Paramagnetic garnet-type transparent ceramic, magneto-optical device, and method for manufacturing paramagnetic garnet-type transparent ceramic

Abstract

The present invention relates to a paramagnetic garnet-type transparent ceramic having a high laser damage threshold, which is a sintered body of a Tb-containing rare earth aluminum garnet represented by the following formula (1), characterized in that the average sintered particle diameter is 10 μm or more and 40 μm or less, and the insertion loss at a wavelength of 1064 nm in the optically effective region in the length direction of a sample having a length of 20 mm is 0.05 dB or less.(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<0.08, 0≤z<0.2, 0.001 y+z<0.20).

Description

TECHNICAL FIELD

[0001] The present application relates to a paramagnetic garnet-type transparent ceramic having light transmittance in the visible and / or near-infrared region, and more particularly to a paramagnetic garnet-type transparent ceramic containing terbium suitable for constituting a magneto-optical device such as an optical isolator, a magneto-optical device using the same, and a method for manufacturing a paramagnetic garnet-type transparent ceramic. BACKGROUND

[0002] In an industrial laser processing machine, an optical isolator is provided in order to prevent light such as reflected light from being returned, and a terbium-added glass or terbium-gallium garnet (TGG) is mounted as a Faraday rotor inside the optical isolator (for example, Japanese Patent Application Publication No. 2011-213552 (Patent Literature 1)). The size of the Faraday effect is quantified by the Verdet constant, and the Verdet constant of a TGG crystal is 40 rad / (T·m) (0.13 min / (Oe·cm)), and the Verdet constant of a terbium-added glass is 0.098 min / (Oe·cm), and the Verdet constant of the TGG crystal is relatively large, and therefore the TGG crystal is widely used as a standard Faraday rotor. In addition, there is a terbium-aluminum garnet crystal (TAG crystal), and the Verdet constant of the TAG crystal is about 1.3 times that of the TGG crystal, and therefore the length of the Faraday rotor can be shortened, and it is a good crystal that can be used for a fiber laser (for example, Japanese Patent Application Publication No. 2002-293693 (Patent Literature 2), Japanese Patent No. 4107292 (Patent Literature 3)).

[0003] In recent years, a method of producing a TAG in the form of a transparent ceramic has been disclosed (for example, International Publication No. 2017 / 033618 (Patent Literature 4), International Publication No. 2018 / 193848 (Patent Literature 5), “High Verdet constant of Ti-doped terbium aluminum garnet (TAG) ceramics” (Non-Patent Literature 1)). In addition, a YTAG (Tb x Y 1-x )3Al5O 12 (0.2≤x≤0.8, or 0.5≤x≤1.0, or x=0.6) (for example, “Fabrication and properties of (Tb x Y 1-x )3Al5O 12"Development of optical grade (Tb x Y 1-x )3Al5O 12 ceramics as Faraday rotator material" (Non-patent literature 3), "Effect of (Tb+Y) / Al ratio on Microstructure Evolution and Densification Process of (Tb 0.6 Y 0.4 )3Al5O 12 Transparent Ceramics" (Non-patent literature 4)). The rare earth aluminum garnet containing Tb shows a high thermal conductivity compared to TGG, and is expected to be a Faraday element with a small thermal lens effect. Further, an optical isolator equipped with a TAG transparent ceramic with trivalent ion substitution is disclosed, and it is shown that the optical isolator is an optical isolator with a small thermal lens effect compared to an optical isolator equipped with TGG (for example, Japanese Patent Application Publication No. 2020-67523 (Patent Literature 6)).

[0004] As described above, in recent years, reports on rare earth aluminum garnets containing Tb also use ceramics. This is because TAG is an incongruent composition, so it is difficult to perform single crystal production. However, in general, ceramics contain a large number of scattering sources such as bubbles, heterogeneous phases, foreign matter, and microcracks in the system. Therefore, in order to obtain a highly transparent ceramic intended as a Faraday rotator, it is necessary to completely eliminate scattering sources such as bubbles and foreign matter.

[0005] As a method of reducing bubbles and microcracks in the interior of the ceramic, there is a hot isostatic pressing (HIP) treatment. In the case of HIP treatment, for a sintered body (pre-sintered body) that is previously densified to a relative density of 94% or more, plastic flow of the ceramic is caused by high-temperature and high-pressure treatment, so that defects can be compressed and removed. In the HIP treatment, a large number of bubbles are removed from the system, but a part of the bubbles often remains in the system in a compressed state. Therefore, if the HIP body is exposed to a pressure of less than atmospheric pressure at a high temperature, the bubbles that were compressed and hidden can expand again, and an increase in scattering intensity is observed.

[0006] As a method for further reducing the bubbles and inhomogeneities in the interior of the ceramic that are not expelled by HIP processing, there is a method of performing re-sintering after HIP processing, and expelling to the outside of the system by grain growth. Ichikawa et al. showed a method of re-sintering a transparent ceramic that was pre-sintered at 1600°C for 3 hours under vacuum, and HIP-processed at 1500 to 1700°C for 3 hours, at 1750°C, which is higher than the HIP processing temperature, for 20 hours (for example, "Microstructure and Optical Properties of Hot Isostatic Pressed Nd:YAG Ceramics" (Non-Patent Literature 5)). In addition, in Japanese Patent No. 2638669 (Patent Literature 7), a method of manufacturing a ceramic body is disclosed, in which a green compact having a proper shape and composition is formed, a pre-sintering process is performed at a temperature range of 1350 to 1650°C, a HIP processing process is performed at a temperature of 1350 to 1700°C, and then a re-sintering process is performed at a temperature exceeding 1650°C, whereby pores are removed.

[0007] In recent years, in order to perform fine processing, high power and short pulse are being promoted in the pulse laser processing machine. If the pulse width is shortened, the peak intensity is increased, and therefore short pulse laser transmits (transmits), and thus the problem of Faraday rotor damage often occurs. For example, in "Optical properties and Faraday effect of ceramic terbium gallium garnet for a room temperature Faraday rotator" (Non-Patent Literature 6), information about the laser damage threshold caused by pulse laser of wavelength 1064 nm with respect to TGG single crystal and TGG transparent ceramic is disclosed. If the Faraday rotor is damaged, the transmittance, isolation, and beam quality are deteriorated, and in the worst case, the optical isolator fails. In general, it is considered that the cause of optical damage by a pulse laser is ionization caused by multi-photon absorption, relaxation collapse of electrons, and absorption caused by impurities, and it is particularly pointed out that the presence of scattering sources such as grain boundaries and bubbles of transparent ceramics reduces the laser damage threshold (for example, "Investigation of bulk laser damage in transparent YAG ceramics controlled with microstructural refinement" (Non-Patent Literature 7)). Therefore, in order to provide a ceramic Faraday rotator having a high laser damage threshold, it is important to manage absorption and scattering, and to exert the potential of the material to the limit.

[0008] Prior art documents

[0009] Patent Literature

[0010] Patent Literature 1: Japanese Patent Application Laid-Open No. 2011-213552

[0011] Patent Literature 2: Japanese Patent Application Laid-Open No. 2002-293693

[0012] Patent Literature 3: Japanese Patent No. 4107292

[0013] Patent Literature 4: International Publication No. 2017 / 033618

[0014] Patent Literature 5: International Publication No. 2018 / 193848

[0015] Patent Literature 6: Japanese Patent Application Laid-Open No. 2020-67523

[0016] Patent Literature 7: Japanese Patent No. 2638669

[0017] Non-Patent Literature

[0018] Non-Patent Literature 1: “High Verdet constant of Ti-doped terbium aluminum garnet (TAG) ceramics”, Optical Materials Express, Vol. 6, No. 1 191-196 (2016)

[0019] Non-Patent Literature 2: “Fabrication and properties of (TbxY1-x)3Al5O12 transparent ceramics by hot isostatic pressing”, Optical Materials, 72 58-62 (2017)

[0020] Non-Patent Literature 3: “Development of optical grade (TbxY1-x)3Al5O12 ceramics as Faraday rotator material”, Journal of American Ceramics Society, 100, 4081-4087 (2017)

[0021] Non-Patent Literature 4: "Effect of (Tb+Y) / Al ratio on Microstructure Evolution and Densification Process of (Tb0.6Y0.4)3Al5O12 Transparent Ceramics", Materials, 12, 300 (2019)

[0022] Non-Patent Literature 5: "Microstructure and Optical Properties of Hot Isostatic Pressed Nd:YAG Ceramics", Journal of American Ceramics Society, 79, 1927-1933 (1996)

[0023] Non-Patent Literature 6: "Optical properties and Faraday effect of ceramic terbium gallium garnet for a room temperature Faraday rotator", Optical Materials Express, Vol. 19, No. 16 15181-15187 (2011)

