Paramagnetic garnet-type transparent ceramics, magneto-optical materials and magneto-optical devices

Abstract

Provided is a paramagnetic garnet-type transparent ceramic which is truly transparent and has high optical homogeneity, the transparent ceramic being a sintered object of a composite oxide represented by formula (1), containing SiO2 as a sintering aid in an amount larger than 0 mass% but not larger than 0.1 mass%, and having an average sinter-grain diameter of 5 μm or larger. The transparent ceramic has a total light transmittance of 84.0% or greater and a forward scatter of 0.5% or less at an optical path length of 25 mm and a wavelength of 1,064 nm and has a total light transmittance of 84.0% or greater and a forward scatter of 0.5% or less at an optical path length of 25 mm and a wavelength of 1,300 nm.　Formula (1): (Tb1-x-yYxScy)3(Al1-zScz）5O12 (In the formula, 0.05≤x<0.4, 0≤y<0.004, 0.6≤1-x-y<0.95, 0≤z<0.004, and 0.001<y+z<0.005.)

Description

[Technical field]

[0001] The present invention relates to paramagnetic garnet-type transparent ceramics, and more particularly to a magneto-optical material made of garnet-type transparent ceramics containing terbium that is suitable for forming magneto-optical devices such as optical isolators, and a magneto-optical device using the magneto-optical material. [Background technology]

[0002] In recent years, it has become possible to increase the output of fiber lasers, and laser processing machines using these fiber lasers have become increasingly popular. However, when light from outside enters the laser light source built into the laser processing machine, the resonance state becomes unstable, causing the oscillation state to become disturbed. In particular, when the oscillated light is reflected by the optical system along the way and returns to the light source, the oscillation state is greatly disturbed. To prevent this, an optical isolator is usually installed on the light output side of the light source, such as between the laser light source and the optical fiber.

[0003] An optical isolator consists of a Faraday rotator, a polarizer arranged on the light input side of the Faraday rotator, and an analyzer arranged on the light output side of the Faraday rotator. The Faraday rotator is used by applying a magnetic field parallel to the light's traveling direction. In this case, the polarization line of the light only rotates in a fixed direction whether it moves forward or backward through the Faraday rotator. Furthermore, the Faraday rotator is adjusted to a length that rotates the polarization line of the light exactly 45 degrees. Here, if the polarization planes of the polarizer and the analyzer are shifted 45 degrees in the direction of rotation of the forward light, the polarization of the forward light will be transmitted because it matches the polarizer position and the analyzer position. On the other hand, the polarization of the backward light will rotate 45 degrees in the opposite direction to the deviation angle of the polarization plane of the polarizer, which is shifted 45 degrees from the analyzer position. Then, the polarization plane of the return light at the polarizer position will be shifted 45 degrees - (-45 degrees) = 90 degrees from the polarization plane of the polarizer, and it cannot be transmitted through the polarizer. In this way, it functions as an optical isolator that transmits and emits forward-moving light and blocks backward-moving returning light.

[0004] The material used for the Faraday rotator that constitutes the optical isolator is conventionally TGG crystal (Tb 3 Ga 5 O 12 ) and TSAG crystal ((Tb (3-x) Sc x )Sc 2 Al 3 O 12 ) is known (JP Patent Publication No. 2011-213552 (Patent Document 1), JP Patent Publication No. 2002-293693 (Patent Document 2)). TGG crystals are currently widely used in standard fiber laser devices. On the other hand, the Verdet constant of TSAG crystals is said to be about 1.3 times that of TGG crystals, and this is also a material that could be used in fiber laser devices. However, because Sc is an extremely expensive raw material, its adoption has not progressed in terms of manufacturing costs. Since then, development of TSAG crystals has continued, as in Patent Publication No. 5611329 (Patent Document 3) and Patent Publication No. 5935764 (Patent Document 4). However, neither of these has been able to reduce the amount of Sc used, and they have not yet become widespread.

[0005] In addition to the above, TAG crystal (Tb 3 Al 5 O 12 ) is also known. However, because TAG crystals are decomposed melting type crystals, there is a restriction that the perovskite phase is generated first at the solid-liquid interface, and then the TAG phase is generated. In other words, the garnet phase and perovskite phase of the TAG crystal can only be grown in a constant mixed state, and the growth of large-sized, high-quality TAG crystals has not been realized.

[0006] In Japanese Patent No. 3642063 (Patent Document 5) and Japanese Patent No. 4107292 (Patent Document 6), a method is proposed as a means for suppressing this mixed crystal, in which the polycrystalline raw material rod for FZ growth or the seed crystal is made porous, thereby preferentially precipitating the initial phase, the perovskite phase, in the porous medium. However, in reality, as the melting position moves, the position where the perovskite phase is likely to precipitate also moves, so that it is essentially impossible to completely suppress the precipitation of the perovskite phase just by making the interface between the seed crystal and the polycrystalline raw material rod porous.

[0007] In spite of these constraints, JP 2008-7385 A (Patent Document 7) proposes a material in which an oxide of TAG composition is made into a ceramic, and which also has translucency. Ceramics can be sintered at temperatures 100°C or lower than the melting point, which makes it possible to overcome the problem of decomposition and melting that is an issue with single crystal growth. Since TAG actually begins to decompose at temperatures above 1840°C, if it can be sintered and densified to the very limit of theoretical density below this temperature, it will be possible to obtain a transparent sintered body of single-phase TAG.

[0008] Patent Document 7 describes a method for producing ceramics having a garnet structure and made of terbium aluminum oxide, which includes a step of mixing raw materials, a step of calcining, a step of crushing the calcined powder, a step of forming, and a step of firing. In the step of crushing the calcined powder, the average particle size of the calcined powder after crushing is 0.2 to 1.6 μm, and in the step of forming, the density after forming is 3.26 g / cm. 3 It is said that above this level, TAG ceramics with high light transmittance can be produced.

[0009] However, in Patent Document 7, the light transmittance is extremely insufficient, and even at a thickness of 1.5 mm, the linear transmittance is only up to 35%. Incidentally, when TAG is used as a Faraday element such as an optical isolator, for example, for a 1.06 μm band laser, the element length required to rotate the light by 45 degrees is about 15 mm, which is roughly 10 times the length in the document. If the material transmits only 35% of light at a thickness of 1.5 mm, extending the element length by 10 times will result in a transmittance of less than 0.01%, i.e., almost zero, and will not function at all. In other words, even if there was a ceramic manufacturing method that could suppress the generation of heterogeneous phases, no practical level of TAG had existed until now.

[0010] Patent Document 6 shows that when part of the Tb in the TAG crystal is replaced with Ce, the Verdet constant becomes larger than that of TAG. If the Verdet constant becomes larger, the element length required to rotate the incident light by 45 degrees can be shortened, so the total absorption amount decreases, but with a linear transmittance of 35% at a thickness of 1.5 mm, even if the element length is halved, the 45-degree rotation thickness transmittance is less than 1%, which is far from practical use.

