Terbium-containing ferromagnetic garnet-type transparent ceramics and magneto-optical devices

Abstract

To provide a terbium-containing paramagnetic garnet-type transparent ceramic having low absorption at a wavelength of 1,064 nm and a temperature coefficient of refractive index that is half or less that of existing TGG crystals.SOLUTION: A sintered compact of a composite oxide comprises terbium, yttrium and aluminum, wherein: a volume molar concentration of terbium is equal to or more than the volume molar concentration of yttrium; the Verde constant at a wavelength of 1,064 nm is 30 rad / (T-m) or more; and the average value (dn(1064) / dt)ave of a temperature coefficient of refractive index at 1,064 nm and temperatures of 20, 30, and 40°C is equal to or less than 9.0×10-6(K-1).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to terbium-containing paramagnetic garnet-type transparent ceramics, and more particularly to garnet-type transparent ceramics containing terbium suitable for forming magneto-optical devices such as optical isolators, and magneto-optical devices using the garnet-type transparent ceramics as magneto-optical materials.

Background Art

[0002] In recent years, with the increasing output power of fiber lasers, the spread of laser processing machines using such fiber lasers has been remarkable. By the way, when external light is incident on a laser light source incorporated in a laser processing machine, a phenomenon occurs in which the resonance state becomes unstable and the oscillation state is disturbed. In particular, when the oscillated light is reflected by an intermediate optical system and returns to the light source, the oscillation state is greatly disturbed. To prevent this, an optical isolator is usually provided on the light output side of the light source, such as between the laser light source and the optical fiber.

[0003] An optical isolator includes a Faraday rotator, a polarizer disposed on the light incident side of the Faraday rotator, and an analyzer disposed on the light output side of the Faraday rotator. The Faraday rotator is used by applying a magnetic field parallel to the traveling direction of light. At this time, the polarized wave component of light rotates only in a certain direction whether it advances or retreats in the Faraday rotator. Further, the Faraday rotator is adjusted to a length such that the polarized wave component of light is rotated exactly 45 degrees. Here, if the polarization planes of the polarizer and the analyzer are shifted by 45 degrees in the rotation direction of the advancing light, the polarized wave of the advancing light coincides at the polarizer position and the analyzer position and thus passes through. On the other hand, the polarized wave of the returning light rotates 45 degrees in the reverse rotation to the deviation angle direction of the polarization plane of the polarizer shifted by 45 degrees from the analyzer position. Then, the polarization plane of the returning light at the polarizer position is shifted by 45 degrees - (-45 degrees) = 90 degrees with respect to the polarization plane of the polarizer and cannot pass through the polarizer. In this way, it functions as an optical isolator that transmits and emits the advancing light and blocks the returning light.

[0004] As a material used as the Faraday rotator constituting the above optical isolator, conventionally, TGG crystal (Tb3Ga5O 12 ) and TSAG crystal ((Tb (3-x) Sc x )Sc2Al3O 12 ) have been known (Japanese Patent Application Laid-Open No. 2011-213552 (Patent Document 1), Japanese Patent Application Laid-Open No. 2002-293693 (Patent Document 2)). The TGG crystal is currently widely used for standard fiber laser devices. On the other hand, the Verdet constant of the TSAG crystal is said to be about 1.3 times that of the TGG crystal, and this is also a material that would not be strange to be mounted on a fiber laser device. However, since Sc is an extremely expensive raw material, its adoption has not progressed from the perspective of manufacturing cost.

[0005] Since the TGG crystal (Tb3Ga5O 12 ) is relatively easy to manufacture, it can be pulled up to a 4-inch diameter crystal, and both its supply capacity and cost are high. It is still widely used as a Faraday rotator for fiber laser devices. However, several problems have become apparent, and it has been revealed that it is particularly difficult to use for high-power band fiber laser devices. Specifically, the absorption rate inherent in the material is high (absorption coefficient at a wavelength of 1064 nm ~ 0.16% / cm), and the temperature coefficient of the refractive index dn / dt is large (dn / dt = 18×10 -6 (K -1 )) is the bottleneck.

[0006] Therefore, there is a strong demand for a new material that is not as expensive as the TSAG crystal and has lower absorption and a smaller temperature coefficient of the refractive index dn / dt than the TGG crystal. One such candidate material is the TAG crystal (Tb3Al5O 12 ), but the production of high-quality single crystal TAG has not been invented so far.

