Garnet type crystal, production method for same, optical isolator using same, and optical processing equipment

Abstract

The present invention provides a garnet-type crystal in which the occurrence of cracks is suppressed, and provides a production method for the same. A crystal according to one embodiment of the present invention contains at least terbium (Tb), aluminum (Al), oxygen (O), and hydrogen (H), and has a garnet-type crystal structure or a garnet-like crystal structure. This crystal may have an absorption peak in the wavenumber range of 3000 cm-1 or more to 4000 cm-1 or less in an infrared absorption spectrum. Said absorption peak may be an absorption peak derived from an OH group.

Description

Garnet-type crystal, its manufacturing method, optical isolator using the same, and optical processing device

[0001] The present invention relates to a garnet-type crystal, a method for producing the same, and an optical isolator and an optical processing device using the same.

[0002] In recent years, with the spread of optical communications and laser processing machines for precision machining, there has been a demand for even higher output from various lasers used as light sources. To stabilize the light source and prevent damage, optical isolators that prevent optical feedback are important.

[0003] Conventionally, terbium gallium garnet (Tb ３ Ga ５ O １２ Terbium aluminum garnet (Tb) crystals have been used as a material with a larger Faraday rotation angle than TGG. ３ Al ５ O １２ In recent years, the development of terbium scandium aluminum garnet (Tb ３ Sc ２ Al ３ O １２ Research is being conducted on the growth of TAG or TSAG crystals, as well as on the growth of crystals with modified compositions based on TAG or TSAG.

[0004] It is known that crystals generally contain defects, and that the presence of such defects significantly affects many of the crystal's properties. For example, crystal defects can reduce transmittance and resistance to high-power lasers in crystals used as optical isolator materials. Furthermore, crystal defects caused by a lack of oxygen (oxygen defects) and crystal defects caused by a lack of some of the cations of the constituent elements (hereinafter referred to as "cation defects" for convenience) can also be factors that degrade the crystal's properties.

[0005] It has been reported that the above-mentioned TSAG can be grown as a crystal by the Czochralski (CZ) method (Non-Patent Document 1). There are also reports on growing a crystal having a composition in which a portion of the Tb in TSAG is replaced with Sc by the CZ method (Patent Documents 1 and 2). The CZ method is a method that allows a crystal to be grown without contact with the container, and is known as a bulk crystal growth method. However, crystals such as TSAG grown by the CZ method sometimes develop cracks. Furthermore, there is a risk of new cracks developing when selecting a crack-free portion to cut out a crystal of the desired shape.

[0006] In the CZ method, raw materials must be heated and melted, and the crystal must be grown by pulling it up from the melt surface. Therefore, during the growth process (crystal growth process) of the target crystal, a relatively steep temperature gradient at the crystal growth interface is unavoidable, which increases the likelihood of defects occurring during crystal growth and may prevent the crystal from growing with the most stable composition. Therefore, crystals grown under the high-temperature conditions used in the CZ method are likely to have many defects and residual instability. In fact, according to experiments conducted by the inventors, it is possible to reduce the frequency of the above-mentioned defects and residual instability by reducing the temperature gradient during crystal growth and lowering the temperature at the growth interface. However, even with such various crystal growth conditions, it has been found that crystals such as TSAG produced by the CZ method often do not fully achieve the characteristics required for optical isolator materials. Furthermore, using containers such as iridium crucibles, which are essential in the CZ method, at high temperatures for long periods of time is prone to breakage and shortens the container's lifespan, which is undesirable from the perspective of manufacturing costs.

[0007] JP 2002-293693 A International Publication No. 2012 / 014796

[0008] A Yoshikawa et al., Czochralski growth of Tb3Sc2Al3O12 single crystal for Faraday rotator, Materials Research Bulletin, Volume 37, Issue 1, 2002, Pages 1-10, ISSN 0025-5408, https: / / doi.org / 10.1016 / S0025-5408(01)00788-7.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a garnet-type crystal in which cracking is suppressed, particularly to provide a garnet-type crystal useful as an optical isolator material. It is also an object of the present invention to provide a method for producing the above garnet-type crystal under milder conditions than conventional methods, particularly at lower temperatures. It is also an object of the present invention to provide an optical isolator and an optical processing tool using the above garnet-type crystal.

[0010] In one embodiment, the present invention provides a garnet-type crystal, which contains at least terbium (Tb), aluminum (Al), oxygen (O) and hydrogen (H) and has a garnet-type crystal structure or a garnet-like crystal structure, thereby solving the above-mentioned problems. The garnet-type crystal of the present invention has a wavelength of 3000 cm in an infrared absorption spectrum. －１ More than 4000cm －１ The absorption peak may be in the wave number range of 3000 cm or less. －１ More than 4000cm －１ The absorption peaks present in the following wave number ranges may be absorption peaks derived from OH groups. The garnet-type crystal of the present invention may further contain an alkali metal and / or alkaline earth metal. The concentration of the alkali metal and / or alkaline earth metal is 1×10 １４ atoms / cm ３ 1x10 or more ２２ atoms / cm ３ In the garnet-type crystal of the present invention, the hydrogen concentration may be in the range of 1×10 １７atoms / cm ３ 1x10 or more ２１ atoms / cm ３ The following ranges may also be used:

[0011] The garnet-type crystal of the present invention has a crystal composition of Tb ３ Al ５ O １２ It may be expressed as:

[0012] The garnet-type crystal of the present invention may have a crystal composition represented by the following general formula (1): (Tb ａ－ｘ Sc ｘ ) (Sc ｂ－ｙ Al ｙ ) Al ｃ O １２－ｖ (1) (In formula (1), a, b, c, x, y, and v each independently satisfy the following: 2.8≦a≦3.2, 1.8≦b≦2.2, 2.5≦c≦3.5, 0.0≦x<0.3, 0.0≦y≦0.3, 0.0≦v≦0.5)

[0013] The garnet-type crystal of the present invention may have a crystal composition represented by the following general formula (2): (Tb ａ－ｘ－ｚ Sc ｘ Lu ｚ ) (Sc ｂ－ｙ－ｗ Al ｙ Lu ｗ ) (Al ｃ－ｔ Sc ｔ ) O １２－ｖ (2) (In formula (2), a, b, c, t, v, x, y, z, and w each independently satisfy the following: 2.8≦a≦3.2 1.8≦b≦2.2 2.8≦c≦3.2 0.0≦t≦0.5 0.0≦v≦0.5 0.0≦x≦0.5 0.0≦y≦0.3 0.0≦z+w≦0.6)

[0014] The garnet-type crystal of the present invention may have a crystal composition represented by the following general formula (3): (Tb ａ－ｘ－ｚ Sc ｘ M ｚ ) (Sc ｂ－ｙ－ｗ Al ｙ M ｗ ) (Al ｃ－ｔ Sc ｔ ) O１２－ｖ (3) (In formula (3), M contains at least one element selected from the group consisting of lutetium (Lu), thulium (Tm), ytterbium (Yb), yttrium (Y), and cerium (Ce), and a, b, c, t, v, x, y, z, and w each independently satisfy the following: 2.8≦a≦3.2 1.8≦b≦2.2 2.8≦c≦3.2 0.0≦t≦0.5 0.0≦v≦0.5 0.0≦x≦0.5 0.0≦y≦0.3 0.0≦z+w≦0.6) M may contain at least Lu.

