Paramagnetic garnet-type transparent ceramic and its manufacturing method

Abstract

Paramagnetic garnet type transparent ceramic is represented by the following formula (1)(Tb 1‑x‑y Y x Sc y )3(Al 1‑z Sc z )5O 12 A sintered body of rare earth aluminum garnet containing Tb represented by (1) (wherein 0<x<0.45, 0<y≤0.1, and 0.004<z<0.2), wherein, as a total light transmittance spectrum at an optical path length of 24 mm, when the total light transmittance at a wavelength of 900 nm is set to a%, and the total light transmittance at an arbitrary wavelength λ on the wavelength side longer than 900 nm is set to b%, |a-b|≤0.1 at least when 900 nm<λ<1100 nm, no thermal lens effect occurs even for a laser output of 100 W, and the sintered body can be used as a Faraday rotator for a high-output fiber laser.

Description

Technical Field

[0001] The present invention relates to paramagnetic garnet-type transparent ceramics that can be used as magneto-optical materials. More specifically, it relates to magneto-optical materials composed of terbium-containing paramagnetic garnet-type transparent ceramics suitable for constituting magneto-optical disks such as optical isolators, paramagnetic transparent ceramics that can be used in high-output fiber lasers of 100 W or more, and methods for manufacturing the same. Background Art

[0002] In recent years, with the increasing output of lasers, laser processing using fiber lasers has become increasingly popular. To ensure stable laser processing, it is necessary to eliminate external light to prevent oscillation disturbances. In particular, when light reflects off the fiber end face, the reflected light reaches the laser source, significantly disrupting oscillation. Therefore, in conventional fiber lasers, components called isolators are installed at the boundaries between connecting fibers to completely suppress reflected light.

[0003] An optical isolator consists of a Faraday rotator, a polarizer placed on the light-entry side of the Faraday rotator, and an analyzer placed on the light-exit side (light-emitting side) of the Faraday rotator. The Faraday rotator is utilized by applying a magnetic field parallel to the direction of light travel. In this case, the polarization wave segments of light rotate in a specific direction, whether traveling forward or backward through the Faraday rotator. Furthermore, the Faraday rotator is adjusted to a length that allows the polarization wave segments of light to rotate exactly 45 degrees. If the polarization planes of the polarizer and analyzer are offset by 45 degrees in the direction of rotation of the advancing light, the polarization of the advancing light aligns at the polarizer and analyzer positions, allowing it to pass through. Meanwhile, the polarization of the retreating light rotates 45 degrees in the opposite direction of the polarization wave plane's deviation from the analyzer position by 45 degrees. Consequently, the polarization wave plane of the returning light at the polarizer position is offset by 45 degrees - (-45 degrees) = 90 degrees relative to the polarization wave plane of the polarizer, preventing it from passing through the polarizer. In this way, it functions as an optical isolator that transmits and emits forward light and blocks backward returning light.

[0004] As the existing materials for Faraday rotators, there are garnet-based Tb3Ga5O 12 (hereinafter referred to as TGG) (for example, Japanese Patent No. 4878343 (Patent Document 1)), C-type rare earth (Tb x Re (1-x) )2O3 (e.g., Japanese Patent No. 5704097 (Patent Document 2)), fluoride-based KTb3F 10 (Hereinafter referred to as KTF) (Non-Patent Document 1) These materials all contain terbium, which has low light absorption at a wavelength of 1064 nm used as a laser and a large Verdet constant (magneto-optical constant).

[0005] With the recent increase in the output of fiber lasers, the characteristics required of Faraday rotators have also changed. A small light absorption coefficient is more important than a large Verdet constant. If the Faraday rotator absorbs laser light, the light energy is converted into heat, forming temperature unevenness inside and outside the Faraday rotator. The temperature unevenness directly leads to refractive index unevenness, and the Faraday rotator has a refractive index distribution similar to that of a lens. This is called the thermal lens effect, and it can be observed as a deterioration in laser quality and a change in focal length. This thermal lens effect is not a problem in low-output lasers, but at high output, the thermal lens effect becomes prominent because the Faraday rotator is heated to above 40°C. Therefore, a small light absorption coefficient is required for high-output Faraday rotators.

[0006] TGG, commonly used in Faraday rotators, absorbs light in the target wavelength band, limiting its output to 70W. C-type rare earth metals offer the advantage of maximizing the Verdet constant, but their light absorption coefficient is more than twice that of TGG, forcing their output to 30W. On the other hand, fluoride-based KTF exhibits very low light absorption, making it possible to handle laser outputs exceeding 400W. However, from the perspectives of crystal stability and manufacturing costs, KTF still faces many unknowns, and its Verdet constant is comparable to that of TGG, so further improvements are not foreseen. Materials with lower absorption and a higher Verdet constant than the existing TGG are needed.

[0007] As a material having a lower absorption than the above-mentioned TGG and a higher Verdet constant, Tb3Al5O 12 (hereinafter referred to as TAG) (for example, Japanese Patent No. 3642063 (Patent Document 3)), Tb3Sc2Al3O 12 (hereinafter referred to as TSAG) (for example, Japanese Patent No. 5935764 (Patent Document 4)), (Y x Tb 1-x )3Al5O 12(Non-patent document 2). They have a Verdet constant of about 1.4 times that of TGG, and on the other hand, the light absorption is also small, so it is believed that they can be installed in fiber lasers at the 100W level. However, TAG is unstable as a crystal, so it is difficult to manufacture. In addition, TSAG contains a large amount of expensive Sc, which makes it disadvantageous in terms of cost. On the other hand, YTAG, which replaces part of the Tb of TAG with Y, is more stable than TAG as a crystal and does not use expensive elements, so it is a very promising material. However, in non-patent document 2, there is no information on thermal lenses in the high-output field, nor is there information on light absorption losses under actual installation lengths (above 14 mm). Based on non-patent document 2 alone, it is not clear whether YTAG ceramics can be used as high-output Faraday rotators.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent No. 4878343

[0011] Patent Document 2: Japanese Patent No. 5704097

[0012] Patent Document 3: Japanese Patent No. 3642063

[0013] Patent Document 4: Japanese Patent No. 5935764

[0014] Non-patent literature

[0015] Non-patent document 1: Laser Technik Journal 13 (2016): 18-21

[0016] Non-patent document 2: J. Am. Ceram. Soc. 100 (2017), 4081-4087 Summary of the Invention

[0017] Problems to be solved by the invention

[0018] The present invention has been made in view of the above-mentioned actual situation, and its object is to provide a paramagnetic garnet-type transparent ceramic which is a transparent sintered body of paramagnetic garnet-type oxide containing Tb, Y, and Al, which does not produce thermal lensing even at a laser output of 100 W and can be used as a Faraday rotator for high-output fiber lasers, and a method for producing the same.

[0019] Means for solving problems

[0020] The present inventors have developed various transparent ceramics for Faraday rotators as high-output Faraday rotators. 1-x-y Yx Sc y )3(Al 1-z Sc z )5O 12 In their research, they found that absorption from oxygen deficiencies or cation defects has a greater impact on the thermal lens effect than ever before at actual installation lengths. Based on this insight, they conducted in-depth research and completed a transparent ceramic that minimizes absorption in the 1064nm band and minimizes the generation of thermal lenses even when irradiated with a 100W laser.

[0021] That is, the present invention provides the following paramagnetic garnet-type transparent ceramics and a method for producing the same.

[0022] 1. A paramagnetic garnet-type transparent ceramic, comprising a sintered body of a rare earth aluminum garnet containing Tb represented by the following formula (1), wherein, as a total light transmittance spectrum at an optical path length of 24 mm, when the total light transmittance at a wavelength of 900 nm is represented by a % and the total light transmittance at an arbitrary wavelength λ on the wavelength side longer than 900 nm is represented by b %, at least when 900 nm < λ < 1100 nm, |ab| ≤ 0.1,

[0023] (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1)

[0024] In the formula, 0<x<0.45, 0<y≤0.1, 0.004<z<0.2.

[0025] 2. The paramagnetic garnet-type transparent ceramic according to item 1, wherein a minimum wavelength λ1 on the wavelength side longer than 900 nm, which satisfies |ab|>0.1, is 1100 nm or longer.

