JPWO2006064882A1 - Method for producing boric acid compound crystal and boric acid compound crystal obtained thereby - Google Patents

Abstract

Provided is a method for producing a boric acid compound crystal capable of easily removing a light scattering source. The boric acid compound raw material crystal is heated from the melting point of the raw material crystal to −140 ° C. to the melting point or the temperature in the range of the decomposition point to −140 ° C. Remove. In the heating, for example, it is preferable to raise the temperature so as not to cause cracks in the raw material crystal, and hold in this heated state for 2 hours or more. Moreover, it is preferable that the said cooling rapidly cools the temperature range of at least 650-300 degreeC with the cooling rate of 60 degreeC / min, for example. An example of the crystal obtained by the production method of the present invention is shown in FIG. As shown in the figure, the crystal obtained by the production method of the present invention has high quality with light scattering removed.

Description

  The present invention relates to a method for producing a boric acid compound crystal and a boric acid compound crystal obtained thereby.

Among boric acid compound crystals, CsB ₃ O ₅ crystal (hereinafter also referred to as “CBO crystal”) is a material whose nonlinear optical properties were reported in 1993, and is excellent in wavelength conversion applications to the ultraviolet region. (Non-Patent Document 1). In particular, as a third-harmonic generation (THG) element (generated by the sum frequency mixing of the fundamental wave and the second harmonic) of light having a wavelength of 1064 nm, such as an Nd: YAG laser, the existing LiB ₃ O _It has performance far exceeding ₅ crystals (LBO) (Non-patent Documents 2 and 3). However, since CBO crystals are difficult to grow, they have not been put to practical use, and there are only a few reports on crystal growth. As a typical crystal growth method of the CBO crystal, a top-seed solution growth (TSSG) method using self-flux can be mentioned. This method is a method for growing crystals in the liquid while lowering the temperature of the solution while the seed crystals are immersed in the Cs ₂ O—B ₂ O ₃ solution surface dissolved at high temperature and rotated. In this method, it has been reported by Kagebayashi et al. That a relatively large crystal can be obtained by rotating a seed crystal at a high speed using a growth solution having a B ₂ O ₃ concentration of 73.3 mol% (non-patent document). Reference 4). However, although the crystals obtained by this method appear to be single crystals of good quality, they are very practical in terms of damage due to the occurrence of ultraviolet light because minute light scattering sources are distributed throughout. I have a problem (Non-Patent Document 3). On the other hand, the present inventors have found that in the TSSG method, when the B ₂ O ₃ concentration of the growth solution is set to 70 mol%, a crystal having no light scattering source inside can be obtained (Non-patent Document 5). In addition, the present inventors have also found out that crystal growth is extremely difficult under the conditions under the influence of evaporation of the growth solution. Then, the present inventors have, when growing a _B 2 _{O 3} concentration in the grown solution from the stoichiometric ratio (75 mol%) near the composition 74 mol% is a crystalline composition of the CBO crystals, the result of such Kagerin and It has also been confirmed that large single crystals can be obtained. However, the crystal grown under the condition of 74 mol% has light scattering sources uniformly distributed therein. As described above, the present inventors have found that the growth conditions suitable for the CBO crystal from the viewpoint of crystal growth (degree of difficulty) and the optimum growth conditions for the quality of the crystal (the presence or absence of a light scattering source) are different. Heading. Such problems of the growth conditions and the light scattering source are not limited to CBO crystals but may be a problem in other boric acid compound crystals.
Y. Wu, T .; Sasaki, S .; Nakai, A .; Yokotani, H .; Tang, and C.I. Chen, Appl. Phys. Lett. 62, 2614 (1993). Y. Wu, P .; Fu, J. et al. Wang, Z .; Xu, L .; Zhang, Y. et al. Kong, and C.K. Chen, Op. Lett. 22, 1840 (1997). H. Kitano, T .; Matsui, K .; Sato, N .; Ushiyama, M .; Yoshimura, Y. et al. Mori, and T.M. Sasaki, Opt. Lett. 28, 263 (2003). Y. Kagebayashi, Y. et al. Mori, and T.M. Sasaki, Bull. Mater. Sci. 22, 971 (1999). T. T. Saji, N .; Hisaminato, M .; Nishioka, M .; Yoshimura, Y. et al. Mori, and T.M. Sasaki, J .; Crystal Growth, in press.