[0011] In the above situation, the composition of (Tb x Y 1-x ) 3 Al 5 O 12 It has been disclosed that a dense ceramic sintered body with a TGG crystal (x=0.5-1.0) has a higher extinction ratio (improved from the existing 35 dB to 39.5 dB or more) and can reduce insertion loss (improved from the existing 0.05 dB to 0.01-0.05 dB) compared to the existing TGG crystal (Yan Lin Aung, Akio Ikesue, Development of optical grade (Tb x Y 1-x ) 3 Al 5 O 12"Ceramics as Faraday rotator material," J.Am.Ceram.Soc.,(2017),100(9),4081-4087 (Non-Patent Document 1)". The material disclosed in Non-Patent Document 1 is a ceramic, so there is no precipitation of perovskite heterophase, which is a problem with TGG crystals, and by replacing some of the Tb ions with Y ions, it is possible to further reduce loss, and it is a material that can be used to obtain a very high-quality garnet-type Faraday rotator.

[0012] Recently, International Publication No. 2018 / 193848 (Patent Document 8) has disclosed a paramagnetic garnet-type transparent ceramic which is a sintered body of a complex oxide represented by the following formula (1) and which is characterized by having an in-line transmittance of 83% or more at a wavelength of 1064 nm with an optical path length of 15 mm. (T 1-x-y Sc x Ce y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0 <x<0.08、0≦y≦0.01、0.004<z<0.16である。)

[0013] In Patent Document 8, the fiber has a Verdet constant comparable to that of TAG, and the in-line transmittance is improved to be 83% or more even with an optical path length of 15 mm, so that it can be said to have almost reached a practical level. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2011-213552 A [Patent Document 2] JP 2002-293693 A [Patent Document 3] Patent No. 5611329 [Patent Document 4] Patent No. 5935764 [Patent Document 5] Patent No. 3642063 [Patent Document 6] Patent No. 4107292 [Patent Document 7] JP 2008-7385 A [Patent Document 8] International Publication No. 2018 / 193848

[0015] [Non-Patent Document 1] Yan Lin Aung, Akio Ikesue, Development of optical grade (TbxY1-x)3Al5O12 ceramics as Faraday rotator material, J.Am.Ceram.Soc.,(2017),100(9),4081-4087 Summary of the Invention [Problem to be solved by the invention]

[0016] However, when the present inventors actually performed follow-up tests on the material in Non-Patent Document 1, they found that the reproducibility was quite poor and that it was difficult to obtain a high-quality ceramic sintered body having an insertion loss smaller than that of a TGG crystal. In addition, when the inventors actually irradiated a sample reproducing the material of the example of Patent Document 8 with a laser beam having a wavelength of 1064 nm and an incident power of 100 W after adjusting the beam diameter to 1.6 mm, it became clear that the amount of change in the incident laser beam diameter due to the occurrence of thermal lensing exceeded 15%. Since the amount of change in the beam diameter when a laser beam having a wavelength of 1064 nm and an incident power of 100 W is irradiated is desirably 10% or less, it is difficult to say that the material of Patent Document 8 is truly applicable to high power.

[0017] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a truly transparent and highly optically homogeneous paramagnetic garnet-type transparent ceramic, a magneto-optical material, and a magneto-optical device using the magneto-optical material, which is made of a sintered body of a paramagnetic garnet-type oxide containing terbium and yttrium. [Means for solving the problem]

[0018] In order to achieve the above object, the present invention provides the following paramagnetic garnet-type transparent ceramics, magneto-optical material, and magneto-optical device. 1. It is a sintered body of a composite oxide represented by the following formula (1), and contains SiO as a sintering aid. 2 a total light transmittance of 84.0% or more at a wavelength of 1064 nm and an optical path length of 25 mm, and a forward scattering of 0.5% or less; and further a total light transmittance of 84.0% or more at a wavelength of 1300 nm and an optical path length of 25 mm, and a forward scattering of 0.5% or less. (T 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05≦x≦0.4, 0≦y<0.004, 0.6≦1-xy<0.95, 0≦z<0.004, 0.001 <y+z<0.005である。) 2. The paramagnetic garnet-type transparent ceramic according to 1, having a Verdet constant of 32 rad / (T·m) or more at a wavelength of 1064 nm. 3. 3. The paramagnetic garnet-type transparent ceramic according to 1 or 2, which has an extinction ratio of 42 dB or more over the entire optical effective diameter when laser light having a wavelength of 1064 nm is incident on the ceramic with an optical path length of 25 mm. 4. 4. The paramagnetic garnet-type transparent ceramic according to any one of 1 to 3, wherein when a laser beam having a wavelength of 1064 nm and an optical path length of 25 mm is incident with a beam diameter of 1.6 mm and an incident power of 100 W, the change in the beam diameter is 10% or less. 5. 5. The paramagnetic garnet-type transparent ceramic according to any one of 1 to 4, having a thermal conductivity of 4.8 W / (m·K) or more. 6. 6. A magneto-optical material comprising the paramagnetic garnet-type transparent ceramic according to any one of 1 to 5. 7. 7. A magneto-optical device constructed using the magneto-optical material according to claim 6. 8. 8. The magneto-optical device according to 7, which is an optical isolator having the paramagnetic garnet-type transparent ceramic as a Faraday rotator and having polarizing materials in front of and behind the optical axis of the Faraday rotator and usable in the wavelength range of 0.9 μm or more and 1.1 μm or less. Effect of the Invention

[0019] According to the present invention, a truly transparent paramagnetic garnet-type ceramic with high optical homogeneity can be provided, which is a paramagnetic garnet-type oxide containing terbium and yttrium. Furthermore, since it has high thermal conductivity and good optical homogeneity, it can be applied to a high-output laser device with an output of 100 W or more, and since it is a ceramic sintered body, it can be easily scaled up, making it truly practical. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view showing an example of the configuration of an optical isolator using the magneto-optical material according to the present invention as a Faraday rotator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] <Paramagnetic garnet-type transparent ceramics> The paramagnetic garnet-type transparent ceramics according to the present invention will now be described. The transparent ceramic material according to the present invention is a sintered body of a complex oxide represented by the following formula (1), and contains SiO as a sintering aid: 2 The paramagnetic garnet-type transparent ceramics is characterized in that it contains more than 0 mass % and 0.1 mass % or less of a compound represented by the formula (1), has an average sintered grain size of 5 μm or more, has a total light transmittance of 84.0% or more at a wavelength of 1064 nm when the optical path length is 25 mm, and has a forward scattering of 0.5% or less, and further has a total light transmittance of 84.0% or more at a wavelength of 1300 nm when the optical path length is 25 mm, and has a forward scattering of 0.5% or less. (T 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05≦x≦0.4, 0≦y<0.004, 0.6≦1-xy<0.95, 0≦z<0.004, 0.001 <y+z<0.005である。)

[0022] In formula (1), terbium (Tb) is the material with the largest Verdet constant among the paramagnetic elements except for iron (Fe). In particular, when contained in an oxide having a garnet structure, terbium is completely transparent at a wavelength of 1064 nm, making it the most suitable element for use in optical isolators in this wavelength range.

[0023] Yttrium (Y) has an ionic radius that is about 2% smaller than that of terbium, and when it combines with aluminum to form a composite oxide, it is a material that can stably form a garnet phase rather than a perovskite phase and reduce residual strain in the crystallite, which can prevent scattering due to different phases, deterioration of the extinction ratio due to internal stress, and ff transition absorption of terbium ions, so it is an important constituent element in the present invention. Furthermore, by replacing a part of the terbium ions with yttrium ions, the sinterability (compound reaction during heating, sudden phase change, and sudden change in specific gravity associated with these) is leveled, so that the amount of remaining porosity in the ceramic sintered body can be more effectively limited than when it is not replaced with yttrium ions, so it is a suitable constituent element in the present invention.