[0024] Non-Patent Literature 7: "Investigation of bulk laser damage in transparent YAG ceramics controlled with microstructural refinement", Proc. of SPIE, Vol. 7132, 713215 (2008)

[0025] Non-Patent Literature 8: "Lineal Intercept Technique for Measuring Grain Size in Two-Phase Polycrystalline Ceramics", Journal of the American Ceramic Society, 55, 109 (1972)

[0026] Non-Patent Document 9: "Wavelength Dependence of Laser-Induced Damage: Determining the Damage Initiation Mechanisms", Physical Review Letters, 91, 127402 (2003) SUMMARY

[0027] PROBLEMS TO BE SOLVED BY THE INVENTION

[0028] As described above, with the miniaturization of the processing of the pulse laser processing machine, a Faraday rotator having a high laser damage threshold is required. In the above such circumstances, recently, a dense ceramic sintered body composed of (Tb x Y 1-x )3Al5O 12 (x = 0.5 ~ 1.0) has been disclosed, which has a high extinction ratio (improvement from the existing 35 dB to 39.5 dB or more) and a reduced insertion loss (improvement from the existing 0.05 dB to 0.01 ~ 0.05 dB) compared to the existing TGG crystal (Non-Patent Document 3). The material disclosed in this Non-Patent Document 3 is a ceramic in the first place, so there is no problem of the precipitation of a perovskite heterogeneous phase that is a problem in the TGG crystal, and further, by substituting a part of the Tb ions with Y ions, further low loss can be achieved, and it is a material that can obtain a garnet-type Faraday rotator of extremely high quality. However, the present inventors conducted additional experiments with reference to the literature, and in an optical isolator equipped with a trial-manufactured Faraday rotator, the transmittance of the laser during operation was drastically reduced, and a problem occurred in which the optical isolator no longer functioned. Therefore, the improvement of the stability of the optical isolator equipped with a rare earth aluminum garnet ceramic containing Tb became a problem. The failed optical isolator was analyzed, and it was found that the internal Faraday rotator was destroyed due to laser damage, and thus the transmittance of the optical isolator was reduced.

[0029] The present invention was completed in view of the above actual situation, and aims to provide a paramagnetic garnet-type transparent ceramic of a TAG system, a TYAG system, or a TYSAG system, which has a high laser damage threshold, a magneto-optical device using the same, and a manufacturing method of the paramagnetic garnet-type transparent ceramic.

[0030] MEANS FOR SOLVING THE PROBLEMS

[0031] The present inventors have conducted research on the above problem, and as a result, have found that: by making the ceramic used as a Faraday rotor have a sintered particle size of (i) a certain size or more, reducing the amount of bubbles, grain boundaries, heterogeneous phases, and foreign matter inside the ceramic to a certain amount, and (ii) performing oxidation annealing treatment, thereby reducing oxygen defect (e.g., F or F+ center) absorption, the improvement of the laser damage threshold of the Faraday rotor is effective. In particular, a Faraday rotor having a laser damage threshold of 20 J / cm 2 The Faraday rotor optical isolator described above does not experience a decrease in transmittance even when a picosecond pulse laser is transmitted (transmitted) therethrough, and stably functions, based on this knowledge, in-depth research was conducted, and the present invention was completed.

[0032] That is, the present invention provides the following paramagnetic garnet-type transparent ceramic, magneto-optical device, and method for manufacturing a paramagnetic garnet-type transparent ceramic.

[0033] 1. A paramagnetic garnet-type transparent ceramic, which is a sintered body of a Tb-containing rare earth aluminum garnet represented by the following formula (1), characterized in that the average sintered particle size is 10 μm or more and 40 μm or less, and the insertion loss at a wavelength of 1064 nm in the optically effective region in the length direction of a sample having a length of 20 mm is 0.05 dB or less.

[0034] (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1)

[0035] (In the formula, 0≤x<0.45, 0≤y<0.08, 0≤z<0.2, and 0.001

[0036] 2. The paramagnetic garnet-type transparent ceramic according to 1, wherein the laser damage threshold at a wavelength of 1064 nm and a pulse width of 5 ns is 20 J / cm 2 or more.

[0037] 3. A magneto-optical device configured using the paramagnetic garnet-type transparent ceramic according to 1 or 2.

[0038] 4. The magneto-optical device according to 3, which is an optical isolator configured to have the paramagnetic garnet-type transparent ceramic as a Faraday rotor, and polarizing materials in front of and behind the optical axis of the Faraday rotor, and which is usable at a wavelength band of 0.9 μm or more and 1.1 μm or less.

[0039] 5. The method for producing a paramagnetic garnet-type transparent ceramic according to claim 1 or 2, characterized by performing pressure sintering on a sintered body of a Tb-containing rare earth aluminum garnet represented by the following formula (1), further performing re-sintering on the pressure sintered body by heating it to a temperature exceeding that of the pressure sintering, to produce a re-sintered body having an average sintered particle diameter of 10 μm or more, and further performing oxidation annealing on the re-sintered body in an oxidizing atmosphere at 1400°C or more.

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

[0041] (in the formula, 0≤x<0.45, 0≤y<0.08, 0≤z<0.2, 0.001

[0042] Effects of the Invention

[0043] According to the present application, it is possible to provide a paramagnetic garnet-type transparent ceramic having a high laser damage threshold of 20 J / cm 2 2 or more, and in particular, it is possible to provide a transparent ceramic suitable for use as a Faraday rotator constituting a magneto-optical device such as an optical isolator. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 A cross-sectional schematic view showing a configuration example of an optical isolator using the paramagnetic garnet-type transparent ceramic of the present application as a Faraday rotator. DETAILED DESCRIPTION

[0045] [Paramagnetic garnet-type transparent ceramic]

[0046] The paramagnetic garnet-type transparent ceramic involved in the present application will be described below.

[0047] The paramagnetic garnet-type transparent ceramic involved in the present application is a sintered body of a Tb-containing rare earth aluminum garnet represented by the following formula (1), characterized by having an average sintered particle diameter of 10 μm or more and 40 μm or less, and an insertion loss of 0.05 dB or less at a wavelength of 1064 nm in an optically effective region in the length direction of a sample having a length of 20 mm.

[0048] (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1)

[0049] (In the formula, 0≤x<0.45, 0≤y<0.08, 0≤z<0.2, 0.001

[0050] Further, in the garnet crystal structure represented by formula (1), the site mainly occupied by Tb, i.e., the bracket of the first half of formula (1), is referred to as an A site, and the site mainly occupied by Al, i.e., the bracket of the second half of formula (1), is referred to as a B site.

[0051] In the A site of formula (1), terbium (Tb) is an element having the largest molar refraction among trivalent rare earth ions, and has a very small absorption in the 1070 nm region (wavelength band of 0.9 μm or more and 1.1 μm or less) used in fiber lasers, and thus is the most suitable element for a material for an optical isolator in this wavelength range. However, Tb(III) ions are easily oxidized to produce Tb(IV) ions. If Tb(IV) ions are produced in a metal oxide, light is absorbed in a wide range of wavelengths from the ultraviolet to the near infrared region, and the transmittance decreases, and thus it is desirable to exclude Tb(IV) ions as much as possible. As one strategy for not producing Tb(IV) ions, it is effective to adopt a crystal structure that is unstable to Tb(IV) ions, i.e., a garnet structure.

[0052] Yttrium (Y) has an ion radius about 2% smaller than terbium, and in the case of forming a composite oxide by combining with aluminum, a garnet phase can be stably formed compared to a perovskite phase, and thus is an element that can be preferably used in the present application.

[0053] In the B site of formula (1), aluminum (Al) is a material having the smallest ion radius among 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 possible to reduce the lattice constant of the garnet structure without changing the content of Tb, and it is possible to increase the molar refraction per unit length, and thus is preferable. Further, aluminum is a light metal, and thus is weaker in diamagnetism than gallium, and it is expected to relatively improve the effect of increasing the magnetic flux density generated inside a Faraday rotor, and it is possible to increase the molar refraction per unit length, and thus is preferable. In fact, the molar refraction of TAG ceramics is increased to 1.25 to 1.5 times the molar refraction of TGG. Thus, even in the case where a part of terbium ions is replaced with yttrium ions to reduce the relative concentration of terbium, it is possible to make the molar refraction per unit length equivalent to that of TGG or to remain at a slightly reduced level, and thus is a preferable constituent element in the present application.