  Therefore, an object of the present invention is to provide a method for producing a boric acid compound crystal that can be easily grown and can be removed even if a light scattering source is generated.

  In order to achieve the above object, a manufacturing method of the present invention is a manufacturing method of a boric acid compound crystal, wherein a boric acid compound raw crystal having a light scattering source inside is converted from a melting point of the raw crystal to -140 ° C. Or it is a manufacturing method which has the heat processing process heated at the temperature of the range of decomposition point -140 degreeC to a decomposition point, and the cooling process process which cools the said said raw material crystal | crystallization heated to 300 degrees C or less.

  Thus, the manufacturing method of the present invention includes the light scattering source by removing the light scattering source by applying the heat treatment step and the cooling treatment step to the raw material crystal having the light scattering source therein. This is a method of obtaining no boric acid compound crystals. The production method of the present invention is a practical method that can remove the light scattering source by a simple process of heating and cooling. In addition, the production method of the present invention is a method for removing a light scattering source from a raw material crystal having a light scattering source, and the raw material crystal can be produced under conditions that allow easy growth as described above. Therefore, according to the production method of the present invention, it is possible to easily produce a high-quality boric acid compound crystal from which a light scattering source has been removed, and this method is particularly effective for producing a CBO crystal. Although the reason why the light scattering source can be removed by the manufacturing method of the present invention is unknown, the present inventors presume that the light scattering source dissolves in the heat treatment step and does not behave as a light scattering body. ing. Note that this estimation does not limit the present invention.

FIG. 1 is a photograph showing the light scattering state of a crystal obtained by an example of the production method of the present invention. FIG. 2 is a graph showing cooling conditions in another example of the manufacturing method of the present invention. FIG. 3 is a photograph showing an example of a raw material crystal obtained by the TSSG method. FIG. 4 is a photograph showing light scattering of the raw material crystal of the above example. FIG. 5 is a photograph showing the light scattering state of the crystals obtained by yet another example of the production method of the present invention. FIG. 6 is a photograph showing light scattering of the raw material crystal of the above example.

Next, the production method of the present invention will be described by taking the production method of CBO crystal as an example. Other boric acid compound crystals, such as LiB ₃ O ₅ crystals (decomposition point about 834 ° C.), Li ₂ B ₄ O ₇ crystals (melting point about 917 ° C.), CsLiB ₆ O ₁₀ crystals (melting point about 850 ° C.), etc. Can be carried out in the same manner as the CBO crystal.

  In the present invention, the temperature of the heat treatment step and the cooling treatment step means the temperature of the heating atmosphere and the cooling atmosphere. For example, when the raw material crystal is put in a container (for example, a crucible), the heat treatment and the cooling treatment are performed. Is the temperature inside the container. The measurement of the atmospheric temperature is not particularly limited, and can be measured by, for example, a thermometer or a temperature sensor arranged in the atmosphere. For example, the temperature in the vicinity of the CBO crystal may be measured in the heat treatment step and the cooling treatment step. For example, a thermocouple can be used for this measurement. For the heat treatment step, for example, a resistance heating type heater can be used.

In the present invention, the light scattering source refers to a portion where the light is scattered when a visible light laser is irradiated inside the crystal and a point light source can be visually confirmed. The crystal having a light scattering source handled in the present invention particularly refers to a crystal that shows a tendency that minute point light sources are distributed over the entire area inside the crystal. Although the generation mechanism of this light scattering source is unknown, for example, in the case of CsB ₃ O ₅ crystal, in the cooling process immediately after growth, the Cs component diffuses from the inside of the CsB ₃ O ₅ crystal and evaporates from the surface. The present inventors presume that the region where Cs generated inside the crystal is deficient is involved in the generation of the light scattering source. Note that this estimation does not limit the present invention. Moreover, in this invention, the removal of the light-scattering source of the said boric-acid-compound raw material crystal | crystallization in the said heat processing process and the said cooling process process may be removed entirely, and the one part removal may be sufficient as it. Even if the light scattering source is partially removed, it can be used without any problem in practice, and the crystal from which the light scattering source has been partially removed is cut to obtain an element without the light scattering source. Because it is possible.