[0024] Aluminum (Al) is a material having the smallest ionic 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 terbium. If the lattice constant of the garnet structure can be reduced without changing the content of terbium, it is preferable because the Verdet constant per unit length can be increased. In fact, the Verdet constant of TAG is improved to 1.25 to 1.5 times that of TGG. Therefore, even if the relative concentration of terbium is reduced by replacing some of the terbium ions with yttrium ions, it is possible to keep the Verdet constant per unit length equal to or slightly lower than that of TGG, so it is a preferred constituent element in the present invention.

[0025] Scandium (Sc) is a material with an intermediate ionic radius that can dissolve in the terbium site and in some of the aluminum sites in oxides having a garnet structure, and is a buffer material that can adjust the distribution ratio of the rare earth elements consisting of terbium and yttrium and the aluminum site to the stoichiometric ratio and thereby minimize the energy required to generate crystallites when the compounding ratio of the rare earth elements consisting of terbium and yttrium and aluminum deviates from the stoichiometric ratio due to variations in weighing. Also, it is an element that has the effect of suppressing the precipitation of alumina heterophase and perovskite-type heterophase, and is an essential element in the present invention.

[0026] However, since scandium can be easily dissolved at both the terbium site and the aluminum site, if the amount of scandium added is increased too easily, i.e., if the proportion of scandium in the mixed raw material increases significantly, the effect of the unevenness in the concentration of scandium cannot be ignored, and a sintered particle aggregate is formed in which the amount of scandium dissolved at the terbium site and the aluminum site differs for each sintered particle in the sintered body after the sintering process. As a result, not only is there a problem that (i) the effective refractive index of each sintered particle varies, and the forward scattering caused by the unevenness in the refractive index deteriorates as a whole sintered body, but there is also a problem that (ii) since scandium has an excessive sintering suppression effect, the sintered body coalesces and becomes a large grain size, thereby hindering the process of homogenization. This makes it difficult to reduce the grain boundary surface area, leading to the retention of distortion and subtle interface scattering inside the sintered body, resulting in a local decrease in the extinction ratio, a local decrease (local decrease) in the thermal conductivity, and a decrease in the average thermal conductivity (average value of thermal conductivity). In this case, for example, if there is a local decrease in thermal conductivity, the amount of change in the beam diameter when a laser beam with an incident power of 100 W is incident increases to 15% or more, which is not preferable.

[0027] In view of the above-mentioned contradictory properties, it is preferable to find a range in which the amount of scandium added is as small as possible while maintaining the effect of suppressing the precipitation of different phases, and to manage the amount within that range.

[0028] In formula (1), the range of x is 0.05≦x≦0.4, preferably 0.06≦x≦0.3995, and more preferably 0.1≦x≦0.399. When x is within this range, the perovskite-type heterogeneous phase can be reduced to a level that is not detectable by X-ray diffraction (XRD) analysis.

[0029] If x is less than 0.05, the effect of substituting part of the terbium with yttrium is not obtained, and the conditions are essentially the same as those for producing TAG, which makes it difficult to stably produce a high-quality ceramic sintered body with low scattering and low absorption, which is undesirable. Also, if x is more than 0.4, the Verdet constant at a wavelength of 1064 nm is less than 32 rad / (T·m), which is undesirable. Furthermore, if the relative concentration of terbium becomes excessively diluted, the total length required to rotate a laser beam with a wavelength of 1064 nm by 45 degrees exceeds 25 mm, which is undesirable because it becomes difficult to manufacture.

[0030] In formula (1), the range of y is 0≦y<0.004, preferably 0.0005≦y<0.004, and more preferably 0.001≦y<0.004. When y is in this range, the perovskite-type heterophase can be reduced to a level that is not detectable by X-ray diffraction (XRD) analysis, which is preferable. Furthermore, it is preferable because it is possible to prevent an excessive decrease in thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0031] When y is 0.004 or more, the effect of inhibiting the precipitation of the perovskite-type heterophase or the alumina heterophase saturates and remains unchanged, while the sintering inhibition effect of scandium is excessively effective, resulting in uneven sintering, residual sintering distortion, or residual grain boundary scattering, which is not preferable as a result of localized decreases in the extinction ratio and a decrease in the average value of the thermal conductivity.

[0032] In formula (1), the range of 1 - x - y is 0.6 ≦ 1 - x - y < 0.95, and 0.6 ≦ 1 - x - y < 0.899 is more preferable. When 1 - x - y is within this range, a large Verdet constant can be ensured and high transparency can be obtained at a wavelength of 1064 nm.

[0033] (1) In the formula, the range of z is 0 ≦ z < 0.004, 0.0005 ≦ z < 0.004 is more preferable, and 0.001 ≦ z < 0.004 is even more preferable. When z is within this range, it is preferable because the perovskite - type heterogeneous phase can be reduced to a level where it cannot be detected by X - ray diffraction (XRD) analysis. Furthermore, it is preferable because excessive reduction of the thermal conductivity due to the homogeneity of the sintered body and grain - boundary scattering can be prevented.

[0034] When z is 0.004 or more, while the effect of suppressing the precipitation of the perovskite - type heterogeneous phase or alumina heterogeneous phase saturates and does not change, uneven sintering, residual sintering strain, or residual grain - boundary scattering occurs due to the excessive effect of the sintering - suppressing effect of scandium, and as a result, local reduction of the extinction ratio and reduction of the average value of the thermal conductivity occur, which is not preferable.

[0035] (1) In the formula, the range of y + z is 0.001 < y + z < 0.005, 0.0015 < y + z < 0.005 is more preferable, and 0.002 < z < 0.005 is even more preferable. When y + z is within this range, it is preferable because the perovskite - type heterogeneous phase can be reduced to a level where it cannot be detected by X - ray diffraction (XRD) analysis. Furthermore, it is preferable because excessive reduction of the thermal conductivity due to the homogeneity of the sintered body and grain - boundary scattering can be prevented.

[0036] When y + z is 0.001 or less, the risk of precipitation of the perovskite - type heterogeneous phase or alumina heterogeneous phase increases, which is not preferable. When y + z is 0.005 or more, while the effect of suppressing the precipitation of the perovskite - type heterogeneous phase or alumina heterogeneous phase saturates and does not change, uneven sintering, residual sintering strain, or residual grain - boundary scattering occurs due to the excessive effect of the sintering - suppressing effect of scandium, and as a result, local reduction of the extinction ratio and reduction of the average value of the thermal conductivity occur, which is not preferable.

[0037] The paramagnetic garnet-type transparent ceramics of the present invention contain the composite oxide represented by the above formula (1) as a main component, and SiO 2 acting as a sintering aid as a subcomponent. 2 The content is within the range of 0.1 mass% or less. SiO 2 Adding a small amount of SiO suppresses the precipitation of perovskite-type heterophases and alumina heterophases, and therefore further improves the transparency of paramagnetic garnet-type transparent ceramics. 2 During sintering at 1400°C or higher, SiO can be vitrified to bring about a liquid phase sintering effect, which can promote the densification of garnet-type ceramic sintered bodies. 2 If more than 0.1 mass % is added, when a 100 W laser beam with a wavelength of 1064 nm and a beam diameter of 1.6 mm is incident on a paramagnetic garnet-type transparent ceramic with a length (optical path length) of 25 mm, the change in the beam diameter exceeds 10%, which is undesirable.