[0054] In the present application, by adding scandium (Sc) as a constituent element, a composition deviation due to a slight weighing error is eliminated. Sc is a material having an intermediate ionic radius that can be solid-solved at both the A site and the B site in an oxide having a garnet structure, and is a buffer material that can automatically adjust the distribution ratio to the A site (rare earth site composed of Tb and Y) and the B site (aluminum site) and solid-solve to make the stoichiometric ratio just right, and thereby minimize the generation of crystallites, in the case where the mixing ratio of rare earth elements composed of Tb and Y to Al deviates from the stoichiometric ratio due to a weighing error. In addition, it is an element that can limit the presence ratio of alumina heterogeneous phases with respect to the garnet parent phase to 1 ppm or less, and the presence ratio of perovskite-type heterogeneous phases with respect to the garnet parent phase to 1 ppm or less, and is an element added to improve the yield of the product.

[0055] 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, further preferably 0.20≤x≤0.40. If x is in this range, the Verdet constant at normal temperature (23±15°C) and a wavelength of 1064 nm becomes 30 rad / (T·m) or more, and it can be used as a Faraday rotator. In addition, within this range, there is a tendency that the larger x is, the smaller the thermal lens effect is, and thus it is preferable. Furthermore, within this range, there is a tendency that the larger x is, the smaller the diffuse transmittance is, and thus it is preferable. In the case where x is 0.45 or more, the Verdet constant at a wavelength of 1064 nm is less than 30 rad / (T·m), and thus it is not preferable. That is, if the relative concentration of Tb is excessively reduced, in the case of using a general magnet, the total length of the Faraday rotator required to rotate laser light at a wavelength of 1064 nm by 45 degrees exceeds 30 mm, the total length of the Faraday rotator becomes long, and the production becomes difficult, and thus it is not preferable.

[0056] In formula (1), the range of y is 0≤y<0.08, preferably 0<y<0.08, more preferably 0.002≤y≤0.07, further preferably 0.003≤y≤0.06. If y is in this range, the perovskite-type heterogeneous phase can be reduced to a level that is not detected by X-ray diffraction (XRD) analysis. Furthermore, in the presence amount of the perovskite-type heterogeneous phase (typically, a particle-shaped heterogeneous phase having a size of 1 to 1.5 μm in diameter and appearing to be colored light green) in a field of view of 150 μm x 150 μm in an optical microscope observation, it is 1 or less, and thus it is preferable. The presence ratio of the perovskite-type heterogeneous phase with respect to the garnet parent phase at this time becomes 1 ppm or less.

[0057] In the case where y is 0.08 or more, in addition to the substitution of a part of Tb with Y, a part of Tb is substituted with Sc, as a result, the solid solution concentration of Tb excessively decreases, and thus the feld constant becomes small and is not preferable. In addition, the raw material price of Sc is high, and thus it is not preferable to unnecessarily excessively dope Sc from the viewpoint of manufacturing cost. Further, in the case where y is 0.08 or more, the risk of anti-site defect absorption in which Tb and Y enter the B site and Al enters the A site increases, and thus it is not preferable.

[0058] In formula (1), the range of z is 0≤z<0.2, preferably 0

[0059] In the case where z is 0.2 or more, the precipitation suppression effect of the perovskite-type heterogeneous phase is saturated and does not change, and with an increase in the value of z, the value of y, that is, the substitution ratio of Tb by Sc also increases in linkage, and thus, as a result, the solid solution concentration of Tb unnecessarily decreases, and the feld constant becomes small and is not preferable. Further, the raw material price of Sc is high, and thus it is not preferable to unnecessarily excessively dope Sc from the viewpoint of manufacturing cost. Further, in the case where z is 0.16 or more, the risk of anti-site defect absorption in which Tb and Y enter the B site and Al enters the A site increases, and thus it is not preferable.

[0060] In formula (1), the range of y+z is 0.001

[0061] Further, in the paramagnetic garnet-type transparent ceramic of the present application, it is preferable that the sintered body described above further contain a sintering aid. Specifically, as the sintering aid, it is preferable to contain Si02in an amount of more than 0 mass% and 0.1 mass% or less (more than 0 ppm and 1000 ppm or less). If the content exceeds 0.1 mass% (1000 ppm), it is possible that a slight light absorption occurs due to crystal defects caused by the excess Si.

[0062] Further, as the sintering aid, an oxide of magnesium (Mg) or calcium (Ca) can be further added. Both Mg and Ca are divalent ions, and are elements that can compensate for the deviation of the charge balance in the interior of the garnet structure accompanying the addition of Si02, and thus can be preferably added. As for the amount of addition, it is preferable to adjust it in accordance with the amount of addition of Si02.

[0063] Further, the paramagnetic garnet-type transparent ceramic of the present application has an average sintered particle diameter of 10 μm or more and 40 μm or less, and an insertion loss of 0.05 dB or less at a wavelength of 1064 nm in the optically effective region in the length direction of a sample having a length of 20 mm.

[0064] Further, in the garnet-type composite oxide sintered body transparent ceramic of the present application, the average sintered particle diameter is 10 μm or more and 40 μm or less, and preferably 20 μm or more and 40 μm or less. If the average sintered particle diameter is less than 10 μm, the amount of scattering in the interior of the ceramic increases, and as a result, it is sometimes not suitable as a Faraday rotor mounted in the interior of a laser processing machine.

[0065] Further, the average particle diameter of the sintered particles in the resintered body (average sintered particle diameter) is obtained by measuring the particle diameter of the sintered particles of the object sintered body using a metal microscope, and in detail, is obtained as described below.

[0066] That is, for the resintered body, using the transmission mode of a metal microscope, using an objective lens of 50 times, a transmission open Nicol image of the sintered body sample whose both end faces have been polished is photographed. In detail, an optically effective region at a prescribed depth of the object sintered body is photographed, a diagonal line is drawn in the photographed image, the total number of sintered particles that cross the diagonal line is counted, and then the value obtained by dividing the length of the diagonal line by the counted total number is defined as the average sintered particle diameter of the sintered particles in the image. Further, the average particle diameters of each of the photographed images read by the analysis process are added (summed), and then divided by the number of photographs, and the value obtained is taken as the average sintered particle diameter of the object sintered body (hereinafter the same in the manufacturing method of the paramagnetic garnet-type transparent ceramic and the examples).

[0067] Further, in the case of the paramagnetic garnet transparent ceramic of the present application, the insertion loss at a wavelength of 1064 nm in the optically effective region in the length direction of a sample having a length of 20 mm is 0.05 dB or less, preferably 0.04 dB or less, more preferably 0.03 dB or less, and further preferably 0.02 dB or less. Thus, in the case where this laser light is transmitted, a high beam quality M 2 .

[0068] Note that the optically effective region herein refers to a region that is optically effective in the optical surface of the paramagnetic garnet transparent ceramic, i.e., a region that functions as a magneto-optical material when incident light is transmitted and exits inside the paramagnetic garnet transparent ceramic. In the case of a cylindrical paramagnetic garnet transparent ceramic, for example, it refers to a region in the optical surface (circular surface) on the axis of optical use, excluding the end surface outer edge portion that is not optically usable, i.e., a region excluding the optical surface outer edge portion corresponding to 19% in terms of the area ratio of the optical surface, i.e., a region of 81% in terms of the area ratio from the outer edge of the optical surface to the inside.

[0069] Further, the insertion loss herein is the linear transmittance expressed in dB. That is, in the case where 10 to 20 mW of laser light at a wavelength of 1064 nm is focused into a beam diameter of 200 to 350 μm, the optical surface of the subject paramagnetic garnet transparent ceramic is vertically (in the axis direction of optical use) irradiated, the light intensity is measured with a semiconductor light receiver, and the decrease in the light intensity relative to the light intensity at this time without the insertion of the ceramic (incident light intensity) is expressed in dB.

[0070] Further, the paramagnetic garnet transparent ceramic of the present application preferably has a laser damage threshold of 20 J / cm 2 The paramagnetic garnet transparent ceramic of the present application is preferably not damaged by pulsed laser light (has laser damage resistance) because it is intended to be used as a Faraday rotator. It is preferable that the damage threshold be extremely high, i.e., 20 J / cm 2 , preferably 22 J / cm 2 , more preferably 25 J / cm 2 .

[0071] Note that the "laser damage threshold at a wavelength of 1064 nm and a pulse width of 5 ns" refers to the case where the irradiation position is fixed for an arbitrary position inside the subject paramagnetic garnet transparent ceramic, and pulsed laser light at a wavelength of 1064 nm and a pulse width of 5 ns having a prescribed energy density (e.g., a beam diameter of 100 μm (Gaussian distribution 1 / e 2The laser irradiation is performed once, and the presence or absence of damage at each irradiation is confirmed, and the minimum value of the energy density at which laser damage occurs is set as the laser damage threshold (i.e., N-on-1 method) while the irradiation energy is gradually increased.

