JP4258308B2 - Wavelength conversion crystal growing device and crystal made from this device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for growing a wavelength conversion crystal using a seed crystal cut in a specific phase matching orientation, and a crystal made from the apparatus . More specifically, a lithium tetraborate seed crystal cut in a phase matching orientation inclined by 74 ± 5 degrees from the c-axis is used, and a wavelength conversion crystal for a 5th harmonic wave of a lithium tetraborate Nd: YAG laser is obtained by the Czochralski method. it relates growing apparatus and a wavelength conversion crystal for fifth harmonic wave made from this device.
[0002]
[Prior art]
Lithium tetraborate (Li ₂ B ₄ O ₇ ) is easy to make high-quality large crystals, has low deliquescence, is stable, has excellent handleability, and has good workability. The use as a conversion element attracts attention.
Conventionally, a Czochralski method using a lithium tetraborate seed crystal cut in a phase-matching orientation inclined by 74 ± 5 degrees from the c-axis, which is a pulling orientation suitable for mass production of Nd: YAG laser 5th harmonic elements. When a single crystal is grown by the (CZ method), the plane perpendicular to the pulling direction becomes the laser light incident surface of the desired laser element, so that the number of laser elements that can be taken from one grown single crystal may increase. Are known.
[0003]
[Problems to be solved by the invention]
However, when a lithium tetraborate single crystal is grown in a pulling orientation suitable for mass production, there is a problem that a minute scatterer is incorporated into the entire crystal. This scatterer causes a transmission loss of incident light and SHG (second harmonic) light. In particular, when a crystal is used inside the laser resonator, the transmission loss becomes a serious problem. In addition, when used as a crystal for a high-power laser, there is a disadvantage that the damage threshold of the crystal is greatly reduced. Furthermore, when used as an ultraviolet material, a higher quality is required than usual, so that the scatterer is a big problem.
Scatterer uptake is observed in crystals grown in crystal orientations other than 74 ± 5 degrees from the c-axis, such as <100>, <110>, <001>, etc., or crystal orientations for fourth harmonics. However, there is a problem that the number of laser elements that can be taken from one grown single crystal is small because the surface that is not perpendicular to the pulling direction is the incident surface of the laser beam.
An object of the present invention is to provide a wavelength conversion crystal growth apparatus that does not reduce the damage threshold of the crystal without causing a minute scattering body to be taken into the wavelength conversion crystal, causing no transmission loss of incident light and SHG light, and this The object is to provide crystals made from the device .
[0004]
[Means for Solving the Problems]
In the invention according to claim 1, as shown in FIG. 1, a seed crystal cut out in a specific phase matching orientation in a wavelength conversion crystal melt 21a stored in a crucible 21 provided with heat insulating walls 25 and 26 on the top. 10, in a device for growing the wavelength conversion crystal by rotating the seed crystal 10 while rotating the seed crystal 10 by the rotation / pull-up mechanism 27 and penetrating through the heat insulating walls 25 and 26, the tip is close to the upper surface of the melt 21 a. Extending drying gas introduction pipes 31 and 32 are provided, and during the growth of the crystal, the drying gas having a relative humidity of 10% or less is drawn through the introduction pipes 31 and 32 while flowing into the heat insulating walls 25 and 26 so as to hit the melt 21a. 1. A wavelength conversion crystal growth apparatus characterized by being configured to be raised.
During the growth, a dry gas having a relative humidity of 10% or less is pulled up while flowing into the heat insulating walls 25 and 26 so as to hit the melt 21a through the introduction pipes 31 and 32 penetrating the heat insulating walls 25 and 26, thereby increasing It is possible to reduce the amount of bubbles based on the residual moisture in the melt that is the cause of the scatterer. As a result, the scatterer can be prevented from being taken into the crystal.
[0005]
The invention according to claim 2 is the invention according to claim 1, wherein the wavelength conversion crystal is a lithium tetraborate single crystal, and the seed crystal 10 is cut out in a phase matching direction inclined by 74 ± 5 degrees from the c-axis. This is an apparatus for growing a wavelength conversion crystal for 5th harmonics of an Nd: YAG laser in the growth furnace 20 by the Czochralski method.
When a lithium tetraborate single crystal is grown under the above conditions, the incorporation of scatterers into the crystal is significantly reduced.
[0006]
The invention according to claim 3 is the growth apparatus according to claim 1 or 2, wherein the dry gas is dry air, dry argon or dry nitrogen.