[0038] Incidentally, "containing as a main component" means containing 90% by mass or more of the composite oxide represented by the above formula (1). The content of the composite oxide represented by the formula (1) is preferably 99% by mass or more, more preferably 99.9% by mass or more, even more preferably 99.99% by mass or more, and particularly preferably 99.999% by mass or more.

[0039] The paramagnetic garnet-type transparent ceramics of the present invention are composed of the above-mentioned main components and subcomponents, and may further contain other elements, such as rare earth elements such as lutetium (Lu) and cerium (Ce), or various impurities (unavoidable components) such as sodium (Na), calcium (Ca), magnesium (Mg), phosphorus (P), tungsten (W), and molybdenum (Mo).

[0040] The content of other elements is preferably 10 parts by mass or less, more preferably 0.1 parts by mass or less, and particularly preferably 0.001 parts by mass or less (substantially zero), when the total amount of Tb and Y is 100 parts by mass.

[0041] The average sintered grain size of the paramagnetic garnet-type transparent ceramic of the present invention is 5 μm or more, preferably 5.5 μm or more. There is no particular upper limit to the average sintered grain size of the paramagnetic garnet-type transparent ceramic of the present invention, but it is usually 30 μm or less. If the average sintered grain size is less than 5 μm, there is an increased risk that the thermal conductivity will fall below 4.8 W / (m K).

[0042] The average sintered grain size of the paramagnetic garnet-type transparent ceramics referred to here is the average grain size of the crystals of the secondary sintered body after HIP treatment in the manufacturing method described later, and can be determined by directly observing the polished surface with a microscope, etc., and an example is a backscattered electron image of a scanning electron microscope (SEM). If it is difficult to determine the grain size from the polished surface, thermal etching at 1200 to 1300°C or treatment with 0.1M dilute hydrochloric acid may be performed to highlight the grain boundaries. The crystal grain size (grain size) is calculated by the following formula, where C is the length of a line drawn arbitrarily on a high-resolution image such as an SEM, N is the number of particles on this line, and M is the magnification of the image ("Linear Intercept Technique for Measuring Grain Size in Two-Phase Polycrystalline Ceramics" Journal of the American Ceramic Society, 55, 109 (1972)). D=1.56C / (MN) In this case, N is preferably 10 or more, and more preferably 100 or more.

[0043] The paramagnetic garnet-type transparent ceramic of the present invention has a colorless and transparent appearance, and has a total light transmittance of 84.0% or more and a forward scattering of 0.5% or less at a wavelength of 1064 nm with an optical path length of 25 mm, and further has a total light transmittance of 84.0% or more and a forward scattering of 0.5% or less at a wavelength of 1300 nm with an optical path length of 25 mm. The paramagnetic garnet-type transparent ceramic of the present invention not only has high transmittance at the wavelength (1064 nm) expected for use, but also has a total light transmittance of 84.0% or more and a forward scattering of 0.5% or less in a wavelength band longer than the wavelength expected for use, similar to the value at a wavelength of 1064 nm, and is preferable because it improves the extinction ratio, and when a 100 W laser beam with a beam diameter of 1.6 mm is incident at a wavelength of 1064 nm with an optical path length of 25 mm, the change in the beam diameter is 10% or less, and the thermal conductivity is 4.8 W / (m·K) or more.

[0044] In the present invention, the term "total light transmittance" refers to the ratio of the integrating sphere intensity of light of a target wavelength after it has passed through a transparent ceramic sample (total light transmittance) to the integrating sphere transmission spectrum (light intensity) of the target wavelength measured in a blank (space) state without placing a sample in the measurement optical path, which is taken as 100%. In other words, the light intensity of the target wavelength measured in the blank state (incident light intensity) is expressed as I 0 If the intensity of light collected by the integrating sphere, including the scattered light after passing through a transparent ceramic sample, is I, then I / I 0 ×100(%) (the same applies in the following Examples). "Forward scattering" is defined as follows. That is, after measuring the "total light transmittance" with the sample placed in the measurement light path, the exit window opposite the entrance window of the integrating sphere is opened. In this state, light is again made to enter the sample. Of the light components emitted from the sample, only the transmitted light that has traveled straight without being scattered is allowed to escape outside the integrating sphere, and the intensity I of the light that has been slightly scattered within the transparent ceramic sample and entered the integrating sphere at an angle is measured. S Then, the I 0 Using I S ( / I 0The light intensity that can be expressed as 1×100 (%) is the “forward scattering” of the target sample (the same applies in the following Examples).

[0045] The paramagnetic garnet-type transparent ceramics of the present invention preferably have a Verdet constant at a wavelength of 1064 nm of 32 rad / (T·m) or more, and more preferably 36 rad / (T·m) or more. If the Verdet constant is 32 rad / (T·m) or more, compatibility with isolators using TGG single crystals can be achieved without increasing the overall external dimensions of the isolator through the design and ingenuity of the external magnet, and if the Verdet constant is 36 rad / (T·m) or more, replacement with the existing material, TGG single crystal, can be easily achieved without changing the design of the parts.

[0046] The paramagnetic garnet-type transparent ceramic of the present invention, as a Faraday rotator (ceramic element alone), preferably has an extinction ratio of 42 dB or more at a wavelength of 1064 nm with an optical path length of 25 mm, and particularly preferably has an extinction ratio of 42 dB or more over the entire optical effective diameter when a laser beam with a wavelength of 1064 nm is incident with an optical path length of 25 mm, more preferably 44 dB or more, and even more preferably 45 dB or more. With the garnet composition range of the present invention, local distortion is reduced while excessive grain growth suppression does not work, so a transparent ceramic sintered body that is homogeneous over the entire optical effective surface and has little grain boundary scattering is completed, and therefore it is possible to stably manage the extinction ratio of 42 dB or more over the entire optical effective diameter at a wavelength of 1064 nm with an optical path length of 25 mm as a Faraday rotator (ceramic element alone)

[0047] The "extinction ratio" referred to here is the maximum value (I 0The value is calculated from the first value (I') and the minimum value (I') using the following formula (the same applies in the following examples). Extinction ratio (dB / 25mm)=-10×log 10 (I' / I 0 ')

[0048] Moreover, the term "optically effective diameter" refers to the optically effective area (optically effective region) of the optical surface of the transparent ceramic, and more specifically, in the case of a cylindrical paramagnetic garnet-type transparent ceramic, it refers to the area of ​​the optical surface (circular surface) on the optically utilized axis excluding the outer edge of the end face that cannot be optically utilized, and here it refers to the area excluding the outer edge of the optical surface that corresponds to 10% of the area ratio of the optical surface, that is, the area that is 90% of the area inward from the outer edge of the optical surface. Moreover, the term "optically effective region" refers to the region that functions effectively as a magneto-optical material when incident light passes through and exits the paramagnetic garnet-type transparent ceramic.