[0072] The laser damage threshold (LIDT) depends on the wavelength, pulse width, and beam spot diameter of the irradiated laser. Therefore, in the case where the laser damage test under the conditions of a wavelength of 1064 nm, a pulse width of 5 ns, and a beam diameter of 100 μm (Gaussian distribution 1 / e 2 intiation mechanisms" (Non-Patent Document 9), as a general rule of scaling (transforming) from the initial conditions of the wavelength (λ1), pulse width (τ1), and beam diameter (φ1) to new conditions of the wavelength (λ2), pulse width (τ2), and beam diameter (φ2), Equation (S1) can be applied.

[0073] LIDT (λ2, τ2, φ2) = LIDT (λ1, τ1, φ1) x (λ1 / λ2) x (τ2 / τ1) 1 / 2 x (φ1 / φ2) 2 (S1)

[0074] Therefore, according to Equation (S2) below, the laser damage threshold under the conditions of a wavelength of 1064 nm, a pulse width of 5 ns, and a beam diameter of 100 μm (Gaussian distribution 1 / e 2 intiation mechanisms" (Non-Patent Document 9), as a general rule of scaling (transforming) from the initial conditions of the wavelength (λ1), pulse width (τ1), and beam diameter (φ1) to new conditions of the wavelength (λ2), pulse width (τ2), and beam diameter (φ2), Equation (S1) can be applied.

[0075] LIDT (1064, 5, 100) = LIDT (λ1, τ1, φ1) x (λ1 / 1064) x (5 / τ1) 1 / 2 x (φ1 / 100) 2 (S2)

[0076] [Method for producing paramagnetic garnet-type transparent ceramic]

[0077] The method for producing the paramagnetic garnet-type transparent ceramic according to the present application is a method for producing the above-described paramagnetic garnet-type transparent ceramic according to the present application, characterized by performing a heat treatment on a ceramic body obtained by a method according to the following formula (1)

[0078] (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1)

[0079] (In the formula, 0≤x<0.45, 0≤y<0.08, 0≤z<0.2, 0.001

[0080] The sintered body of the Tb-containing rare earth aluminum garnet represented by the above formula (1) is subjected to pressure sintering, and then the pressure sintered body is heated to a temperature higher than that of the pressure sintering, and is subjected to re-sintering to produce a re-sintered body having an average sintered particle diameter of 10 μm or more, and then the re-sintered body is subjected to oxidation annealing treatment in an oxidizing atmosphere at 1400°C or higher.

[0081] wherein the following steps are employed to produce the paramagnetic garnet-type transparent ceramic.

[0082] (Sintering raw material powder)

[0083] First, a sintering raw material powder corresponding to the composition of the garnet-type composite oxide of the above formula (1) is produced.

[0084] The method for producing the sintering raw material powder of the above garnet-type composite oxide used in the present application is not particularly limited, and metal oxide powders of respective component elements corresponding to the garnet-type composite oxide can be used as initial raw materials, and they are weighed in a prescribed amount so as to have a composition corresponding to formula (1), and are mixed to produce the sintering raw material powder. The initial raw materials at this time are not particularly limited as long as they can be transparentized, and from the viewpoint of suppressing absorption from impurities, the purity is preferably 99.9 mass% or more, more preferably 99.99 mass% or more, and most preferably 99.999 mass% or more. In addition, the particle diameter of primary particles of the raw material powder is not particularly limited as long as it can be transparentized, and from the viewpoint of easy sinterability, it is preferably 50 nm or more and 1000 nm or less. The shape of the primary particles is selected from card house, spherical, and rod, and is not particularly limited as long as it can be transparentized.

[0085] Alternatively, as the method for producing the raw material powder for sintering of the above-mentioned garnet-type composite oxide used in the present application, a coprecipitation method, a pulverization method, a spray pyrolysis method, a sol-gel method, an alkoxide hydrolysis method, a complex polymerization method, a homogeneous precipitation method, all other synthesis methods can be used. Depending on the situation, in order to make the obtained ceramic raw material of the rare earth composite oxide into a desired particle size, wet ball milling, bead milling, jet milling, dry jet milling, hammer milling and the like can be appropriately used. For example, the following methods can be used to produce the raw material powder for sintering: a solid phase reaction method in which a plurality of oxide particles are mixed and fired, uniformity is produced by thermal diffusion of ions; or a coprecipitation method in which hydroxides, carbonates and the like are precipitated from an ion-containing solution in which oxide particles are dissolved, and uniformity is produced by firing to produce oxides.

[0086] In the case of the solid phase reaction method in which a plurality of metal oxide particles are mixed and fired, and uniformity is produced by thermal diffusion of ions, as the initial raw material, metal powders composed of terbium, yttrium, scandium, aluminum, or products in which the above-mentioned metal powders are dissolved in aqueous solutions of nitric acid, sulfuric acid, uric acid and the like, or oxide powders of the above-mentioned elements and the like can be preferably used. In addition, the purity of the above-mentioned raw material is preferably 99.9 mass% or more, and particularly preferably 99.99 mass% or more. A prescribed amount of these initial raw materials can be weighed so as to become a composition corresponding to formula (1), mixed and fired, and a fired raw material of the desired metal oxide is obtained, which is pulverized to produce the raw material powder for sintering. In this case, the firing temperature is preferably 1100°C or lower, more preferably 1050°C or lower, and further preferably 1000°C or lower. If it exceeds 1100°C, sintering of the raw material powder occurs, and in the subsequent pulverization process, it sometimes cannot be sufficiently pulverized. As the firing time, 1 hour or more can be performed, and the temperature increase rate at this time is preferably 100°C / h or more and 500°C / h or less. The atmosphere for firing is preferably an oxygen-containing atmosphere such as air, oxygen and the like, and a nitrogen atmosphere, an argon atmosphere, a hydrogen atmosphere and the like are not suitable. In addition, the firing device can be exemplified by a vertical muffle furnace, a horizontal tubular furnace, a rotary kiln and the like, and there is no particular limitation as long as the target temperature can be reached and an oxygen flow can be produced.

[0087] Further, the sintering raw material powder preferably contains a sintering aid. For example, tetraethoxysilane (TEOS) as a sintering aid can be added in an amount of more than 0 ppm and 1000 ppm or less (more than 0 mass% and 0.1 mass% or less) in the entire raw material powder (garnet-type composite oxide powder + sintering aid) in terms of SiO2, or SiO2 powder can be added in an amount of more than 0 ppm and 1000 ppm or less (more than 0 mass% and 0.1 mass% or less) in the entire raw material powder (garnet-type composite oxide powder + sintering aid), mixed, fired as necessary, and a sintering raw material powder can be produced. When the amount of addition exceeds 1000 ppm, crystal defects due to excess Si can cause a small amount of light absorption. Further, the purity is preferably 99.9 mass% or more. The sintering aid can be added at the time of preparation of the raw material powder slurry. Further, Si elements can sometimes be mixed from the environment of glassware and the like used in the manufacturing process, and when sintering is performed under reduced pressure, a part of the Si elements can sometimes be volatilized, and thus the content of Si contained in the final ceramic can sometimes be unintentionally increased or decreased, and thus attention is required. Further, when no sintering aid is added, it is preferable to select a sintering raw material powder in which the particle size of primary particles is in the nanometer range and the sintering activity is extremely high, for the sintering raw material powder used (i.e., the initial raw material mixed powder or the composite oxide powder) described above. Such selection can be appropriately performed.

[0088] When the fired raw material is pulverized to produce a sintering raw material powder, either dry or wet pulverization can be selected in terms of the pulverization method, but it is necessary to pulverize in a manner such that the target ceramic becomes highly transparent. For example, in the case of wet pulverization, the fired raw material is slurried using various pulverization (dispersion) methods such as ball milling, bead milling, homogenization, jet milling, and ultrasonic irradiation, and is pulverized (dispersed) to primary particles. The dispersion medium for this wet slurry is not particularly limited as long as it enables the highly transparent ceramic to be obtained, and for example, alcohols such as lower alcohols having 1 to 4 carbon atoms, and pure water can be mentioned. Further, various organic additives can sometimes be added to the wet slurry for the purpose of quality stability and yield improvement in the subsequent ceramic manufacturing process. In the present application, they are also not particularly limited. That is, various dispersants, binders, lubricants, plasticizers, and the like can be preferably used. However, as these organic additives, a high-purity type that does not contain unnecessary metal ions is preferably selected. In the case of wet pulverization, the sintering raw material powder is produced by finally removing the dispersion medium of the slurry.

