O.sub.5, Bi.sub.2O.sub.3 and MgO with purity of 99.99% are weighed for formulating, wherein the molar ratio of [Li] and [Nb] is 1.00, the molar percentage of Bi.sub.2O.sub.3 in the mixture is 0.5%, the molar percentage of MgO in the mixture is 6.0%, the mixture is mixed by grinding sufficiently with a planetary ball mill at 320 r/min for 3 hours, then it is kept at a constant temperature of 850° C. for 3 hours to decompose Li.sub.2CO.sub.3 sufficiently, calcined at 1150° C. for 10 hours to make the mixed materials take place full solid phase reaction, such that the powder of bismuth and magnesium co-doped lithium niobate can be obtained;

[0036] 2) The powder of the bismuth and magnesium co-doped lithium niobate prepared from the step 1) is compacted, put into a platinum crucible and heated with medium-frequency induction, then the bismuth and magnesium co-doped lithium niobate crystal is grown along the C-axis direction following the procedures of seeding, pulling neck, diameter enlarging, diameter equaling and ending by Czochralski method; process parameters are: pulling rate of 0.5 mm/h, rotating speed of 10 r/min, temperature gradient in the melt of 0.5-2.0° C./mm, and temperature gradient above the melt of 0.5-2.0° C./mm.

[0037] The crystal obtained from the step 2) by Czochralski method is annealed at 1190° C. for single domain, orientation, cutting and polishing process, to be made into 3 mm and 1 mm-thickness optical grade polished plates in the y-direction. The photorefractive experiment of the bismuth and magnesium co-doped lithium niobate is carried out under the same experimental conditions as Embodiment 1, the test results (as shown in FIG. 1 and FIG. 2) indicated that: the photorefractive diffraction efficiencies are 7.15% and 17.89%, respectively; the photorefractive response times are 1 s and 170 ms, respectively; and the photorefractive sensitivities are 2.23 cm.sup.2/J and 21 cm.sup.2/J, respectively. The photorefractive response time at 488 nm can be shortened to 0.17 s. The results of optical damage resistance ability test (as shown in FIG. 3(d)) indicated that: the optical damage resistance threshold of the crystal is: 10.sup.6 W/cm.sup.2, thus the crystal can be used in the fields of laser frequency conversion, parametric oscillation, Q-switch, electro-optical modulation, holographic storage or holographic display.

Embodiment 4

[0038] An application of the bismuth and magnesium co-doped lithium niobate crystal, includes the application of the bismuth and magnesium co-doped lithium niobate crystal in the laser frequency conversion, parametric oscillation, Q-switch, electro-optical modulation, holographic storage and holographic display.

[0039] The Embodiments described above are only preferred embodiments of the present invention, but not the limitations of the present invention. All the modifications, equivalents, substitutions and improvements etc. made within the spirit and principle of the present invention should fall within the protection scope of the present invention.