[0015] In another embodiment, the present invention provides a method for producing a garnet-type crystal, comprising a step of reacting raw materials containing each element to be contained in the crystal by a solvothermal method in the presence of a mineralizer containing an alkali metal and / or alkaline earth metal, an acid mineralizer, or a mixture of both. (In this specification, the term "solvothermal method" may be interpreted as "hydrothermal synthesis" when water is used as the solvent.) The concentration of the mineralizer may be in the range of 1 M to 50 M. In the method for producing a garnet-type crystal of the present invention, the raw materials may be prepared so that the Al content is in excess relative to the composition of the target crystal. The raw materials may contain Tb and Sc, and the Al content may be 1.2 times or more the total of Tb and Sc in molar ratio terms. In the solvothermal reaction step, the reaction may be carried out at a temperature range of 400°C to 800°C and a pressure range of 25 MPa to 250 MPa.

[0016] The optical isolator according to the present invention has an optical isolator material made of the above-mentioned garnet-type crystal and is either polarization-dependent or polarization-independent, thereby solving the above-mentioned problems. The optical isolator of the present invention may be polarization-independent. The optical processing tool according to the present invention has the above-mentioned optical isolator and a laser light source, and the optical isolator is arranged on the optical path of the laser light emitted from the laser light source, thereby solving the above-mentioned problems.

[0017] According to the garnet-type crystal of one embodiment of the present invention, it is possible to provide a garnet-type crystal in which the occurrence of cracks is suppressed, and in particular to provide a garnet-type crystal useful as an optical isolator material. The occurrence of cracks is suppressed, and the occurrence of cracks is also suppressed when cutting out the crystal into a desired shape, for example, as a Faraday rotator to be used in an optical isolator.

[0018] The method for producing garnet-type crystals according to one embodiment of the present invention allows synthesis at lower temperatures than the conventional CZ method. As a result, the resulting crystals have controlled defects and a stable composition. Furthermore, the present invention does not require the use of expensive iridium crucibles, which are essential for the conventional CZ method, and therefore reduces the production costs of the target crystals. Furthermore, the solvothermal method is a technique suitable for mass production, making it advantageous in practical use.

[0019] 1 is a schematic diagram showing an embodiment of an optical isolator using a garnet-type crystal according to the present invention; FIG. 2 is a schematic diagram showing an embodiment of an optical processing device using a garnet-type crystal according to the present invention; FIG. 3 is a diagram showing a microscope image of the crystal of Example 1; FIG. 4 is a diagram showing a microscope image of the crystal of Example 1; and FIG. 5 is a diagram showing the results of powder X-ray diffraction measurement of the crystals of Example 1 and Comparative Example 1. (a) The crystals of Example 1 and Comparative Example 1 at a wavenumber of 1500 cm －１ From 6700 cm －１ 1A is a diagram showing an infrared absorption spectrum in the range of 1. (b) is a diagram showing a spectrum obtained by dividing the infrared absorption spectrum of the crystal of Comparative Example 1 from the infrared absorption spectrum of the crystal of Example 1 shown in (a). FIG. 1B is a diagram showing the result of secondary ion mass spectrometry of the crystal of Example 1.

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0021] [Optical Isolator] Fig. 1 is a schematic diagram showing one embodiment of an optical isolator according to the present invention. As shown in Fig. 1, the optical isolator 100 includes a polarizer 110, an analyzer 120, and a Faraday rotator 130 disposed between the polarizer 110 and the analyzer 120. The polarizer 110 and the analyzer 120 are disposed so that their transmission axes are non-parallel to each other, for example, at an angle of 45°.

[0022] A magnetic flux density B is applied to the Faraday rotator 130, for example, in a direction from the polarizer 110 toward the analyzer 120, i.e., along the incident direction of the light L. By applying the magnetic flux density B, the Faraday rotator 130 rotates the polarization plane of the light L that has passed through the polarizer 110 and causes it to pass through the transmission axis of the analyzer 120.

[0023] The optical isolator 100 is not limited to the above configuration and may have at least one of a polarizer and an analyzer. That is, the polarizer 110 may be replaced with the analyzer 120, making both the polarizers analyzers, or the polarizer 110 may be replaced with the analyzer 120, making both the polarizers polarizers. While this configuration is called a polarization-dependent type, the optical isolator configuration is not limited to this and may be, for example, a polarization-independent type. A polarization-independent type is an optical isolator in which a birefringent crystal wedge is used instead of the polarizer 110 and the analyzer 120. The birefringent crystal wedge on the light input side separates polarized light into ordinary and extraordinary light, which then pass through a Faraday rotator before entering the birefringent crystal wedge on the light output side, where they are combined into a single beam before exiting. However, the light beams traveling in the opposite direction do not ultimately combine into a single beam. The polarization-independent type configuration can be used regardless of the state of the incident light and can be used as a highly versatile optical isolator.

[0024] [Optical Isolator Material (Faraday Rotator)] Next, the Faraday rotator 130 will be described.

[0025] The Faraday rotator 130 is made of an optical isolator material made of a garnet-type crystal according to the present invention. That is, the optical isolator material is made of a crystal containing at least terbium (Tb), aluminum (Al), oxygen (O), and hydrogen (H) and having a garnet-type crystal structure or a garnet-like crystal structure. More preferably, the crystal has a wavelength of 3000 cm in the infrared absorption spectrum. －１ More than 4000cm －１ It has an absorption peak in the following wave number range, and more preferably, the absorption peak is an absorption peak derived from OH groups. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the garnet-type crystal according to the present invention will be described in detail.

[0026] <Composition> (First embodiment) In one embodiment, the crystal according to the present invention has a composition of Tb ３ Al ５ O １２ That is, the crystal of this embodiment is a terbium aluminum garnet crystal, which can be expressed as TAG. However, it should be noted that the garnet-type crystal of this embodiment is a novel compound that differs from conventional TAG in that it contains H in addition to Tb, Al, and O as constituent elements and contains OH groups in the crystal.

[0027] Second Embodiment In another embodiment, the garnet-type crystal of the present invention further contains scandium (Sc), and the composition of the crystal is represented by the following general formula (1), and also contains hydrogen (H): (Tb a－ｘ Sc ｘ ) (Sc ｂ－ｙ Al ｙ ) Al ｃ O １２－ｖ (1) (In formula (1), a, b, c, x, y, and v each independently satisfy the following: 2.8≦a≦3.2 1.8≦b≦2.2 2.5≦c≦3.5 0.0≦x<0.3 0.0≦y≦0.3 0.0≦v≦0.5) The garnet-type crystal of this embodiment has a Faraday rotation angle that is equivalent to or greater than that of conventional crystals over a wide wavelength range.