[0026] 3. The paramagnetic garnet-type transparent ceramic according to item 1 or 2, wherein the absorption coefficient at a wavelength of 1064 nm is 0.0030 cm -1 the following.

[0027] 4. The paramagnetic garnet-type transparent ceramic according to any one of 1 to 3, wherein the total light transmittance at the wavelength of 900 nm is 84% or more and 85% or less.

[0028] 5. The paramagnetic garnet-type transparent ceramic according to any one of 1 to 4, wherein when a laser beam with a wavelength of 1064 nm at an optical path length of 24 mm is incident with a beam diameter of 1.6 mm and an incident power of 100 W, the focal length variation rate caused by the thermal lens is less than 10%.

[0029] 6. A method for producing a paramagnetic garnet-type transparent ceramic according to any one of 1 to 5, characterized in that a sintered body of a rare earth aluminum garnet containing Tb represented by the following formula (1) is pressure-sintered, the pressure-sintered body is heated to a temperature exceeding the pressure-sintering temperature, and the re-sintered body is subjected to an oxidation annealing treatment in an atmosphere containing oxygen at least 15% by volume at a temperature of 1300° C. to 1500° C. for 10 hours or more.

[0030] (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1)

[0031] In the formula, 0<x<0.45, 0<y≤0.1, 0.004<z<0.2.

[0032] 7. The method for producing a paramagnetic garnet-type transparent ceramic according to 6, wherein the re-sintered body is pressure-sintered again before the oxidation annealing treatment, and then subjected to the oxidation annealing treatment.

[0033] Effects of the Invention

[0034] According to the present invention, a paramagnetic garnet-type transparent ceramic is provided, which is a transparent sintered body of a paramagnetic garnet-type composite oxide containing Tb and Al, wherein the total light transmittance spectrum satisfies a predetermined light absorption condition on the wavelength side longer than 900 nm based on the total light transmittance at a wavelength of 900 nm, and the absorption coefficient at 1064 nm at an actual mounting length of 24 mm is 0.0030 cm -1 The following are suitable as Faraday rotators for high output. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic cross-sectional view showing a configuration example of an optical isolator using the paramagnetic garnet-type transparent ceramic of the present invention as a Faraday rotator. DETAILED DESCRIPTION

[0036] In this specification, when a numerical range is expressed as "A to B", both ends of the numerical values are included, and it means that it is greater than or equal to A and less than or equal to B.

[0037] [Paramagnetic garnet-type transparent ceramics]

[0038] The paramagnetic garnet-type transparent ceramics according to the present invention will be described below.

[0039] The paramagnetic garnet type transparent ceramics of the present invention are represented by the following formula (1):

[0040] (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1)

[0041] (Wherein, 0<x<0.45, 0<y≤0.1, 0.004<z<0.2.)

[0042] The sintered body of rare earth aluminum garnet containing Tb represented has a total light transmittance spectrum at an optical path length of 24 mm. When the total light transmittance at a wavelength of 900 nm is set to a%, and the total light transmittance at an arbitrary wavelength λ on the wavelength side longer than 900 nm is set to b%, |ab|≤0.1 is satisfied at least when 900 nm<λ<1100 nm.

[0043] In the garnet crystal structure represented by formula (1), the site mainly occupied by Tb, i.e., the site in the first half of formula (1) is called an A site, and the site mainly occupied by Al, i.e., the site in the second half of formula (1) is called a B site.

[0044] In the A site of formula (1), terbium (Tb) is an element with the largest Verdet constant among trivalent rare earth ions. It has extremely low absorption in the 1064nm region (including a wavelength of 1070nm) used in fiber lasers, and is therefore the most suitable element for optical isolator materials in this wavelength range. However, Tb(III) ions are easily oxidized to produce Tb(IV) ions. If Tb(IV) ions are produced in metal oxides, light is absorbed at a wide range of wavelengths from the ultraviolet to the near-infrared region, and the transmittance is reduced. Therefore, it is desirable to exclude Tb(IV) ions as much as possible. As a strategy for not producing Tb(IV) ions, it is effective to adopt a crystal structure in which Tb(IV) ions are unstable, i.e., a garnet structure.

[0045] Yttrium (Y) has an ion radius approximately 2% smaller than that of terbium. When combined with aluminum to form a composite oxide, it can form a garnet phase more stably than a perovskite phase. Therefore, it is an element that can be preferably used in the present invention.

[0046] In the B site of formula (1), aluminum (Al) is a material with the smallest ionic radius among the trivalent ions that can exist stably in an oxide having a garnet structure, and is an element that can minimize the lattice constant of a paramagnetic garnet-type oxide containing Tb. It is preferred because it can reduce the lattice constant of the garnet structure without changing the Tb content, and can increase the Verdet constant per unit length. Furthermore, aluminum is a light metal, so its anti-magnetism (anti-magnetism) is weaker than gallium, and it is expected to relatively increase the effect of the magnetic flux density generated inside the Faraday rotator, and can also increase the Verdet constant per unit length, so it is preferred. In fact, the Verdet constant of TAG ceramics is increased to 1.25 to 1.5 times the Verdet constant of TGG. Therefore, even if a part of the terbium ions is replaced by yttrium ions to reduce the relative concentration of terbium, the Verdet constant per unit length can be made equal to that of TGG or remain at a slightly lower level, so it is a preferred constituent element in the present invention.

[0047] Among them, for the composite oxide whose constituent elements are only Tb, Y and Al, due to a small weighing error, it is sometimes not provided with a garnet structure, and it is difficult to stably manufacture a transparent ceramic that can be used in optical applications. Therefore, in the present invention, by adding scandium (Sc) as a constituent element, the composition deviation caused by a small weighing error is eliminated. Sc is a material with an intermediate ionic radius that can be solid-dissolved at both the A site and the B site in the oxide with a garnet structure. When the ratio of the rare earth element consisting of Tb and Y and Al deviates from the stoichiometric ratio due to the deviation during weighing, it is possible to automatically adjust the distribution ratio to the A site (the rare earth site consisting of Tb and Y) and the B site (aluminum site) and solid-dissolve so as to just meet the stoichiometric ratio and thereby minimize the formation energy of the crystallite. In addition, it is an element that can limit the presence ratio of the alumina heterophase relative to the garnet parent phase to less than 1ppm and the presence ratio of the perovskite heterophase relative to the garnet parent phase to less than 1ppm, and is an element added to improve the yield of the product.

[0048] In formula (1), the range of x is 0<x<0.45, preferably 0.05≤x<0.45, more preferably 0.10≤x≤0.40, and further preferably 0.20≤x≤0.40. If x is within this range, the Verdet constant at room temperature (25°C) and a wavelength of 1064nm becomes 30rad / (T·m) or more, and can be used as a Faraday rotator. In addition, within this range, the larger x is, the smaller the thermal lens effect tends to be, so it is preferred. Furthermore, within this range, the larger x is, the smaller the diffuse transmittance tends to be, so it is preferred. The same is true for lasers with a wavelength of 1070nm. However, when x is greater than 0.45, the Verdet constant at a wavelength of 1064nm is less than 30rad / (T·m), so it is not preferred. That is, if the relative concentration of Tb is excessively reduced, when a general magnet is used, the total length of the Faraday rotator required to rotate laser light of a wavelength of 1064 nm by 45 degrees exceeds 30 mm, making production difficult, which is not preferable.

[0049] In formula (1), the range of y is 0<y≤0.1, preferably 0<y<0.1, more preferably 0<y<0.08, further preferably 0.002≤y≤0.07, and particularly preferably 0.003≤y≤0.06. If y is within this range, the perovskite-type heterophase can be reduced to a level that cannot be detected by X-ray diffraction (XRD) analysis. Furthermore, in optical microscope observation, the amount of perovskite-type heterophase (typically a granular heterophase with a diameter of 1 to 1.5 μm and appearing to be colored light brown) in a field of view of 150 μm×150 μm is 1 or less, so it is preferred. At this time, the ratio of the perovskite-type heterophase to the garnet parent phase is 1 ppm or less.