The raw material crystal has a light scattering source therein. The crystal immediately after the growth has, for example, a size of 30 × 40 × 40 mm ^{3 in the} a-axis × b-axis × c-axis direction. However, when performing the heat treatment process, the wavelength conversion element is used so that cracking due to thermal strain does not occur. It is desirable to cut out in advance to a small size for use. The shape of the element is generally a quadrangular prism shape, and the size required for application varies depending on the laser used and its application, but for example, a square cross section of (3-5) × (3-5) mm ² is used. There is an element having a length of 8 to 18 mm. For example, when 355 nm light is generated from an Nd: YAG laser, high-output wavelength conversion is performed using an element having a cross section of 4 × 4 mm ² and a length of 8 mm. As an example of a large size that does not break by heat treatment, a 6 × 10 × 12 mm ³ square columnar shape can be given. In the present invention, the size of the raw crystal and the crystal obtained therefrom is not particularly limited.

The raw material crystal can be produced, for example, by a solution growth method. The solution growth method is a method using self-flux containing Cs ₂ O—B ₂ O ₃ , and the ratio (mol%) of B ₂ O ₃ in the self-flux is 71 mol% or more and 75 mol% or less. The method is preferred. This is because this method makes it easy to grow CBO crystals. In the solution growth method, the solution may contain a small amount of additives such as NaF and CsF. Examples of the solution growth method include a top-seed solution growth (TSSG) method, a submerged-seed solution growth method, a Czochralski method, and the TSSG method is preferable. From the viewpoint of large crystals are obtained, in the TSSG _method, the ratio of _B 2 _{O 3} in the _{CsO 2 -B 2 O 3 (mol} %) , for example, is preferably from more than 71 mol% 75 mol%, more preferably Is in the range of 73.5-74.5 mol%. Below, an example of manufacture of the raw material crystal by TSSG method is shown. In addition, the said raw material crystal | crystallization may use what was made homemade, and may use what was manufactured by the third party (for example, commercial item).

In this example, a crystal manufacturing method using the TSSG method by self-flux when the B ₂ O ₃ concentration is 74 mol% is shown. The temperature program for growth can be appropriately determined depending on the composition ratio used. First, a platinum crucible is filled with cesium carbonate and boron oxide as raw materials mixed at a predetermined raw material ratio. In addition, as the raw material compound for producing CsB ₃ O ₅ , other materials may be used. Here, the raw materials may be effectively mixed in advance using a liquid such as water. In some cases, the mixed raw material is heated in advance to 700 ° C. and is made into a crystalline powder using a solid phase reaction. This platinum crucible is set in a generally used resistance heating type crystal growth furnace (resistance heating type heater), heated to 850 ° C., and mixed with stirring by a platinum propeller for about 12 hours. After the stirring of the solution is completed, it is cooled to 830 ° C. which is the crystal growth temperature. After the temperature is stabilized, the seed crystals are immersed in the solution from above the solution, and then the solution is cooled at a rate of about 0.1 ° C./day. Cool down. The seed crystal is obtained by cutting a CBO crystal into a square column shape, and the size is, for example, 3 × 3 × 5 mm ³ . For example, the seed crystal may be set in the growth furnace so that the a-axis of the crystal is in the vertical direction. The seed crystal is preferably rotated at a high speed such as about 60 rpm in order to stir the solution. When crystal growth is performed in this state for about 7 days, for example, a crystal having a size as shown in the photograph of FIG. 3 grows. Thereafter, the crystal is pulled up from the solution, cooled to near room temperature at a cooling rate of about 17 ° C./hour, and the crystal is taken out. Thereafter, the crystal is cut into a size suitable for the heat treatment step and an orientation suitable for wavelength conversion application to obtain a raw material crystal.

  Subsequently, the heat treatment step and the cooling step in the production method of the present invention will be described by taking the following two forms as examples. In addition, the manufacturing method of this invention is not limited by these forms.

