JP4061468B2 - Single crystal for laser oscillator and laser oscillator using this as laser medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a single crystal for a laser oscillator and a laser oscillator using this as a laser medium.
[0002]
[Prior art]
Conventionally, a laser medium used for a solid-state laser is generally manufactured by a crystal pulling method from a melt by a Czochralski method (CZ method).
Most of the manufacturing cost of the solid-state laser oscillator is due to the laser medium and the excitation light source. For this reason, in order to reduce the manufacturing cost, first, a single crystal serving as a laser medium must be provided at a low cost. However, since many of the single crystals serving as the laser medium are oxides, the conventional single crystal growth method such as the CZ method must be performed at a temperature equal to or higher than the melting point of the single crystal to be obtained. Actually, in Nd: YAG and titanium sapphire, which are typical solid-state laser media, this melting point is a high temperature of 1900 ° C. or higher. Therefore, the furnace body for crystal growth becomes quite large, and a crucible using an expensive material such as platinum or iridium is required.
[0003]
Further, the growth rate of the single crystal is, for example, about 0.2 mm / h in Nd: YAG, and requires a long time. For these reasons, at present, it is considered difficult to reduce the cost of a single crystal serving as a laser medium.
[0004]
In addition, single crystals obtained from melt growth have optical inhomogeneities due to growth fringes, cores, facet formation, etc., and although these reductions are required for laser oscillator applications, they are quite difficult in principle. is there.
[0005]
[Problems to be solved by the invention]
Therefore, the main object of the present invention is to efficiently produce a single crystal excellent as a laser medium or the like.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the problems of the prior art, the present inventor has found that a single crystal obtained by a specific process can achieve the above object.
[0007]
That is, the present invention relates to the following laser oscillator single crystal and a laser oscillator using this as a laser medium.
[0008]
  1.Nd-added YAG, Ti-added sapphire or Nd-added YVO ₄ A single crystal for a laser oscillator substantially composed of a single crystal of
  1) The size of the single crystal is 1 inch in diameter x 22 mm in height,
  2) The number n (pieces / cm) per unit area of crystal grains forming a low-angle grain boundary ² ) Is 0,
  3) Dislocation density (however, excluding dislocations constituting a low-angle grain boundary) is 10 / cm. ² Less thanIs
A single crystal for a laser oscillator.
[0010]
  2.General formula Re ₃ M ₅ O ₁₂ (However, Re is Y, Ca, Sr and at least one of lanthanide rare earth elements having atomic numbers 62 to 71, M is at least one of transition metal elements having atomic numbers 22 to 30, Si, Mg, Al, Ga, In, and Sn. A single crystal for a laser oscillator substantially composed of an oxide single crystal having a composition represented by:
  1) The size of the single crystal is 1 inch in diameter x 22 mm in height,
  2) The number n (pieces / cm) per unit area of crystal grains forming a low-angle grain boundary ² ) Is 0,
  3) Dislocation density (however, excluding dislocations constituting a low-angle grain boundary) is 10 / cm. ² Less thanIs
A single crystal for a laser oscillator.
[0015]
  3. The pore volume is 100 ppm by volume or lessItem 1 or 2A single crystal for a laser oscillator according to 1.
[0016]
  4). Purity is 99.5% by weight or moreAny one of said items 1-3A single crystal for a laser oscillator according to 1.
[0019]
5. Re (where Re represents Y, Ca, Sr and at least one of lanthanide rare earth elements having atomic numbers 62 to 71) and M (where M is a transition metal element having atomic numbers 22 to 30, Si, Mg, And at least one of Al, Ga, In, and Sn.) After contacting the oxide single crystal containing at least one of the oxide single crystal as a seed crystal, the melting point of the sintered compact A method for producing a single crystal of an oxide containing at least one of Re and M by heat treatment at a temperature of 75 to 95%, wherein (a) a seed crystal portion And (b) cooling of the end part other than the part concernedBy applyingA method for producing a single crystal body for a laser oscillator, wherein an average temperature gradient of 10 ° C./cm or more is applied to the sintered body.
[0020]
6). The sintered body has a relative density of 99% or more.Item 5The manufacturing method as described.
[0021]
7. The (100) face, (110) face or (111) face of the single crystal is polished, and the polished face is brought into contact with the sintered body.Item 5 or 6The manufacturing method as described in.
[0022]
  8). The polished surface has an average surface roughness Ra = 1.0 nm or less and a flatness λ (λ = 633 nm) or less.Item 7The manufacturing method as described.
[0023]
9. Part or all of the sintered body is polished to an average surface roughness Ra = 1.0 nm or less and a flatness λ (λ = 633 nm) or less, and the polished surface is brought into contact with the single crystal.Item 5-8The manufacturing method in any one of.
[0024]
  10. An aqueous solution containing at least one of the elements constituting the single crystal (excluding oxygen) is applied to at least one contact surface of the sintered body and the single crystal.Said items 5-9The manufacturing method in any one of.
[0025]
  11. Re (where Re represents Y, Ca, Sr and at least one of lanthanide rare earth elements having atomic numbers 62 to 71) and M (where M is a transition metal element having atomic numbers 22 to 30, Sc, Si, A single crystal seed crystal is formed by irradiating a sintered laser of an oxide containing at least one of Mg, Al, Ga, In, and Sn.) A method for producing a single crystal of an oxide containing at least one of Re and M by heat-treating at a temperature of 75 to 95% of the melting point of the bonded body. a) heating to the seed crystal part and (b) cooling to the terminal part other than the part.By applyingA method for producing a single crystal body for a laser oscillator, wherein an average temperature gradient of 10 ° C./cm or more is applied to the sintered body.
[0026]
  12 The wavelength of the laser beam is 0.2 to 11 μm (however, the transmission wavelength of the single crystal is excluded).Item 11The manufacturing method as described.
[0027]
  13. Laser beam irradiation area is 1mm²IsItem 11 or 12The manufacturing method as described in.
[0028]
  14 The sintered body is irradiated with a laser beam while being heated at a temperature less than 90% of the melting point of the sintered body.Any of the above items 11 to 13The manufacturing method as described in.
[0029]
  15. An oxide capable of forming a liquid phase during crystal growth is present in the compact or sintered body.Item 5 or 11The manufacturing method as described in.
[0030]
  16. When the crystal is grown, the heating rate is 50 ° C./h or less.5 or 11 aboveThe manufacturing method as described in.
[0031]
  17. Cooling is carried out by spraying refrigerant on the end portionItem 5 or 11The manufacturing method as described in.
[0032]
  18. Cooling is performed by bringing a heat sink material made of metal or an inorganic material into contact with the end portion and bringing the refrigerant into contact with the heat sink material.Item 5 or 11The manufacturing method as described in.
[0033]
  19. Control crystal growth of single crystal by changing both (i) heating rate or (ii) heating rate and refrigerant flow rateItem 5 or 11The manufacturing method as described in.
[0034]
  20.In any one of said items 1-4A laser oscillator using the described single crystal for laser oscillator as a laser medium.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
1. Single crystal of the present invention
The single crystal for laser oscillator of the present invention has Re (where Re represents at least one of Y, Ca, Sr and a lanthanide rare earth element having atomic number 62-71) and M (where M is atomic number 22). ˜30 transition metal elements, Sc, Si, Mg, Al, Ga, In and Sn.) Consists essentially of a single crystal of an oxide containing at least one, and has a low-angle grain boundary. Number of crystal grains to be formed per unit area n (pieces / cm²) Is 0 ≦ n ≦ 10²(Hereinafter also referred to as “first single crystal”).
[0036]
The single crystal for laser oscillator of the present invention includes Re (where Re represents at least one of Y, Ca, Sr and lanthanide rare earth elements having atomic numbers of 62 to 71) and M (where M is an atom). A transition metal element consisting of at least one of transition metal elements Nos. 22 to 30, Sc, Si, Mg, Al, Ga, In, and Sn.) (However, dislocations constituting a low-angle grain boundary are excluded.)^FivePiece / cm²It is characterized by the following (hereinafter also referred to as “second single crystal”). In the present invention, the first single crystal and the second single crystal are collectively referred to as “the present single crystal”.
[0037]
In particular, in the present invention, those satisfying the requirements of both the first single crystal body and the second single crystal body are preferable. That is, Re (where Re represents Y, Ca, Sr and at least one of the lanthanide rare earth elements having atomic numbers 62 to 71) and M (where M is a transition metal element having atomic numbers 22 to 30, Sc, It represents at least one of Si, Mg, Al, Ga, In, and Sn.) Per unit area of crystal grains substantially composed of a single crystal of an oxide containing at least one and forming a low-angle grain boundary Number n (pieces / cm²) Is 0 ≦ n ≦ 10²And the dislocation density (excluding dislocations forming a low-angle grain boundary) is 1 × 10.^FivePiece / cm²The following single crystal for laser oscillator is desirable.