[0028] In the above formula (1), the a is usually 2.8 or more, preferably 2.9 or more, and usually 3.2 or less, preferably 3.1 or less. The b is usually 1.8 or more, preferably 1.9 or more, and usually 2.2 or less, preferably 2.1 or less. The c is usually 2.8 or more, preferably 2.9 or more, and usually 3.2 or less, preferably 3.1 or less. The v is usually 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less, even more preferably 0.2 or less, particularly preferably 0.1 or less, and most preferably 0.0. When the a, b, c, and v are within the above-mentioned ranges, the crystal structure is stabilized as a garnet or garnet-like crystal structure. In a particularly preferred specific embodiment, c = 3.0 and v = 0.0, and at this time, the decrease in the transmittance of the crystal is more reliably suppressed.

[0029] In the general formula (1), x is usually 0.0 or more, preferably 0.0<x, and is usually smaller than 0.3, preferably x<0.2. ３ Sc ２ Al ３ O １２ When the composition is based on this, the substitution of a portion of Tb with Sc is expected to stabilize the garnet structure, which can more effectively prevent cracks from occurring in the crystal when it is cut out.

[0030] In a specific embodiment, x in the general formula (1) may satisfy 0.1≦x<0.2. In a conventional TSAG crystal produced by the CZ method, when x is 0.1 or more, a second phase may crystallize in the crystal. However, in this embodiment, even when x satisfies the above condition, a garnet-type crystal in which cracking is suppressed can be obtained.

[0031] In the general formula (1), y satisfies 0.0≦y≦0.3. Preferably, y is 0.02 or more, and more preferably, y is 0.28 or less. When y is within the above range, the decrease in transmittance of the crystal is sufficiently suppressed.

[0032] In the above general formula (1), when x is 0.0, y is 0.0, z is 0.0, and v is 0.0, the composition of the crystal is Tb ３ Sc ２ Al ３ O １２ As described above, the garnet-type crystal of this embodiment is a crystal having a composition based on terbium scandium aluminum garnet (which may be expressed as TSAG). However, it should be noted that the garnet-type crystal of this embodiment is a novel compound that differs from conventional TSAG in that it contains H in addition to Tb, Sc, Al, and O as constituent elements.

[0033] As will be understood from the manufacturing method described below, in the manufacturing method of a garnet-type crystal according to an embodiment of the present invention, the raw materials (or raw material mixture) are reacted by a solvothermal method, so that the resulting crystal has the most stable composition. In conventional TSAG crystals manufactured by the CZ method, the number of oxygen atoms may be less than 12 due to defects in the crystal, but in the garnet-type crystal of this embodiment, such oxygen defects are sufficiently suppressed. As a result, the decrease in the transmittance of the crystal is sufficiently suppressed.

[0034] (Third Embodiment) In yet another embodiment, the garnet-type crystal of the present invention has a crystal composition represented by the following general formula (2): (Tb ａ－ｘ－ｚ Sc ｘ Lu ｚ ) (Sc ｂ－ｙ－ｗ Al ｙ Lu ｗ ) (Al ｃ－ｔ Sc ｔ ) O １２－ｖ (2) (In formula (2), a, b, c, t, v, x, y, z, and w each independently satisfy the following: 2.8≦a≦3.2 1.8≦b≦2.2 2.8≦c≦3.2 0.0≦t≦0.5 0.0≦v≦0.5 0.0≦x≦0.5 0.0≦y≦0.3 0.0≦z+w≦0.6)

[0035] The garnet structure is {C ３} [A ２ ](D ３ ) O１２ When the composition formula is expressed by the general formula (2), the crystal expressed by the general formula (2) is (Tb ａ－ｘ－ｚ Sc ｘ Lu ｚ ) indicates that a part of Tb in the {C} site can be substituted with at least one of Sc and Lu, and (Sc ｂ－ｙ－ｗ Al ｙ Lu ｗ ) indicates that a part of Sc in the [A] site can be substituted with at least one of Lu and Al, and (Al ｃ－ｔ Sc ｔ ) indicates that a part of Al in the (D) site can be substituted with Sc.

[0036] In the above formula (2), a, b, y, t, and v can each independently be the same as the value in the formula (1) in a normal and preferred embodiment, and the effects obtained by the values ​​being in each range are also the same as those in formula (1). In one embodiment, in formula (2), c is 2.8 or more, preferably 2.9 or more, and c is 3.2 or less, preferably 3.1 or less. When c is in the above range, the crystal structure is stabilized.

[0037] In formula (2), x is usually 0.0 or more and 0.5 or less. x is preferably 0.4 or less, more preferably 0.3 or less, even more preferably 0.2 or less, and particularly preferably 0.1 or less. When x is within the above range, it is possible to obtain crystals in which the decrease in the Verdet constant is suppressed.

[0038] In the general formula (2), z is usually 0.0 or more and 0.6 or less. z is preferably 0.01 or more, and preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.3 or less, and particularly preferably 0.2 or less. When z is within the above range, the garnet-type crystal of this embodiment has a Faraday rotation angle greater than that of conventional TGG crystals over a wide wavelength range, and a decrease in the transmittance of the crystal is sufficiently suppressed. Furthermore, the garnet-type crystal of this embodiment has very few defects, and the occurrence of cracks is suppressed.

[0039] In a preferred specific embodiment, in the above general formula (2), a is 3.0 and b is 2.0, but each can vary within the above range due to the occurrence of defects, etc. However, in the garnet-type crystal of this embodiment, the occurrence of such defects, etc. is very small compared to crystals produced by the conventional CZ method, and therefore the range of variation of a and b is considered to be small.

[0040] In another specific embodiment, in the general formula (2), a is 3.0, b is 2.0, z satisfies 0.0<z≦0.6, and w, y, v, t, and x are 0.0. In this case, the composition of the crystal is (Tb ３－ｚ Lu ｚ ) Sc ２ Al ３ O １２ Thus, the garnet-type crystal of this embodiment may be a terbium scandium lutetium aluminum garnet (which may be abbreviated as TSLAG) crystal. However, it should be noted that the garnet-type crystal of this embodiment is a novel compound that differs from conventional TSLAG in that it contains H in addition to Tb, Sc, Lu, Al, and O as constituent elements.

[0041] In one embodiment, (Tb ａ－ｘ－ｚ Sc ｘ Lu ｚ In the portion of (1), Lu may be a combination of Lu and at least one element selected from the group consisting of ytterbium (Yb), thulium (Tm), and cerium (Ce), as long as the elements in the combination satisfy the above-mentioned condition for z.

[0042] (Fourth embodiment) In still another embodiment, the garnet-type crystal of the present invention is a crystal whose composition is represented by the following general formula (3): (Tb ａ－ｘ－ｚ Sc ｘ M ｚ ) (Sc ｂ－ｙ－ｗ Al ｙ M ｗ ) (Al ｃ－ｔ Sc ｔ ) O １２－ｖ(3) (In formula (1), M includes at least one element selected from the group consisting of lutetium (Lu), thulium (Tm), ytterbium (Yb), yttrium (Y), and cerium (Ce), and a, b, c, t, v, x, y, z, and w each independently satisfy the following: 2.8≦a≦3.2, 1.8≦b≦2.2, 2.8≦c≦3.2, 0.0≦t≦0.5, 0.0≦v≦0.5, 0.0≦x≦0.5, 0.0≦y≦0.3, and 0.0≦z+w≦0.6.)