(First form)
First, the raw crystal is subjected to a heat treatment. In this heat treatment step, it is preferable to heat to a temperature near the melting point (or decomposition point, the same shall apply hereinafter) of the raw crystal, and hold in this state for a certain time. The temperature in the vicinity of the melting point is in the range from the melting point −140 ° C. to the melting point, preferably in the range from the melting point −120 ° C. to the melting point, and more preferably in the range from the melting point −40 ° C. to the melting point. More preferably, the melting point is in the range of -20 ° C to the melting point. Since the melting point of the CBO crystal is about 835 ° C., the temperature of the heat treatment is specifically, for example, in the range of 785 to 835 ° C., preferably in the range of 795 to 835 ° C., more preferably Is in the range of 815 to 835 ° C. Moreover, the said heat processing temperature from another viewpoint becomes like this. Preferably it is 790 degreeC or more, More preferably, it is the range of 815-830 degreeC, More preferably, it is the range of 815-825 degreeC. The holding time in the heated state is, for example, 2 hours or more, and preferably 3 hours. If held in a heated state for 3 hours, the light scattering source can be more effectively removed. Further, from the viewpoint of removal of the light scattering source and prevention of crystal dissolution, a more preferable heating state holding time is 2 to 5 hours, and particularly preferably 3 to 5 hours. The rate of temperature rise to the constant heating temperature is not particularly limited, and is preferably a rate of temperature rise that does not cause cracks in the raw material crystal, for example, more than 0 and 60 ° C./min. The method of raising the temperature is not particularly limited, and may be a continuous temperature increase or a stepwise temperature increase, and the temperature increase rate may be changed in the middle. In the heat treatment step, for example, the resistance heating heater used in the production (growth) of the raw material crystals described above can be used. This heater controls the heating rate and the cooling rate by turning on and off the current. In addition, this heat treatment step is preferably performed in a state where the crystal growth solution of the raw crystal is similarly heated below the crystal. In this state, the evaporation component containing Cs fills the atmosphere from the lower crystal growth solution. As a result, it becomes difficult for the surface of the crystal to dissolve, and heat treatment at a temperature closer to the melting point can be performed. As a result, the light scattering source can be removed more effectively. Although this mechanism is unknown, the presence of Cs in the atmosphere can suppress the diffusion of Cs from the inside of the crystal and from the surface, can suppress the dissolution of the surface as a self-flux solution lacking Cs, and Although it is speculated that the dissolution of microcrystals considered to be an internal light scattering source can be sufficiently promoted, this inference does not limit the present invention. Various methods can be envisaged as a method for generating the evaporation component containing Cs other than heating the raw crystal growth solution or a solution having a different composition as it is, but the means is not particularly limited.

  Following the heat treatment step, the cooling treatment step of cooling to 300 ° C. or lower is performed. In this cooling treatment step, for example, it is preferable to rapidly cool at least a temperature zone between 600 ° C. and 300 ° C., and more preferably, rapidly cool a temperature zone between 650 ° C. and 300 ° C. The speed of the rapid cooling is not particularly limited, but is, for example, 50 ° C./min or more, and preferably 60 ° C./min or more. The upper limit of the rapid cooling rate is not particularly limited, but is, for example, 200 ° C./min or less, preferably 100 ° C./min or less, from the viewpoint of preventing the occurrence of cracks in crystals. Therefore, the specific conditions for the rapid cooling rate are, for example, in the range of 50 to 200 ° C./min, preferably in the range of 60 to 200 ° C./min, and more preferably in the range of 50 to 100 ° C. Yes, particularly preferably in the range of 60 to 100 ° C. In addition, the method of temperature drop (cooling) to 600 ° C. or 650 ° C. is not particularly limited, and may be rapidly cooled to 300 ° C. or less at once, similarly to the above, or up to 600 ° C. or 650 ° C. Alternatively, the temperature may be gradually decreased, and rapid cooling may be performed from 600 ° C. or 650 ° C. as described above. Moreover, it is preferable to cool from 300 degrees C or less to room temperature, The cooling conditions in particular are not restrict | limited, For example, you may rapidly cool at a stretch on the above-mentioned conditions from 600 degrees C or 650 degrees C to room temperature. The cooling treatment step can be performed, for example, with the above-described resistance heating heater. Also, in order to implement rapid cooling, in addition to or instead of the above-described current on / off, a cooling method in which the crystal is brought out of the furnace and brought into contact with the outside air, or a cooling method using a coolant such as water or air Etc. may be applied. Like the heat treatment step, this cooling treatment step is also preferably performed in a Cs gas atmosphere, and the method is the same as described above.