[0089] [Manufacturing Process]

[0090] In the present application, the above-mentioned sintering raw material powder is preferably used, and after being formed into a prescribed shape, a mold-pressing is performed, followed by a debinding, and then a pre-sintering, to produce a pre-sintered body composed of a composite oxide having a relative density of 94% or more and an average sintered particle diameter of 3 μm or less. Next, the pre-sintered body is subjected to a pressure sintering (Hot Isostatic Pressing (HIP) treatment) at a pressure of 50 MPa or more and 300 MPa or less and a temperature of 1000°C or more and 1780°C or less. Further, the pressure-sintered body is heated to a temperature higher than the pre-sintering temperature, and a re-sintering is performed, to obtain a re-sintered body having an average sintered particle diameter of 10 μm or more.

[0091] Note that the average particle diameter of the sintered particles (average sintered particle diameter) is obtained by measuring the particle diameter of the sintered particles of the object sintered body using a metal microscope, and in detail, is obtained as follows.

[0092] That is, for the pre-sintered body, a metal microscope is used, a reflection mode is adopted, a 50-fold objective lens is used, and a reflection image of the surface of the sintered body is captured. In detail, considering the effective image size of the objective lens, the entire region of the optically effective area of the object sintered body is captured, and the captured image is subjected to an analysis process. At this time, first, a diagonal line is drawn in each captured image, the total number of sintered particles intersected by the diagonal line is counted, and then the average particle diameter of the sintered particles in the image is defined as the value obtained by dividing the length of the diagonal line by the counted total number. Further, the average particle diameters of each of the captured images read by the analysis process are added (summed), and then divided by the number of captured images, and the obtained value is defined as the average sintered particle diameter of the object sintered body (the same applies hereinafter).

[0093] (Forming)

[0094] In the production method of the present application, a general mold-pressing process can be preferably used. That is, a uniaxial pressing process in which a mold is filled and pressed from a certain direction, a cold isostatic pressing (CIP) process in which a deformable waterproof container is tightly accommodated and pressed with hydrostatic pressure, and a warm isostatic pressing (WIP) process are extremely common, and can be preferably used. Further, as for the applied pressure, it can be appropriately adjusted while confirming the relative density of the obtained formed body, and is not particularly limited, and if it is managed in a pressure range of 300 MPa or less which can be dealt with by, for example, a commercially available CIP device or WIP device, the production cost can be suppressed. Further, instead of the mold-pressing method, a casting method can also be used to produce the formed body. By optimizing the shape and size of the composite oxide powder as the initial raw material in combination with various organic additives, a pressure casting method, a centrifugal casting method, an extrusion molding method, and the like can also be used.

[0095] However, in the present invention, in order to manage the size and amount of scattering sources such as heterogeneous phases, foreign matter, dirt, and microcracks within the specified range, the molding jig and molding machine are preferably clean dedicated equipment that has been thoroughly cleaned and dried, and the environment for the molding operation is preferably a clean space below level 1000.

[0096] (skimmed)

[0097] In the production method of the present invention, a conventional degreasing process can be preferably utilized. Specifically, a heating furnace-based degreasing process can be performed. Furthermore, the type of atmospheric gas used in this process is not particularly limited; air, oxygen, hydrogen, and the like can be preferably used. The degreasing temperature is also not particularly limited; however, when using raw materials mixed with organic additives, the temperature is preferably raised to a temperature at which the organic components can be decomposed and removed.

[0098] (Pre-sintering)

[0099] In this step, a pre-sintered body is prepared, preferably densified to a relative density of 94% or higher and preferably with an average sintered grain size of 3 μm or less, as a sintered body before heating and sintering. The temperature and holding time must be controlled to keep the sintered grain size within the desired range.

[0100] Here, a conventional 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. More preferably, sintering under reduced pressure (in a vacuum) can be used. The vacuum degree of the pre-sintering is preferably less than 1×10 -1 Pa, more preferably less than 1×10 -2 Pa, particularly preferably less than 1×10 -3 Pa.

[0101] The sintering temperature in the preliminary sintering step of the present invention is preferably 1450-1650°C, particularly preferably 1500-1600°C. This temperature range is preferred because it promotes densification while suppressing heterogeneous phase precipitation and grain growth. The sintering hold time in the preliminary sintering step of the present invention is sufficient for a period of several hours, preferably to achieve a relative density of 94% or higher.

[0102] The average sintered particle size of the sintered particles of the pre-sintered body of the present invention is preferably 3 μm or less, more preferably 2.5 μm or less, and particularly preferably 1 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 3 μm, plastic deformation is difficult to occur during the subsequent HIP treatment step, and the removal of bubbles remaining in the pre-sintered body may become difficult.

[0103] (Additive pressure sintering (Hot Isostatic Pressing (HIP)))

[0104] In the production method of the present application, after the pre-sintering step, a step of pressure-sintering (HIP treatment) is provided, preferably at a pressure of 50 MPa or more and 300 MPa or less, and at a temperature of 1000°C or more and 1780°C or less, on the pre-sintered body. As to the type of the pressure medium at this time, it is preferable to use an inactive gas such as argon or nitrogen, or Ar-O2. The pressure of the pressure medium is preferably 50 to 300 MPa, and more preferably 100 to 300 MPa. If the pressure is less than 50 MPa, it is possible that the effect of improving the transparency is not obtained, and if the pressure exceeds 300 MPa, even if the pressure is increased, the transparency is not improved beyond that, the load on the device becomes excessive, and it is possible that the device is damaged. If the pressure applied is 196 MPa or less, which is the processing limit of a commercially available HIP device, it is simple and preferable. In addition, the processing temperature (the prescribed holding temperature) at this time is preferably in the range of 1000 to 1780°C, and more preferably in the range of 1100 to 1700°C. If the heat treatment temperature is higher than 1780°C, grain growth occurs in the HIP treatment, and the removal of bubbles becomes difficult, and thus it is not preferable. In addition, if the heat treatment temperature is less than 1000°C, it is possible that the effect of improving the transparency of the sintered body is hardly obtained. In addition, there is no particular limitation on the holding time of the heat treatment temperature, and if the holding time is too long, the risk of oxygen deficiency increases, and thus it is not preferable. Typically, it is preferable to set it in the range of 1 to 3 hours. In addition, there is no particular limitation on the heater material, the heat insulating material, and the processing container for the HIP treatment, and it is preferable to use graphite, or molybdenum, tungsten, platinum (Pt), and as the processing container, yttria or gadolinia is further preferable. In the case where the processing temperature is 1500°C or more, graphite is preferable as the heater material and the heat insulating material, and in this case, any one of graphite, molybdenum, and tungsten is selected as the processing container, and further, any one of yttria and gadolinia is selected as a double container inside thereof, and further, when an oxygen releasing material is filled in the container, the amount of oxygen deficiency in the HIP treatment can be greatly suppressed, and thus it is preferable.

[0105] (Re-sintering)

[0106] In the production method of the present application, after the HIP treatment is completed, the pressure-sintered body is heated to a temperature higher than that of the pressure-sintering described above, and re-sintering is performed to cause grain growth, and a re-sintered body having an average sintered grain diameter of 10 μm or more is obtained. At this time, the conditions of the temperature and the holding time are controlled so that the sintered grain diameter finally obtained converges in the desired range.

[0107] The kind of the atmosphere gas at this time is not particularly limited, and air, oxygen, hydrogen, or the like can be preferably used, and more preferably, the treatment is performed under reduced pressure (under a vacuum of less than 1 x 10 -2 The temperature of the re-sintering is preferably 1650°C or higher and 1800°C or lower, and more preferably 1700°C or higher and 1800°C or lower. If it is less than 1650°C, no grain growth occurs, and thus it is not preferable. The average particle diameter of the sintered particles resulting from the re-sintering is preferably 10 μm or more, more preferably 15 μm or more, and further preferably 20 μm or more, and is preferably 40 μm or less. The holding time of the re-sintering process is not particularly limited, and is preferably 5 hours or more, more preferably 10 hours or more, and particularly preferably 20 hours or more. Generally, the longer the holding time, the more the grain growth of the sintered body develops. The temperature and the holding time of the re-sintering process can be appropriately adjusted by confirming the average sintered particle diameter. However, generally, when the sintering temperature is excessively increased, unexpected abnormal grain growth occurs, and it is difficult to obtain a homogeneous sintered body. Therefore, it is preferable to have some degree of margin in the temperature of the re-sintering, and to adjust the size of the average sintered particle diameter of the re-sintered body by extending the holding time.

[0108] (Oxidation Annealing)

[0109] The re-sintered body that has undergone the above series of processes is particularly reduced in the HIP treatment process or the like, and some oxygen defects are generated, and sometimes has a gray to dark blue appearance. Therefore, the oxidation annealing treatment (oxygen defect recovery treatment) is performed in an atmospheric or oxygen-containing atmosphere. The annealing treatment temperature is 1400°C or higher, and is preferably 1450°C or higher. In addition, it is preferably 1500°C or lower. The holding time at this time is not particularly limited, and is preferably selected to be a time sufficient for the oxygen defect recovery and within a time in which the electric power is not unnecessarily consumed by a long time of the treatment. In addition, the micro-oxidation HIP treatment can be performed. By these treatments, even if the re-sintered body is colored, the oxygen defect recovery can be performed, and thus the size and the number of the scattering sources (scattering contrast sources) can be managed within a prescribed range, and a paramagnetic garnet-type transparent ceramic having little absorption from the oxygen defects can be produced. Of course, the coloring (absorption) of the material due to the addition of a coloring element for imparting a function or an impurity or the like cannot be removed.