[0043] The garnet structure is {C ３} [A ２ ](D ３ ) O １２ When the composition formula is expressed by the general formula (3), the crystal represented by the general formula (3) is (Tb ａ－ｘ－ｚ Sc ｘ M ｚ ) indicates that a part of Tb in the {C} site can be substituted with at least one of Sc and M elements, and (Sc ｂ－ｙ－ｗ Al ｙ M ｗ ) indicates that a part of Sc in the [A] site can be substituted with at least one of the M element and Al, and (Al ｃ－ｔ Sc ｔ ) indicates that a part of Al in the (D) site can be substituted with Sc. However, it should be noted that the garnet-type crystal of this embodiment is a novel compound that differs from conventional crystals in that it contains H in addition to Tb, Sc, the M element, Al, and O as constituent elements.

[0044] In the formula (3), the values ​​of a, b, c, x, y, z, w, t, and v can be the same as those in the formula (2) in a normal and preferred embodiment, and the effects obtained thereby are also the same as those in the formula (2).

[0045] In formula (3), the value of x is usually 0.0 or more and 0.3 or less. x is preferably greater than 0.0, and preferably 0.40 or less, more preferably 0.30 or less, even more preferably 0.20 or less, particularly preferably 0.10 or less, and most preferably 0.05 or less. When the value of x is within the above range, the crystal structure becomes more stable. In another embodiment, x may be 0.0. In this case, the Tb concentration in the crystal becomes higher than when x is greater than 0.0, and as a result, the Faraday rotation angle of the crystal can become larger.

[0046] In the above general formula (3), z and w satisfy 0.0≦z+w≦0.6, and x satisfies 0.0≦x≦0.5, so that the garnet structure of the garnet-type crystal of this embodiment is expected to be stabilized. As a result, the generation of cracks in the garnet-type crystal of this embodiment is suppressed. Furthermore, the garnet-type crystal of this embodiment has extremely few defects and has a transmittance and Faraday rotation angle that are equivalent to or greater than those of conventional crystals over a wide wavelength range.

[0047] In a preferred embodiment, in the general formula (3), z and w each independently satisfy 0.0≦z≦0.3, 0.0≦w≦0.3, and satisfy z>w. This further stabilizes the garnet structure. More preferably, x and y each independently satisfy 0.0≦z≦0.2, 0.0≦w≦0.2.

[0048] In a particularly preferred embodiment, in the general formula (3), a is 3.0 and b is 2.0, but each can vary within the above range due to the occurrence of defects, etc. However, in the garnet-type crystal of this embodiment, the occurrence of such defects, etc. is very small compared to crystals produced by the conventional CZ method, and therefore the range of variation of a and b is considered to be small.

[0049] In another preferred embodiment, x = 0.0 and y = 0.0. Preferably, x is greater than 0.0, and preferably 0.40 or less, more preferably 0.30 or less, even more preferably 0.20 or less, particularly preferably 0.10 or less, and most preferably 0.05 or less. In another particularly preferred embodiment, in the general formula (3), y is 0.0, t is 0.0, and v is 0.0. This more reliably suppresses the decrease in the transmittance of the crystal. Furthermore, the garnet-type crystal of this embodiment has a Faraday rotation angle that is equivalent to or greater than that of conventional crystals over a wide wavelength range.

[0050] In one embodiment, the M element in the general formula (3) includes at least one element selected from the group consisting of Tb, Ce, Y, Lu, Yb, Tm, Mg, Ca, Hf, and Zr. In this case, it is sufficient that the element satisfies the above-mentioned conditions of x and y. More preferably, the M element includes Lu, and particularly preferably, the M element consists of Lu.

[0051] The garnet-type crystals according to the second, third, and fourth embodiments have a Faraday rotation angle greater than that of conventional TGG crystals over a wide wavelength range, and the decrease in crystal transmittance is sufficiently suppressed, making them suitable for Faraday rotators and optical isolators equipped with such Faraday rotators. Furthermore, the garnet-type crystals according to the present embodiments have extremely few defects and are less susceptible to cracking, making them suitable for use as optical isolator materials with excellent properties such as transmittance, thermal conductivity, laser resistance, Faraday rotation angle, and Verdet constant. The use of such optical isolator materials enables the optical isolator to have a longer life. Furthermore, in optical processing equipment, the frequency of replacing optical isolators can be reduced.

[0052] In the second, third and fourth embodiments, the number of oxygen atoms may be less than 12 due to defects in the crystal, but as described above, in the method for producing a garnet-type crystal according to the embodiment of the present invention, the raw materials (or raw material mixture) are reacted by a solvothermal method, and therefore, in the garnet-type crystal of the present embodiment, such oxygen defects are sufficiently suppressed compared to garnet-type crystals produced by the conventional Czochralski method. Note that the composition analysis of the general formulae (1) to (3) can be specified by single crystal structure analysis.

[0053] (Optional Constituent Elements) The garnet-type crystal of the present invention may further contain optional constituent elements other than Tb, Al, O, H, and the elements listed in the above-described embodiments.

[0054] In a typical embodiment, the garnet-type crystal further contains an alkali metal and / or an alkaline earth metal as an optional constituent element. In one exemplary embodiment, the alkali metal is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), and among these, it is preferably selected from the group consisting of K, Rb, and Cs. The alkaline earth metal is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra), and among these, it is preferably selected from the group consisting of Ca, Sr, and Ba. The alkali metal and alkaline earth metal may be a single metal or a combination of two or more metals. It is expected that the inclusion of an alkali metal and / or alkaline earth metal in the garnet-type crystal will passivate defects within the crystal.

[0055] In the embodiment in which the garnet-type crystal of the present invention contains an alkali metal and / or an alkaline earth metal, the concentration of the alkali metal and / or the alkaline earth metal is 1×10 １４ atoms / cm ３ 1x10 or more ２２ atoms / cm ３ The range is preferably 1×10１５ atoms / cm ３ 1x10 or more ２１ atoms / cm ３ The range is preferably 1×10 １６ atoms / cm ３ 1x10 or more ２０ atoms / cm ３ The range is as follows:

[0056] The method for measuring the concentration of alkali metals and / or alkaline earth metals in the crystal of the present invention is not particularly limited, and can be confirmed by conventional methods, for example, secondary ion mass spectrometry (SIMS) can be used. The same applies to the concentrations of elements other than alkali metals and alkaline earth metals (for example, the hydrogen concentration described below). Here, when SIMS is used, the concentrations of alkali metals and alkaline earth metals are values ​​at a depth of 3 μm, and the same applies to the hydrogen concentration. Note that SIMS measurement examples will be described in the Examples section.