[0038]
The number n (pieces / cm 2) per unit area of crystal grains forming the above-mentioned low-angle grain boundaries is generally 0 ≦ n ≦ 10.²  Preferably, 0 ≦ n ≦ 20, more preferably 0 ≦ n ≦ 5. When it is out of the above range, there is a possibility that refraction or scattering at the grain boundary of the laser beam becomes remarkable.
The above dislocation density (excluding dislocations constituting a small-angle grain boundary) is generally 1 × 10.^FivePiece / cm²1 × 10 below^FourPiece / cm²Or less, more preferably 1 × 10^ThreePiece / cm²It is as follows. When it is out of the above range, there is a possibility that the electron state of the electrons excited to the upper level of the laser changes and the quantum efficiency is lowered.
[0039]
In the single crystal body of the present invention, there is no crystal grain boundary (so-called large tilt grain boundary), but a crystal has a misorientation with an adjacent crystal in the process of crystal growth, and as a result, a small tilt grain boundary is formed. (Generally, the orientation difference at the grain boundary is 10 ° or less). This small-angle grain boundary rotates with respect to each other about an angle grain boundary (interface formed by parallel edge dislocations) and a twist grain boundary (the orientation of two crystals sandwiching the grain boundary is perpendicular to the dislocation plane) Both). That is, the low-angle grain boundary is an interface constituted by a complicated arrangement of edge dislocations and screw dislocations. The low-angle grain boundary is created by the region surrounded by the interface when the single crystal grows. Therefore, if the number per unit area increases, it means that the small-angle grain boundaries increase, and the quality as a single crystal is inferior.
[0040]
Even in the case of a single crystal, dislocations may exist. If the dislocation density is too high, there may be a problem in the quality of the single crystal as in the case of the low-angle grain boundaries.
[0041]
The low-angle grain boundary is a three-dimensional continuity of edge dislocations and screw dislocations. That is, while the low-angle grain boundary is a defect at the interface, the dislocation density is a defect generated inside the crystal grain, and the present invention distinguishes both (the low-angle grain boundary and the dislocation density).
[0042]
The lower limit value of these transitions or low-angle grain boundary densities is not particularly defined from the viewpoint of laser performance, and is generally preferably as low as possible. It is determined according to the yield in the sense of reducing production costs.
[0043]
In the single crystal of the present invention, the pore volume is preferably 100 ppm by volume or less, particularly preferably 10 ppm by volume or less. By setting the pore volume within the above range, it is possible to obtain more excellent optical characteristics and the like. This is a rule for reducing the loss of input energy and is reflected in the running cost of the laser resonator.
The purity of the single crystal of the present invention is preferably as high as possible, particularly 99.5% by weight or more, preferably 99.9% by weight or more. When a large amount of impurities is contained, the electronic state of electrons excited to the upper level of the laser becomes non-uniform and the quantum efficiency may be lowered.
[0044]
A common composition can be adopted as the composition of the first single crystal and the second single crystal. That is, Re (where Re represents Y, Ca, Sr and at least one kind of lanthanide rare earth element having atomic number 62 to 71) and M (where M is a transition metal element having atomic number 22 to 30, Sc, It represents at least one of Si, Mg, Al, Ga, In, and Sn.) The composition may include at least one. More specifically, an oxide having the following composition can be preferably used as a single crystal for a laser oscillator.
(1) General formula Re_ThreeM_FiveO₁₂(However, Re is Y, Ca, Sr and at least one kind of lanthanide rare earth element having atomic number 62 to 71, M is a transition metal element having atomic number 21 to 30, Mg, Al, Ga, In, and Sn. Oxide having a composition represented by
Examples of the oxide include Nd-added YAG (Nd_xY_3-xAl_FiveO₁₂), Yb added YAG (Yb_xY_3-xAl_FiveO₁₂), Nd-added GGG (Nd_xGd_3-xGa_FiveO₁₂), Nd-added YSAG (Nd_xY_3-xSc_yAl_5-yO₁₂) And the like.
(2) General formula ReMO_Three(However, Re is Y, Ca, Sr and at least one of lanthanide rare earth elements having atomic numbers 62 to 71, M is a transition metal element having atomic numbers 21 to 30, Si, Mg, Al, Ga, In, and Sn. An oxide having a composition represented by the formula:
Examples of the oxide include Nd-added YAP (Nd_xY_1-xAlO_Three), Er-added YAGP (Nd_xY_1-xGa_yAl_1-yO_Three) And the like.
[0045]
(3) General formula ReV_1-xM_xO_Four(However, Re is Y, Ca, Sr and at least one of lanthanide rare earth elements having atomic numbers 62 to 71, M is a transition metal element having atomic numbers 21 to 30, Si, Mg, Al, Ga, In, and Sn. An oxide having a composition represented by the formula:
Examples of the oxide include Nd-added YVO._FourNd added GdVO_FourEtc.
[0046]
(4) General formula M_xAl_2-xO_Three(However, M represents at least one transition metal element having an atomic number of 22 to 28.)
Examples of the oxide include ruby (Cr_xAl_2-xO_Three), Titanium sapphire (Ti_xAl_2-xO_Three) And the like.
[0047]
(5) General formula Ti³⁺ _xAl_2-xO_Three(However, 0 <= x <= 2 is shown.) The oxide which has a composition represented.
[0048]
Among these oxides (1) to (5), particularly Nd: YAG, Nd: YVO_FourIn addition, titanium sapphire can be used more effectively for laser oscillators.
2. Method for producing single crystal of the present invention (first method)
The first method is Re (wherein Re represents at least one of Y, Ca, Sr and a lanthanide rare earth element having atomic number 62 to 71) and M (where M is a transition metal element having atomic number 22 to 30). , Sc, Si, Mg, Al, Ga, In, and Sn)) is formed, and the obtained molded body or the sintered body is formed into the sintered body. A method of producing a single crystal of an oxide containing at least one of Re and M by performing crystal growth by heat treatment at a temperature of 75 to 95% of a melting point of
When crystal growth is performed, an average temperature gradient of 10 ° C./cm or more is applied to the molded body or by subjecting at least one of (a) heating to a crystal growth start portion and (b) cooling to a terminal portion other than the portion. It is given to a sintered compact.
[0049]
The said oxide powder can be suitably selected according to the composition of the oxide finally obtained. The oxide powder may be one kind of oxide powder (for example, a composite oxide or mixed oxide containing two or more elements of Re and M), or two or more kinds of oxide powder. It may be a mixed powder obtained by mixing.
[0050]
In the first method, it is desirable to use the following powder as the oxide powder. That is, as an oxide powder of Re (where Re represents at least one of Y, Ca, Sr, and a lanthanide rare earth element having an atomic number of 62 to 71), the primary particle diameter is 20 to 500 nm and the BET specific surface area is 5 to 50 m.²/ G and M (wherein M represents a transition metal element having an atomic number of 22 to 30, Sc, Si, Mg, Al, Ga, In, and Sn). Primary particle diameter of 100 to 1000 nm and BET specific surface area of 3 to 30 m as powder²/ G powder is preferably used.
[0051]
The primary particle size of these powders can be determined by the half-value width of a diffraction peak in X-ray diffraction analysis, or SEM (scanning electron microscope) or TEM (transmission electron microscope). That is, in the case of SEM or TEM, the value obtained by calculating the average value of the major axis of 100 particles selected arbitrarily is shown.
[0052]
In the present invention, 0.01 to 1% by weight of an oxide capable of forming a liquid phase during crystal growth may be added. For example, SiO₂, B₂O_Three, Li₂O, Na₂O, K₂O, GeO₂, P₂O_FiveEtc. can be used. By this addition, a low-melting-point substance is formed from the molded body, and a single crystal can be grown in a state where a liquid phase is present at the crystal growth interface (single crystal and polycrystalline interface) when the crystal is grown. In this case, since a very small amount of the liquid phase component is present at the crystal growth interface, crystal growth via the liquid phase (that is, after the constituent particles of the polycrystalline body are once dissolved in the liquid phase, it is re-appeared at the single crystal growth interface). Single crystallization can also be caused by repeating precipitation).
[0053]
When this method is applied, the molded body or sintered body containing the above-mentioned predetermined amount of oxide is prepared, and then the method of this item is applied. However, the oxide is introduced into the grown crystal. There is a case. For this reason, oxide content shall be in the range of the said predetermined amount.
[0054]
The above-mentioned oxide powder itself is a known method such as a solid phase method in which constituent element oxides are blended, a coprecipitation method to obtain a uniform powder by chemically treating constituent elements in advance, a uniform precipitation method, an alkoxide method, etc. The powder obtained by the manufacturing method or a commercial item can be used. In particular, since the composition of the single crystal of the present invention is often complicated, the above-mentioned solid composition can be obtained more reliably by simply weighing each oxide powder with an electronic balance or the like. The phase method is preferred. The purity of these powders is not limited, but is preferably 99.8% by weight or more.