[0050] When y is greater than 0.1, in addition to replacing part of the Tb with Y, part of the Tb is also replaced with Sc, resulting in an unnecessary decrease in the solid solution concentration of Tb, which in turn reduces the Verdet constant. This is not preferred. Furthermore, since the raw material price of Sc is high, unnecessary excessive doping with Sc is also undesirable from a manufacturing cost perspective. Furthermore, when y is greater than 0.08, the risk of anti-site defect absorption, where Tb and Y enter the B site and Al enters the A site, may increase.

[0051] In formula (1), when 0.05 ≤ x < 0.45 and 0 < y < 0.1, the range of 1-xy is preferably 0.5 < 1-xy < 0.95, more preferably 0.55 ≤ 1-xy < 0.95, and even more preferably 0.6 ≤ 1-xy < 0.95. When 1-xy is within this range, a large Verdet constant can be ensured while achieving high transparency at a wavelength of 1064 nm. The same applies to a wavelength of 1070 nm.

[0052] In formula (1), the range of z is 0.004<z<0.2, preferably 0.004<z<0.16, more preferably 0.01≤z≤0.15, and further preferably 0.03≤z≤0.15. If z is within this range, no perovskite-type heterophase can be detected in the XRD analysis. Furthermore, in optical microscope observation, the amount of perovskite-type heterophase (typically a granular heterophase with a diameter of 1 to 1.5 μm and appearing to be colored light brown) in a field of view of 150 μm×150 μm is 1 or less, so it is preferred. At this time, the ratio of the perovskite-type heterophase to the garnet parent phase is 1 ppm or less.

[0053] When z is 0.2 or greater, the effect of suppressing the precipitation of the perovskite-type heterogeneous phase saturates and remains unchanged. As the value of z increases, the value of y, i.e., the ratio of Tb substitution by Sc, also increases in tandem. Consequently, the Tb solid solution concentration decreases unnecessarily, and the Verdet constant decreases, which is not preferable. Furthermore, Sc raw material prices are high, so unnecessary excessive Sc doping is also undesirable from a manufacturing cost perspective. Furthermore, when z is 0.16 or greater, the risk of anti-site defect absorption, where Tb and Y enter the B site and Al enters the A site, may increase.

[0054] In the paramagnetic garnet-type transparent ceramic of the present invention, the sintered body preferably further contains a sintering aid. Specifically, the sintering aid preferably contains SiO2 in an amount exceeding 0% by mass and not exceeding 0.1% by mass (exceeding 0 ppm and not exceeding 1000 ppm). If the content exceeds 0.1% by mass (1000 ppm), crystal defects caused by the excessive Si content may cause slight light absorption.

[0055] Furthermore, the paramagnetic garnet-type transparent ceramic of the present invention has a total light transmittance spectrum at an optical path length of 24 mm, where the total light transmittance at a wavelength of 900 nm is defined as a% and the total light transmittance at any wavelength λ on the wavelength side longer than 900 nm is defined as b%. At least when 900 nm < λ < 1100 nm, |ab| ≤ 0.1 is satisfied. Furthermore, preferably, |ab| ≤ 0.1 is maintained at all times when 900 nm < λ < 1100 nm, and more preferably, the minimum (shortest) wavelength λ1 on the wavelength side longer than 900 nm at which |ab| > 0.1 is 1100 nm or longer. Specifically, this means that the spectral shape is such that the wavelength at which the absolute value (|ab|) of the difference between the total light transmittance at a wavelength of 900 nm at an actual installation length of 24 mm, defined as a% and the total light transmittance b on the wavelength side longer than 900 nm, first exceeds 0.1% is 1100 nm or longer.

[0056] When the paramagnetic garnet-type transparent ceramic of the present invention is used for a Faraday rotator, it is necessary to suppress the occurrence of a thermal lens effect so as to minimize absorption of laser light.

[0057] Among the causes of light absorption in transparent ceramics, oxygen vacancies caused by sintering at high temperatures and cation defects associated with crystal strain caused by making the sintered body transparent under high temperature and high pressure are believed to be among the possible causes. The oxygen vacancies are significantly enhanced by the addition of Y, resulting in a broad absorption band centered in the wavelength range of 750 to 900 nm, giving the sintered body a black appearance. This absorption tails into the operating wavelength range of 1000 to 1100 nm, naturally affecting the thermal lens effect. Meanwhile, while the cause of cation defects is unclear, they tend to form when making the sintered body transparent under high temperature and high pressure, resulting in an absorption pattern that gradually decreases from 900 nm toward the shorter and longer wavelengths. The absorption on the shorter and longer wavelengths can also be linearly linked, giving the sintered body a brown appearance. The shorter wavelength range is outside the operating wavelength range of the Faraday rotator and therefore does not affect its characteristics. However, the absorption from 900 nm toward the longer wavelengths does affect the thermal lens effect.

[0058] Furthermore, when the oxygen deficiency has broad absorption centered at wavelengths of 750 to 900 nm and spanning the near-infrared region, b is larger than a in the total light transmittance. On the other hand, when the cation deficiency exists, a is larger than b.

[0059] If the wavelength at which the absolute value of the difference between a and b (|ab|) first exceeds 0.1% is less than 1100 nm, there is a high probability that a broad absorption tail centered at 750 nm will be affected by oxygen deficiency, while a moderate absorption tail centered at 900 nm will be generated by cation deficiency. In either case, a thermal lens effect will occur if a 100W laser with a wavelength of 1000 to 1100 nm is input.

[0060] However, if the absolute value of the difference between a and b (|ab|) first exceeds 0.1% at any wavelength above 1100 nm, the occurrence of the thermal lens effect is small even when a 100W laser with a wavelength of 1000 to 1100 nm is input. If it is above 1150 nm, its occurrence is further reduced.

[0061] Furthermore, the absorption coefficient of the paramagnetic garnet-type transparent ceramic of the present invention at a wavelength of 1064 nm is preferably 0.0030 cm -1 less than 0.0015 cm, more preferably 0.0015 cm -1The absorption coefficient is a parameter that indicates the degree of light absorption of an optical material. The smaller its value, the smaller the thermal lens effect. If the actual installation length is 24mm, the absorption coefficient is 0.0030cm -1 In the case of 100W, the thermal lens effect can be suppressed. -1 In the case of 100W laser irradiation, the paramagnetic garnet-type transparent ceramic (Faraday rotator) heats up, causing a thermal lens effect.

[0062] The absorption coefficient is measured using the following method. Specifically, the absorption coefficient is calculated from the transmittance, using the difference between the theoretical transmittance obtained from the refractive index and the measured total light transmittance. The calculation method in this case is based on the following formula (2).

[0063] Absorption coefficient = -10 × log 10 (I / I0) / L (2)

[0064] (where I: measured transmittance, I0: theoretical transmittance, L: sample length (cm))

[0065] The total light transmittance measurement method may refer to JIS K7361-1 (ISO 13468-2: 1999) and JIS K7375: 2008, and examples thereof include a double-beam method or a single-beam method using a commercially available ultraviolet-visible spectrometer, and transmission loss measurement using laser light.

[0066] Furthermore, when measuring the total light transmittance of a paramagnetic garnet-type transparent ceramic without an antireflection coating, the total light transmittance at a wavelength of 900 nm at an actual mounting length of 24 mm is preferably 84% or higher and 85% or lower. In this case, assuming that this total light transmittance is a%, and the total light transmittance at any wavelength on the wavelength side longer than 900 nm is b%, the wavelength at which the absolute value of the difference between a and b (|ab|) first exceeds 0.1% is 1100 nm or higher, and more preferably 1150 nm or higher.

[0067] Furthermore, for the paramagnetic garnet-type transparent ceramic of the present invention, when a laser beam with a wavelength of 1064 nm is incident at an optical path length of 24 mm, a beam diameter of 1.6 mm, and an incident power of 100 W, the focal length variation due to the thermal lensing effect is preferably less than 10%, preferably less than 9%, more preferably less than 8%, and even more preferably less than 7%. If the focal length variation due to the thermal lensing effect is less than 10% at a certain incident power, the system can be deployed at that incident power, i.e., the thermal lensing characteristics meet the requirements. The paramagnetic garnet-type transparent ceramic of the present invention can control the focal length variation due to the thermal lensing effect to less than 10% even at a high incident power of 100 W, and therefore, the material can be used in high-power 100 W laser systems.

