JPH08151298A - Method for heat-treating solid laser crystal - Google Patents

Abstract

PURPOSE: To relax a strain present in the interior of a crystal. CONSTITUTION: A yttrium vanadate single crystal 10 containing neodymium added thereto is inserted into a boat 1, having a pair of reflecting plates 2a and 2b, rotating shafts 3a and 3b and thermocouple thermometers 4a and 4b at both ends of the boat body 1a and equipped with a rotating mechanism such as a pulley 5, a motor having a pulley 6 for rotating the whole in the circumferential direction and a rotating belt 7. Indicated values of the thermocouple thermometers 4a and 4b are set within the range of 1600±5 deg.C in a gas atmosphere containing 1% oxygen mixed in nitrogen in a high-temperature electric furnace and the single crystal is kept in the set state of the indicated values thereof for 30hr. The boat 1 is then continued to rotate at 1 r.p.m. rotational frequency. Thereby, the single crystal is annealed to ambient temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for a solid-state laser crystal for relaxing the strain existing inside the crystal of the solid-state laser crystal grown by the Czochralski method.

[0002]

2. Description of the Related Art For example, yttrium vanadate (Nd: Y) doped with neodymium used as a solid-state laser crystal is used.
The VO ₄ ) single crystal is grown by the Czochralski method from a raw material to which neodymium is added by several%. This crystal is
Generally, crystals are grown in the a-axis and c-axis directions, and after the crystals are produced, oxygen defects are removed by holding the crystals in a nitrogen atmosphere containing oxygen at a temperature within about 1400 ° C. for 1 hour or more.

N formed by such a heat treatment method
In the d: YVO ₄ single crystal, the wafer a-plane-cut by a-axis growth has less influence of striation and oxygen defects, and the laser oscillation performance is superior to the c-axis-grown a-plane cut wafer. A heat treatment method for this type of solid-state laser crystal is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-14900.

[0004]

However, in such an Nd: YVO ₄ single crystal, in the growth of the a-axis orientation, the a-axis and the c-axis are orthogonal to each other in the cross section orthogonal to the growth axis, and the growth The developments of the a-plane and the c-plane appearing on the side surface are different from each other, which deteriorates the symmetry of the crystal. Also,
When neodymium is added at a high concentration of several%, a large amount of strain is further generated inside the crystal due to the difference in ionic radius when it is replaced with yttrium of the host crystal. When a crystal in such a state is cut into a wafer or a prism, a large number of large and small cracks are instantly generated along with cleavage, and there is a problem that the value as a product is completely lost.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and its purpose is to alleviate the strain existing inside the crystal of an Nd: YVO ₄ single crystal grown by the Czochralski method. It is an object of the present invention to provide a heat treatment method for a solid-state laser crystal that can be performed.

[0006]

In order to achieve such an object, a heat treatment method for a solid-state laser crystal according to the present invention comprises:
Nd: YVO ₄ single crystal with neodymium added was kept at a temperature of 1600 ± 5 ° C for 30 hours in a gas atmosphere in which 1% oxygen was mixed in nitrogen, and then gradually cooled to room temperature. Is.

Further, a heat treatment method for a solid-state laser crystal according to another invention is a boat having a pair of thermocouple thermometers and heat reflecting plates at both ends and having a rotating mechanism for rotating the whole in a circumferential direction. Insert Nd: YVO ₄ single crystal with neodymium inside, and set the reading of thermocouple thermometer at 1600 ± 5 ℃ in a high temperature electric furnace in a gas atmosphere of 1% oxygen mixed in nitrogen.
After being kept for 30 hours in the state set to 1, the boat is continuously rotated at a rate of 1 rotation per minute and gradually cooled to room temperature.