[0057] In the first to fourth embodiments described above, the hydrogen concentration is 1×10 １７ atoms / cm ３ 1x10 or more ２１ atoms / cm ３ The range is preferably 1×10 １８ atoms / cm ３ 1x10 or more ２１ atoms / cm ３ The range is preferably 1×10 １８ atoms / cm ３ 1x10 or more ２０ atoms / cm ３ The range is as follows:

[0058] <Crystal Structure> The crystal according to the present invention has a garnet-type crystal structure or a garnet-like crystal structure. Here, the garnet-type crystal structure generally means a cubic crystal system, for example, one belonging to the space group Ia-3d. Furthermore, the garnet-like crystal structure is intended to mean one belonging to a subgroup of the space group Ia-3d, specifically, one belonging to the space group I4 of the tetragonal crystal system. １ / acd, I4 １ / a, space groups R-3c and R-3 of a rhombohedral crystal system, space groups Fddd and Ibca of an orthorhombic crystal system, space group I2 / a of a monoclinic crystal system, space group I-1 of a triclinic crystal system, etc. In other words, the garnet-type crystal according to the present invention is not limited to those having cubic symmetry, but also includes those in which the symmetry is changed.

[0059] The garnet-type crystal according to one embodiment of the present invention has an infrared absorption spectrum with a wave number of 3000 cm －１ More than 4000cm －１ In particular, the absorption peak is an absorption peak derived from OH groups, and as will be understood from the production method described later, the reaction system contains water (H ２ This is due to the inclusion of a protic solvent such as HCl, and is unique to the garnet-type crystal of the present invention, and is not found in crystals produced by the conventional CZ method.

[0060] In addition, the 3000 cm in the infrared absorption spectrum －１ More than 4000cm －１ In addition to the OH group, peaks due to NH stretching and CH stretching are known to exist in the following wave number range. However, if O and H are detected as the main constituent elements in the composition analysis of the obtained crystal, the peaks at 3000 cm in the infrared absorption spectrum of the garnet-type crystal of the present invention can be obtained. －１ More than 4000cm－１ The peaks in the following wave number ranges may be identified as absorption peaks derived from OH groups.

[0061] In other words, for example, Tb ３ Sc ２ Al ３ O １２ Although the crystal represented by the formula (I) may be expressed as TSAG, the garnet-type crystal according to one embodiment of the present invention is a novel compound that differs from conventional TSAG in that it contains H in addition to Tb, Sc, Al, and O as constituent elements and contains OH groups in the crystal. Furthermore, the inclusion of OH groups in the garnet-type crystal of the present invention is a result of the inclusion of a protic solvent such as water in the reaction system, and is produced at a lower temperature than conventional crystals, which is thought to contribute to the suppression of oxygen defects and cation defects, resulting in a high-quality crystal with controlled defects. Furthermore, the inclusion of hydrogen in the garnet-type crystal of the present invention is expected to inactivate defects in the crystal. Not all of the hydrogen contained in the garnet-type crystal of the present invention is in the form of OH groups, and the arrangement of hydrogen in the crystal may be random. It is thought that among these hydrogens, those located close to oxygen act as OH groups (or atomic groups having properties equivalent to OH groups), thereby exhibiting a specific absorption peak derived from OH groups in the above-mentioned wavenumber range in the infrared absorption spectrum.

[0062] [Method for Manufacturing Optical Isolator Material (Faraday Rotator)] Next, a method for manufacturing the optical isolator material (Faraday rotator 130) will be described. Below, as a representative embodiment, a method for manufacturing the garnet-type crystal according to the second embodiment will be described in detail. However, those skilled in the art will understand that it is also possible to manufacture garnet-type crystals according to other embodiments by making appropriate design changes based on the manufacturing steps, conditions, etc. described below.

[0063] A method for producing a garnet-type crystal constituting an optical isolator material according to an embodiment of the present invention comprises reacting a raw material containing terbium (Tb), a raw material containing aluminum (Al), and a raw material containing scandium (Sc) by a solvothermal method in the presence of a mineralizer containing an alkali metal and / or an alkaline earth metal, or an acid mineralizer, or a mixed mineralizer of both. An example of the production method will be described below.

[0064] <Step S110: Step of Preparing Raw Materials> In step S110, raw materials necessary for obtaining a compound that satisfies the composition of the target crystal are prepared.

[0065] Specifically, a Tb-containing raw material, an Al-containing raw material, and a Sc-containing raw material are prepared, and one or more compounds of these are converted into oxides. For convenience, the raw materials containing each of the constituent elements prepared in step S110 are also referred to as the raw materials of each of the constituent elements in this specification. For example, a "Tb-containing raw material" and a "Tb raw material" are synonymous.

[0066] As each raw material, a simple substance of the constituent element, an oxide, a hydroxide, a halide, an inorganic salt (sulfate, nitrate, carbonate, etc.), an organic salt (acetate, etc.), etc. can be used. Each compound other than the simple substance may be an anhydride or a hydrate. Non-limiting examples of usable raw materials for each constituent element that can be contained in the garnet-type crystal of the present invention are shown below.

[0067] The raw material of Tb is, for example, Tb ４ O ７ , Tb ２ O ３ As a raw material of Al, for example, Al ２ O ３ As the raw material of Sc, for example, Sc ２ O ３ can be used.

[0068] In the production of the garnet-type crystal according to the third embodiment, the raw material of Lu is, for example, Lu ２ O ３In the production of the garnet-type crystal according to the fourth embodiment, for example, an oxide of the M element can be used as the raw material of the M element. Specifically, when the M element is Lu, Lu ２ O ３ can be used, and if Tm, Tm ２ O ３ can be used, and in the case of Yb, Yb ２ O ３ can be used, and if Y, Y ２ O ３ When the M element is Ce, for example, CeO ２ , Ce ２ O ３ , CeF ３ Furthermore, the raw material may contain two or more of the elements exemplified above.

[0069] In one embodiment, the above-mentioned raw materials are in the ratio of the above general formula (1), more specifically, Tb ３ Sc ２ Al ３ O １２ In another embodiment, the raw material is prepared so that the Al content is in excess of the designed composition that satisfies the ratio of the general formula (1). For example, when the composition (designed composition) of the target garnet-type crystal is Tb ３ Sc ２ Al ３ O １２ In the embodiment, the amount of Al may be 1.2 times or more, 1.3 times or more, 1.4 times or more, or 1.5 times or more, in terms of molar ratio, relative to the total amount of Tb and Sc. ３ Sc ２ Al ３ O １２ is the designed composition, and the above-mentioned raw materials are prepared so that the molar ratio of the sum of Tb and Sc to Al is 3:5. In this embodiment, the composition at the stage of step S110 is ０．６ Sc ０．４ ) ３ Al ５ O １２In any of the embodiments, a raw material mixture containing each raw material may be prepared as needed.

[0070] <Step S120: Step of reacting raw materials by a solvothermal method in the presence of a mineralizer> In step S120, the raw materials prepared in step S110 (or a raw material mixture prepared by mixing the respective raw materials) are reacted by a solvothermal method in the presence of a mineralizer.