[0055]
Moreover, when using said mixed powder, although mixing of these powders should just follow a well-known mixing method, it is desirable to wet-mix especially. Specifically, for example, a solvent (water, alcohol, etc.) and, if necessary, a dispersant, a binder, etc. may be blended with two or more kinds of oxide powders and wet-mixed using a pot mill or the like. The mixing time is not particularly limited, but is usually 5 hours or longer. The slurry obtained by wet mixing can be made into a mixed granular powder by drying by spray drying or the like.
[0056]
Next, the oxide powder is molded. A known molding method may be employed as the molding method, and examples thereof include a uniaxial press method and a cold isostatic pressing method. The density of the molded body is not limited, and may be set as appropriate according to the use of the final product.
Moreover, you may bake the said molded object according to a well-known method as needed. For example, a sintered body can be obtained by firing the molded body in an oxidizing atmosphere. In this case, the firing temperature is lower than the crystal growth temperature in the composition. The sintered body may be any of a calcined body, a sintered body, and the like. In particular, a sintered body having a relative density of 95% or more is desirable.
[0057]
Next, the molded body or the sintered body is heat-treated at a temperature of about 75 to 95%, preferably 80 to 95% of the melting point of the sintered body, and crystal growth is performed. This temperature can be appropriately set according to the composition of the molded body to be used. For example, when Nd is substituted for Re, the Nd amount is determined. In addition, the heat treatment atmosphere may be any of an oxidizing atmosphere, an inert gas atmosphere, the air, and the like, and may be appropriately changed according to the composition of the single crystal. The heat treatment time may be set as appropriate according to the heat treatment temperature, the size of the desired single crystal, and the like.
[0058]
In the first method, it is desirable to adjust the rate of temperature rise during crystal growth. Specifically, it is 50 ° C./h or less, preferably 20 ° C./h or less. By adjusting to such a heating rate, efficient crystal growth can be performed.
In the first method, at the time of crystal growth, an average temperature gradient of 10 ° C./cm or more is obtained by performing at least one of (a) heating on the crystal growth start portion and (b) cooling on the end portion other than the portion. Is applied to the molded body or sintered body.
[0059]
The crystal growth start portion can be any portion of the compact or sintered body. The terminal portion is generally a portion that is finally crystallized, and can be appropriately determined according to the shape of the molded body or sintered body, the desired crystal growth direction, and the like. The crystal growth start part and the terminal part can also include the peripheral part of these parts as long as the effects of the present invention are not hindered. For example, when the formed body or sintered body is a cube or a cylindrical body as shown in FIG. 1A, the center portion X of one surface (the intersection of the diagonal lines of the surface or the center of the circle) is used as the crystal growth start portion. For example, the center portion Y of the surface facing the surface or the peripheral portion thereof can be the end portion.
[0060]
In particular, in the first method, similarly to the Bridgman method, a single crystal can be obtained more efficiently by forming the crystal growth start portion in a sharp shape. For example, as shown in FIG. 1B, if the tip of the compact or sintered body is conical, the tip X tends to be a single crystal (seed crystal). Thus, the single crystal of the present invention can be produced efficiently.
[0061]
The average temperature gradient in the present invention refers to a value obtained by dividing the temperature difference between the highest temperature portion and the lowest temperature portion of the compact or sintered body by the shortest distance between the highest temperature portion and the lowest temperature portion. Usually, the highest temperature portion is a crystal growth start portion, and the lowest temperature portion is the end portion. In addition, the said temperature difference can be measured by installing a thermocouple in the said highest temperature part and the said lowest temperature part.
[0062]
In the present invention, a temperature gradient is applied to the molded body so that the average temperature gradient is 10 ° C./cm or more, preferably 50 ° C./cm or more. When the average temperature gradient is less than 10 ° C./cm, there are fears that many low-angle grain boundaries are generated in the obtained single crystal or the dislocation density is excessive. In addition, the upper limit value of the average temperature gradient is not particularly limited, but is usually about 200 ° C./cm.
[0063]
The method of the heat treatment (a) is not limited so that the crystal growth start portion can be heated intensively. For example, it can be appropriately carried out by heating with a heater, a laser beam or the like. These heat treatments can be used in combination with heating by an electric furnace or the like.
In addition, the cooling method (b) is not limited as long as the end portion can be cooled intensively. For example, a method of spraying a refrigerant such as air, oxygen, or nitrogen, a method of bringing a heat sink material made of a metal or an inorganic material into contact with or contacting the end portion, and a method of contacting or spraying a coolant such as air on the heat sink material, or the like can be given. As the heat sink material, for example, ceramics such as alumina and YAG sintered body, and metals such as platinum can be used. Further, these metals or inorganic materials may be either single crystals or polycrystals. The shape of the heat sink material is not limited, but usually a plate-like material may be used.
[0064]
The treatments (a) and (b) can be used in combination. That is, the end portion can be cooled while heating the crystal growth start portion. If both processes are used together, a larger average temperature gradient can be obtained.
[0065]
By heat-treating the shaped body in this manner, single-crystal coarse particles are generated, and a single-crystal body having a desired size can be obtained by growing the single-crystal coarse particles. In the present invention, for example, a single crystal having a side of about 10 to 30 mm or more can be produced.
3. Method for producing single crystal of the present invention (second method)
The second method consists of Re (wherein Re represents at least one of Y, Ca, Sr and a lanthanide rare earth element of atomic number 62-71) and M (where M is a transition metal element of atomic number 22-30). And at least one of Sc, Si, Mg, Al, Ga, In, and Sn.) After contacting the oxide single crystal containing at least one of the oxide single crystals as seed crystals, A method for producing a single crystal of an oxide containing at least one of Re and M by heat-treating at a temperature of 75 to 95% of the melting point of the sintered body to grow a crystal,
When the crystal is grown, an average temperature gradient of 10 ° C./cm or more is applied to the sintered body by performing at least one of (a) heating on the seed crystal portion and (b) cooling on the end portion other than the portion. It is characterized by giving.
[0066]
The second method can use the same sintered body as the first method. As the sintered body, it is possible to preferably adopt a composition that is the same as the composition of the target single crystal body or has a molar ratio that differs within an error of 1%. For example, when a Nd: YAG single crystal is manufactured, Re (Nd + Y) is 3.0 mol and M (Al) is 5.0 mol as the sintered body, but ± 0.03 mol and ± 0 respectively. It can be produced by employing a sintered body having a composition variation range of .05 mol.
[0067]
As the sintered body, basically, a polycrystalline body (preferably an average crystal grain size of 20 μm or less) may be used. The sintered body can be manufactured by a known method. As a sintering method, any method such as atmospheric pressure sintering, hot pressing, HIP (hot isostatic pressing) and the like can be employed.
[0068]
The relative density of the sintered body is not limited, but is usually 99% or more, particularly preferably 99.8% or more. Thereby, a higher quality single crystal can be obtained. The size of the sintered body can be changed depending on the size of the desired single crystal, but it is usually sufficient to have a size larger than the volume of the single crystal. The relative density can be controlled by the density of the compact before sintering, the sintering temperature, the time, and the like.
[0069]
In the second method, any one single crystal present in the polycrystalline body obtained by sintering the molded body produced by the first method at an appropriate temperature and time can be suitably used.
[0070]
In the second method, 0.01 to 1% by weight of an oxide capable of forming a liquid phase during crystal growth can be added to the sintered body in advance. As such an oxide, for example, SiO₂, B₂O_Three, Li₂O, Na₂O, K₂O, GeO₂, P₂O_FiveEtc. can be used. With this addition, a low-melting-point material is formed from the base material, and a single crystal is grown with a liquid phase present at the crystal growth interface (single crystal and polycrystal interface) when single crystal is formed from the seed crystal toward the sintered body. You can also In this case, since a very small amount of the liquid phase component is present at the crystal growth interface, crystal growth via the liquid phase (that is, after the constituent particles of the polycrystalline body are once dissolved in the liquid phase, it is re-appeared at the single crystal growth interface). Repeating precipitation) can also cause single crystallization. When this method is applied, the sintered body containing the predetermined amount of oxide is prepared, and then the first method may be applied. However, the oxide may be introduced into the grown crystal. . For this reason, oxide content shall be in the range of the said predetermined amount.
[0071]
As the single crystal used as the seed crystal, not only the single crystal obtained by the first method and the third method but also a single crystal obtained by a known single crystal production method such as FZ method, flux method, TSSG method, etc. be able to. The size (volume) of the single crystal used is not particularly limited, but is usually 1 mm.^ThreeIt may be more than about.
[0072]
The single crystal may be the same as the composition of the sintered body or may be different from each other.