[0049] Furthermore, the paramagnetic garnet-type transparent ceramics of the present invention preferably exhibit a change in beam diameter of 10% or less, more preferably 9% or less, and even more preferably 8% or less, when a laser beam having a wavelength of 1064 nm and an optical path length of 25 mm is incident with a beam diameter of 1.6 mm and an incident power of 100 W. If the change in beam diameter is 10% or less, the energy density at the processing point of the laser for marking, scribing, and other precision processing falls within the specified range, and therefore the ceramics can be substantially adopted in a high-power laser system for 100 W.

[0050] The "amount of change in beam diameter" is calculated as follows. That is, when a collimated laser beam (spatial parallel beam) with a wavelength of 1064 nm, output power of 100 W, and diameter of 1.6 mm is incident on the optical surface of the target paramagnetic garnet-type transparent ceramic, the beam diameter of the light (incident light) is measured with a beam profiler, and the value at this time is called r 0 Then, this light is passed through a target paramagnetic garnet-type transparent ceramic with a length of 25 mm. The beam diameter of the light (transmitted light) is measured and expressed as r, as (1-r / r 0) × 100(%) is the amount of change in beam diameter. Note that the amount of change in beam diameter also changes depending on the setting position and angle of the target paramagnetic garnet-type transparent ceramic in the measurement system, as well as daily error, and therefore it is advisable to measure by changing the setting position and angle of the target paramagnetic garnet-type transparent ceramic in the measurement system and to measure several times (at least twice) on different days, and to use the maximum value of the measured values ​​as the amount of change in beam diameter.

[0051] The paramagnetic garnet-type transparent ceramics of the present invention preferably have a thermal conductivity of 4.8 W / (m·K) or more. The thermal conductivity here is measured by the laser flash method in accordance with JIS R1611, and is the average thermal conductivity described above. However, the sample for evaluating thermal conductivity in the laser flash method does not need to be elongated to an optical path length of 25 mm, which is assumed to be used as a magneto-optical material, and a thickness of 1 mm and an outer diameter of about 10 mmφ are sufficient for measuring the thermal conductivity. However, it is necessary to finish the sample for evaluating thermal conductivity, which is manufactured in the same manner as the magneto-optical paramagnetic garnet-type transparent ceramics, except for the shape of the molded body. By measuring this sample for evaluating thermal conductivity, the thermal conductivity of the magneto-optical paramagnetic garnet-type transparent ceramics can be obtained.

[0052] <Method of manufacturing paramagnetic garnet-type transparent ceramics> [Raw materials] As the raw material used in the present invention, metal powders of terbium, yttrium, scandium, and aluminum, or the above metal powders dissolved in an aqueous solution of nitric acid, sulfuric acid, uric acid, or the like, or oxide powders of the above elements can be suitably used. Also, the above elements can be suitably coprecipitated as the raw material. The purity of the above raw materials is preferably 99.9% by mass or more, and particularly preferably 99.99% by mass or more.

[0053] The starting material can be prepared by weighing out and mixing the elements in a predetermined amount so as to obtain a composition corresponding to formula (1). Alternatively, the mixed raw material weighed in a predetermined amount may be fired to obtain a fired raw material mainly composed of a cubic garnet-type oxide of a desired composition, and the fired raw material may be pulverized into a powder form and used as the starting raw material. The firing temperature at this time is preferably 950°C or higher and lower than the temperature of the subsequent sintering, and more preferably 1100°C or higher and lower than the temperature of the subsequent sintering. The term "mainly composed" here refers to the fact that the main peak obtained from the powder X-ray diffraction result of the fired raw material is a diffraction peak derived from the garnet structure. Note that when the ratio of the perovskite-type heterophase or alumina heterophase to the garnet mother phase is 1% or less, even the main peaks of these powder X-ray diffraction patterns are hardly detectable, so that the powder X-ray diffraction results obtained are substantially similar to a garnet single-phase pattern.

[0054] The shape of the powder as the starting material is not particularly limited, and for example, angular, spherical, or plate-shaped powders can be suitably used. In addition, powders that have undergone secondary aggregation can also be suitably used, and granular powders granulated by a granulation process such as a spray-drying process can also be suitably used. Furthermore, the preparation process of the powder in the starting material is not particularly limited. Raw material powders prepared by coprecipitation, pulverization, spray pyrolysis, sol-gel, alkoxide hydrolysis, or any other synthesis method can be suitably used. In addition, the obtained raw material powder may be appropriately processed by a wet ball mill, a bead mill, a jet mill, a dry jet mill, a hammer mill, or the like.

[0055] In the garnet-type oxide powder raw material used in the present invention, various organic additives may be added for the purpose of improving the quality stability and yield in the subsequent ceramic manufacturing process. In the present invention, these are not particularly limited. That is, various dispersants, binders, lubricants, plasticizers, etc. can be suitably used. However, it is preferable to select high-purity types of these organic additives that do not contain unnecessary metal ions.

[0056] [Manufacturing process] In the present invention, the starting materials are pressed into a predetermined shape, degreased, and then sintered to produce a sintered body with a relative density of at least 94%. It is preferable to perform a hot isostatic pressing (HIP) process as a post-process. If the hot isostatic pressing (HIP) process is performed directly, the paramagnetic garnet-type transparent ceramics will be reduced and some oxygen deficiency will occur. Therefore, it is preferable to perform a slight oxidation HIP process, or an annealing process in an oxidizing atmosphere (oxidation annealing process) after the HIP process to recover the oxygen deficiency. This makes it possible to obtain a transparent garnet-type oxide ceramics without defect absorption.

[0057] (molding) In the manufacturing method of the present invention, a normal press molding process can be suitably used. That is, a very common uniaxial pressing process in which the material is filled into a mold and pressed from a certain direction, or a cold isostatic pressing (CIP) process or a warm isostatic pressing (WIP) process in which the material is sealed and stored in a deformable waterproof container and pressed with hydrostatic pressure can be suitably used. The applied pressure can be appropriately adjusted while checking the relative density of the resulting molded body, and is not particularly limited. For example, the manufacturing cost can be reduced by controlling the pressure within a pressure range of about 300 MPa or less that can be handled by a commercially available CIP device or WIP device. Alternatively, a hot press process, a discharge plasma sintering process, a microwave heating process, etc., in which not only the molding process but also sintering is performed at once during molding, can be suitably used. Furthermore, it is possible to produce a molded body by a casting molding method instead of a press molding method. Molding methods such as pressurized casting molding, centrifugal casting molding, and extrusion molding can also be adopted by optimizing the combination of the shape and size of the oxide powder, which is the starting material, and various organic additives.

[0058] (Degreasing) In the manufacturing method of the present invention, a normal debinding process can be suitably used. That is, a heating debinding process using a heating furnace can be used. In addition, the type of atmospheric gas used in this process is not particularly limited, and air, oxygen, hydrogen, etc. can be suitably used. There is also no particular limit to the debinding temperature, but if a raw material containing an organic additive is used, it is preferable to heat the raw material to a temperature at which the organic component can be decomposed and eliminated.

[0059] (Sintering) In the manufacturing method of the present invention, a general sintering process can be preferably used. That is, a heat sintering process such as a resistance heating method or an induction heating method can be preferably used. The atmosphere at this time is not particularly limited, and sintering can be performed in various atmospheres such as an inert gas, oxygen gas, hydrogen gas, helium gas, or under reduced pressure (vacuum). However, since it is preferable to prevent the occurrence of oxygen deficiency in the final sintered body, the more preferred atmosphere is an oxygen gas or reduced pressure oxygen gas atmosphere.