[0071] The mineralizer may be a mineralizer containing an alkali metal and / or alkaline earth metal, an acid mineralizer, or a mixture of both. The mineralizer containing an alkali metal and / or alkaline earth metal is a compound containing an alkali metal and / or alkaline earth metal, and examples of the mineralizer include hydroxides and inorganic salts (carbonates, etc.) of alkali metals and / or alkaline earth metals. Non-limiting examples of the mineralizer include KOH, K ２ CO ３ , RbOH, Rb ２ CO ３ , CsOH, Cs ２ CO ３ , Ca(OH) ２ , CaCO ３ , Sr(OH) ２ , SrCO ３ , Ba(OH) ２ , BaCO ３ It is preferable to select at least one compound from the group consisting of these compounds. The alkali metal and / or alkaline earth metal contained in the mineralizer can be contained in the finally obtained garnet-type crystal. Examples of acid mineralizers include, but are not limited to, hydrochloric acid, nitric acid, sulfuric acid, formic acid, etc.

[0072] The method for preparing the solution (reaction solution) to be used for synthesis by the solvothermal method is not particularly limited. For example, when the raw material mixture is prepared in the above-mentioned step S110, a solution of a mineralizer may be added to the raw material mixture, and further mixing may be performed as needed. Alternatively, a mineralizer (preferably in powder or tablet form) may be added to the raw material mixture, and further mixing may be performed as needed. Alternatively, the above-mentioned raw materials may be added to an aqueous solution of a mineralizer and appropriately mixed. Here, the concentration of the mineralizer in the finally prepared reaction solution is preferably 1 M or more and 50 M or less, more preferably 5 M or more and 40 M or less, and even more preferably 10 M or more and 30 M or less.

[0073] Here, the pH of the reaction solution changes depending on the type of alkali metal and / or alkaline earth metal contained in the mineralizer used and the concentration of the mineralizer, and by utilizing this, the reaction conditions (specifically, temperature conditions) in the solvothermal method can be adjusted. Although a certain degree of care is required in handling highly alkaline solutions, a desired reaction solution can be prepared by appropriately adjusting the concentration of the mineralizer. It is also preferable to select the type of mineralizer depending on the raw materials used and / or the types of constituent elements of the target garnet-type crystal.

[0074] The reaction conditions for the solvothermal method are not particularly limited, and conditions used in conventional solvothermal methods can be applied. The temperature conditions are preferably in the range of 400°C or higher and 800°C or lower. This ensures that the desired garnet-type crystals can be obtained. If the reaction temperature is lower than 400°C, the desired garnet-type crystals may not be produced, and if the reaction temperature exceeds 800°C, the reaction temperature may exceed the heat-resistant temperature of the reaction vessel used in the solvothermal method. The temperature conditions are preferably in the range of 450°C or higher and 750°C or lower, more preferably in the range of 500°C or higher and 750°C or lower, even more preferably in the range of 550°C or higher and 750°C or lower, and particularly preferably in the range of 600°C or higher and 750°C or lower. The pressure conditions are preferably in the range of 25 MPa or higher and 250 MPa or lower. It is preferable to adjust the pressure conditions depending on the amount of a protic solvent, such as water, contained in the reaction vessel.

[0075] The time for the reaction step by the solvothermal method can be adjusted appropriately from the viewpoint of completing the reaction depending on the type and amount of raw materials used. Here, two or more temperature conditions may be set within the above-mentioned temperature range to set a predetermined temperature profile. Such a temperature profile can be designed taking into consideration the viewpoints of further improving the homogeneity and stability of the reaction solution, and more efficiently producing the target garnet-type crystal. An example of a specific temperature profile will be shown in the examples described below.

[0076] In the manufacturing method of the present invention, the raw material (or raw material mixture) is reacted by the solvothermal method at a temperature significantly lower than that of the conventional CZ method, so that the evaporation phenomenon described above in relation to the CZ method is unlikely to occur. In addition, in the case of the solvothermal method, the obtained crystals are generally obtained with the most stable composition, and although there is a possibility that the composition may deviate slightly from the target composition, even if such a deviation occurs, it is considered that the difference from the target composition is very small and can be adjusted.

[0077] [Uses of Crystal] Next, uses of the garnet-type crystal according to the present invention will be described.

[0078] The garnet-type crystal of the present invention is suitable for use as the optical isolator material described above, although there is no particular limitation on its application. In one embodiment, an optical processing device can be constructed using an optical isolator material (Faraday rotator) made of the garnet crystal of the present invention.

[0079] <Optical Processing Apparatus> Here, an optical processing apparatus according to the present invention will be described with reference to Fig. 2. In Fig. 2, components that are the same as or equivalent to those in Fig. 1 are given the same reference numerals, and duplicated descriptions will be omitted.

[0080] Fig. 2 is a schematic diagram showing one embodiment of an optical processing apparatus according to the present invention. As shown in Fig. 2, the optical processing apparatus 200 includes a laser light source 210 and an optical isolator 100 arranged on an optical path P of the laser light L emitted from the laser light source 210. According to this optical processing apparatus 200, the laser light L emitted from the laser light source 210 passes through the optical isolator 100, and the emitted light can be used to process a workpiece Q. Such an optical processing apparatus can be used as a laser processing machine.

[0081] Here, the garnet-type crystal used in the Faraday rotator (130 in FIG. 1) of the optical isolator 100 is transparent, so that the absorption of light by the garnet-type crystal is reduced. Therefore, in the optical processing instrument 200 according to this embodiment, the laser light source 210 can be made more resistant to damage caused by light from the Faraday rotator.

[0082] Furthermore, the garnet-type crystal used as the Faraday rotator has very few defects within the crystal, which prevents cracks from occurring. Therefore, in the optical processing device 200 according to this embodiment, the optical isolator 100 can have a long life. As a result, the optical isolator 100 in the optical processing device 200 needs to be replaced less frequently.

[0083] The laser light source 210 is not particularly limited, but may be, for example, a laser light source with an oscillation wavelength of 1064 nm or more (e.g., an Nd:YAG laser) or an Yb-doped fiber laser with an oscillation wavelength of 1080 nm. Alternatively, a laser light source with an oscillation wavelength of less than 1064 nm may be used as the laser light source 210. Examples of laser light sources with an oscillation wavelength of less than 1064 nm include laser light sources with an oscillation wavelength of 400 to 700 nm. Examples of laser light sources with an oscillation wavelength of 400 to 700 nm include GaN-based semiconductor lasers with an oscillation wavelength of 405 nm and titanium sapphire lasers with an oscillation wavelength of 700 nm. The oscillation wavelength of the laser light source 210 may be in the range of 700 to 1064 nm, for example, around 800 nm, or in the range of 1030 to 1080 nm.

[0084] In the above embodiment, the optical isolator material made of the garnet-type crystal according to the present invention is used in the optical isolator of the optical processing device, but it is not limited to the optical isolator. The garnet-type crystal of the present invention can also be applied to an optical magnetic field sensor that observes changes in a magnetic field by measuring changes in the Faraday rotation angle using a Faraday rotator. Furthermore, the garnet-type crystal of the present invention can be used for applications other than the Faraday rotator.