[0073]
The method for bringing the sintered body into contact with the single crystal is not particularly limited, but it is preferable to bring the sintered body and the single crystal into contact so that there is no gap between them. In this case, the sintered body and the single crystal may be heat-treated while being brought into pressure contact with each other. What is necessary is just to change suitably the pressure in a press contact according to the kind of sintered compact and a single crystal, a contact area, etc. For example, when a YAG single crystal and a YAG sintered body are used, the pressure may be about 9.8 MPa or less.
[0074]
In the second method, it is desirable to polish at least one surface (contact surface) when the sintered body and the single crystal are brought into contact with each other. In the single crystal, it is desirable to polish its (100) plane, (110) plane, or (111) plane. In this case, it is preferable to polish so that the polished surface has an average surface roughness Ra = 1.0 nm or less and a flatness λ (λ = 633 nm) or less. On the other hand, the sintered body is preferably polished so that at least the surface in contact with the single crystal has an average surface roughness Ra = 1.0 nm or less and a flatness λ (λ = 633 nm) or less.
[0075]
Next, the crystal is grown by heat treatment at a temperature of about 75 to 95%, preferably 80 to 95% of the melting point of the sintered body. The heat treatment temperature can be appropriately set according to the composition of the sintered body or seed crystal. The heat treatment atmosphere is not particularly limited, and may be the same as that of the first method. The heat treatment time may be appropriately set according to the heat treatment temperature, the desired single crystal size, and the like.
[0076]
In the second method, it is desirable to adjust the rate of temperature rise during crystal growth. Specifically, it is 50 ° C./h or less, preferably 20 ° C./h or less. By adjusting to such a heating rate, efficient crystal growth can be performed.
In the second method, when the crystal is grown, an average temperature gradient of 10 ° C./cm or more is obtained by performing at least one of (a) heating on the seed crystal part and (b) cooling on the terminal part other than the part. It gives to the said sintered compact.
[0077]
The seed crystal part includes not only the seed crystal itself but also a part where the seed crystal and the sintered body are in contact with each other. This portion can be heated by partial heating with a heater, white light, laser beam, or the like. The terminal portion is usually a portion that is finally crystallized, and can be appropriately determined according to the shape of the sintered body, the desired crystal growth direction, and the like. The seed crystal part and the terminal part can also include the peripheral part of the part as long as the effects of the present invention are not hindered. For example, when the sintered body is a cube or a cylindrical body, if a seed crystal is arranged at the central portion of one surface (the intersection of diagonal lines or the center of a circle), the surface facing the surface or the central portion thereof is the end portion. can do.
[0078]
The average temperature gradient in the present invention refers to a value obtained by dividing the temperature difference between the highest temperature portion and the lowest temperature portion of the sintered body by the shortest distance between the highest temperature portion and the lowest temperature portion. Usually, the highest temperature portion is a crystal growth start portion, and the lowest temperature portion is the end portion. In addition, the said temperature difference can be measured by installing a thermocouple in the said highest temperature part and the said lowest temperature part.
[0079]
In the present invention, the sintered body is given a temperature gradient such that the average temperature gradient is 10 ° C./cm or more, preferably 50 ° C./cm or more. When the average temperature gradient is less than 10 ° C./cm, there are fears that many low-angle grain boundaries are generated in the obtained single crystal or the dislocation density is excessive. In addition, the upper limit value of the average temperature gradient is not particularly limited, but is usually about 200 ° C./cm.
[0080]
The method of the heat treatment (a) is not limited so that the seed crystal part can be heated intensively. For example, it can be appropriately carried out by heating with a heater, white light, laser beam or the like. These heat treatments can be used in combination with heating by an electric furnace or the like. FIG. 2 shows an embodiment (cross-sectional view) in which the seed crystal is directly heated with a heater. The heater is installed in direct contact with the seed crystal, and the seed crystal is heated by this heater. The heated seed crystal grows toward the sintered body (polycrystal). You may install an auxiliary heater (electric furnace) on both sides of a sintered compact as needed.
[0081]
In addition, the cooling method (b) is not limited as long as the end portion can be cooled intensively. For example, a method of spraying a refrigerant such as air, oxygen, nitrogen or the like, a method of bringing a heat sink material made of a metal or an inorganic material into contact with or contacting the end portion, and a method of spraying a coolant such as air onto the heat sink material can be cited. As the heat sink material, a material having a thermal conductivity of 5 W / mk or more, particularly 10 W / mk or more is preferable. As such a material, for example, ceramics such as alumina and YAG sintered body, and metals such as platinum and tungsten can be used. These materials may be either a single crystal or a polycrystal. The shape of the heat sink material is not limited, but usually a plate-like material may be used. FIG. 3 shows a mode (cross-sectional view) in which a heat sink material is brought into contact with the end portion and a gas medium is sprayed on the heat sink material to cool it. As shown in FIG. 3, when the sintered body (polycrystalline body) is a cube or a cylindrical body and a seed crystal is placed on the center of a certain surface and crystal growth is performed, a heat sink material ( A plate-like material) is brought into contact, gas is supplied from below the heat sink material, and brought into contact with the heat sink material. By blowing a gas below the furnace temperature from below the heat sink material, the heat sink material and the polycrystalline body itself are cooled, and the temperature distribution in the unsteady state (curve temperature distribution, that is, abruptly with the crystal growth interface as a boundary). Temperature fluctuations) can be provided in the material. This can suppress the grain growth of the polycrystalline body below the crystal growth interface as much as possible. Furthermore, if the cooling condition from the lower end is made constant and the inside of the furnace is heated at a constant speed, the crystal growth start temperature can be sequentially moved downward, so that crystal growth can be performed only from one direction at a constant speed. It becomes possible. This is not only advantageous for crystal growth in a non-molten state, but also makes it possible to smoothly remove residual pores in the polycrystalline body before single crystallization from the outside of the system (outside of the single crystal) using the movement of the crystal interface. Therefore, light scattering inside the material (that is, insertion loss during semiconductor laser irradiation) can be reduced, leading to higher quality.
[0082]
The treatments (a) and (b) can be used in combination. That is, it is possible to cool the end portion while heating the seed crystal portion. If both processes are used together, a larger average temperature gradient can be obtained.
[0083]
In addition, as other means, the furnace temperature is set to a crystal growth start temperature or higher, and cooling is performed while supplying a gas so that the junction between the single crystal and the polycrystal body is about the crystal growth start temperature, By reducing the degree of cooling in accordance with the degree of crystal growth, the crystal growth interface can be moved, and a high-quality single crystal can be obtained similarly.
In the case of irradiating the seed crystal portion with a laser beam, the laser beam may be irradiated to a part or all of the portion in contact with the seed crystal and the sintered body. The energy density of the laser beam (laser light) varies depending on the beam spot diameter or the like, but is usually 10⁷W / cm²The following should be done. The wavelength is usually about 0.2 to 11 μm (however, the transmission wavelength of the single crystal is excluded). A known or commercially available apparatus can be used as the laser generator itself. The type of laser beam is not limited, for example, CO₂A laser beam or the like can be used. Further, for example, after the sintered body in which a single crystal having the same composition as the single crystal is brought into contact as a seed crystal is placed in a heating furnace, laser beam irradiation may be performed while heat-treating the sintered body.
[0084]
In the second method, if necessary, an aqueous solution containing at least one of Re and M can be applied to at least one contact surface of the sintered body and the single crystal. As such an aqueous solution, an aqueous solution of water-soluble salts (organic acid salt, inorganic acid salt, etc.) containing at least one of Re and M can be used. For example, YCl_Three, Y (NO_Three)_ThreeAn aqueous solution such as In this case, Re and M in the aqueous solution are preferably the same as Re and M contained in the sintered body. By using the aqueous solution, the adhesion between the single crystal and the sintered body can be improved, and a high-quality single crystal can be more reliably produced. The concentration of the aqueous solution is not particularly limited, but is usually about 0.5 to 10% by weight.
4). Method for producing single crystal of the present invention (third method)
The third method consists of Re (wherein Re represents at least one of Y, Ca, Sr and lanthanide rare earth elements having atomic numbers 62 to 71) and M (where M is a transition metal element having atomic numbers 22 to 30). , Sc, Si, Mg, Al, Ga, In, and Sn.) A single crystal seed crystal is formed by irradiating a laser beam to a sintered body of an oxide containing at least one of Then, a method for producing a single crystal of an oxide containing at least one of Re and M by heat treatment at a temperature of 75 to 95% of the melting point of the sintered body and crystal growth,
When the crystal is grown, an average temperature gradient of 10 ° C./cm or more is applied to the sintered body by performing at least one of (a) heating on the seed crystal portion and (b) cooling on the end portion other than the portion. It is characterized by giving. The third method is preferable in that a single crystal can be produced faster than the first method.