(Second form)
In the second embodiment, a container in which the raw crystal growth solution is disposed is prepared, and at least one of the raw crystal components in the solution is evaporated in the container, and the heating is performed in the component atmosphere. It is a method of performing a processing step. In addition, all the components of the raw material crystal component in the solution may be evaporated. Similarly, in the cooling treatment step, a container in which the raw crystal growth solution is arranged is prepared, and the component atmosphere in which at least one component of the raw crystal components in the solution is evaporated in the container. It is preferable to carry out both of the heat treatment step and the cooling treatment step continuously in the atmosphere. The component atmosphere is preferably a Cs gas atmosphere in the case of CBO crystals.

The growing solution is not particularly limited as long as it is a solution that can be used for growing a boron compound raw material crystal, and examples thereof include a solution containing Cs ₂ O—B ₂ O ₃ . In this case, the ratio (mol%) of B ₂ O _{3 in} the solution is, for example, 60 mol% or more, preferably in the range of 66 to 81 mol%, more preferably in the range of 67 to 75 mol%. The ratio of Cs ₂ O in the solution (mol%) is, for example, not more than 40 mol%, preferably in the range of 19～34Mol%, more preferably from 25~33mol%.

  The heat treatment step (optionally a cooling treatment step) in the component atmosphere is preferably performed, for example, by closing the container, and as a specific example, an openable / closable sealed container is used. By covering the opening of the container with platinum foil or the like, the inside of the container can be sealed. The sealed state may not be completely sealed.

  In the heat treatment step, the heating temperature ranges from the melting point −140 ° C. to the melting point, preferably the melting point −125 ° C. to the melting point, more preferably the melting point −115 ° C. to the melting point. It is a range, More preferably, it is the range of the said melting | fusing point-115 degreeC to melting | fusing point -85 degreeC. For example, in the case of CBO crystal, the heating temperature is in the range of 695 ° C. or higher and the melting point or lower, preferably 720 ° C. or higher and the melting point or lower, more preferably 720 ° C. to 750 ° C. Further, as in the first embodiment, it is preferable to hold for a certain period of time while being heated to the temperature in the above range, and the heating and holding time is not particularly limited, and may be appropriately determined depending on the size and type of the boric acid compound crystal raw material. For example, 36 hours or more. In addition, the temperature increase rate, the heating method, and the like can be implemented in the same manner as in the first embodiment, for example.

  Following the heat treatment step, the cooling treatment step of cooling to 300 ° C. or lower is performed. The conditions for the cooling treatment step are not particularly limited, and may be gradually cooled, for example, or may be cooled in the same manner as in the first embodiment. For example, it cools from heating temperature to room temperature over 2 to 48 hours. Further, the cooling rate is not particularly limited, and is, for example, 0.1 to 10 ° C./min.

By passing through the heat treatment step and the cooling treatment step shown in these first and second embodiments, the light scattering source in the raw material crystal can be removed, and the intended CsB ₃ O ₅ nonlinear optical crystal can be obtained. . Even if this crystal is used for an ultraviolet laser, since there is no scattering, the laser output is improved and the deterioration characteristics of the device are greatly improved. As a result, it can be expected to be used for a long time with high efficiency. In addition, the manufacturing method of this invention is not limited to the said 1st form and 2nd form, You may implement in another form.

  Next, the light scattering source removal method of the present invention is a method for removing the light scattering source of a boric acid compound crystal having a light scattering source, wherein the melting point or decomposition point of the raw material crystal is −140 ° C. It is the processing method including the heat processing process heated at the temperature of the range to a decomposition point, and the cooling process process which cools the said heated said raw material crystal to 300 degrees C or less. In this method, the heat treatment step and the cooling step can be performed in the same manner as the manufacturing method of the present invention.