[0110] Further, if the high-temperature long-time treatment is excessively performed in the oxidation annealing process, sometimes the size and the amount of the residual bubbles in the sintered body increase. Thus, the size and the amount of the bubbles and the micro-cracks remaining in the sintered body at the final stage cannot be managed within a prescribed range, and thus it is not preferable. In this case, if the oxidation annealing treatment is newly performed after the HIP treatment is performed again on the sintered body, the size and the amount of the bubbles and the micro-cracks remaining in the sintered body can be managed within a prescribed range, and thus it is preferable.

[0111] In the method for producing the paramagnetic garnet-type transparent ceramic of the present invention, it is preferred that after the oxidation annealing treatment, both end faces are optically mirror-finished, and then antireflection films are formed on each of the end faces.

[0112] (Optical grinding)

[0113] In the production method of the present invention, the paramagnetic garnet-type transparent ceramic that has undergone the above-described series of production steps is preferably cylindrical or prismatic in shape, and its two end faces (optical end faces) located on the axis for optical use are preferably optically polished and finished (optical mirror finish). The optical surface accuracy at this time is preferably λ / 2 or less, and particularly preferably λ / 8 or less, at a measurement wavelength of λ = 633 nm.

[0114] 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 preferred to carefully clean the optical surface with a liquid before applying the anti-reflection film treatment, and check the cleanliness with a solid mirror or microscope. If the cleanliness is judged to be low during the cleanliness inspection, wiping and cleaning can also be performed. In order to avoid scratching the optical surface or wiping off dirt during the wiping and cleaning process, it is preferred to select an operating fixture made of a soft material, and a wiping tool with low dust generation as the wiping tool.

[0115] In this way, after the above-mentioned molded body is subjected to pre-sintering-pressure sintering-re-sintering treatment under specified conditions, an oxidation annealing treatment is performed, and then when the optical end faces (incident surface and exit surface) are provided with an anti-reflection film, the total light transmittance at a wavelength of 1064nm under an optical path length of 20mm can be made to be above 99.9%.

[0116] (Insertion Loss)

[0117] The paramagnetic garnet-type transparent ceramic of the present invention, which has undergone the above-described series of manufacturing steps, can reduce absorption and scattering of transmitted light. One method for evaluating absorption and scattering of transmitted light is preferably to utilize insertion loss, which is the linear transmittance expressed in dB. The insertion loss is preferably low, being 0.05 dB or less, preferably 0.04 dB or less, more preferably 0.03 dB or less, and even more preferably 0.02 dB or less at a wavelength of 1064 nm.

[0118] As described above, a paramagnetic garnet-type transparent ceramic, which is a sintered body of a paramagnetic garnet-type composite oxide containing at least terbium and aluminum, has an average sintered particle diameter of 10 μm or more and 40 μm or less, and an insertion loss at a wavelength of 1064 nm of 0.05 dB or less. In addition, it is possible to preferably provide a laser damage threshold of 20 J / cm2at a wavelength of 1064 nm and a pulse width of 5 ns. 2 The above transparent sintered body.

[0119] [Magneto-optical device]

[0120] Further, the paramagnetic garnet-type transparent ceramic of the present application is envisaged to be utilized as a magneto-optical material, and therefore it is preferable that the paramagnetic garnet-type transparent ceramic is utilized in a manner that a magnetic field is applied in parallel to the optical axis thereof, and a polarizer and an analyzer are disposed so that their optical axes are offset by 45 degrees from each other, to constitute a magneto-optical device. That is, the paramagnetic garnet-type transparent ceramic of the present application is suitable for a magneto-optical device use, and in particular, is suitable for use as a Faraday rotator for an optical isolator for light having a wavelength of 0.9 to 1.1 μm.

[0121] Figure 1 A cross-sectional schematic view showing an example of an optical device, i.e., an optical isolator, having a Faraday rotator constituted by the magneto-optical material of the present application as an optical element.

[0122] In the Figure 1 In the optical isolator 100, a Faraday rotator 110 constituted by the paramagnetic garnet-type transparent ceramic of the present application is provided, and a polarizer 120 and an analyzer 130 as polarizing materials are provided in front of and behind the Faraday rotator 110. In addition, in the case of the optical isolator 100, it is preferable 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.

[0123] In addition, the above optical isolator 100 can be suitably utilized in an industrial optical fiber laser device. That is, it is suitable for preventing return of reflected light of laser light emitted from a laser light source to the light source, and for stabilizing oscillation.

[0124] Example

[0125] The present application is more specifically described below by citing examples, comparative examples, and reference examples, but the present application is not limited to these examples.

[0126] [Example 1]

[0127] As Example 1, a case where y = 0.004, z = 0.03, y + z = 0.034 in Formula (1), and the value of x is 0 ≤ x ≤ 0.396 is shown.

[0128] Tb4O7 powder, Y2O3 powder, Sc2O3 powder, and AI2O3 powder were prepared. Further, tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. and polyethylene glycol 200 manufactured by Kanto Chemical Co., Inc. were prepared. In terms of purity, the powder raw materials were 99.9 mass% or more, and the liquid raw materials were 99.999 mass% or more. Using the above raw materials, the mixing ratio was adjusted, and the following oxide raw materials having a total of four crystal structures were produced to have the final composition shown in Table 1.

[0129] (Raw materials for Example 1-1 and Comparative Example 1-1)

[0130] (Tb0.794Y0.194Sc0.162)3(Al4.850)5O12was weighed so that the molar numbers of terbium, yttrium, scandium, and aluminum would become Tb:Y:Sc:Al = 1.794:1.194:0.162:4.850, respectively, and mixed with the powder. 0.598 Y 0.398 Sc 0.004 )3(Al 0.97 Sc 0.03 )5O 12 The mixed powder was then weighed and TEOS was added as a sintering aid so that the addition amount would become 100 ppm in terms of SiO2, and a raw material was prepared.

[0131] (Raw materials for Example 1-2 and Comparative Example 1-2)

[0132] (Tb0.794Y0.194Sc0.162)3(Al4.850)5O12was weighed so that the molar numbers of terbium, yttrium, scandium, and aluminum would become Tb:Y:Sc:Al = 1.794:1.194:0.162:4.850, respectively, and mixed with the powder. 0.697 Y 0.299 Sc 0.004 )3(Al 0.97 Sc 0.03 )5O 12 The mixed powder was then weighed and TEOS was added as a sintering aid so that the addition amount would become 100 ppm in terms of SiO2, and a raw material was prepared.

[0133] (Raw materials for Example 1-3 and Comparative Example 1-3)

[0134] (Tb0.794Y0.194Sc0.162)3(Al4.850)5O12was weighed so that the molar numbers of terbium, yttrium, scandium, and aluminum would become Tb:Y:Sc:Al = 1.794:1.194:0.162:4.850, respectively, and mixed with the powder. 0.797 Y 0.199 Sc 0.004 )3(Al 0.97 Sc 0.03 )5O 12The mixed powder was then weighed and TEOS was added as a sintering aid, with the amount of TEOS added being 100 ppm in terms of SiO2.

[0135] (Starting materials for Examples 1-4 and Comparative Examples 1-4)

[0136] A mixture of (Tb0.988Sc0.162)5O12and Al powder was prepared by weighing the powders in a manner such that the molar amounts of terbium, scandium, and aluminum were Tb:Sc:Al = 2.988:0.162:4.850, respectively. 0.996 Sc 0.004 )3(Al 0.97 Sc 0.03 )5O 12 The mixed powder was then weighed and TEOS was added as a sintering aid, with the amount of TEOS added being 100 ppm in terms of SiO2.

[0137] Next, the mixture was placed in a polyethylene container while taking care to prevent mixing with each other, and polyethylene glycol 200 was added as a dispersant so that the amount of polyethylene glycol 200 was 0.5 mass% relative to the oxide powder. Dispersion and mixing were performed using a ball mill device in ethanol. The treatment time was 24 hours. Then, spray drying was performed to produce granular starting materials having an average particle diameter of 20 μm.

[0138] Next, uniaxial die molding was performed on each of the four kinds of powder starting materials, and hydrostatic pressure pressing was performed at a pressure of 198 MPa to produce CIP molded bodies. The resulting molded bodies were subjected to debinding treatment in a muffle furnace under conditions of 1000°C for 2 hours.