[0008]

In the present invention, strain in the crystal in the orientation in which the growth side surface is likely to be remarkably asymmetric due to the difference in the growth rate depending on the plane and the ionic radius of neodymium added as an impurity is larger than the ionic radius of yttrium of the host crystal. Because of the large size, the large strain generated inside the replaced crystal is relaxed, and this reduces shocks and heat shocks as well as cracks that occur during cleavage during cleavage.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of essential parts showing the configuration of a heat treatment apparatus used in the heat treatment method for a solid-state laser crystal according to the present invention. In FIG. 1, reference numeral 1 is a cylinder having a large number of openings 1b having a diameter of about 5 mm on the peripheral surface of the boat body 1a and having a mechanism capable of opening and closing in the vertical direction, and having no thermal reaction with crystals and having excellent thermal conductivity. Type platinum boats 2a and 2b are attached and fixed to both ends of the boat 1 and platinum reflection plates 3a and 3b are inserted in the central axes of the reflection plates 2a and 2b to suppress temperature fluctuations in the boat 1. It is a cylindrical rotation shaft that is fixed and that rotates the boat 1 in the circumferential direction.

Further, 4a and 4b are cylindrical rotary shafts 3a,
A thermocouple thermometer 5 which is inserted close to the inner side of the boat 1 in 3b and measures the temperature for adjusting the temperature in the boat 1 is fixed to one rotating shaft 3a and fixed to the boat 1 in the circumferential direction. A pulley having a pulley 6a connected to the motor rotating shaft, and 7 a rotating shaft 3a.
The rotating belt 10 connected between the pulley 5 and the pulley 6a of the motor 6 is N stored in the boat 1.
d: YVO ₄ single crystal.

The heat treatment apparatus constructed as described above is disposed in a nitrogen gas atmosphere containing oxygen in a high temperature electric furnace during the heat treatment process, and when the motor 6 is rotated, its rotational force is changed to the belt 7. It is transmitted to the boat 1 via the so that the entire boat 1 is rotated in the circumferential direction.

Next, a heat treatment method for a solid-state laser crystal using the heat treatment apparatus configured as described above will be described. First, the growth section with 1% neodymium grown in the a-axis direction grown by the Czochralski method has an elliptical growth section with a growth length of about 45 mm.
After taking out the Nd: YVO ₄ single crystal 10 from the growth furnace (not shown), the seed side and the tail side of the crystal were quickly set in the boat 1 shown in FIG. As an atmospheric gas, nitrogen gas is 99% and oxygen is 1%
Continue flowing the mixed gas containing at a rate of about 2 liters per minute,
The indicated values by the thermocouple thermometers 4a and 4b at both ends of the boat 1 were set to 1600 ° C ± 5 ° C as shown in Fig. 2, and about 3
After keeping it for 0 hour, the boat 1 is continuously rotated at a condition of 1 revolution per minute and gradually cooled to room temperature for about 24 hours.

According to such a heat treatment method, the strain in the crystal in the orientation in which the growth side surface is likely to be remarkably asymmetric due to the difference in the growth rate depending on the surface and the ionic radius of neodymium added as an impurity is the yttrium of the host crystal. It is possible to relax a large strain generated inside the substituted crystal because it is larger than the ionic radius, and to reduce cracks accompanied by cleavage caused by impact, heat shock and processing.

Further, in such a heat treatment method, by gradually cooling to room temperature under the condition that the boat 1 is rotated once per minute, the temperature difference of the entire crystal is further reduced, and the heat treatment effect is further greatly enhanced. be able to.

Next, Nd: YVO taken out from the boat 1
₄ Single crystal 10 with diamond slicing saw, elliptical cross section (long axis 27 mm, short axis 15 mm) and thickness a of about 2 mm
One surface wafer was cut out for about 15 minutes. No cracking accompanying cleavage was observed on the wafer, and a remarkable effect of the heat treatment was obtained.

In the above-mentioned embodiment, the case where the amount of oxygen mixed in nitrogen is set to 1% has been described, but if the amount of oxygen exceeds 1%, new scatter is generated inside the crystal and coloring ( The crystals are blue, for example, while they are blue). On the other hand, if it is less than 1%, no improvement in coloring (disappearance of brown color) cannot be obtained. Therefore, the oxygen content was good at 1%.