  Next, examples of the present invention will be described. In addition, this invention is not restrict | limited to the following Example.

(Manufacture of raw crystal)
Cs ₂ CO ₃ and B ₂ O ₃ were used as raw materials, mixed in pure water, and then water was evaporated to prepare a dried powder. This was heated to 700 ° C., and a sintered body having a CBO crystal phase was produced by a solid phase reaction. This raw material was filled in a growth crucible made of platinum. _B 2 _{O 3} concentration in the growth material here was a 74 mol%. Crystal growth was performed by the above-described TSSG method growth furnace. The orientation of the seed crystal was the a-axis direction of the crystal, and the seed crystal rotation speed for stirring the solution was 60 rpm. The saturation point (about 830 ° C.) at which crystal growth began was maintained, and then the temperature of the entire furnace was decreased at a rate of 0.1 ° C./day. As a result, 31 × 41 × 41 mm ³ CsB ₃ O ₅ single crystals were obtained in 7 days. This raw crystal is shown in the photograph of FIG. A fragment having a (011) natural surface was cut out from the raw crystal to obtain an element. For this element, a red He—Ne laser (4 mW, incident direction ⊥ (011) plane, polarization direction <100>, perpendicular to the natural surface, the observation direction is perpendicular to the incident direction, another (011 ) Surface) and light scattering was observed. The result is shown in the photograph of FIG. As shown in the figure, it was confirmed that a light scattering source was inserted along the optical path in this raw crystal element. The irradiation and observation directions described here are the results of selecting conditions that facilitate observation of light scattering through experiments. The element is cut out using an as-grown facet, but the present invention is not limited to this. In addition, it is possible to cut out in the phase matching direction.

(Heat treatment process and cooling process)
Next, the heat treatment and the cooling treatment were performed on the raw crystal element, and the light scattering source was removed. That is, first, after the growth, the raw material remaining in the platinum crucible was directly put into the growth furnace, and the temperature in the furnace was raised to the heating temperature. In this state, the space inside the furnace was filled with steam containing Cs. A raw material crystal to be heat-treated was fixed to a support rod and introduced from a hole opened in the upper lid of the growth furnace, and the crystal was heated. At this time, a thermocouple for measuring the temperature was attached in the vicinity of the crystal, and the temperature was raised from room temperature to 825 ° C. over 15 minutes. This temperature was maintained for 3 hours (heat treatment step), and then rapidly cooled to room temperature (cooling treatment step) within 10 minutes to obtain the intended CsB ₃ O ₅ crystal. This crystal was irradiated with red He—Ne laser light in the same manner as described above to confirm the presence or absence of light scattering. The result is shown in the photograph of FIG. As shown in the figure, in this crystal, no light scattering occurs, and it can be seen that the light scattering source could be removed.

A raw material crystal was produced in the same manner as in Example 1, and an element was obtained in the same manner as in Example 1. About this element, heat treatment was performed in the same manner as in Example 1 except that the element was heated to 825 ° C. at a temperature increase rate that did not cause cracks in the crystal and maintained at this temperature for 3 hours. Thereafter, in various conditions will be described later, cooling treatment to obtain a _CsB 3 _{O 5} crystal of interest. The cooling conditions were from 825 ° C. to two constant cooling rates of 17 ° C./hour or 69 ° C./hour to a certain temperature, followed by rapid cooling at 60 ° C./minute. And about the obtained crystal | crystallization, it carried out similarly to Example 1, and investigated the light scattering, and confirmed the presence or absence of the light-scattering source. The result is shown in the graph of FIG. In the figure, the solid line is a graph cooled to a constant temperature at a cooling rate of 17 ° C./hour, and the dotted line is a graph cooled to a constant temperature at a cooling rate of 69 ° C./hour. In this graph, disappearance of the light scattering source was observed in any cooling pattern. Among them, if the temperature zone from 600 ° C. to 300 ° C. is rapidly cooled at a rate of 60 ° C./min, the light scattering source will almost disappear and the temperature zone from 650 ° C. to 300 ° C. will be 60 ° C./min. If it was rapidly cooled at a speed, no light scattering could be confirmed by the irradiation of the aforementioned He—Ne laser.