The invention according to claim 4 is a wavelength conversion crystal made by the growing apparatus according to any one of claims 1 to 3.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the growing apparatus according to the present invention, a dry gas having a relative humidity of 10% or less passes through the double heat insulating walls 25 and 26 and the tip of the growing apparatus hits the melt through the introduction pipes 31 and 32 extending to the vicinity of the upper surface of the melt 21a. In the heat insulating walls 25 and 26. The relative humidity is more preferably 5% or less, and 0 (zero)% is optimal. When the relative humidity of the dry gas exceeds 10%, it is not preferable because the amount of residual moisture in the melt that is a cause of scatterers in the crystal cannot be reduced.
Lithium tetraborate is preferably used as the seed material used for growing the wavelength conversion crystal of the present invention and the crystal material constituting the melt. In addition, BBO (BaB ₂ O ₄ ), LBO (LiB ₃ O ₅ ), CLBO (CsLiB ₃ O ₁₈ ) and the like can be used. A seed crystal cut into a specific phase matching orientation is used according to the type of crystal. When the crystal is lithium tetraborate and a wavelength conversion crystal for Nd: YAG laser 5th harmonic, a seed crystal cut in a phase matching direction inclined by 74 ± 5 degrees from the c-axis is used.
[0008]
One embodiment of the growing apparatus of the present invention will be described with reference to the drawings. That is, as shown in FIGS. 1 and 2, in the Czochralski method, a lithium tetraborate single crystal growth furnace 20 has a platinum crucible 21 in which a lithium tetraborate polycrystal melt 21a is stored. Since lithium tetraborate has a low melting point among oxides, it can be grown in a platinum crucible. Around the platinum crucible 21, a heating device 24 such as a resistance heater for melting the lithium tetraborate polycrystal in the crucible 21 is provided via heat insulating materials 22 and 23. The temperature of the melt 21 a in the crucible 21 is detected by a thermocouple 29. The upper part of the crucible 21 is provided with double heat insulating walls 25, 26, and a rotation / lifting mechanism 27 is provided through the heat insulating walls 25, 26. A seed crystal 10 is disposed at the tip of the mechanism 27. Further, dry gas introduction pipes 31 and 32 are provided through the heat insulating walls 25 and 26.
[0009]
In this apparatus , after the lithium tetraborate polycrystal in the crucible 21 is melted by the heating device 24, the seed crystal 10 is brought into contact with the melt 21 a, and the seed crystal 10 is pulled up while being rotated by the rotation / pull-up mechanism 27. As a result, a lithium tetraborate single crystal 28 as shown is grown.
The characteristic structure of the present invention is that crystals are produced while flowing dry gas having a relative humidity of 10% or less through the dry gas introduction pipes 31 and 32 into the heat insulating walls 25 and 26 so as to hit the melt 21a as indicated by arrows. Is to raise. The dry gas hits the melt 21a and is then discharged to the outside through the space between the rotation / lifting mechanism 27 and the heat insulating walls 25 and 26. As a result, the amount of bubbles based on the residual moisture in the melt 21a that is the cause of the scatterer in the crystal can be reduced, and the scatterer is prevented from being taken into the crystal.
[0010]
【Example】
Next, examples of the present invention will be described together with comparative examples.
<Example 1>
A wavelength conversion crystal for 5th harmonic was produced by the following method. First, 1300 g of a lithium tetraborate polycrystalline raw material powder having a purity of 99.99% in a predetermined molar ratio is filled in a platinum crucible 21 having a diameter of 90 mm and a height of 100 mm shown in FIG. Then, it was pulled up to a predetermined pulling direction by the CZ method. That is, in this example, the seed crystal 10 cut at 74 degrees from the c-axis was used. The temperature gradient (temperature decrease gradient) 10 mm immediately above the melt surface and the melt was 120 ° C./cm, and the temperature decrease gradient above it was 20 ° C./cm. The growth rate of the single crystal 28 is 0.3 to 1 mm / hour, the rotation speed is 1 to 5 rpm, and the rate of 0.6 liter / min of dry air with a relative humidity of 0% during the raw material charging and the single crystal growth. Then, the lithium tetraborate single crystal 28 having a diameter of 50 mm and a length of 120 mm was grown. The grown single crystal was cut into a 10 mm × 10 mm × 10 mm dice, and then the cut surface was optically polished to obtain a sample of Example 1.
[0011]
<Comparative Example 1>
A sample of Comparative Example 1 which is a wavelength conversion crystal for 5th harmonic was obtained in the same manner as in Example 1 except that dry air was not passed during the growth of the single crystal.