In the third method, the same sintered body as that in the first method can be used. The sintered body is not particularly limited as long as it has the same composition or molar ratio as the composition of the target single crystal and a composition that is different within an error of 1%. For example, when a Nd: YAG single crystal is manufactured, Re (Nd + Y) is 3.0 mol and M (Al) is 5.0 mol as the sintered body, but ± 0.03 mol and ± 0 respectively. It can be produced by employing a sintered body having a composition variation range of .05 mol.
[0085]
As the sintered body, basically, a polycrystalline body (preferably an average crystal grain size of 20 μm or less) may be used. The sintered body can be manufactured by a known method. As a sintering method, any method such as atmospheric pressure sintering, hot pressing, HIP (hot isostatic pressing) and the like can be employed. In the third method, any one single crystal present in the polycrystalline body obtained by sintering the molded body produced by the first method at an appropriate temperature and time can be suitably used.
[0086]
In the third method, the relative density of the sintered body is not limited, but is usually 99% or more, particularly preferably 99.8% or more. Thereby, a higher quality single crystal can be obtained. The size of the sintered body can be changed according to the size of the desired single crystal, but it is usually sufficient to set the size to be equal to or larger than the volume of the subsequent single crystal. The relative density can be controlled by the density of the compact before sintering, the sintering temperature, the time, and the like.
[0087]
In the third method, 0.01 to 1% by weight of an oxide capable of forming a liquid phase during crystal growth can be added to the sintered body in advance. As such an oxide, for example, SiO₂, B₂O_Three, Li₂O, Na₂O, K₂O, GeO₂, P₂O_FiveEtc. can be used. With this addition, a low-melting-point material is formed from the base material, and a single crystal is grown with a liquid phase present at the crystal growth interface (single crystal and polycrystal interface) when single crystal is formed from the seed crystal toward the sintered body. You can also In this case, since a very small amount of the liquid phase component is present at the crystal growth interface, crystal growth via the liquid phase (that is, after the constituent particles of the polycrystalline body are once dissolved in the liquid phase, it is re-appeared at the single crystal growth interface). Repeating precipitation) can also cause single crystallization. When this method is applied, the sintered body containing the predetermined amount of oxide is prepared, and then the first method may be applied. However, the oxide may be introduced into the grown crystal. . For this reason, oxide content shall be in the range of the said predetermined amount.
[0088]
In the third method, a seed crystal having the same composition as the target single crystal is generated by laser beam irradiation. That is, abnormal grain growth (particularly grain growth to a size of about 10 times or more of the unirradiated part) is caused in the irradiated part. Therefore, the irradiation conditions are not particularly limited as long as this abnormal grain growth occurs. For example, the energy density of a laser beam (laser light) is 10⁷W / cm²The following should be done. The wavelength is usually about 0.2 to 11 μm (however, the transmission wavelength of the single crystal is excluded).
[0089]
A known or commercially available apparatus may be used as the laser generator itself. The type of laser beam is not limited, for example, CO₂A laser beam or the like can be used. The irradiation area when the laser beam is irradiated is not limited, but is usually 1 mm.²The following is preferable.
[0090]
The above-mentioned sintered body can be irradiated with a laser beam while heating if necessary. Although the heating temperature in this case is not limited, the temperature is lower than the temperature at which crystal growth occurs from the single crystal to the polycrystal side, but this greatly varies depending on the material composition. For example, when growing a pure Nd: YAG single crystal, it is usually about 1000 to 1760 ° C., preferably 1200 to 1650 ° C. Heating can be performed using, for example, a heating furnace.
[0091]
Next, the crystal is grown by heat treatment at a temperature of 75 to 95%, preferably 80 to 95% of the melting point of the sintered body. These methods may be carried out in the same manner as the second invention. For example, it can be determined appropriately according to the composition of the sintered body used. The heat treatment time may be appropriately set according to the heat treatment temperature, the size of the desired single crystal, and the like.
[0092]
In the third method, it is desirable to adjust the rate of temperature rise during crystal growth. Specifically, it is 50 ° C./h or less, preferably 20 ° C./h or less. By adjusting to such a heating rate, efficient crystal growth can be performed.
[0093]
In the third method, when the crystal is grown, an average temperature gradient of 10 ° C./cm or more is obtained by applying at least one of (a) heating to the seed crystal part and (b) cooling to the terminal part other than the part. It gives to the said sintered compact.
[0094]
The seed crystal part includes not only the seed crystal itself but also a part where the seed crystal and the sintered body are in contact with each other. This portion can be heated by partial heating with a heater, white light, laser beam, or the like. The terminal portion is usually a portion that is finally crystallized last, and can be appropriately determined according to the shape of the sintered body, the desired crystal growth direction, and the like. For example, when the sintered body is a cube or a cylinder, if a seed crystal is present in the central part of one surface (intersection or central point of diagonal lines), the central part of the surface facing the surface is the terminal part. Can do.
[0095]
The average temperature gradient in the present invention has the same meaning as in the second method. In the present invention, the sintered body is given a temperature gradient such that the average temperature gradient is 10 ° C./cm or more, preferably 50 ° C./cm or more. When the average temperature gradient is less than 10 ° C./cm, there are fears that many low-angle grain boundaries are generated in the obtained single crystal or the dislocation density is excessive. In addition, the upper limit value of the average temperature gradient is not particularly limited, but is usually about 200 ° C./cm.
[0096]
The heating method (a) and the cooling method (b) can be performed in the same manner as the second method. The treatments (a) and (b) can be used in combination. That is, it is possible to cool the end portion while heating the seed crystal portion. If both processes are used together, a larger average temperature gradient can be obtained.
[0097]
When a seed crystal is irradiated with a laser beam, the energy density of the laser beam (laser light) varies depending on the beam spot diameter and the like, but is usually 10⁷W / cm²The following should be done. The wavelength is usually about 0.2 to 11 μm (however, the transmission wavelength of the single crystal is excluded). As the laser beam apparatus itself, a known or commercially available apparatus can be used. The type of laser beam is not limited, for example, CO₂A laser beam or the like can be used.
[0098]
When laser beam irradiation is used in combination with heating, for example, the sintered body in which a single crystal and a seed crystal are formed may be placed in a heating furnace, and then the seed crystal may be irradiated with a laser beam while being heat-treated.
[0099]
[Action]
In the present invention, crystal growth is performed by heat treatment at 75 to 95% of the melting point of the laser medium (for example, 1470 to 1860 ° C. in the case of Nd: YAG, which is the mainstream of laser materials). The existing platinum crucible (for example, an iridium crucible that is more expensive than platinum in the case of Nd: YAG growth) and an ultrahigh-temperature facility of 1900 ° C. or higher (for example, 1980 to 2000 ° C. in the case of Nd: YAG growth) are not required. In addition, since a crystal growth rate of 1 mm / h or more can be effectively obtained, the manufacturing period is greatly shortened as compared with the case where the conventional method is used.
[0100]
In general, when a single crystal having a composition system of two or more components is produced by a melt solidification method, there is a limit to improvement in composition uniformity due to the influence of gravity. Improvement of the compositional uniformity inside the material is a common problem in the melt solidification method, but no clue has been found to solve it.
[0101]
With respect to this problem, the present invention has been found that the ceramics process is a breakthrough for its elucidation. In the ceramic process, basically, since the raw materials are not melted and sintered in a non-molten state, each constituent element is always constrained in a solid (crystal). That is, in view of the fact that each constituent element in the solid is hardly affected by gravity, the problems of non-uniformity and segregation that occur in the production of a single crystal should be almost eliminated. However, in the ceramics process, if the composition distribution of the starting materials in the green compact is not uniform, the moving distance of the constituent components in the sintering process is very short, so that only inferior uniformity can be obtained compared to single crystals by the melt solidification method. It will not be. For this reason, it is difficult to ensure composition uniformity in the manufacturing process with conventional ceramic technology (firing method), so even if single crystallization can be achieved by the firing method, it is produced by the melt solidification method. It was considered to be more heterogeneous than single crystals.
[0102]
On the other hand, in the present invention, the use of a material having a specific composition as a starting material has succeeded in solving the problems in the conventional firing method, and a single crystal having a higher quality than ever before is industrially produced. It can be provided on a scale.
[0103]
For example, in a single crystal, optical nonuniform parts such as growth stripes, facets, and cores are generated inside the crystal, whereas in a single crystal produced by a sintering method, such optical nonuniform parts are not generated. rare. Until now, the portion where the core was generated could not be used as a laser crystal, and there were restrictions such as that the laser emission direction had to be perpendicular to the growth stripes and facets. Further, for example, in the case of an Nd: YAG laser, <211> facets are generated, so that it is difficult to take out the laser crystal in an orientation that can reduce thermal birefringence, which is a problem during high output operation.