[0139] As an example, the debound molded bodies were loaded into a vacuum heating furnace, and were subjected to presintering treatment at 1600°C for 2 hours to produce four kinds of presintered bodies. At this time, the relative densities of the samples were all 94% or more. The resulting presintered bodies were loaded into a HIP furnace equipped with a carbon heater, and were subjected to pressure sintering (HIP) treatment under conditions of Ar, 196 MPa, 1600°C, and 3 hours. Next, the pressure-sintered bodies subjected to HIP were again loaded into a vacuum heating furnace, and were subjected to resintering treatment at 1700°C for 20 hours under reduced pressure of less than 1.0 x 10 -3 Pa. Finally, the resintered bodies were subjected to oxidation annealing treatment at 1450°C for 30 hours in a normal pressure atmosphere to produce four kinds of oxidation annealed bodies. The ceramic appearances after the oxidation annealing treatment were all colorless and transparent.

[0140] As comparative examples, the above defatted shaped bodies were charged into a vacuum heating furnace and treated at 1600°C for 2 hours to obtain four kinds of pre-sintered bodies in total. At this time, the relative densities of the sintered phases of the samples were all 94% or more. Each of the obtained pre-sintered bodies was charged into a carbon heater HIP furnace and subjected to press sintering (HIP) treatment under Ar at 196 MPa at 1600°C for 3 hours. According to the prior art literature, no re-sintering treatment or oxidation annealing treatment of the press sintered bodies subjected to HIP treatment under anaerobic conditions (oxygen-free atmosphere) was performed.

[0141] For the oxidation annealed bodies (Examples) and the press sintered bodies (Comparative Examples) thus obtained, the samples were ground into a cylindrical shape to have a diameter of 5 mm (for insertion loss measurement) and a diameter of 10 mm (for laser damage threshold measurement), and the samples were optically polished to have a length of 20 mm (for insertion loss measurement) and a length of 14 mm (for laser damage threshold measurement) with an optical surface accuracy of λ / 8 (in the case of a measurement wavelength λ = 633 nm) for both end surfaces.

[0142] Further, for the optically polished samples for insertion loss measurement, an antireflection film designed so as to have a center wavelength of 1064 nm and a reflectance of 0.1% or less was applied to both end surfaces.

[0143] For the samples thus obtained, the following measurements were performed.

[0144] (laser damage threshold)

[0145] As for the laser damage threshold, a pulse laser having a wavelength of 1064 nm, a pulse width of 5 ns, and an irradiation size (beam diameter) of 100 μm φ (Gaussian distribution 1 / e 2 intensity) was used, the focal position of the optical system was adjusted so that the laser was incident from the inside of the material, i.e., 5 mm inside the laser incidence surface of the material, and the measurement was performed using an N-on-1 test. That is, the irradiation position of the optically effective region of the optical end surface of the sample was fixed, the energy was slowly increased from a low irradiation energy density, and the energy density at which damage occurred was determined. As for the determination of damage occurrence, a bright spot (scattered light) due to damage was visually determined by causing a He-Ne laser for a probe to be incident on the material. It should be noted that, taking into account the reflectance R of the incidence surface, a value of (1-R) times the incident intensity was used as the effective damage threshold. For example, in the case of a ceramic having a refractive index of n = 1.84, the reflectance is R = {(1-1.84) / (1+1.84)} 2= 0.087, and thus a value of 0.913 times the incident intensity was used. The measurement was performed three times for each sample, and the average value was calculated to two significant digits as the damage threshold. In this test, the value of damage in the interior of the material was used, and in the case where the exit end surface was damaged due to contamination or damage of the polishing surface, surface roughness, and the like, the data was excluded.

[0146] (insertion loss)

[0147] The insertion loss was measured in dB based on the following equation, using a light source manufactured by NKT Photonics, and an optical system using a collimator lens, a stage, a power meter manufactured by Gentec, and a Ge photodetector, so as to reduce the light of wavelength 1064 nm to a size of beam diameter 200 μmφ, by intensity measurement of the light in the optical effective area surface of the sample. Then, a mechanism for moving the sintered body sample up and down and left and right using an automatic stepping motor was provided on the stage on which the sintered body sample was placed, and the insertion loss distribution in the entire optical effective diameter (area) surface was measured by moving the sintered body sample at an interval of 100 μm from the end to the end while repeating the above insertion loss measurement, and the average value was read as the insertion loss based on the value of the center 2 mm square of the optical effective area at that time.

[0148] Insertion loss (dB / 20 mm) = -10 x log 10 (I / I0)

[0149] (In the equation, I represents the transmitted light intensity (intensity of light of a sample of linear transmission length 20 mm), and I0represents the incident light intensity.)

[0150] (Average sintered particle diameter D)

[0151] The average sintered particle diameter of the grains of the ceramic was determined by referring to "Lineal Intercept Technique for Measuring Grain Size in Two-Phase Polycrystalline Ceramics", Journal of the American Ceramic Society, 55, 109 (1972) (Non-Patent Literature 8). Specifically, the grain boundaries of the end surface of a mirror-polished transparent ceramic sample used in the laser damage threshold measurement, which was heat-etched by treatment at 1300°C for 6 hours in the atmosphere, were observed using an optical microscope, and the average sintered particle diameter D (μm) was determined as the value of two significant digits of the value obtained from the following equation.

[0152] D = 1.56C / (MN)

[0153] The above results and the literature value of the single crystal TGG of Reference Example 1-1 (Non-Patent Literature 7) are shown in Table 1.

[0154] [Table 1]

[0155]

[0156] From the above results, the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics of Examples 1-1 to 1-4 was 22 μm or more, and the insertion loss was 0.05 dB or less. In addition, the laser damage threshold of the paramagnetic garnet-type transparent ceramics at this time was all 20 J / cm 2 The laser damage threshold was confirmed to be 4 times or more that of the TGG single crystal (Reference Example 1-1).

[0157] In contrast, the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics of Comparative Examples 1-1 to 1-4 was 4.5 μm or less, and the insertion loss was 0.08 dB or more. In addition, the laser damage threshold of the paramagnetic garnet-type transparent ceramics at this time was all 10 J / cm 2 or less.

[0158] That is, in the case where the average sintered particle diameter was 22 μm or more and the insertion loss was 0.05 dB or less, it was confirmed that a transparent ceramic having a high damage threshold was obtained.

[0159] [Example 2]

[0160] As Example 2, a case where x = 0.40 in Formula (1) was fixed, and y = 0.001, z = 0.001, y + z = 0.002 was set, a case where y = 0.04, z = 0.08, y + z = 0.12 was set, and a case where y = 0.05, z = 0.13, y + z = 0.18 was set were shown. In addition, as Reference Example 2-1, a case where y = z = y + z = 0 was shown.

[0161] As with Example 1, a terbium oxide powder, a yttrium oxide powder, a scandium oxide powder, and an alumina powder manufactured by Showa Denko K.K. were prepared. Furthermore, a tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. and a liquid of polyethylene glycol 200 manufactured by Kanto Chemical Co., Inc. were prepared. In terms of purity, the powder raw materials were 99.9 mass% or more, and the liquid raw materials were 99.999 mass% or more. Using the above raw materials, the mixing ratio was adjusted, and the following oxide raw materials having a total of 4 crystal structures were produced to become the final composition shown in Table 2.

[0162] (Starting materials for Example 2-1)

[0163] (Tb0.797Y0.200Sc0.008Al4.995)O6.996 0.599 Y 0.4 Sc 0.001 )3(Al 0.999 Sc 0.001 )5O 12 The mixed powder was used. Next, TEOS was weighed and added as a sintering aid, and the added amount was made 100 ppm in terms of SiO2, to prepare the raw material.

[0164] (Raw material for Example 2-2)

[0165] (Tb0.797Y0.200Sc0.008Al4.995)O6.996 0.56 Y 0.4 Sc 0.04 )3(Al 0.92 Sc 0.08 )5O 12 The mixed powder was used. Next, TEOS was weighed and added as a sintering aid, and the added amount was made 100 ppm in terms of SiO2, to prepare the raw material.

[0166] (Raw material for Example 2-3)

[0167] (Tb0.797Y0.200Sc0.008Al4.995)O6.996 0.55 Y 0.4 Sc 0.05 )3(Al 0.87 Sc 0.13 )5O 12 The mixed powder was used. Next, TEOS was weighed and added as a sintering aid, and the added amount was made 100 ppm in terms of SiO2, to prepare the raw material.

[0168] (Raw material for Reference Example 2-1)

[0169] (Tb0.797Y0.200Sc0.008Al4.995)O6.996 0.6 Y 0.4 )3Al5O 12 The mixed powder was used. Next, TEOS was weighed and added as a sintering aid, and the added amount was made 100 ppm in terms of SiO2, to prepare the raw material.