[0085] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0086] [Crystal Production] In this example, terbium scandium aluminum garnet (TSAG) crystal was grown.

[0087] Example 1 As raw materials for Tb, Sc, and Al, Tb ２ O ３ , Sc ２ O ３ and Al ２ O ３ was prepared. Here, Tb ２ O ３ is a commercially available Tb ４ O ７ (Purity 99.99%, powder form, manufactured by Furuuchi Chemical Co., Ltd.) was compressed and molded by isostatic pressing, and then fired in a reducing atmosphere to produce ceramics. ２ O ３ and Al ２ O ３ All of the raw materials used were commercially available (purity 99.99%, powder form, manufactured by Furuuchi Chemical Co., Ltd.). ０．６ Sc ０．４ ) ３ Al ５ O １２The raw materials were weighed to satisfy the ratio. The total mass of the raw materials was 0.3366 g. The prepared raw materials and KOH (tablets equivalent to a 20 M aqueous solution) as a mineralizer were placed in a silver ampoule (diameter 5 mm x length 10 cm), and this ampoule was placed in a container containing water (10 mL), and synthesis was carried out by the solvothermal method. The synthesis conditions by the solvothermal method were to heat the material to 700 °C over 12 hours, hold it for 24 hours (maximum pressure reached at this time was 214 MPa), and then cool it to 450 °C over 250 hours to terminate the reaction. The temperature reduction program from 450 °C to room temperature at the end of the reaction was set to 1 hour, and then the material was allowed to cool naturally. This resulted in the crystals of Example 1.

[0088] Example 2 Crystals of Example 2 were obtained in the same manner as in Example 1, except that the temperature during heating was set to 730° C. as a condition for synthesis by the solvothermal method.

[0089] Example 3 Crystals of Example 3 were obtained in the same manner as in Example 1, except that the temperature during heating was set to 620° C. as a condition for synthesis by the solvothermal method.

[0090] Comparative Example 1 A mixture prepared using the same raw materials as in Example 1 (except that the composition was Tb ３ Sc ２ Al ３ O １２ The raw material mixture was then heated by high-frequency induction heating to a temperature at which it melted, and a seed crystal (prepared by growing a Tb ３ Sc ２ Al ３ O １２ The seed crystal was then rotated at 10 rpm and pulled upward at a speed of 1 mm / h to crystallize it, thereby obtaining the crystal of Comparative Example 1.

[0091] [Crystal Analysis] <Microscopic Observation> The crystals obtained in Examples 1 to 3 above were observed under an optical microscope. Figures 3A and 3B show microscopic images of the crystals of Example 1. Figure 3A shows several relatively large crystals selected from the obtained crystals, while Figure 3B shows that a large number of crystals of different sizes were obtained. The scale bars in the microscopic images of Figures 3A and 3B are 1 mm and 2 mm, respectively.

[0092] 3A and 3B, the crystals of Example 1 were confirmed to be highly transparent when observed under a microscope. Furthermore, no cracks were observed in the crystals of Example 1. Although not shown, a large number of crystals of different sizes were also obtained in Examples 2 and 3, and all of the crystals were confirmed to be highly transparent when observed under a microscope, and no cracks were observed.

[0093] <X-ray Diffraction Analysis> Powder samples were prepared from the crystals of Example 1 and Comparative Example 1 and subjected to powder X-ray diffraction measurement. The results are shown in Figure 4. In Figure 4, the intensity on the vertical axis is in arbitrary units.

[0094] According to FIG. 4, the crystals of Example 1 and Comparative Example 1 have a high degree of coincidence in peak positions (angle 2θ) in the diffraction charts, which indicates that a single-phase TSAG single crystal was obtained in Example 1. Although the diffraction charts of both samples share the same peak intensity at approximately 32°, the intensity ratios of other peaks relative to this peak tend to differ. Although not shown, the results of powder X-ray diffraction measurements of the crystals of Examples 2 and 3 were similar to those of the crystals of Example 1, confirming that a single-phase TSAG single crystal was also obtained in Examples 2 and 3. When structural analysis was performed on the crystals of Example 1 using a single crystal structural analysis method, it was found that the crystals of Example 1 were single crystals with a garnet-type structure and a composition of Tb ３ Sc ２ Al ３ O １２The crystals of Examples 2 and 3 also had a garnet-type structure. The single crystal structure analysis was carried out at 296 K using a single crystal structure analyzer (Rigaku Corporation, XtaLAB Synergy-R / DW Custom, Mo Ka radiation, 1 = 0.71073 Å) and a HyPix detector. Lattice refinement and data processing were carried out using CrysAlis. Ｐｒｏ The software program was used. A preliminary structure analysis was performed using SHELXT, followed by squared structure factors (F) using SHELXL in the Olex2 program package. ２ ) was refined by full-matrix least squares fitting.

[0095] <Transmittance Analysis> The transmittance of the crystals of Example 1 and Comparative Example 1 was analyzed by infrared spectroscopy. A Fourier transform infrared spectrometer (Spectrum GX FT-IR system, manufactured by PERKIN ELMER) was used as the analyzer. The thickness of the sample used for analysis was 367 μm for the crystal of Example 1 and 1135 μm for the crystal of Comparative Example 1. Note that no cracks were observed in the crystal of Example 1 when cutting out the sample for analysis.

[0096] The results are shown in Figure 5(a). Figure 5(a) shows the crystals of Example 1 and Comparative Example 1 at a wave number of 1500 cm －１ From 6700 cm －１ 5(a) shows the infrared absorption spectrum in the wavenumber range of 1500 cm between the crystal of Example 1 and the crystal of Comparative Example 1. －１ Approximately 2,400 cm from －１ and about 4000 cm －１ From 6700 cm －１ The spectral shapes in the range of wavenumbers are relatively similar, whereas the spectral shapes in the range of wavenumbers around 2400 cm －１ Approximately 4000 cm from －１ In particular, in the range of about 3000 cm －１ Approximately 4000 cm from －１ It was found that the crystal of Example 1 was different in that it had a characteristic absorption peak (peak pattern) in the spectrum in this range.

[0097] Therefore, by dividing the infrared absorption spectrum of the crystal of Comparative Example 1 shown in FIG. 5(a) by the infrared absorption spectrum of the crystal of Example 1, the spectrum shown in FIG. 5(b) was obtained. From FIG. 5(b), the difference between the crystal of Example 1 and the crystal of Comparative Example 1 described above with reference to FIG. 5(a) can be more clearly understood. This characteristic absorption peak was identified in light of the characteristic absorption peaks observed in various functional groups, and was found to be derived from OH groups. The infrared absorption spectrum of the crystal of Comparative Example 1 did not have an absorption peak derived from OH groups. Although not shown, the crystals of Examples 2 and 3 were also analyzed for translucency, and as a result, characteristic absorption peaks derived from OH groups were confirmed, similar to those of the crystal of Example 1.