[0012]
<Comparison evaluation, part 1>
The polished surfaces of the samples of Example 1 and Comparative Example 1 were each irradiated with a He—Ne laser (632 nm), and the presence or absence of a scatterer was visually examined. The results are shown in the photograph of FIG. 3 (sample of Example 1) and the photograph of FIG. 4 (sample of Comparative Example 1). Further, the refractive index variation of the sample of Example 1 was measured using a laser interferometer. The result is shown in the photograph of FIG.
As apparent from FIGS. 3 and 4, in the sample of Comparative Example 1, the scatterers are uniformly distributed throughout the crystal, whereas in the sample of Example 1, the amount of scatterers is greatly reduced. I found out. The refractive index variation in FIG. 5 was 2 × 10 ⁻⁶ / mm. This indicates that the crystals are of high quality.
[0013]
<Example 2>
1300 g of the lithium tetraborate polycrystalline raw material powder used in Example 1 is filled in a platinum crucible 21 having a diameter of 90 mm and a height of 100 mm shown in FIG. 1, and the raw material powder is melted with a heating device 24 in a dry air atmosphere. A sample of lithium tetraborate that was held at 1 ° C. for 1 hour and then rapidly cooled to vitrify was obtained.
[0014]
<Comparative example 2>
The raw material powder is melted with the heating device 24, held at 1000 ° C. for 1 hour, and then rapidly cooled to prepare vitrified lithium tetraborate in the atmosphere having a relative humidity of about 65% instead of the dry air atmosphere. did. Otherwise, in the same manner as in Example 2, a vitrified lithium tetraborate sample of Comparative Example 2 was obtained.
[0015]
<Comparison evaluation, part 2>
The OH content of the vitrified lithium tetraborate samples of Example 2 and Comparative Example 2 was analyzed by infrared spectroscopy. As a result, the OH amount of the sample of Comparative Example 2 was 1940 ppm, whereas the OH amount of the sample of Example 2 was 140 ppm. That is, in a dry air atmosphere, the amount of water can be reduced to about 1/10 or less in comparison with an atmospheric atmosphere having a relative humidity of 65%, so that bubbles based on residual moisture in the melt, which is a cause of scatterers in the crystal, are reduced. It has been found that the amount can be reduced and scatterers can be prevented from being incorporated into the crystal.
[0016]
【The invention's effect】
As described above, according to the present invention, in a device for growing a wavelength conversion crystal using a seed crystal cut out in a specific phase matching orientation, a dry gas having a relative humidity of 10% or less during By pulling up the crystal while flowing into the heat insulating wall so as to hit the melt through the introduction tube penetrating and extending to the vicinity of the upper surface of the melt, it is possible to prevent inconvenience that a minute scatterer is taken into the crystal. As a result, it is possible to obtain an effect of not reducing the crystal damage threshold without causing a transmission loss of incident light and SHG light.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an apparatus for growing a lithium tetraborate single crystal by the Czochralski method of the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is a photograph obtained by irradiating the sample of Example 1 with a He—Ne laser.
4 is a photograph obtained by irradiating the sample of Comparative Example 1 with a He—Ne laser. FIG.
FIG. 5 is a photograph obtained by measuring the refractive index variation of the sample of Example 1 using a laser interferometer.
[Explanation of symbols]
10 Seed crystal 20 Single crystal growth furnace 21a Lithium tetraborate melt 28 Lithium tetraborate single crystal 31, 32 Drying gas introduction tube

Claims (4)

A seed crystal (10) cut in a specific phase matching orientation is brought into contact with the wavelength conversion crystal melt (21a) stored in a crucible (21) provided with an insulating wall (25, 26) at the top, In the apparatus for growing the wavelength conversion crystal by pulling up the seed crystal (10) by the pulling mechanism (27),
Dry gas introduction pipes (31, 32) that penetrate the heat insulating walls (25, 26) and whose tips extend to the vicinity of the top surface of the melt (21a) are provided, and the crystals are dried at a relative humidity of 10% or less during growth. Growing a wavelength conversion crystal characterized by being configured to pull up gas while flowing into the heat insulating wall (25, 26) so as to hit the melt (21a) through the introduction pipe (31, 32) Equipment . The wavelength conversion crystal is a lithium tetraborate single crystal, and the seed crystal (10) is cut into a phase matching orientation inclined by 74 ± 5 degrees from the c-axis, and Nd: in the growth furnace (20) by the Czochralski method. The growth apparatus according to claim 1, wherein a wavelength conversion crystal for a fifth harmonic of a YAG laser is grown. The growth apparatus according to claim 1 or 2, wherein the dry gas is dry air, dry argon, or dry nitrogen. A wavelength conversion crystal made by the growth apparatus according to any one of claims 1 to 3.

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