Further, in the above-mentioned embodiments, the case where the heat treatment temperature is set to 1600 ° C. ± 5 ° C. has been described, but when the heat treatment temperature exceeds 1605 ° C., the crystal melts, and below 1595 ° C., No heat treatment effect can be obtained. Therefore, the heat treatment temperature was favorable in the range of 1600 ° C ± 5 ° C.

Further, in the above-mentioned embodiment, the case where the holding time at the heat treatment temperature of 1600 ° C. ± 5 ° C. was set to about 30 hours was explained, but if the holding time exceeds 30 hours, a large amount of heat energy is consumed. Therefore, it is economically a loss, and the heat treatment effect cannot be obtained when the time is less than 30 hours. Therefore, the holding time was good at about 30 hours.

Further, in the above-mentioned embodiment, the case where the rotation condition of the boat is set to 1 rotation per minute has been described, but the rotation of the boat is to keep the temperature of the whole crystal uniform, Increasing the number of rotations is structurally difficult, such as the boat being formed of a soft metal such as platinum and twisting because it is rotated at high temperature, and even if the number of rotations is increased. Since the temperature holding effect does not change, one rotation per minute was sufficient.

[0020]

As described above, according to the present invention,
Strains in crystals that tend to be asymmetrical depending on the growth axis direction and large internal strains caused by the difference in radius of the yttrium ion that is substituted for the added neodymium ion can be relaxed. Therefore, it is possible to obtain an extremely excellent effect that it is possible to surely prevent the occurrence of cracks during cutting, such as impact and heat shock.

Further, by using a mixed gas containing 1% oxygen in nitrogen as a gas atmosphere during the heat treatment, it is possible to obtain an effect that oxygen defects generated during crystal growth can be improved.

By adjusting the temperature with a pair of thermocouples provided at both ends of the platinum boat, the temperature fluctuation given to the yttrium vanadate single crystal can be reduced, and the temperature fluctuation can be further increased by the pair of heat reflection plates. It is improved, and since the entire boat made of platinum rotates, the heat fluctuation given to the yttrium vanadate single crystal becomes extremely small.Therefore, when the crystal is highly cleaved and the asymmetry is remarkable, the thermal strain is preserved and cracked. A remarkable effect is obtained on the generated crystals.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing the configuration of a heat treatment apparatus used in a heat treatment method for a solid-state laser crystal according to the present invention.

FIG. 2 is a diagram showing a relationship between heat treatment temperature and time in a heat treatment method for a solid-state laser crystal according to the present invention.

[Explanation of symbols]

1 ... platinum boat, 1a ... boat body, 1b ... opening, 2
a, 2b ... Heat reflection plate, 3a, 3b ... Cylindrical rotation axis, 4
a, 4b ... thermocouple thermometer, 5 ... pulley, 6 ... motor, 6
a ... pulley, 7 ... rotating belt, 10 ... Nd: YVO ₄
Single crystal.

Claims (2)

[Claims] 1. A yttrium vanadate single crystal to which neodymium is added is held for 30 hours in a gas atmosphere of 1% oxygen mixed in nitrogen at a temperature of 1600 ± 5 ° C., and then gradually cooled to room temperature. A method for heat-treating a solid-state laser crystal, comprising: 2. A yttrium vanadate single crystal containing neodymium in a boat having a pair of thermocouple thermometers and a heat reflecting plate at both ends and having a rotating mechanism for rotating the whole in the circumferential direction. Insert and add oxygen to nitrogen in high temperature electric furnace 1
% After holding the indicated value of the thermocouple thermometer at 1600 ± 5 ° C. for 30 hours in a mixed gas atmosphere, the boat is continuously rotated at a rate of 1 revolution per minute and gradually cooled to room temperature. A method for heat-treating a solid-state laser crystal characterized by the above.