[0170] Next, while paying attention to prevent mixing with each other, the powders were put in a polyethylene-made jar, and polyethylene glycol 200 was added as a dispersant so that the polyethylene glycol 200 becomes 0.5 mass% with respect to the oxide powder. Each of the powders was dispersed and mixed in ethanol using a ball mill device. The treatment time was 24 hours. Then, spray drying treatment was performed, and granular raw materials each having an average particle diameter of 20 μm were produced.

[0171] Next, for each of the four kinds of the obtained powder raw materials, uniaxial die molding, hydrostatic pressure pressing treatment at a pressure of 198 MPa were performed, and CIP molded bodies were obtained. The obtained molded bodies were subjected to debinding treatment in a muffle furnace under conditions of 1000°C for 2 hours.

[0172] The debound molded bodies were put in a vacuum furnace, and subjected to presintering treatment at 1600°C for 2 hours under a reduced pressure of less than 1.0 x 10 -3 Pa, and four kinds of presintered bodies were obtained. At this time, the relative densities of the samples were all 94% or more. The obtained presintered bodies were put in a HIP furnace equipped with a carbon heater, and subjected to pressure sintering (HIP) treatment under conditions of Ar, 196 MPa, 1600°C for 3 hours. Next, the pressure sintered bodies were again put in a vacuum furnace, and subjected to resintering treatment at 1700°C for 20 hours under a reduced pressure of less than 1.0 x 10 -3 Pa, and resintered bodies were obtained. Finally, the resintered bodies were subjected to oxidation annealing treatment at 1450°C for 30 hours in the air.

[0173] For the oxidation annealed bodies thus obtained, each of the bodies was ground into a cylindrical shape, and optically polished so that both end surfaces become mirror surfaces, and a sample for insertion loss measurement (diameter 5 mm, length 20 mm) and a sample for laser damage threshold measurement (diameter 10 mm, length 14 mm) were prepared. Further, for the optically polished sample for insertion loss measurement, an antireflection film designed so that the center wavelength becomes 1064 nm and the reflectance becomes 0.1% or less was applied to both end surfaces.

[0174] For the samples thus obtained, the laser damage threshold, the average sintered particle diameter, and the insertion loss were evaluated in the same manner as in Example 1.

[0175] The results are shown in Table 2.

[0176] [Table 2]

[0177]

[0178] From the above results, the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics of Examples 2-1 to 2-3 was 27 μm or more, and the insertion loss was 0.05 dB or less. In addition, the laser damage threshold at this time was 25 J / cm 2 or more.

[0179] [Example 3]

[0180] In Example 2-2, the time for re-sintering was made 2 hours (Comparative Example 3-1), 6 hours (Example 3-1), and 40 hours (Example 3-2), and, except for this, the conditions were made the same as in Example 2-2, and samples of paramagnetic garnet-type transparent ceramics were produced.

[0181] The evaluation results thereof are shown in Table 3.

[0182] [Table 3]

[0183]

[0184] From the above results, the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics of Examples 3-1 and 3-2 was 12 to 40 μm, the insertion loss was 0.02 to 0.04 dB, and the laser damage threshold was 22 to 27 J / cm 2 . In contrast, the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics of Comparative Example 3-1 was 6.9 μm, the insertion loss was 0.07 dB, and the laser damage threshold was 12 J / cm 2 . That is, by adjusting the re-sintering conditions (re-sintering time), the average sintered particle diameter can be made 10 μm or more, the insertion loss can be made 0.05 dB or less, and the laser damage threshold of the paramagnetic garnet-type transparent ceramics at this time becomes 20 J / cm 2 or more.

[0185] [Example 4]

[0186] In Example 2-2, the temperature of the oxidation annealing treatment was made 1300°C (Comparative Example 4-1), 1400°C (Example 4-1), and 1500°C (Example 4-2), and, except for this, the conditions were made the same as in Example 2-2, and samples of paramagnetic garnet-type transparent ceramics were produced.

[0187] The evaluation results thereof are shown in Table 4.

[0188] [Table 4]

[0189]

[0190] From the above results, the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics of Examples 4-1 and 4-2 was 29 to 30 μm, the insertion loss was 0.03 to 0.04 dB, and the laser damage threshold was 25 to 26 J / cm 2 While the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics of Comparative Example 4-1 was 30 μm, the insertion loss was 0.08 dB, and the laser damage threshold was 7.6 J / cm 2 . That is, by making the oxidation annealing conditions (oxidation annealing temperature) 1400°C or more, the average sintered particle diameter of the paramagnetic garnet-type transparent ceramics was made 10 μm or more, the insertion loss was made 0.05 dB or less, and the laser damage threshold at this time was 20 J / cm 2 or more.

[0191] [Example 5]

[0192] As an example of a magneto-optical device, an example of constructing an optical isolator using the paramagnetic garnet-type transparent ceramics (Example 1-4) having a laser damage threshold of 20 J / cm 2 2 An example of constructing an optical isolator using the paramagnetic garnet-type transparent ceramics (Comparative Example 1-4) having a laser damage threshold of 2.6 J / cm 2 The optical isolator was constructed in the same configuration as in Patent Document 6 using each of the transparent ceramics as a Faraday rotator.

[0193] (Durability test of optical isolator)

[0194] For the durability test of the optical isolator, a pulse laser having a wavelength of 1030 nm, a pulse width of 14 ps, an average power of 150 W, and a repetition frequency of 600 kHz was made to pass through the optical isolator. The beam diameter was set to be substantially parallel light of 1.0 mmφ (Gaussian distribution 1 / e 2 The transmitted light was enlarged with a expander, and the durability of the optical isolator was evaluated by observing the time dependence of the transmitted light intensity with a power meter.

[0195] For the optical isolator (Example 5) equipped with the paramagnetic garnet-type transparent ceramics (Example 1-4) having a laser damage threshold of 20 J / cm 2

[0196] While in the optical isolator (Comparative Example 5) equipped with the paramagnetic garnet-type transparent ceramics (Comparative Example 1-4) having a laser damage threshold of 2.6 J / cm 2 the intensity of the transmitted light was reduced to a value of 50% or less relative to the intensity of the incident light almost simultaneously with the start of the test, and thus the test was discontinued.

[0197] As described above, it was confirmed that the laser damage threshold was 20 J / cm 2 In the above case, a high durability optical isolator having no decrease in transmittance even after continuous operation for 100 hours or more can be obtained.

[0198] Note that, although the present application has been described above with reference to the embodiments, the present application is not limited to these embodiments, and other embodiments, additions, changes, deletions, and the like can be made within the scope that can be conceived by those skilled in the art, and all modes of the present application that exert the effects of the present application are included in the scope of the present application.

[0199] Explanation of Reference Signs

[0200] 100 Optical isolator

[0201] 110 Faraday rotator

[0202] 120 Polarizer

[0203] 130 Analyzing polarizer

[0204] 140 Magnet

Claims

1. A paramagnetic garnet-type transparent ceramic, which is a sintered body of rare earth aluminum garnet containing Tb represented by the following formula (1), characterized in that: The paramagnetic garnet-type transparent ceramic has an average sintered particle size of 10 μm or more and 40 μm or less, and an insertion loss of 0.05 dB or less at a wavelength of 1064 nm in an optically effective region in the longitudinal direction of a sample having a length of 20 mm. (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<0.08, 0≤z<0.2, 0.001<y+z<0.

20.

2. The paramagnetic garnet-type transparent ceramic according to claim 1, wherein The laser damage threshold with a wavelength of 1064nm and a pulse width of 5ns is 20J / cm 2 above.

3. A magneto-optical device comprising the paramagnetic garnet-type transparent ceramic according to claim 1 or 2.

4. The magneto-optical device according to claim 3 is an optical isolator usable in a wavelength range of 0.9 μm to 1.1 μm, comprising the paramagnetic garnet-type transparent ceramic as a Faraday rotator and polarizing materials provided before and after the optical axis of the Faraday rotator.

5. A method for producing a paramagnetic garnet-type transparent ceramic, the method for producing a paramagnetic garnet-type transparent ceramic according to claim 1 or 2, characterized in that: A pre-sintered body of a rare earth aluminum garnet containing Tb represented by the following formula (1) is pressure-sintered, and the pressure-sintered body is heated to a temperature exceeding the pressure-sintering temperature and then re-sintered to obtain a re-sintered body having an average sintered grain size of 10 μm or more, and the re-sintered body is subjected to an oxidation annealing treatment in an oxidizing atmosphere at 1400° C. or higher. (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<0.08, 0≤z<0.2, 0.001<y+z<0.20.

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