[0068] That is, according to the paramagnetic garnet-type transparent ceramic of the present invention, even when high-power laser light is incident, the occurrence of the thermal lens effect is suppressed, and the ceramic can be used as a Faraday rotator for a high-power fiber laser of 100 W or more.

[0069] [Method for producing paramagnetic garnet-type transparent ceramics]

[0070] The method for producing a paramagnetic garnet type transparent ceramic according to the present invention is the method for producing a paramagnetic garnet type transparent ceramic according to the present invention, characterized in that:

[0071] (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1)

[0072] (Wherein, 0<x<0.45, 0<y≤0.1, 0.004<z<0.2.)

[0073] The sintered body of the rare earth aluminum garnet containing Tb is pressure-sintered, and then the pressure-sintered body is heated to a temperature exceeding the above-mentioned pressure-sintering temperature and re-sintered. The re-sintered body is then subjected to an oxidation annealing treatment in an oxygen-containing atmosphere of more than 15 volume % at a temperature of more than 1300°C and less than 1500°C for more than 10 hours.

[0074] The paramagnetic garnet-type transparent ceramics were manufactured according to the following steps.

[0075] (Raw material powder for sintering)

[0076] First, a raw material powder for sintering corresponding to the composition of the garnet-type composite oxide represented by the above-mentioned formula (1) is prepared.

[0077] (In the case of mixed powder of starting materials)

[0078] There is no particular limitation on the method for preparing the above-mentioned raw material powder for sintering used in the present invention. The oxide powders of the respective component elements corresponding to the garnet-type composite oxide can be used as the starting raw materials, and they can be weighed in predetermined amounts so as to form a composition corresponding to formula (1), and mixed to form the raw material powder for sintering. Alternatively, an oxide powder in which each component is evenly distributed can be synthesized to form the raw material powder for sintering. As for the synthesis method of the oxide powder in which each component is evenly distributed, coprecipitation method, complex polymerization method, and uniform precipitation method can be exemplified. As long as it can be transparent, there is no particular limitation. Here, they are referred to as the starting raw material mixed powder. At this time, the starting raw material is not particularly limited as long as it can be transparent. From the perspective of suppressing absorption from impurities, the purity is preferably 99.9% by mass or more, more preferably 99.99% by mass or more, and most preferably 99.999% by mass or more. In addition, the particle size of the primary particles of the raw material powder is not particularly limited as long as it can be transparent. From the perspective of easy sintering, it is preferably 50 nm or more and 1000 nm or less. The shape of the primary particles is not particularly limited as long as they can be made transparent and is selected from a card house shape, a spherical shape, and a rod shape.

[0079] (Case of garnet-type composite oxide powder)

[0080] Alternatively, the method for producing the raw material powder for sintering used in the present invention may include coprecipitation, pulverization, spray pyrolysis, sol-gel, alkoxide hydrolysis, and any other synthesis method. Depending on the circumstances, wet ball milling, bead milling, jet milling, dry jet milling, hammer milling, and the like may be appropriately employed to obtain the desired particle size of the ceramic raw material of the rare earth composite oxide. For example, the raw material powder for sintering may be produced by a solid-phase reaction method in which a plurality of oxide particles are mixed and sintered to achieve uniformity through thermal diffusion of ions; or a coprecipitation method in which hydroxides, carbonates, and the like are precipitated from an ion-containing solution in which the oxide particles are dissolved, and the resulting oxides are sintered to achieve uniformity.

[0081] In the case of a solid phase reaction method in which a plurality of oxide particles are mixed and fired, and uniformity is produced by thermal diffusion of ions, metal powders composed of terbium, yttrium, scandium, and aluminum, or products obtained by dissolving the above metal powders in aqueous solutions such as nitric acid, sulfuric acid, and uric acid, or oxide powders of the above elements can be preferably used as starting materials. In addition, the purity of the above raw materials is preferably 99.9% by mass or more, particularly preferably 99.99% by mass or more. These starting materials can be weighed in predetermined amounts to form a composition corresponding to formula (1), mixed and fired to obtain a fired raw material having a cubic garnet-type oxide of the desired composition as the main component, which is then pulverized to form a raw material powder for sintering (garnet-type composite oxide powder). As for the firing temperature at this time, in order to form a garnet structure, it is preferably a temperature of 950°C or more and lower than the subsequent sintering temperature, and more preferably a temperature of 1100°C or more and lower than the subsequent sintering temperature. As for the firing time, it can be carried out for more than 1 hour, and the heating rate at this time is preferably more than 100°C / h and less than 500°C / h. The firing atmosphere is preferably an oxygen-containing atmosphere such as air or oxygen, and a nitrogen atmosphere, an argon atmosphere, a hydrogen atmosphere, etc. are not suitable. In addition, the firing apparatus can be exemplified by a vertical muffle furnace, a horizontal tubular furnace, a rotary kiln, etc., and there is no particular limitation as long as it can reach the target temperature and generate an oxygen flow. It should be noted that the "main component..." mentioned here means that the main peak obtained from the powder X-ray diffraction result of the fired raw material is composed of a diffraction peak from a garnet structure. Furthermore, when the ratio of the presence of the perovskite-type heterogeneous phase relative to the garnet parent phase is less than 1ppm, basically only a garnet single-phase pattern is detected in the powder X-ray diffraction pattern.

[0082] In addition, the raw material powder for sintering preferably includes a sintering aid. For example, SiO can be added together with the above-mentioned initial raw material. Tetraethoxysilane (TEOS) as a sintering aid can be added in an amount exceeding 0ppm and 1000ppm or less (exceeding 0% by mass and 0.1% by mass) in the raw material powder as a whole (initial raw material mixed powder or garnet-type composite oxide powder + sintering aid) or SiO2 powder can be added in an amount exceeding 0ppm and 1000ppm or less (exceeding 0% by mass and 0.1% by mass) in the raw material powder as a whole (garnet-type composite oxide powder + sintering aid). Mix and sinter as needed (in the case of making garnet-type composite oxide powder) to make the raw material powder for sintering. When the addition amount exceeds 1000ppm, due to the crystal defects caused by the Si contained excessively, it is possible to produce a trace of light absorption. In addition, its purity is preferably 99.9% by mass or more. A sintering aid can be added when preparing the raw material powder slurry. In addition, when no sintering aid is added, the raw material powder for sintering (i.e., the initial raw material mixed powder or composite oxide powder) used should preferably be one having a nanometer-sized primary particle size and extremely high sintering activity. Such selection can be made as appropriate.

[0083] (In the case of mixed powder of starting materials)

[0084] The above-mentioned initial raw material mixed powder (a product obtained by mixing various oxide powders, or oxide powders in which each component is evenly distributed) is in an condensed state, so it needs to be dispersed to primary particles. In order to form a slurry, wet dispersion is preferably performed. As wet dispersion, ball milling, bead milling, jet milling, and homogenization can be exemplified. As long as it can be dispersed to primary particles, there is no particular limitation. As for the solvent for wet dispersion, pure water, alcohols such as lower alcohols having 1 to 4 carbon atoms, and acetone can be exemplified. As long as it is a solvent that can be transparent and easy to separate solid and liquid, there is no particular limitation. When the condensed state is to be released, an organic additive (dispersant) can be used. Examples of such agents include polyethylene glycol dispersants, polyacrylate ether dispersants, phosphoric acid dispersants, and sulfonic acid dispersants. Polyethylene glycol or polyacrylate ether dispersants that can be easily removed by heat treatment and thus have little residue are preferred.

[0085] (Case of garnet-type composite oxide powder)

[0086] The obtained calcined raw material is crushed to make a raw material powder for sintering. As far as the crushing method is concerned, both dry and wet methods can be selected, but it is necessary to crush the target ceramic in a way that becomes highly transparent. For example, in the case of wet crushing, the calcined raw material is slurried by various crushing (dispersion) methods such as ball milling, bead milling, homogenization, jet milling, ultrasonic irradiation, etc., and crushed (dispersed) to primary particles. As the dispersion medium of the wet slurry, there is no particular restriction as long as it can achieve a high degree of transparency of the final ceramic obtained. For example, alcohols such as pure water and lower alcohols with 1 to 4 carbon atoms can be listed. In addition, various organic additives are sometimes added to the wet slurry for the purpose of quality stability and yield improvement in the subsequent ceramic manufacturing process. In the present invention, there is no particular limitation on them. That is, various dispersants, binders, lubricants, plasticizers, etc. can be preferably used. However, as these organic additives, it is preferred to select a high-purity type that does not contain unnecessary metal ions.