[0104]
【The invention's effect】
By applying the present invention, the platinum crucible and the ultra-high temperature equipment of 1900 ° C. or higher, which has been necessary in the manufacture of the conventional solid-state laser medium, are no longer necessary, and the manufacturing period is greatly shortened. Manufacturing costs can be greatly reduced.
[0105]
In addition, it is possible to efficiently produce a single crystal having a relatively small angle boundary or a single crystal having a relatively low dislocation density and no optical nonuniformity. Therefore, for example, a large, high-quality single crystal can be provided. As a result, an inexpensive high-performance solid-state laser oscillator can be provided.
[0106]
【Example】
Examples are given below to further clarify the features of the present invention. However, the scope of the present invention is not limited to the scope of the examples.
[0107]
In each of the following Examples 1 and 2, an alumina sintered body having a purity of 99.9% by weight or tungsten was used as a heat sink material, and the sintered body was placed on the heat sink material as shown in FIG. Crystals were grown while blowing air and cooling. The temperature of the air as the refrigerant was set lower than the furnace atmosphere temperature.
[0108]
In Example 3, crystal growth was performed while directly cooling with air without using a heat sink. In all the examples, the temperature difference between the air and the furnace atmosphere is 150 ° C., and the sample length is 25 mm. Therefore, the average temperature gradient is 60 ° C./cm.
[0109]
The calculation of the number per unit area of crystal grains forming the low-angle grain boundaries and the measurement of dislocation density and refractive index distribution in each example and comparative example were performed as follows.
In addition, it confirmed from the X-ray diffraction image that it was single-crystallized.
(1) Number of crystal grains forming a small-angle grain boundary per unit area, dislocation density
By etching the sample in a hot phosphoric acid solution (stock solution) at a temperature of about 100 ° C., a concave image appears on the sample surface. When a small-angle grain boundary or dislocation exists, a concave image as shown in FIG. 4 is obtained. In FIG. 4, the dot-shaped concave image (A) is a dislocation. In FIG. 4, the linear concave image is a small-angle grain boundary (B).
[0110]
In the present invention, the number per unit area of the point-like concave image is expressed as “dislocation density (pieces / cm²) ”. Moreover, in FIG. 4, it is a crystal grain (C) which forms a low-inclination grain boundary, this is counted as one, and the number of such parts is the observation area (cm²) Divided by “the number of crystal grains forming a small-angle grain boundary per unit area (pieces / cm²) ”.
(2) Refractive index distribution
Measurement was performed using a Twiman type interferometer. Light source is wavelength λ₁= 1.3 μm YAG laser was used. A detection image obtained from the interferometer was detected by an InSb detector, and a refractive index distribution in the sample surface was obtained from the obtained interference fringes. The sample has an average surface roughness (Ra) of 0.3 nm or less and a flatness λ₂/ 10 (λ₂= 633 nm) and below, precision processing was performed within 3 sec of parallelism.
(3) Pore volume
One surface of the sample was mirror-polished, and the pore area exposed on the surface was integrated 100 to 500 times with a reflection microscope, and the ratio to the measurement area was obtained as the pore volume. In this case, the calculated value is the area ratio, but this value was simply set as the pore volume. However, the measurement area is at least 1 cm²It was.
(4) Average temperature gradient
As shown in FIG. 5, a thermocouple is previously installed in the crystal growth start part or the seed crystal part (X) and the terminal part (Y), and the temperature difference ΔT (° C.) is measured. A value (ΔT / L) obtained by dividing ΔT by the sample length L (cm) was defined as an average temperature gradient (° C./cm). For example, in Example 1, since ΔT is 150 ° C. and the sample length is 2.5 cm, the average temperature gradient is 60 ° C./cm.
[0111]
Example 1
As Example 1, a 1 mol% Nd-added YAG single crystal was produced.
[0112]
Nd having a purity of 99.9% by weight and an average particle size of 100 nm produced by the coprecipitation method_0.03Y_2.97Al_FiveO₁₂After the powder was prepared and pulverized and mixed in a ball mill, the obtained mixed powder was CIP molded at a pressure of 98 MPa.
[0113]
The obtained molded body was sintered at 1550 ° C. for 3 hours to prepare a sintered body having a relative density of 99.8%. By cutting this sintered body, the cone shown in FIG. 2 is formed (the tip of the cone is φ8 mm, and this portion is finished to Ra = 1.0 nm and flatness λ / 2), and the same processing is performed. An accurately finished φ8 × t1 mm YAG single crystal (<111> orientation) was used as a seed crystal, and both were bonded together by heat treatment at 1500 ° C. for 1 hour. Thereafter, the temperature range of 1600 ° C. to 1800 ° C. is raised by 5 ° C./h (heat treatment time 40 hours) in an oxygen atmosphere (electric furnace) and at the same time the lower end of the sample is cooled by a heat sink (oxygen gas is blown into the alumina sintered body). The sample was given a temperature gradient of 60 ° C./cm on average. The sample that reached 1800 ° C. was cooled to room temperature.
[0114]
The average growth rate was 0.88 mm / h because the single crystal was formed from the portion joined to the single crystal to a depth of 35 mm (diameter 2 inches). There is no small-angle grain boundary in the single crystallized portion, and the other dislocation density is 10¹Piece / cm²The residual pore volume was 1 ppm by volume.
[0115]
FIG. 6A shows the obtained Nd: YAG single crystal observed through a polarizing plate. The Nd: YAG single crystal produced by the conventional melt solidification method (FIG. 6B) (Shintaro Miyazawa) Author, "Optical Crystal" (published by Bafukan), quoted from p253) Observed core (distorted part (1)), facet (refractive index part (2)), growth stripes, etc. could not. The refractive index distribution was measured with a Fizeau interferometer. As shown in Fig. 7 (b) (Ginya Adachi et al., "New Technology for Advanced Materials" (published by Kagaku Dojin), p186) Whereas several single-crystal fringes are observed in the single crystal, the single crystal produced by this method (FIG. 7 (a)) has a slight bending of the interference fringes, and the refractive index when viewed at the ingot level. It was confirmed that the uniformity was excellent.
[0116]
Example 2
As Example 2, a 5.0 mol% Nd-added YAG single crystal was produced. Nd with a purity of 99.99% by weight and an average particle size of 200 nm, 50 nm and 300 nm₂O_Three, Y₂O_Three, Al₂O_ThreePowder Nd_0.15Y_2.85Al_FiveO₁₂After the composition was weighed and pulverized and mixed with a ball mill, the obtained mixed powder was CIP molded at a pressure of 196 MPa.
[0117]
The obtained molded body was sintered at 1600 ° C. for 3 hours to produce a sintered body having a relative density of 99.9%. By cutting this sintered body, the cone portion shown in FIG. 2 (the tip of the cone portion is φ8 mm, and this portion is finished to Ra = 0.5 nm and flatness λ / 4)) is the same. A φ8 × t1 mm YAG single crystal (<111> orientation) finished with processing accuracy was used as a seed crystal, and both were bonded by heat treatment at 1500 ° C. for 1 hour. Thereafter, the temperature of 1600 to 1800 ° C. in an oxygen atmosphere (electric furnace) is raised by 5 ° C./h (heat treatment time 60 hours), and at the same time, the lower end of the sample is cooled by a heat sink (oxygen gas is blown into the lumina sintered body). As a result, an average temperature gradient of 30 ° C./cm was formed on the sample. The sample that reached 1800 ° C. was cooled to room temperature.
[0118]
The average growth rate was 0.50 mm / h because the single crystal was formed from the portion joined to the single crystal to a depth of 30 mm (diameter 2 inches). There is no low-angle grain boundary in the single crystallized portion, and the other dislocation density is 5 / cm.²The residual pore volume was 0.1 ppm by volume.
[0119]
FIG. 6 (a) shows the obtained Nd: YAG single crystal observed through a polarizing plate. The core, facet, and growth fringe observed in the Nd: YAG single crystal produced by the conventional melt solidification method. Could not be observed at all. Further, a sintered body having a relative density of 99.9% sintered at 1600 ° C. for 3 hours was subjected to growth treatment in an FZ furnace (growth temperature 1990 ° C., moving speed 0.2 mm / h). A large number of inclusions were generated in the single crystal (FIG. 8), and it was not possible to use as an optical material at all.
[0120]
Further, when the refractive index distribution was measured with a Fizeau interferometer, the in-plane refractive index distribution Δn was 5 × 10.^FiveThus, it has been found that the optical characteristics at the ingot level far surpass the conventional technology (even the optical quality of the low concentration Nd: YAG single crystal).
[0121]
Example 3
In Example 3, a 1 mol% Nd-added YAG single crystal similar to Example 1 was produced.
[0122]
Nd with a purity of 99.99% by weight and an average particle size of 80 nm produced by the coprecipitation method_0.03 Y_2.97Al_FiveO₁₂After the powder was prepared and pulverized and mixed in a ball mill, the obtained mixed powder was CIP molded at a pressure of 98 MPa.