[0060] The sintering temperature in the sintering step is preferably 1500 to 1780° C., particularly preferably 1550 to 1750° C. If the sintering temperature is in this range, densification is promoted while suppressing heterogeneous phase precipitation, which is preferable.

[0061] A sintering holding time of a few hours is sufficient in the sintering process, but the relative density of the sintered body must be densified to at least 94%. It is even more preferable to hold the sintered body for 10 hours or more to densify the relative density of the sintered body to 99% or more, as this improves the final transparency.

[0062] (Hot Isostatic Pressing (HIP)) In the manufacturing method of the present invention, an additional step of hot isostatic pressing (HIP) can be provided after the sintering step.

[0063] The type of pressurized gas medium used here is an inert gas such as argon or nitrogen, or Ar-O 2can be suitably used. The pressure applied by the pressurized gas medium is preferably 50 to 300 MPa, more preferably 100 to 300 MPa. If the pressure is less than 50 MPa, the transparency improvement effect may not be obtained, and if the pressure exceeds 300 MPa, further improvement in transparency cannot be obtained even if the pressure is increased, and the load on the device becomes too heavy, which may damage the device. The applied pressure is preferably 196 MPa or less, which is easy to handle with a commercially available HIP device.

[0064] The treatment temperature (predetermined holding temperature) is set in the range of 1100 to 1780°C, preferably 1200 to 1730°C. If the heat treatment temperature exceeds 1780°C, the risk of oxygen vacancies increases, which is not preferable. If the heat treatment temperature is less than 1100°C, the effect of improving the transparency of the sintered body is hardly obtained. There is no particular restriction on the holding time of the heat treatment temperature, but holding for too long a period of time is not preferable because the risk of oxygen vacancies increases. Typically, it is preferably set in the range of 1 to 3 hours.

[0065] The heater material, heat insulating material, and treatment vessel for the HIP treatment are not particularly limited, but graphite, molybdenum (Mo), tungsten (W), and platinum (Pt) are preferably used, and yttrium oxide and gadolinium oxide are also preferably used for the treatment vessel. In particular, when the treatment temperature is 1500°C or less, platinum (Pt) can be used for the heater material, heat insulating material, and treatment vessel, and Ar-O can be used as the pressurized gas medium. 2 This is preferable because it can prevent the occurrence of oxygen vacancies during HIP treatment. When the treatment temperature exceeds 1500°C, graphite is preferable as the heater material and heat insulating material, but in this case, it is preferable to select graphite, molybdenum (Mo), or tungsten (W) as the treatment container, and further select either yttrium oxide or gadolinium oxide as a double container inside, and fill the container with an oxygen release material, because this can minimize the amount of oxygen vacancies during HIP treatment.

[0066] (Oxidation annealing) In the manufacturing method of the present invention, after the HIP treatment, oxygen deficiency may occur in the obtained transparent ceramic sintered body (HIP body), and the body may have a faint light gray appearance. In that case, it is preferable to perform an oxidative annealing treatment (oxygen deficiency recovery treatment) in an oxygen atmosphere at a temperature equal to or lower than the HIP treatment temperature, typically 1000 to 1500 ° C, preferably more than 1300 ° C and less than 1500 ° C, more preferably 1350 to 1500 ° C, and even more preferably 1400 to 1500 ° C. In this case, the holding time is not particularly limited, but it is preferable to select a time that is sufficient to recover the oxygen deficiency and is within a time that does not consume electricity by performing the treatment for a long time unnecessarily. By the oxidative annealing treatment, even if the transparent ceramic sintered body has a faint light gray appearance in the HIP treatment process, all of them can be made into a colorless, transparent, paramagnetic garnet-type transparent ceramic without defect absorption.

[0067] (optical polishing) In the manufacturing method of the present invention, it is preferable to optically polish both end faces on the optically utilized axis of the paramagnetic garnet-type transparent ceramics that has undergone the above-mentioned series of manufacturing steps. In this case, the optical surface accuracy is preferably λ / 2 or less, and particularly preferably λ / 8 or less, when the measurement wavelength λ=633 nm. It is also possible to further reduce optical loss by appropriately forming an anti-reflection film on the optically polished surface.

[0068] As described above, the above-mentioned paramagnetic garnet-type transparent ceramic of the present invention, that is, a sintered body of a composite oxide containing terbium and yttrium represented by the above formula (1), and containing SiO 2It is possible to provide a paramagnetic garnet-type transparent ceramic containing more than 0 mass % and 0.1 mass % or less of the above, having an average sintered grain size of 5 μm or more, a total light transmittance at a wavelength of 1064 nm and a length (optical path length) of 25 mm of 84.0% or more and a forward scattering of 0.5% or less, and further a total light transmittance at a wavelength of 1300 nm and a length (optical path length) of 25 mm of 84.0% or more and a forward scattering of 0.5% or less. Furthermore, in the paramagnetic garnet-type transparent ceramic thus obtained, the Verdet constant at a wavelength of 1064 nm is preferably 32 rad / (T m) or more, the amount of change in the beam diameter when a laser beam having a wavelength of 1064 nm and an optical path length of 25 mm is incident with a beam diameter of 1.6 mm and an incident power of 100 W is preferably 10% or less, and more preferably the thermal conductivity is 4.8 W / (m K) or more. Furthermore, as a Faraday rotator (single ceramic element), the extinction ratio over the entire optical effective diameter when a laser beam having a wavelength of 1064 nm and an optical path length of 25 mm is incident thereon is preferably 42 dB or more.

[0069] [Magneto-optical devices] Furthermore, since the paramagnetic garnet-type transparent ceramic of the present invention is intended to be used as a magneto-optical material, it is preferable to apply a magnetic field parallel to the optical axis of the paramagnetic garnet-type transparent ceramic, and then set a polarizer and an analyzer so that their optical axes are shifted by 45 degrees from each other to form a magneto-optical device. That is, the magneto-optical material of the present invention is suitable for use in magneto-optical devices, and is particularly suitable for use as a Faraday rotator for an optical isolator with a wavelength of 0.9 to 1.1 μm.

[0070] Fig. 1 is a schematic cross-sectional view showing an example of an optical isolator, which is an optical device having a Faraday rotator made of the magneto-optical material of the present invention as an optical element. In Fig. 1, the optical isolator 100 includes a Faraday rotator 110 made of the magneto-optical material of the present invention, and a polarizer 120 and an analyzer 130, which are polarizing materials, are provided in front of and behind the Faraday rotator 110. In the optical isolator 100, the polarizer 120, the Faraday rotator 110, and the analyzer 130 are preferably arranged in this order, and a magnet 140 is preferably placed on at least one of the side surfaces of the polarizer 120, the Faraday rotator 110, and the analyzer 130.

[0071] The optical isolator 100 can be suitably used in industrial fiber laser devices, that is, to prevent the reflected light of the laser light emitted from the laser light source from returning to the light source, causing the oscillation to become unstable. EXAMPLES

[0072] 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 the examples.