[0087] [Manufacturing process]

[0088] In the present invention, a slurry containing the above-mentioned raw material powder for sintering is used, and after being formed into a specified shape, it is degreased and then pre-sintered to produce a sintered body (pre-sintered body) composed of composite oxides with a relative density of more than 93% and an average sintered particle size of less than 5 μm. The sintered body is then pressure-sintered, and the pressure-sintered body is heated to a temperature exceeding the above-mentioned pressure-sintering temperature and re-sintered. It is pressure-sintered again as needed, and the re-sintered body (or re-pressure-sintered body) is subjected to a specified oxidation annealing treatment.

[0089] (forming)

[0090] The slurried product is subjected to solid-liquid separation and molded into a specified shape. As a molding method, it is roughly divided into dry molding and wet molding, and as long as the specified shape is stably obtained, there is no particular limitation. In the case of dry molding, the following method can be exemplified: using spray drying, making particles from the slurry, and performing compression molding after filling the particles in a fixture. In addition, as wet molding, a casting molding method in which the slurry is flowed into a gypsum mold and the solvent is volatilized can be exemplified. In addition, extrusion molding, sheet molding, centrifugal casting molding, and cold isostatic pressing can be exemplified, all of which can obtain a specified shape and are therefore not limited.

[0091] Before forming, a binder can be added to the slurry. The binder can improve the holding power of the formed body and has the effect of being difficult to cause cracks and ruptures. The type of binder is not particularly limited. It is preferably a binder that is compatible with the solvent and difficult to remain by heat treatment residue. Polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate, polyacrylic acid can be exemplified. Polymers obtained by copolymerizing two or more of these can also be used. The amount of the binder varies according to the forming method or the type of binder. With respect to the raw material powder for sintering, the minimum need is 0.5% by mass and the upper limit is 8% by mass. In addition, with regard to the addition of the binder, it is most preferably added in wet grinding.

[0092] Furthermore, conventional press molding processes can be preferably utilized for the aforementioned press molding. Specifically, the extremely common uniaxial pressing process, in which a mold is filled and pressurized from a fixed direction, the cold isostatic pressing (CIP) process, in which a mold is sealed and hydrostatically pressurized in a deformable waterproof container, and the warm isostatic pressing (WIP) process can be preferably utilized. Furthermore, the applied pressure can be appropriately adjusted while confirming the relative density of the resulting molded article, and there are no particular limitations. However, by managing the applied pressure within a range of approximately 300 MPa or less, which can be handled by commercially available CIP or WIP equipment, manufacturing costs can be reduced.

[0093] However, in the present invention, in order to manage the size and amount of scattering sources such as foreign matter and dirt within the specified range, it is preferred that the molding jig and molding machine use clean dedicated equipment that has been thoroughly cleaned and dried, and the environment in which the molding operation is performed is a clean space below level 1000.

[0094] (skimmed)

[0095] Since the molded body contains organic additives such as binders and dispersants, a process called degreasing is performed in which heat treatment is performed to decompose the organic matter. The degreasing temperature can be above the temperature at which the organic additives are decomposed, and is preferably above 270°C and below 1200°C in an atmosphere containing air, oxygen, hydrogen, etc., preferably in the atmosphere. If the temperature is lower than 270°C, the organic matter is not burned and may remain as carbon. On the other hand, if the temperature exceeds 1200°C, densification begins to develop in the molded body, and the sintering property deteriorates in the subsequent sintering process, so it is not preferred. As for the confirmation of the complete combustion of the organic matter, for the molded body after degreasing, thermogravimetric differential thermal analysis (TG / DTA) can be used to confirm that there is no weight loss and exothermic peak associated with the combustion of the organic matter.

[0096] (Sintering process)

[0097] The degreased molded body becomes transparent through a sintering process. The sintering process can achieve transparency through a single sintering step (i.e., until a relative density of 100% is reached), or after a first sintering step (pre-sintering) to a relative density of 93% or higher, transparency can be achieved through pressure sintering (hot isostatic pressing (HIP)). For high-yield production of transparent bodies, the method of pre-sintering followed by pressure sintering is preferred.

[0098] (Pre-sintering)

[0099] In this step, a pre-sintered body is produced that is densified to a relative density of 93% or higher and preferably has an average sintered grain size of 5 μm or less. At this time, the temperature and holding time conditions need to be controlled so that the sintered grain size falls within the desired range.

[0100] When the sintered body is made transparent through the two stages of pre-sintering and pressure sintering (HIP), the density after pre-sintering is preferably 93% or higher, more preferably 94% or higher, and even more preferably 95% or higher. This is because if the relative density is less than 93%, the interior and exterior of the molded body are often connected by bubbles (open pores), making it difficult to make it transparent even after pressure sintering (HIP). There is no particular upper limit on the relative density as long as the bubbles can be removed by pressure sintering.

[0101] The average sintered particle size of the pre-sintered body after pre-sintering is preferably 5 μm or less, more preferably 3 μm or less, and further preferably 2.5 μm or less. The average particle size of the sintered particles can be adjusted by taking into account the type of raw materials, atmosphere, sintering temperature, and holding time. If the sintered particle size is larger than 5 μm, plastic deformation is difficult to occur in the subsequent pressure sintering (HIP), and it may be difficult to remove the bubbles remaining in the pre-sintered body. As far as the lower limit of the sintered particle size is concerned, there is no particular limitation as long as a sintered density of 93% or more is obtained.

[0102] The average particle size of the sintered particles (average sintered particle size) is obtained by measuring the particle size of the sintered particles of the target sintered body using a metal microscope, and is specifically obtained as follows.

[0103] That is, for the pre-sintered body, a metal microscope is used, in reflection mode, and a 50-fold objective lens is used to shoot a reflected image of the sintered body surface. In detail, considering the effective image size of the objective lens, the entire area of the optical effective area of the object sintered body is shot, and the shot image is analyzed. At this time, first, a diagonal line is drawn in each shot image, and the total number of sintered particles cut by the diagonal line is counted, and then the value obtained by dividing the diagonal line length by the total number of counts is defined as the average particle size of the sintered particles in the image. Then, the average particle size of each shot image read by the analytical process is added together, and then divided by the number of shots, and the resulting value is defined as the average sintered particle size of the object sintered body (the same applies to the following embodiments).

[0104] Here, a general sintering process can be suitably used. That is, a heating sintering process such as a resistance heating method or an induction heating method can be suitably used. There is no particular limitation on the atmosphere at this time, and various atmospheres such as air, inert gas, oxygen, hydrogen, and helium can be suitably used. From the perspective of removing bubbles, it is more preferable to use sintering under reduced pressure (in a vacuum). The vacuum degree of the pre-sintering is preferably 1×10 -1 Pa or less, more preferably 1×10 -2 Pa or less, particularly preferably 1×10 -3 Below Pa.

[0105] The sintering temperature in the preliminary sintering step of the present invention is preferably 1450-1650°C, particularly 1500-1600°C. This temperature range is preferred because it promotes densification while suppressing heterogeneous phase precipitation and grain growth. A sintering hold time of several hours is sufficient in the preliminary sintering step of the present invention, but the relative density of the preliminary sintered body must be densified to 94% or higher.