[0123]
The obtained molded body was sintered at 1550 ° C. for 3 hours to produce a relative density of 99.8%. By cutting this sintered body, the cone part shown in FIG. 2 (the tip of the cone part is φ8 mm and this part is finished to Ra = 1.0 nm and flatness λ / 2) is formed with the same machining accuracy. The YAG single crystal (<110> orientation) of φ8 × t1 mm finished as a seed crystal was heat-treated at 1500 ° C. for 1 hour in a state in which both were adhered, and the two were joined. Thereafter, a temperature range of 1650 to 1800 ° C. in a vacuum atmosphere (electric furnace) was heated at 3 ° C./h (heat treatment time 50 hours), and at the same time, the lower end of the sample was cooled with a heat sink (the tungsten plate was cooled with Ar gas). However, an average temperature gradient of 50 ° C./cm was formed on the samples. At this time, 10 samples having a diameter of 2 inches and a length of 65 mm (straight cylinder length of 50 mm) were inserted into the vacuum furnace, and the sample that reached 1800 ° C. was cooled to room temperature.
[0124]
The average growth rate was 1.1 mm / h because the single crystal was formed from the portion joined to the single crystal to a depth of 55 mm. There is no low-angle grain boundary in the single crystallized portion, and the other dislocation density is 10¹Piece / cm²The residual pore volume was 1 ppm by volume. <110> direction crystal extraction that hardly causes thermal birefringence at the time of high-power operation of the laser can be taken out, and the solid-state laser performance can be greatly improved.
[0125]
As comparative data, a 1 at% Nd: YAG single crystal having a 2-inch size was grown by the Czochralski method. The growth temperature was 1980 ° C., and a <111> YAG single crystal was used as a seed crystal, and was pulled up at a growth rate of 0.3 mm / h. It takes about 180 hours to reach a length of 55 mm, and according to simple calculation, the productivity per hour is 1/36 of this technology. Further, in the synthesized single crystal, as in the case of single crystal growth reports by the conventional solidification method, optical non-uniform portions such as a core are generated, and the portion usable as a laser medium is 30 in total. %. For this reason, the productivity as a laser medium is further reduced to 1/100 level of this method. In addition, the occurrence of <211> and <100> facets has a drawback that a laser medium having a crystal orientation effective for reducing thermal birefringence cannot be obtained.
[0126]
Example 4
As Example 4, a 0.1 mol% Ti-added sapphire single crystal was produced. Commercially available Al with a purity of 99.99% by weight and an average particle size of 200 nm₂O_ThreePowder and TiO with a particle size of 60 nm₂The composition of each powder was adjusted at a molar ratio of 999: 2, and then wet mixed by a ball mill, and the resulting mixed powder was CIP molded at a pressure of 98 MPa.
[0127]
The obtained molded body was sintered at 1300 ° C. for 2 hours to produce a sintered body having a relative density of 99.5%, and then capsule-free HIP treatment (pressure 98 MPa) for 1 hour at 1400 ° C. in an Ar atmosphere. Thus, a sintered body having a relative density of 99.91% was obtained. It was. By cutting this sintered body, a cone portion (the tip of the cone portion is φ8 mm and this portion is finished to Ra = 1.0 nm and flatness λ / 2) is formed, and φ8 × finished to the same machining accuracy A t1 mm sapphire single crystal (<0001> orientation) was used as a seed crystal, and both were bonded together by heat treatment at 1420 ° C. for 1 hour. Thereafter, the temperature range of 1450 to 1850 ° C. is raised in a vacuum atmosphere (electric furnace) by 10 ° C./h (heat treatment time 40 hours) and at the same time the lower end of the sample is cooled by a heat sink (oxygen gas is blown into the alumina sintered body). As a result, an average temperature gradient of 60 ° C./cm was formed in the sample. The sample that reached 1850 ° C. was cooled to room temperature.
The average growth rate was 1.25 mm / h because the single crystal was formed from the portion joined to the single crystal to a depth of 50 mm (diameter 2 inches). There is no low-angle grain boundary in the single crystallized portion, and the other dislocation density is 10¹Piece / cm²The residual pore volume was 0.5 ppm by volume. The sapphire single crystal grown by this method is yellow and most of the added Ti is Ti.⁴⁺It was estimated that For this reason, the grown Ti-added sapphire is heat-treated in a hydrogen atmosphere at 1850 ° C. for 10 hours to produce a pink single crystal, that is, Ti³⁺: Sapphire was obtained. In this crystal as well, cores, facets, growth stripes, etc. were not detected as in the case of the Nd: YAG single crystal.
[0128]
Example 5
As Example 5, a 1.0 mol% Ti-added sapphire single crystal was produced. Commercially available Al with a purity of 99.99% by weight and an average particle size of 200 nm₂O_ThreePowder and TiO with a particle size of 60 nm₂The composition of the powder was adjusted at a molar ratio of 990: 20, and wet-mixed with a ball mill, and the obtained mixed powder was CIP molded at a pressure of 98 MPa. The obtained molded body was sintered at 1300 ° C. for 1 hour to produce a sintered body having a relative density of 99.1%, and thereafter subjected to capsule-free HIP treatment at 1300 ° C. for 1 hour in an Ar atmosphere to obtain a relative density of 99. A 93% sintered body was obtained. By cutting this sintered body, a cone portion (the tip of the cone portion is φ8 mm, this portion is finished to Ra = 1.0 nm and flatness λ / 2), and finished to the same machining accuracy is φ8 mm. Xt1 mm sapphire single crystal (<0001> orientation) was used as a seed crystal, and both were bonded by heat treatment at 1420 ° C. for 1 hour. Thereafter, the temperature range of 1450 to 1850 ° C. is raised in a vacuum atmosphere (electric furnace) by 10 ° C./h (heat treatment time 40 hours) and at the same time the lower end of the sample is cooled by a heat sink (oxygen gas is blown into the alumina sintered body). As a result, an average temperature gradient of 50 ° C./cm was formed in the sample. The sample that reached 1850 ° C. was cooled to room temperature.
[0129]
The average growth rate was 0.75 mm / h because the single crystal was formed from the portion joined to the single crystal to a depth of 30 mm (diameter 2 inches). In the single-crystallized part, there are 5 low-angle grain boundaries / cm²The other dislocation density is 10²Piece / cm²The residual pore volume was 1.5 ppm by volume. The sapphire single crystal grown by this method has a beige color, and most of the added Ti is Ti.⁴⁺It was estimated that For this reason, the grown Ti-added sapphire is heat-treated in a hydrogen atmosphere at 1860 ° C. for 10 hours to produce a thick pink single crystal, that is, Ti³⁺: Sapphire was obtained. In the observation using the polarizing plate, no optically inhomogeneous portion could be observed in the crystal. However, 10²Piece / cm²Although a degree of ink was observed, the crystal was sufficiently applicable as a laser material.
[0130]
On the other hand, single crystals of the same composition were grown by HEM (Heat Exchange Method), which is a kind of melt solidification method. However, as in the case of high-concentration Nd: YAG single crystals, the grown crystals are difficult to measure. John was generated and the optical quality could not be measured.
[0131]
Example 6
As Example 6, a 0.1 mol% Ti-added sapphire single crystal was produced. Similar to Example 4, a commercially available Al having a purity of 99.99% by weight and an average particle diameter of 200 nm₂O_ThreePowder and TiO with a particle size of 60 nm₂The composition of each powder was adjusted at a molar ratio of 999: 2, and then wet mixed by a ball mill, and the resulting mixed powder was CIP molded at a pressure of 98 MPa.
[0132]
The obtained molded body was sintered at 1300 ° C. for 2 hours to produce a sintered body having a relative density of 99.5%, and then subjected to capsule-free HIP treatment (pressure 196 MPa) for 1 hour at 1400 ° C. in an Ar atmosphere. Thus, a sintered body having a relative density of 99.95% was obtained. This sintered body was inserted into an electric furnace heated to 1350 ° C. without being processed, and had a beam diameter of 0.1 mm and an output of 50 W (5 × 10 5^ThreeW / cm²CO₂Laser (wavelength: 10 μm) was irradiated for 2 hours to form coarse crystals of about 450 μm (average particle size of the peripheral part other than the coarse crystals was 8 μm). Thereafter, the temperature range of 1550 to 1900 ° C. in a vacuum atmosphere (electric furnace) is raised by 10 ° C./h (heat treatment time 45 hours), and at the same time, the lower end of the sample is cooled by a heat sink (oxygen gas is blown into the alumina sintered body). As a result, an average temperature gradient of 60 ° C./cm was formed on the samples. The sample that reached 1850 ° C. was cooled to room temperature.