  A CBO raw material crystal was produced in the same manner as in Example 1, and an element was obtained in the same manner as in Example 1. For this element, a red He—Ne laser (4 mW, incident direction ⊥ (011) plane, polarization direction <100>, perpendicular to the natural surface, the observation direction is perpendicular to the incident direction, another (011 ) Surface) and light scattering was observed. The result is shown in the photograph of FIG. As shown in the figure, it was confirmed that a light scattering source was inserted along the optical path in this raw crystal element.

Next, 5 g of Cs ₂ O—B ₂ O ₃ solution (Cs ₂ O: B ₂ O ₃ = 30: 70 (molar ratio)) is placed in the platinum crucible (diameter: 20 mm, height: 20 mm), After placing the element on the upper part of the crucible so that the position was 2 to 3 mm from the surface of the solution, the crucible opening was covered with platinum foil and sealed. Subsequently, it heated from room temperature to 730 degreeC over 2 hours, hold | maintained at 730 degreeC for 36 hours (heat-processing process), and cooled to room temperature over 4 hours after that (cooling process process). As a result, the light scattering source of the obtained CBO crystal disappeared. The obtained crystal was irradiated with red He—Ne laser light in the same manner as described above to confirm the presence or absence of light scattering. The result is shown in the photograph of FIG. As shown in the figure, in this crystal, no light scattering occurs, and it can be seen that the light scattering source could be removed.

  As described above, according to the production method of the present invention, a boric acid compound crystal from which the light scattering source is removed can be produced under easy growth conditions. As the boric acid compound crystal, for example, there is a CBO crystal, and this crystal is useful, for example, as a wavelength conversion element for an ultraviolet laser.

Claims (14)

  A method for producing a boric acid compound crystal, wherein a boric acid compound raw material crystal having a light scattering source therein is heated at a temperature ranging from the melting point of the raw material crystal to -140 ° C or the melting point or from the decomposition point to -140 ° C to the decomposition point. A manufacturing method comprising: a heat treatment step for heating; and a cooling treatment step for cooling the heated raw material crystal to 300 ° C. or lower. The manufacturing method according to claim 1, wherein the boric acid compound crystal is a CsB ₃ O ₅ crystal or a CsLiB ₆ O ₁₀ crystal.   The manufacturing method according to claim 1, wherein the cooling treatment step includes a step of cooling at least a range from 600 ° C. to 300 ° C. at a cooling rate of 50 ° C./min or more.   The manufacturing method according to claim 1, wherein the cooling treatment step includes a step of cooling at least a range from 650 ° C. to 300 ° C. at a cooling rate of 60 ° C./min.   The manufacturing method according to claim 2, wherein the heat treatment step is a step of heating at a temperature in a range of 790 ° C or higher and a melting point or lower.   The manufacturing method according to claim 2, wherein the heat treatment step is a step of heating at a temperature in the range of 815 to 825 ° C for 3 hours or more.   A container in which the boric acid compound raw crystal growth solution is arranged is prepared, and the heat treatment step is performed in the container in the component atmosphere in which at least one of the raw crystal components in the solution is evaporated. The manufacturing method according to claim 1.   The manufacturing method according to claim 7, wherein the container is a sealed container.   The manufacturing method according to claim 7, wherein the component atmosphere is a Cs gas atmosphere.   The manufacturing method according to claim 7, wherein the heat treatment step is a step of heating at a temperature in a range of 720 ° C or higher and a melting point or lower than a decomposition point. The production method according to claim 2, wherein the CsB ₃ O ₅ raw material crystal is a crystal produced by a solution growth method. 12. The solution growth method is a method using a self-flux containing Cs ₂ O—B ₂ O ₃ , and a ratio (mol%) of B ₂ O ₃ in the self-flux is 71 mol% or more. The manufacturing method as described.   The manufacturing method according to claim 11, wherein the solution growth method is a top-seed solution growth (TSSG) method.   A boric acid compound crystal obtained by the production method according to claim 1.

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