[0073] [Examples 1 to 7, Comparative Examples 1 to 6] We obtained terbium oxide powder, yttrium oxide powder, and scandium oxide powder manufactured by Shin-Etsu Chemical Co., Ltd., and aluminum oxide powder manufactured by Taimei Chemical Co., Ltd. In addition, we obtained liquid tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. The purity of the powder raw materials was 99.95% by mass or more, and the purity of the liquid raw materials was 99.999% by mass or more. Using the above raw materials, 13 types of oxide raw materials with the final compositions shown in Table 1 were prepared by adjusting the mixing ratio. That is, a mixed powder was prepared by weighing out the moles of terbium, yttrium, aluminum, and scandium so that the mole ratios of each composition in Table 1 were obtained. Next, TEOS was added in an amount of SiO 2 The ingredients were weighed out so as to obtain the mass percentages shown in Table 1 and added to each ingredient. Then, while being careful to prevent each material from being mixed with the other, they were dispersed and mixed in ethanol using an alumina ball mill for 15 hours. After that, they were spray-dried to produce granular raw materials with an average particle size of 20 μm. Next, these powders were placed in an yttria crucible and sintered in a high-temperature muffle furnace at 1100°C for 3 hours to obtain sintered raw materials with the respective compositions. The obtained sintered raw materials were subjected to diffraction pattern analysis (XRD analysis) using a powder X-ray diffractometer manufactured by PANalytical. The crystal system of the sample was identified by comparing the reference data of the X-ray diffraction pattern with the measured pattern. In most cases (oxide raw materials Nos. 1 to 8 and 10 to 13), only the peak of a single garnet phase (cubic crystal) was detected, and in the case of oxide raw material No. 9, a weak peak of a different perovskite phase was detected in addition to the peak pattern of the garnet phase. The above results are summarized in Table 1.

[0074] [Table 1]

[0075] The oxide raw materials thus obtained were dispersed and mixed again in ethanol using a nylon ball mill, taking care to prevent each raw material from being mixed with the others. The processing time was 24 hours for each. After that, a spray drying process was performed to produce granular raw materials with an average particle size of 20 μm. The 13 types of powder raw materials obtained were each subjected to uniaxial press molding and cold isostatic pressing at a pressure of 198 MPa to obtain CIP green bodies. The obtained green bodies were degreased in a muffle furnace at 1000 °C for 2 hours. The degreased green bodies were then loaded into a vacuum sintering furnace and sintered at 1550 °C for 3 hours to obtain 13 types of sintered bodies. At this time, the sintered relative density of the samples was in the range of 94.5% to 98.8%. The obtained sintered bodies were placed in a HIP furnace made of a carbon heater and subjected to HIP treatment under the conditions of 200 MPa, 1600°C, and 2 hours in an Ar atmosphere. Almost no graying (oxygen deficiency absorption) was observed in the appearance of any of the obtained sintered bodies. However, to be on the safe side, each of the obtained ceramic sintered bodies was annealed in an oxygen atmosphere furnace at 1450°C for 20 hours while managing each lot, to sufficiently recover the oxygen deficiency. In this way, 13 types of sintered bodies for the examples and comparative examples were prepared. Next, each of the obtained ceramic sintered bodies was ground and polished into a disk shape with a diameter of 10 mm and a thickness of 1 mm and a rod shape (cylindrical shape) with a diameter of 5 mm and a length of 25 mm, and further, both optical end faces of each sample were subjected to a final optical polishing with an optical surface precision of λ / 8 (when the measurement wavelength λ=633 nm).

[0076] Of the samples obtained as described above, the thermal conductivity of the disk-shaped samples was measured as follows. Then, the samples were thermally etched to measure the average sintered grain size of each sample. Furthermore, the total light transmittance, forward scattering, and extinction ratio of each rod-shaped sample were measured as follows.

[0077] (Method of measuring thermal conductivity) The thermal conductivity was measured by the laser flash method in accordance with JIS R1611. Specifically, for each sample with an outer diameter of 10 mm and a thickness of 1 mm, first, specific heat was measured using a differential scanning calorimeter manufactured by Perkin-Elmer with a measurement number of n being 2, and then, thermal diffusivity was measured using a thermal diffusivity measuring device manufactured by NETZSCH with irradiation by a xenon lamp with a measurement number of n being 2. Using these values ​​and the theoretical density value for each composition, the thermal conductivity was calculated according to the following formula. Thermal conductivity (W / (m K)) = Theoretical density (kg / m 3 ) × Specific heat capacity (J / (kg K)) × Thermal diffusivity (m 2 / s)"

[0078] (Method of measuring average sintered grain size) The average sintered grain size of the crystal grains of the sample was determined with reference to "Linear Intercept Technique for Measuring Grain Size in Two-Phase Polycrystalline Ceramics" Journal of the American Ceramic Society, 55, 109 (1972). Specifically, the final optically polished sample was treated in air at 1300°C for 6 hours, and the grain boundaries of the thermally etched optical end surface were observed under an optical microscope to determine the average grain size. If the average grain size is D, the length of an arbitrarily drawn line is C, the number of grains on this line is N, and the magnification of the image is M, then the following formula can be used: D=1.56C / (MN) The number of N was determined to two significant digits.

[0079] (Method of measuring total light transmittance and forward scattering) The total light transmittance and forward scattering were measured at two wavelengths, 1064 nm and 1300 nm, using a spectrophotometer V-670 manufactured by JASCO Corporation. First, the total light transmittance was measured by irradiating the spectrophotometer V-670 with light dispersed by a spectroscope without setting a workpiece (sample), receiving the light with an integrating sphere set in the device in advance, and receiving the collected light with a detector. The illuminance obtained at this time was defined as I 0 Next, the workpiece is set in the device, and this time the dispersed light is incident on the workpiece, and the transmitted light is again collected by an integrating sphere and received by a detector. The illuminance obtained at this time is I, which is calculated by the following formula. Total light transmittance (% / 25mm)=I / I 0 ×100 Next, to measure forward scattering, the same measurement system is used except that the reflector on the back of the integrating sphere is removed from the state in which the workpiece is set. The dispersed light is again incident on the workpiece, and the transmitted light is again collected by the integrating sphere and received by the detector. The obtained illuminance represents the scattered components other than the linear transmitted component, and is called I S was calculated using the following formula: Forward scatter (% / 25mm)=I S / I 0 ×100 The total light transmittance and forward scattering were both measured at two wavelengths, 1064 nm and 1300 nm.

[0080] (Method of measuring extinction ratio) The extinction ratio as a Faraday rotator was measured as follows. The extinction ratio was measured by using an in-house optical system made with a light source manufactured by NKT Photonics, a collimator lens, a polarizer, a work stage, an analyzer, a power meter manufactured by Gentec, and a Ge photodetector. The light was irradiated onto one optical surface of the sample with a wavelength of 1064 nm and a large beam diameter of 3 mm, and the light was transmitted through the sample. The light intensity I 0 The received light intensity I' (maximum value of the laser light intensity) was then measured again with the polarization plane of the analyzer rotated 90 degrees to be perpendicular to the polarization plane of the polarizer, and the received light intensity I' (minimum value of the laser light intensity) was then calculated based on the following formula. Extinction ratio (dB / 25mm)=-10×log 10 (I' / I 0 ') In addition, if the beam diameter is made thicker than 3 mmφ, the beam begins to be kicked off at the outer periphery of the sample, which has a diameter of 5 mmφ, so this beam diameter of 3 mmφ is defined as a state in which light is actually incident on the entire surface within the optical effective diameter of the sample.