[0133]
The average growth rate was 1.00 mm / h because the single crystal was formed from the portion joined to the single crystal to a depth of 45 mm (diameter 2 inches). There is no low-angle grain boundary in the single crystallized portion, and the other dislocation density is 10¹Piece / cm²The residual pore volume was 1 ppm by volume. The sapphire single crystal grown by this method is yellow and most of the added Ti is Ti.⁴⁺It was estimated that For this reason, the grown Ti-added sapphire is heat-treated at 1880 ° C. in a hydrogen atmosphere for 10 hours to produce a pink single crystal, that is, Ti³⁺: Sapphire was obtained. Even in this crystal, cores, facets, growth fringes, etc. could not be detected as in the case of the Nd: YAG single crystal.
[0134]
Example 7
As Example 7, 1 mol% Nd-added YVO_FourAn example of production of a single crystal is shown. Commercially available purity 99.999% by weight, average particle size 20 nm Y₂O_ThreePowder and commercially available V of purity 99.99% by weight, average particle size 300 nm₂O_FivePowder and Nd with an average particle size of 100 nm₂O_ThreeThe composition of the powders was adjusted at a molar ratio of 49: 50: 1, followed by wet mixing with a ball mill, and the obtained mixed powder was CIP molded at a pressure of 98 MPa.
[0135]
The obtained molded body was sintered at 1550 ° C. for 3 hours to produce a sintered body having a relative density of 96.3%. This sintered body is further 20% O.₂HIP treatment was performed at 1450 ° C. and 98 MPa in a gas atmosphere having a composition of −80% Ar. By cutting this sintered body, the cone portion shown in FIG. 2 (the tip of the cone portion is φ8 mm, and this portion is finished to Ra = 1.0 nm and flatness λ / 2) is formed. Φ6 × t1mm YVO finished with precision_FourA single crystal (<001> orientation) was used as a seed crystal, and the two were bonded together by heat treatment at 1400 ° C. for 1 hour. Thereafter, the temperature range of 1650 to 1750 ° C. is raised by 2 ° C./h (heat treatment time 50 hours) in an oxygen atmosphere (electric furnace), and at the same time, the lower end of the sample is cooled by a heat sink (N in the alumina sintered body)₂-1% O₂When the gas was blown), an average temperature gradient of 15 ° C./cm was formed on the sample. The growth was performed in a high-pressure vessel, and the inside of the vessel was always maintained at 3 atm. The sample that reached 1750 ° C. was cooled to room temperature.
[0136]
The average growth rate was 0.44 mm / h because the single crystal was formed from the portion joined to the single crystal to a depth of 22 mm (diameter 1 inch). There is no low-angle grain boundary in the single crystallized portion, and the other dislocation density is 10¹Piece / cm²The residual pore volume was 0.3 ppm by volume.
[0137]
When the obtained Nd: YAG single crystal was observed through a polarizing plate, an optical non-uniform portion could not be detected.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a positional relationship between a crystal growth start part X and a terminal part Y when a crystal is grown.
FIG. 2 is a schematic diagram (cross-sectional view) showing a state in which a seed crystal part is heated during crystal growth.
FIG. 3 is a schematic diagram (cross-sectional view) showing a state in which a terminal portion of a polycrystal is forcibly cooled when a crystal is grown.
FIG. 4 is a schematic diagram showing crystal grains C forming dislocations A, small tilt grain boundaries B, and small tilt grain boundaries appearing by etching a sample.
FIG. 5 is a schematic diagram showing a method for measuring an average temperature gradient in an example.
FIG. 6 is an image diagram showing the results of observing Nd: YAG single crystals produced by the method (a) and the melt solidification method (b) of the present invention through polarizing plates, respectively.
FIG. 7 is an image view showing a result of measuring a refractive index distribution of a Nd: YAG single crystal produced by the method (a) and the melt solidification method (b) of the present invention using a Fizeau interferometer.
FIG. 8 is an image diagram of a single crystal produced in Example 2 and an ink observed in the single crystal.

Claims (21)

A single crystal for a laser oscillator substantially composed of a single crystal of Nd-added YAG, Ti-added sapphire or Nd-added YVO ₄ ,
1) The size of the single crystal is 1 inch in diameter x 22 mm in height,
2) The number n (pieces / cm ² ) per unit area of crystal grains forming a low-angle grain boundary is 0,
3) A single crystal for a laser oscillator, characterized in that the dislocation density (excluding dislocations constituting a low-angle grain boundary) is 10 / cm ² or less. The single crystal body for a laser oscillator according to claim 1 , wherein the pore volume is 100 ppm by volume or less. The single crystal for a laser oscillator according to claim 1 or 2 , wherein the purity is 99.5% by weight or more. After sintered Nd-doped YAG in a single crystal of the Nd-doped YAG is contacted as a seed crystal, by crystal growth by heat treatment at 75% to 95% of the temperature of the melting point of the sintered body, the Nd-doped A method for producing a single crystal of YAG , in which, when a crystal is grown, an average temperature of 10 ° C./cm or more is obtained by (a) heating the seed crystal part and (b) cooling the end part other than the part. A method for producing a single crystal for a laser oscillator, wherein a gradient is imparted to the sintered body. After the Ti-added sapphire sintered body is brought into contact with the single crystal of the Ti-added sapphire as a seed crystal, the crystal is grown by heat treatment at a temperature of 75 to 95% of the melting point of the sintered body. A method for producing a single crystal of sapphire, in which, when a crystal is grown, an average temperature of 10 ° C./cm or more is obtained by applying (a) heating to a seed crystal part and (b) cooling to a terminal part other than the part. A method for producing a single crystal for a laser oscillator, wherein a gradient is imparted to the sintered body. Nd added YVO ₄ The Nd-added YVO ₄ The Nd-added YVO is obtained by contacting the single crystal of the above as a seed crystal and then heat-treating the sintered body at a temperature of 75 to 95% of the melting point of the sintered body to grow the crystal. ₄ In the method for producing a single crystal, an average temperature gradient of 10 ° C./cm or more is obtained by performing (a) heating on the seed crystal part and (b) cooling on the terminal part other than the part in crystal growth. Is provided to the sintered body. A method for producing a single crystal for a laser oscillator. The manufacturing method according to claim 4, wherein the sintered body has a relative density of 99% or more. The production according to any one of claims 4 to 7, wherein the (100) face, (110) face or (111) face of the single crystal is polished, and the polished face is brought into contact with the sintered body. Method. 9. The method according to claim 8 , wherein the polished surface has an average surface roughness Ra = 1.0 nm or less and a flatness λ (λ = 633 nm) or less. A part or all of the sintered body is polished to an average surface roughness Ra = 1.0 nm or less and a flatness λ (λ = 633 nm) or less, and the polished surface is brought into contact with the single crystal. Item 10. The production method according to any one of Items 4 to 9 . An aqueous solution containing at least one element selected from elements (excluding oxygen) constituting the single crystal is applied to at least one contact surface of the sintered body and the single crystal. The manufacturing method in any one of 4-10 . A single crystal seed crystal is produced by irradiating a sintered body of Ti-added sapphire with a laser beam, and then heat-treated at a temperature of 75 to 95% of the melting point of the sintered body to grow the crystal. A method for producing a single crystal of Ti-added sapphire , in which, when growing a crystal, (a) heating a seed crystal part and (b) cooling a terminal part other than the part, a temperature of 10 ° C./cm or more A method for producing a single crystal for a laser oscillator, wherein an average temperature gradient is applied to the sintered body. The manufacturing method according to claim 12 , wherein the wavelength of the laser beam is 0.2 to 11 μm (excluding the transmission wavelength of the single crystal). The manufacturing method according to claim 12 or 13 , wherein an irradiation area of the laser beam is 1 mm ² or less. The manufacturing method according to any one of claims 12 to 14 , wherein the sintered body is irradiated with a laser beam while being heated at a temperature of less than 90% of the melting point of the sintered body. The manufacturing method according to claim 4, 5, 6, or 12 , wherein an oxide capable of forming a liquid phase at the time of crystal growth is present in the molded body or sintered body. The method according to claim 4, 5, 6, or 12 , wherein the rate of temperature rise is set to 50 ° C / h or less when the crystal is grown. The manufacturing method according to claim 4, 5, 6, or 12 , wherein cooling is performed by spraying a refrigerant on the end portion. The manufacturing method according to claim 4, 5, 6, or 12 , wherein cooling is performed by bringing a heat sink material made of a metal or an inorganic material into contact with the end portion and bringing the refrigerant into contact with the heat sink material. The production method according to claim 4, 5, 6, or 12 , wherein the crystal growth of the single crystal is controlled by changing both (i) the heating rate or (ii) both the heating rate and the flow rate of the refrigerant. The laser oscillator using a laser oscillator for single crystal which is according to any one of claims 1 to 3 as a laser medium.

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