[0106] (Pressure Sintering (Hot Isostatic Pressing (HIP)))

[0107] In the manufacturing method of the present invention, after the pre-sintering step, there is provided a step of pressurizing and sintering the pre-sintered body (performing HIP treatment) preferably at a pressure of 50 MPa to 300 MPa and a temperature of 1000°C to 1780°C. Furthermore, as for the type of pressurized gas medium at this time, inert gases such as argon and nitrogen, or Ar-O2 can be appropriately utilized, with argon being the most preferred. The pressure of the pressurized gas medium is preferably 50 to 300 MPa, more preferably 100 to 200 MPa. If the pressure is less than 50 MPa, the transparency improvement effect may not be obtained. If it exceeds 300 MPa, even if the pressure is increased, the transparency improvement beyond that cannot be obtained, and the load on the device becomes excessive, which may damage the device. If the applied pressure is 196 MPa or less, which can be processed by a commercially available HIP device, it is simple and preferred. In addition, the treatment temperature (prescribed holding temperature) at this time is preferably set in the range of 1000-1780°C, more preferably in the range of 1100-1700°C, and most preferably within the range of ±100°C relative to the pre-sintering temperature. If the heat treatment temperature is higher than 1780°C, grain growth occurs during the HIP process, and the removal of bubbles becomes difficult, so it is not preferred. In addition, if the heat treatment temperature is less than 1000°C, there is a possibility that the transparency improvement effect of the sintered body will be almost unobtainable. In addition, there is no particular restriction on the holding time of the heat treatment temperature. If it is maintained for too long, the risk of oxygen deficiency increases, so it is not preferred. Typically, it is preferably set in the range of 1 to 3 hours. In addition, there is no particular restriction on the heater material, insulation material, and processing container for HIP processing. Graphite, molybdenum, tungsten, platinum (Pt) can be appropriately used as the processing container, and yttrium oxide and gadolinium oxide can also be used. When the processing temperature is above 1500°C, graphite is preferably used as the heater material and the insulation material. In this case, if any one of graphite, molybdenum, and tungsten is selected as the processing container, and any one of yttrium oxide and gadolinium oxide is selected as a double container inside the container, and an oxygen-releasing material is further filled in the container, the amount of oxygen deficiency generated during the HIP process can be suppressed to a minimum as much as possible, which is therefore preferred.

[0108] (Resintering)

[0109] In the manufacturing method of the present invention, after pressure sintering (HIP), the pressure sintered body is heated to a temperature exceeding the pressure sintering temperature and then re-sintered to promote grain growth, resulting in a re-sintered body with an average sintered grain size of 10 μm or greater. During this process, the temperature and holding time must be controlled to ensure that the final sintered grain size falls within the desired range.

[0110] There is no particular limitation on the type of atmospheric gas at this time, and air, oxygen, hydrogen, etc. can be used as appropriate. More preferably, the atmosphere is heated under reduced pressure (less than 1×10-2 Pa in a vacuum). The re-sintering temperature is preferably 1650°C or higher and 1800°C or lower, more preferably 1700°C or higher and 1800°C or lower. If it is less than 1650°C, no grain growth occurs, so it is not preferred. The average particle size of the sintered particles produced by re-sintering is preferably 10 μm or higher, more preferably 15 μm or higher, further preferably 20 μm or higher, and preferably 40 μm or lower. There is no particular restriction on the holding time of the re-sintering process, but it is preferably 5 hours or more, more preferably 10 hours or more. Generally, the longer the holding time is extended, the more developed the grain growth of the sintered body is. The temperature and holding time of the re-sintering process can be appropriately adjusted by confirming the average sintered particle size.

[0111] The average particle size of the sintered particles in the re-sintered body (average sintered particle size) is determined by measuring the particle size of the sintered particles in the target sintered body using a metallurgical microscope. Specifically, the method is as follows. Specifically, a transmission open Nicol image of a sample of the re-sintered body, with both end faces polished, is captured using a 50x objective lens in transmission mode of the metallurgical microscope. Specifically, an optically effective area at a predetermined depth of the target sintered body is imaged, and a diagonal line is drawn on the captured image. The total number of sintered particles intersected by the diagonal line is counted. The value obtained by dividing the length of the diagonal line by the total number of counts is then defined as the average sintered particle size of the sintered particles in the image. Furthermore, the average particle sizes of each captured image, read through the analytical processing, are summed and divided by the number of images captured. The resulting value is used as the average sintered particle size of the target sintered body (this also applies to the average sintered particle size in the re-HIP body and in the Examples).

[0112] (Re-pressure sintering (re-HIP))

[0113] For the above-mentioned re-sintered body, pressure sintering can be performed again before oxidation annealing treatment, and then oxidation annealing treatment is performed. That is, in order to improve the uniformity of the transparent sintered body obtained as described above, it is preferably carried out under the same conditions as the above-mentioned pressure sintering (HIP treatment) to make the average sintered particle size less than 40 μm. If the average sintered particle size exceeds 40 μm, ceramic degranulation is likely to occur, so it is not preferred. Therefore, the above-mentioned re-sintering temperature can be set so as to make the particle size that becomes the target, and similarly, the re-pressure sintering (HIP treatment) temperature is also the temperature that becomes a highly transparent body. In addition, when increasing the crystal grains (sintered grains), as described above, it is not preferred to suddenly increase the crystal grains in pre-sintering, and it is most preferred to increase the crystal grains through two stages.

[0114] (Oxidation Annealing)

[0115] The most important step in the present invention is the oxidation annealing treatment. Paramagnetic garnet-type transparent ceramics treated so far contain oxygen deficiencies and / or cation defects, resulting in coloration. Therefore, oxidation annealing treatment is performed to remove this coloration.

[0116] Here, the oxidation annealing treatment is performed in an atmosphere containing 15% by volume or more of oxygen at a temperature of 1300°C to 1500°C for 10 hours or more, preferably in an atmosphere containing 15% by volume or more of oxygen at a temperature of 1300°C to 1500°C for 20 hours or more. Alternatively, the oxidation annealing treatment may be performed in an atmosphere containing 15% by volume or more of oxygen at a temperature of 1300°C to less than 1400°C for 40 hours or more.

[0117] If the oxygen content of the processing atmosphere is less than 15% by volume, it does not have enough oxygen to restore the oxygen deficiency, so it is not suitable. In addition, if the processing temperature is less than 1300°C, oxygen cannot be diffused into the interior of the sintered body (ceramic), so it is not suitable. On the other hand, if the processing temperature exceeds 1500°C, the hidden (collapsed) bubbles in the pressure sintering (HIP) expand again and become an optical scattering source, so it is not preferred. If the processing time is less than 10 hours, oxygen cannot be diffused into the interior of the sintered body (ceramic), so it is not suitable. In addition, there is no particular limit on the upper limit of the processing time, but excessive extension in vain does not meet the cost requirements, so it can be set to the time when the color falls off. In addition, the sintered body (ceramic) processed here is based on the size of the Faraday rotator of the high-output laser processing machine (fiber laser), for example, a cylindrical shape with a diameter of 4 to 10 mm, or a prism shape with a side of 4 to 10 mm.

[0118] Furthermore, while the oxygen deficiency amount is typically estimated by confirming that the density of a transparent sintered body is approximately the same as its true density, this method is not suitable for estimating the oxygen deficiency amount in the present invention. This is because, while approximately the same density typically refers to a difference of less than 0.1%, even within a range of less than 0.1%, differences in oxygen deficiency amount can occur, and absorption may remain. Therefore, in the present invention, the oxygen deficiency amount of the obtained paramagnetic garnet-type transparent ceramic is not estimated based on density. Instead, the oxygen deficiency amount is determined based on the shape of the total light transmittance spectrum of the transparent sintered body, specifically the shape of the total light transmittance spectrum at a wavelength of 900 nm and on the longer wavelength side.

[0119] In this manner, after the molded body is subjected to a treatment of pre-sintering-pressure sintering-re-sintering, or pre-sintering-pressure sintering-re-sintering-re-pressure sintering under prescribed conditions, if an oxidation annealing treatment is performed, the paramagnetic garnet-type transparent ceramic of the present invention is obtained, in particular, as a total light transmittance spectrum at an optical path length of 24 mm, in which, when the total light transmittance at a wavelength of 900 nm is set to a%, and the total light transmittance at an arbitrary wavelength λ on the wavelength side longer than 900 nm is set to b%, the paramagnetic garnet-type transparent ceramic satisfies |ab|≤0.1 when at least 900 nm < λ < 1100 nm.