[0081] Next, the optically polished sample was coated with an anti-reflection film (AR coat) designed to have a central wavelength of 1064 nm.

[0082] The Verdet constant and the change in the beam diameter of the laser light due to the thermal lens were measured for each ceramic sample thus obtained as follows. That is, as shown in FIG. 1, polarizing elements (polarizer 120, analyzer 130) were set in front of and behind each ceramic sample obtained (corresponding to Faraday rotator 110), and the ceramic sample was inserted into the center of a neodymium-iron-boron magnet (magnet 140) with an outer diameter of 32 mm, an inner diameter of 6 mm, and a length of 40 mm. Then, a high-power laser beam with a wavelength of 1064 nm was applied from both end faces using a high-power laser (beam diameter 1.6 mm) manufactured by IPG Photonics Japan Co., Ltd., to measure the Verdet constant. Furthermore, after removing the neodymium-iron-boron magnet, a high-power laser beam with a wavelength of 1064 nm was applied to each ceramic sample under the same conditions as above. The occurrence of the thermal lens at that time was measured and evaluated as the change in the beam diameter.

[0083] (Method of measuring the Verdet constant) The Verdet constant V was calculated based on the following formula: The magnitude (H) of the magnetic field applied to the ceramic sample was calculated by simulation from the dimensions of the measurement system, the residual magnetic flux density (Br), and the coercive force (Hc). θ=V×H×L (In the formula, 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 (0.025 m in this case).)

[0084] (Method for measuring the change in beam diameter of incident laser light caused by thermal lens) A 100W output parallel beam was emitted from a high power laser (beam diameter 1.6mm) manufactured by IPG Photonics Japan Co., Ltd., and the beam diameter at the focal position was measured using a beam profiler. A ceramic sample was then set on the line of the emitted beam, and the change in beam diameter due to the sample setting was remeasured using the beam profiler, and the difference between the two was calculated as the change in beam diameter due to the thermal lens. Note that, since the change in beam diameter is prone to measurement errors, the same measurement was carried out again on a different day, and the larger value was taken as the change in beam diameter. The above results are shown in Table 2. [Table 2]

[0085] As a result, in all of the examples (Examples 1 to 7) controlled to the composite oxide composition of the present invention, and Comparative Example 5, the total light transmittance was 84.0% or more at wavelengths of 1064 nm and 1300 nm, the forward scattering was 0.5% or less, and the extinction ratio was 42 dB or more, and it was confirmed that highly transparent paramagnetic garnet-type transparent ceramics could be produced. Furthermore, the change in beam diameter due to thermal lensing when a laser beam with an output of 100 W was incident was all suppressed to 10% or less, and it was confirmed that it can be installed in a high-power laser system. However, in Comparative Example 5, the Tb concentration was too low, so the Verdet constant was below 32 rad / (T·m). Furthermore, the existence probability of Tb and Y was almost equivalent, and the average particle size was also small, so the thermal conductivity remained below 4.8 W / (m·K). In Comparative Examples 2 to 4, since no Sc was added, the extinction ratio, total light transmittance, forward scattering, and change in beam diameter were all below the specified ranges. In Comparative Example 1, the Tb ratio was too high, so the extinction ratio, total light transmittance, forward scattering, and change in beam diameter due to thermal lensing when a laser beam with an output of 100 W was incident were all below the specified ranges. In the case of Comparative Example 6, SiO 2 Because the amount of doping was too high, the thermal conductivity, the total light transmittance at a wavelength of 1,300 nm, and the change in beam diameter due to thermal lensing when 100 W of laser light was incident were all below the specified range. In addition, in Examples 1 to 7, since the average sintered grain size was 5 μm or more, the thermal conductivity was all 4.8 W / (m·K) or more. As a result of the above, by controlling x, y, and z in formula (1) within the ranges specified in the present invention, and using SiO as a sintering aid, 2By doping the ceramics with ZnO within a predetermined range, it is possible to provide a highly transparent paramagnetic garnet-type transparent ceramics having an average sintered grain size of 5 μm or more, a linear transmittance of 84.0% or more at a wavelength of 1064 nm with an optical path length of 25 mm, and a forward scattering of 0.5% or less, and further a linear transmittance of 84.0% or more at a wavelength of 1300 nm with an optical path length of 25 mm, and a forward scattering of 0.5% or less. Furthermore, it is possible to provide a highly transparent paramagnetic garnet-type transparent ceramics having a thermal conductivity of 4.8 W / (m K) or more, a verdet at a wavelength of 1064 nm, and a thermal conductivity of 4.8 W / (m K) or more. The paramagnetic garnet-type transparent ceramic has a constant of 32 rad / (T m) or more, and when laser light of 100 W output power and wavelength of 1064 nm is incident on the material with an optical path length of 25 mm, the change in beam diameter due to thermal lensing is 10% or less. As a Faraday rotator, the extinction ratio at a wavelength of 1064 nm with an optical path length of 25 mm is 42 dB or more. When this transparent ceramic is used as a magneto-optical material, a high-performance magneto-optical device that can be used in high-power applications can be provided.

[0086] Although the present invention has been described above using the above-mentioned embodiment, the present invention is not limited to the embodiment, and can be modified within the scope of what a person skilled in the art can imagine, such as other embodiments, additions, modifications, deletions, etc., and any aspect is within the scope of the present invention as long as it achieves the effects of the present invention. [Explanation of symbols]

[0087] 100 Optical isolator 110 Faraday Rotator 120 Polarizer 130 Analyzer 140 Magnet

Claims

1. A sintered body of a complex oxide represented by the following formula (1), containing SiO as a sintering aid. 2 a total light transmittance of 84.0% or more at a wavelength of 1064 nm and an optical path length of 25 mm, and a forward scattering of 0.5% or less; and further a total light transmittance of 84.0% or more at a wavelength of 1300 nm and an optical path length of 25 mm, and a forward scattering of 0.5% or less. (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05≦x≦0.4, 0≦y<0.004, 0.6≦1−x−y<0.95, 0≦z<0.004, and 0.001<y+z<0.005.)

2. 2. The paramagnetic garnet-type transparent ceramic according to claim 1, which has a Verdet constant of 32 rad / (T·m) or more at a wavelength of 1064 nm.

3. 3. The paramagnetic garnet-type transparent ceramic according to claim 1, wherein the extinction ratio over the entire optical effective diameter when a laser beam having a wavelength of 1064 nm is incident on the ceramic with an optical path length of 25 mm is 42 dB or more.

4. 4. The paramagnetic garnet-type transparent ceramic according to claim 1, wherein when a laser beam having a wavelength of 1064 nm is incident with an optical path length of 25 mm, a beam diameter of 1.6 mm, and an incident power of 100 W, the change in the beam diameter is 10% or less.

5. 5. The paramagnetic garnet-type transparent ceramic according to claim 1, which has a thermal conductivity of 4.8 W / (m·K) or more.

6. A magneto-optical material comprising the paramagnetic garnet-type transparent ceramic according to any one of claims 1 to 5.

7. A magneto-optical device formed by using the magneto-optical material according to claim 6.

8. 8. The magneto-optical device according to claim 7, which is an optical isolator having the paramagnetic garnet-type transparent ceramic as a Faraday rotator and having polarizing materials in front of and behind the optical axis of the Faraday rotator and usable in the wavelength range of 0.9 μm to 1.1 μm.

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