[0098] From this, it can be seen that the crystals produced by the solvothermal method using the method of the present invention have a near-infrared absorption spectrum (particularly in the wave number range of 3000 cm). －１ More than 4000cm －１ It was found that the compound had a specific absorption peak due to OH groups in the wavenumber range below.

[0099] <Secondary Ion Mass Spectrometry> The hydrogen (H) concentration and potassium (K) concentration of the crystal of Example 1 were measured using a secondary ion mass spectrometer (IMS-6F, manufactured by Cameca) and a time-of-flight secondary ion mass spectrometer (TOF-SIMS, manufactured by IonTOF, Inc.), respectively. The results are shown in FIG.

[0100] According to FIG. 6, the hydrogen concentration in the obtained crystal was about 1×10 at a depth of 3 μm. １９ atoms / cm ３ and 1×10 ２０ atoms / cm ３ The following is satisfied, and the potassium concentration is about 2 × 10 １８ atoms / cm ３ and 1×10 １９ atoms / cm ３It was found that the following was satisfied. It was also confirmed that the concentration ratios of terbium, scandium, and aluminum were almost identical to the designed composition. Although not shown, the crystals of Examples 2 and 3 were also subjected to a similar component analysis, and the hydrogen concentration was found to be 1×10 １７ atoms / cm ３ 1x10 or more ２１ atoms / cm ３ The potassium concentration is in the range of 1×10 １４ atoms / cm ３ 1x10 or more ２２ atoms / cm ３ It was confirmed that the range was as follows:

[0101] As described above, the crystals according to the examples of the present application contain hydrogen, and the crystals according to the comparative examples have excellent transparency and are less susceptible to cracking, and therefore are suitable for use as optical isolator materials and the like.

[0102] As described above, the present invention can provide a garnet-type crystal in which the occurrence of cracks is suppressed and which is suitable for optical isolators, etc. The present invention can also provide a method for producing the above-mentioned garnet-type crystal under milder conditions than conventional methods, particularly at lower temperatures. The present invention can also provide an optical isolator and an optical processing tool using the above-mentioned garnet-type crystal.

[0103] REFERENCE SIGNS LIST 100 Optical isolator 110 Polarizer 120 Analyzer 130 Faraday rotator (optical isolator material) 200 Optical processing device (laser processing machine) 210 Laser light source L Light (laser light) B Magnetic flux density P Optical path Q Workpiece

Claims

1. A crystal containing at least terbium (Tb), aluminum (Al), oxygen (O) and hydrogen (H), and having a garnet-type crystal structure or a crystal structure similar to the garnet type.

2. In the infrared absorption spectrum, having an absorption peak in the wavenumber range of 3000 cm －１ or more and 4000 cm －１ or less, the crystal according to claim 1.

3. The crystal according to claim 2, wherein the absorption peak is an absorption peak derived from an OH group.

4. The crystal according to any one of claims 1 to 3, further containing an alkali metal and / or an alkaline earth metal.

5. The concentration of the alkali metal and / or alkaline earth metal is 1 × 10 １４ atoms / cm ３ or more and 1 × 10 ２２ atoms / cm ３ or less, and the crystal according to claim 4.

6. The hydrogen concentration is 1 × 10 １７ atoms / cm ３ or more and 1 × 10 ２１ atoms / cm ３ or less, and the crystal according to any one of claims 1 to 5.

7. The composition of the crystal is Tb ３ Al ５ O １２ The crystal according to any one of claims 1 to 6, represented by 8. The crystal according to any one of claims 1 to 6, wherein the composition of the crystal is represented by the following general formula (1). (Tb ａ－ｘ Sc ｘ )(Sc ｂ－ｙ Al ｙ )Al ｃ O １２－ｖ (1) (In formula (1), a, b, c, x, y and v each independently satisfy the following. 2.8 ≤ a ≤ 3.2 1.8 ≤ b ≤ 2.2 2.5 ≤ c ≤ 3.5 0.0 ≤ x < 0.3 0.0 ≤ y ≤ 0.3 0.0 ≤ v ≤ 0.5) 9. The crystal according to any one of claims 1 to 6, wherein the composition of the crystal is represented by the following general formula (2). (Tb ａ－ｘ－ｚ Sc ｘ Lu ｚ )(Sc ｂ－ｙ－ｗ Al ｙ Lu ｗ )(Al ｃ－ｔ Sc ｔ )O １２－ｖ (2) (In formula (2), a, b, c, t, v, x, y, z, and w each independently satisfy the following. 2.8 ≤ a ≤ 3.2 1.8 ≤ b ≤ 2.2 2.8 ≤ c ≤ 3.2 0.0 ≤ t ≤ 0.5 0.0 ≤ v ≤ 0.5 0.0 ≤ x ≤ 0.5 0.0 ≤ y ≤ 0.3 0.0 ≤ z + w ≤ 0.6) 10. The crystal according to any one of claims 1 to 6, wherein the composition of the crystal is represented by the following general formula (3). (Tb ａ－ｘ－ｚ Sc ｘ M ｚ )(Sc ｂ－ｙ－ｗ Al ｙ M ｗ )(Al ｃ－ｔ Sc ｔ )O １２－ｖ (3) (In formula (3), M contains at least one element selected from the group consisting of lutetium (Lu), thulium (Tm), ytterbium (Yb), yttrium (Y), and cerium (Ce), and a, b, c, t, v, x, y, z, and w each independently satisfy the following. 2.8 ≤ a ≤ 3.2 1.8 ≤ b ≤ 2.2 2.8 ≤ c ≤ 3.2 0.0 ≤ t ≤ 0.5 0.0 ≤ v ≤ 0.5 0.0 ≤ x ≤ 0.5 0.0 ≤ y ≤ 0.6 0.0 ≤ z + w ≤ 0.3) 11. The crystal according to claim 10, wherein the M contains at least Lu.

12. A method for producing the crystal according to any one of claims 1 to 11, comprising a step of reacting a raw material containing each element contained in the crystal in the presence of a mineralizer containing an alkali metal and / or an alkaline earth metal, or a mineralizer of an acid, or a mixed mineralizer of both by a solvothermal method.

13. The method according to claim 12, wherein the concentration of the mineralizer is in the range of 1 M or more and 50 M or less.

14. The method according to claim 12 or 13, wherein each raw material is prepared to be Al-excessive with respect to the composition of the target crystal.

15. The method according to any one of claims 12 to 14, wherein the raw material contains Tb and Sc, and in terms of molar ratio, Al is 1.2 times or more with respect to the total of Tb and Sc.

16. The method according to any one of claims 12 to 15, wherein in the step of reacting by the solvothermal method, the reaction temperature is 400 °C or more and 800 °C or less, and the pressure is 25 MPa or more and 250 MPa or less.

17. An optical isolator having an optical isolator material made of the crystal according to any one of claims 1 to 11, and being polarization-dependent or polarization-independent.

18. The optical isolator according to claim 17, which is polarization-independent.

19. An optical processor having the optical isolator according to claim 17 or 18 and a laser light source, wherein the optical isolator is disposed on the optical path of the laser light emitted from the laser light source.