[0120] (Optical grinding)

[0121] In the manufacturing method of the present invention, the paramagnetic garnet-type transparent ceramic that has undergone the above-mentioned series of manufacturing processes is preferably cylindrical or prismatic in shape, and its two end faces (optical end faces) located on the optically utilized axis are preferably optically polished and finished. At this time, the optical surface accuracy is preferably less than λ / 2 when the measurement wavelength λ=633nm, and particularly preferably less than λ / 8. Therefore, it is preferred that a polishing finishing treatment must be performed in the final stage of the optical polishing process. In addition, its surface accuracy (reflected wavefront accuracy) is preferably less than 0.16μm in terms of PV value. As a result, it presents a colorless and transparent appearance in the direction of its optically utilized axis.

[0122] Furthermore, by appropriately forming an anti-reflection film (AR coating) on the optically polished surface, the optical loss can be further reduced. At this time, in order to prevent dirt from remaining on the optical end faces, it is necessary to implement a liquid treatment before implementing the anti-reflection film treatment. As for the liquid, there are examples of acid, alkali, surfactant solution, acetone and other organic solvents. As long as the dirt can be fully removed without corroding the optical end faces, there is no special limitation. In addition, there is also a method of carefully wiping and cleaning the optical surface to clean it, and checking the cleanliness with a stereoscope or microscope. In the case of wiping and cleaning, in order not to scratch the optical surface or rub off dirt during the wiping and cleaning process, it is preferred to select an operating fixture made of a soft material for the operating fixture, and a wiping tool with low dust generation for the wiping tool.

[0123] [Magneto-optical disk]

[0124] Furthermore, the paramagnetic garnet-type transparent ceramic of the present invention is contemplated for use as a magneto-optical material. Therefore, it is preferred that a magnetic field be applied parallel to the optical axis of the paramagnetic garnet-type transparent ceramic, and then a polarizer and analyzer be provided so that the optical axes are offset by 45 degrees relative to each other, to form a magneto-optical disk. Specifically, the paramagnetic garnet-type transparent ceramic of the present invention is suitable for magneto-optical disk applications, and is particularly suitable for use as a Faraday rotator in an optical isolator with a wavelength of 0.9 to 1.1 μm.

[0125] Figure 1 1 is a schematic cross-sectional view showing an example of an optical disk, ie, an optical isolator, having a Faraday rotator made of the magneto-optical material of the present invention as an optical element.

[0126] exist Figure 1 In the embodiment, the optical isolator 100 includes a Faraday rotator 110 made of the paramagnetic garnet-type transparent ceramic of the present invention, and a polarizer 120 and an analyzer 130 as polarizing materials are provided before and after the Faraday rotator 110. Furthermore, in the optical isolator 100, it is preferred that the polarizer 120, the Faraday rotator 110, and the analyzer 130 are arranged in this order, and a magnet 140 is placed on at least one of their side surfaces.

[0127] Furthermore, the optical isolator 100 can be suitably used in industrial fiber laser devices, that is, suitable for preventing reflected light of laser light emitted from a laser light source from returning to the light source and causing oscillation instability.

[0128] Example

[0129] The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0130] [Example 1]

[0131] Terbium oxide and yttrium oxide (99.999% purity, Shin-Etsu Chemical Co., Ltd.), aluminum oxide (99.999% purity, Nippon Light Metal Co., Ltd.), and scandium oxide (99.9% purity, Shin-Etsu Chemical Co., Ltd.) were placed in a resin pot. Ethanol (Kanto Chemical Co., Ltd.), PEG200 (Kanto Chemical Co., Ltd.) as a dispersant, polyvinyl alcohol (Kanto Chemical Co., Ltd.) as a binder, TEOS (in an amount calculated as SiO2 to provide 1000 ppm in the total raw material powder (the total of the initial raw material mixed powder and the sintering aid)) as a sintering aid, and alumina balls (99.9% purity, Nikkato Co., Ltd.) as a grinding medium were added. The pot was sealed and ball milled. The rotation speed was set to 200 rpm. The mixing ratio of the above raw materials was adjusted to achieve the final composition shown in Table 1.

[0132] After ball milling, the slurry was pelletized using a spray dryer, uniaxially pressed, and then CIP molded to produce a 10 mm diameter x 40 mm length molded body with a relative density of 54%. Degreasing was performed at 1000°C to remove organic matter such as binders from the molded body.

[0133] The degreased molded body was then placed in a vacuum sintering furnace and sintered at a vacuum degree of 1×10 -3Pa, 1600 ° C, 2 hours. At this time, the average sintered grain size is about 2 μm. Then, in order to improve the transparency, the pressure sintering (HIP) treatment is carried out under the conditions of 198 MPa, 1600 ° C, and 3 hours under Ar pressure. The transparent pressure sintered body obtained is heated to 1000 ° C in a vacuum of 1 × 10 -3 The sintering was carried out under the conditions of 1700°C at 1200 Pa for 2 hours, and then re-pressure sintering (re-HIP) was carried out under the conditions of 198 MPa at 1600°C for 3 hours under Ar pressure. The average sintered grain size at this time was 20 μm.

[0134] Then, because the resulting transparent body (re-pressurized sintered body) contained absorption sources such as oxygen vacancies, an oxidation annealing treatment was performed in an air atmosphere at 1200 to 1550° C. for 5 to 100 hours, varying the temperature and time. At this time, for samples other than Comparative Examples 1 to 4 that were not subjected to oxidation annealing, the difference between the true density and the measured density was less than 0.1%.

[0135] The transparent sintered body (oxidatively annealed body) thus obtained was ground and polished to a diameter of 5 mmφ x a length of 24 mmL. Both end faces were optically polished to a surface accuracy of λ / 8 (λ = 633 nm) or greater. Comparative Examples 1-4 were not subjected to oxidative annealing; these processes were performed on the re-pressurized sintered body. Therefore, the difference between the true density and the measured density was 0.2%.

[0136] The following measurements were performed on the samples obtained as described above.

[0137] Total light transmittance @ 900nm

[0138] The total light transmittance a of the sample at a wavelength of 900 nm was measured with reference to JIS K7361-1:1997. That is, an entrance opening and an exit opening for light to pass through were set in the integrating sphere, and the sample was placed at the entrance opening. A reflector was installed at the exit opening so that all light emitted from the sample could be detected by the integrating sphere, and the total light transmittance a at a wavelength of 900 nm was measured based on the ratio of the intensity of the detected emitted light to the intensity of the light incident on the sample. As for the apparatus, a spectrophotometer (model V-700) manufactured by JASCO Corporation was used, and the measurement was performed using the attached integrating sphere. At this time, a pinhole was set so that the spot diameter of the irradiated light became 3 mm.

[0139] Similarly, the total light transmittance at a wavelength of 1064 nm was measured, and the total light transmittance b at each wavelength was measured while changing the wavelength λ by 1 nm from 900 nm toward the longer wavelength side up to 1350 nm.

[0140] Absorption coefficient @ 1064 nm

[0141] The absorption coefficient was calculated using the theoretical transmittance at a wavelength of 1064 nm obtained by the refractive index measurement described below and the measured total light transmittance at a wavelength of 1064 nm obtained by the total light transmittance measurement described above, using the above-mentioned formula (2). In the case of a poor S / N ratio in the total light transmittance measurement, smoothing was performed using the average value of the preceding and following 10 nm intervals (i.e., the average value of the measured total light transmittance at wavelengths of 1054 to 1074 nm was used).

[0142] (Refractive Index Measurement)

[0143] The wavelength dependence of the refractive index was measured using a Metrikon prism coupler (Model 2010 / M). A prism with a refractive index similar to that of the object being measured was used, and lasers with wavelengths of 633 nm, 828 nm, and 1550 nm were used as the light source. Using the refractive indices obtained at each wavelength, the wavelength dependence of the refractive index was calculated using the Cauchy dispersion equation. The wavelength dependence of the reflectivity was determined, and the theoretical transmittance at a wavelength of 1064 nm was calculated.

[0144] Minimum wavelength λ1 for |ab| > 0.1

[0145] The absolute value (|ab|) of the difference between the total light transmittance a at a wavelength of 900 nm and the total light transmittance b at wavelengths longer than 900 nm is determined, and the minimum wavelength λ1 at which |ab|>0.1 is determined on the wavelength side longer than 900 nm.

[0146] Verdet constant

[0147] The optically polished sample was coated with an antireflection film (AR coating) designed so that the central wavelength would be 1064 nm.

[0148] like Figure 1 As shown in the figure, each sample coated with an anti-reflection film was inserted into the center of a neodymium-iron-boron magnet with an outer diameter of 32 mm, an inner diameter of 6 mm, and a length of 40 mm. After inserting polarizers at both ends, a high-power laser (beam diameter 1.6 mm) manufactured by IPG Photonics Japan Co., Ltd. was used to allow high-power laser light with a wavelength of 1064 nm to be incident from both end faces, and the Faraday rotation angle θ was determined. The Faraday rotation angle θ is the angle at which the maximum transmittance is obtained when the polarizer on the output side is rotated. The Verdet constant was calculated based on the following formula. In addition, as for the size of the magnetic field (H) applied to the sample, the value calculated by simulation based on the dimensions of the above-mentioned measurement system, the residual magnetic flux density (Br), and the holding force (Hc) was used.

[0149] θ=V×H×L

[0150] (Where θ is the Faraday rotation angle (rad), V is the Verdet constant (rad / T·m), H is the magnitude of the magnetic field (T), and L is the length of the Faraday rotator (0.024m in this case).)

[0151] <Focal length variation due to thermal lensing>

[0152] IPG Photonics Japan Co., Ltd. used a CW laser (wavelength 1070 nm, beam diameter 1.6 mm, maximum output 100 W) for 100 W laser irradiation. The laser's shape was evaluated using a beam propagation analyzer (Modemaster, manufactured by Cohiren Corporation). Specifically, the laser was irradiated with 100 W of laser power. The focal position of the laser without a sample was defined as f0, while the focal position of the sample coated with the antireflection film was defined as f. The focal length variation (%) due to thermal lensing was calculated as |f0 - f| / f0 × 100.

[0153] The above evaluation results are shown in Table 1. In addition, the theoretical transmittance in the composition of Table 1 was 84.70%.

[0154] [Table 1]

[0155]

[0156] The example samples subjected to oxidation annealing at temperatures above 1300°C for 10 hours or longer were able to suppress the absorption coefficient at a wavelength of 1064nm, keeping the focal length variation due to the thermal lens to below 10%. On the other hand, in the case of samples subjected to oxidation annealing at low temperatures, such as Comparative Example 1-1, or for short periods of time, such as Comparative Example 1-3, the absorption coefficient increased, and the focal length variation due to the thermal lens exceeded 10%. Furthermore, in the case of oxidation annealing at temperatures exceeding 1500°C, such as Comparative Example 1-2, there were no problems from the perspective of the thermal lens, but bubble scattering increased, degrading the laser quality and resulting in failure. Furthermore, in Comparative Example 1-4, where oxidation annealing was not performed, residual coloration remained and the absorption coefficient was also high, making it unusable as a magneto-optical material for a 100W laser.

[0157] The above results show that by setting the temperature and time of the oxidation annealing treatment within the above ranges, a sufficient annealing effect can be expected, resulting in a magneto-optical material that can handle a laser output of 100 W. Furthermore, the Verdet constant in the composition of this example is 36 rad·T·m.

[0158] [Example 2]

[0159] In Example 1, except that the oxidation annealing atmosphere was changed from air to oxygen or nitrogen and the oxidation annealing temperature and time were varied, samples of paramagnetic garnet-type transparent ceramics were prepared and evaluated in the same manner as in Example 1.

[0160] The results are shown in Table 2.

[0161] [Table 2]

[0162]

[0163] As shown in Examples 2-1 and 2-2, it is clear that paramagnetic garnet-type transparent ceramics capable of handling a 100W laser output can be produced even when the atmosphere is changed from air to oxygen. On the other hand, when the oxidation annealing conditions (in this case, the treatment time) are outside the range, as in Comparative Example 2-1, absorption remains, making it impossible to handle a 100W laser output. Furthermore, even when annealing is performed in an oxygen-free nitrogen atmosphere, as in Comparative Example 2-2, the oxygen deficiency cannot be recovered, resulting in a naturally high absorption.

[0164] [Example 3]

[0165] A sample of paramagnetic garnet-type transparent ceramic was prepared in the same manner as in Example 2-2 except that the composition was changed, and the sample was evaluated in the same manner as in Example 1.

[0166] The results are shown in Table 3.

[0167] [Table 3]

[0168]

[0169] Even if the composition is changed as in Examples 3-1 to 3-4, a paramagnetic garnet-type transparent ceramic that can cope with a 100W output laser can be obtained by oxidation annealing under specified conditions. Furthermore, by adding a large amount of Sc as in Example 3-4, the transmittance and absorption coefficient can be adjusted to cope with a 100W output laser, but Sc leads to high costs and is not preferred. There is an optimal composition in the present invention. If it is outside the range specified by formula (1), it may not be possible to get rid of the absorption from the cation defects and cannot cope with a 100W output laser. The theoretical transmittance is 84.60% in Example 3-1 and 84.70% in examples with other compositions.

[0170] It should be noted that the present invention has been described using the above-mentioned embodiments, but the present invention is not limited to these embodiments. Other embodiments, additions, changes, deletions, etc. can be changed within the scope that can be conceived by those skilled in the art. In any manner, as long as the effects of the present invention are achieved, they are included in the scope of the present invention.

[0171] Description of Reference Numerals

[0172] 100 Optical Isolator

[0173] 110 Faraday rotor

[0174] 120 polarizer

[0175] 130 Analyzer

[0176] 140 magnets

Claims

1. A paramagnetic garnet-type transparent ceramic, which is a sintered body of a rare earth aluminum garnet containing Tb represented by the following formula (1), characterized in that: The average sintered grain size is 10 μm or more and 40 μm or less. As a total light transmittance spectrum with an optical path length of 24 mm, the total light transmittance at a wavelength of 900 nm is set to a%, and the total light transmittance at an arbitrary wavelength λ on the wavelength side longer than 900 nm is set to b%. At least when 900 nm < λ < 1100 nm, |ab| ≤ 0.1, (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) Where, 0<x<0.45, 0<y≤0.1, 0.004<z<0.2, The sintered body of rare earth aluminum garnet containing Tb, which is the object of measurement of the total light transmittance spectrum, is a sintered body of rare earth aluminum garnet containing Tb without an antireflection film, which is ground and polished to a length of 24 mm, and optical polishing is performed on both ends.

2. The paramagnetic garnet-type transparent ceramic according to claim 1, wherein The minimum wavelength λ1 at which |ab|>0.1 on the wavelength side longer than 900 nm is equal to or longer than 1150 nm.

3. The paramagnetic garnet-type transparent ceramic according to claim 1 or 2, wherein: The absorption coefficient at a wavelength of 1064 nm is 0.0030 cm -1 the following.

4. The paramagnetic garnet-type transparent ceramic according to claim 1 or 2, wherein: The total light transmittance at the wavelength of 900 nm is greater than or equal to 84% and less than or equal to 85%.

5. The paramagnetic garnet-type transparent ceramic according to claim 1 or 2, wherein: When a laser beam with a wavelength of 1064 nm and an incident power of 100 W is incident with an optical path length of 24 mm, the focal length variation rate caused by the thermal lens is less than 10%.

6. A method for producing a paramagnetic garnet-type transparent ceramic, the method for producing a paramagnetic garnet-type transparent ceramic according to any one of claims 1 to 5, characterized in that: A pre-sintered body of a rare earth aluminum garnet containing Tb represented by the following formula (1) is pressure-sintered, the pressure-sintered body is heated to a temperature exceeding the pressure-sintering temperature, and then re-pressure-sintered, and the re-pressure-sintered body is subjected to an oxidation annealing treatment in an atmosphere containing 15% by volume or more of oxygen at a temperature of 1300° C. to 1500° C. for 10 hours or more. (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) In the formula, 0<x<0.45, 0<y≤0.1, 0.004<z<0.

2.

7. The method for producing a paramagnetic garnet-type transparent ceramic according to claim 6, wherein: The average sintered grain size of the pre-sintered body is 5 μm or less.

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