[0007] Under such constraints, recently, the composition is (Tb x Y 1-x )3Al5O 12A dense ceramic sintered body with (x = 0.5 to 1.0) has a higher extinction ratio compared to existing TGG crystals (improved from the existing 35 dB to 39.5 dB or more), and the insertion loss can also be reduced (improved from the existing 0.05 dB to 0.01 to 0.05 dB) (Yan Lin Aung, Akio Ikesue, Development of optical grade (Tb x Y 1-x )3Al5O 12 ceramics as Faraday rotator material, J.Am.Ceram.Soc.,(2017),100(9),4081 - 4087(non - patent document 1)). The material disclosed in this non - patent document 1 is a material similar to TAG crystals, but is characterized in that it is made of ceramics unlike conventional single - crystal materials. As a result, high - quality yttrium - substituted TAG crystals that could not be realized before have been obtained.

[0008] Furthermore, Japanese Patent Application Laid - Open No. 2019 - 199386 (Patent Document 3) discloses paramagnetic garnet - type transparent ceramics having a composition of (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (where 0.05 ≤ x < 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.004 < z < 0.2). This material is a material with a composition similar to that of non - patent document 1, but is different in that Sc is significantly added. When using this material, the extinction ratio is further improved to 40 dB or more compared to non - patent document 1, and even when irradiated with a 100 W laser, the change amount of the focal position due to the thermal lens is small, and it can be used as a practically applicable optical isolator. It is said that a truly practical paramagnetic garnet - type transparent ceramic that is easy to scale up because it is made of ceramics can be provided.

[0009] By the way, in the known examples disclosed in these Non-Patent Document 1 and Patent Document 3, there are indeed cases where the loss can be reduced as expected compared to TGG crystals, and the deterioration of the beam quality can be suppressed even under high-power irradiation. Probably, these findings seem to show the effects based on the fact that the absorption rate inherent to the material is lower than that of TGG crystals. In fact, if a material with a low absorption rate inherent to the material can be used as a Faraday rotator, it is preferable because it enables further increase in the output power of the fiber laser device. On the other hand, in any of the known examples, there is no knowledge about the temperature coefficient dn / dt of the refractive index, and furthermore, the problem is that it is completely unclear what position the new material occupies compared to the temperature coefficient dn / dt = 18×10 -6 (K -1 ) of the conventional TGG crystal.

[0010] The necessary conditions for a Faraday rotator applicable to a high-power fiber laser device are the product of a low absorption rate and a small temperature coefficient dn / dt of the refractive index (that is, both of these requirements are necessary), but there are no such findings or prior art examples.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0012]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] The present invention has been made in view of the above circumstances, and is a sintered body of a complex oxide containing terbium, yttrium, and aluminum, wherein the volume molar concentration of terbium is equal to or higher than the volume molar concentration of yttrium, and has a low absorption rate at a wavelength of 1064 nm, and a temperature coefficient of its refractive index is half or less of that of an existing TGG crystal. An object of the present invention is to provide a terbium-containing paramagnetic garnet-type transparent ceramic and a magneto-optical device using the same.

Means for Solving the Problems

[0014] In order to achieve the above object, the present invention provides the following terbium-containing paramagnetic garnet-type transparent ceramics and magneto-optical devices. 1. represented by the following formula (1) A sintered body of a complex oxide, wherein the Verdet constant at a wavelength of 1064 nm is 30 rad / (T·m) or more, and the average value (dn(1064) / dt) of the temperature coefficient of the refractive index at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C ave is 9.0×10 -6 (K -1 ) or less. A terbium-containing paramagnetic garnet-type transparent ceramic characterized by the above. (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5O 12 (1) (wherein 0.05 ≦ x ≦ 0.4, 0.0005 ≦ y < 0.08, 0.6 < 1 - x - y < 0.95, 0.0004 ≦ z < 0.15, 0.0009 ≦ y + z < 0.2). 2 . Furthermore, it contains more than 0% by mass and 0.1% by mass or less of SiO2 as a sintering aid to 1 the terbium-containing paramagnetic garnet-type transparent ceramics described. 3 . 1 or 2 A magneto-optical device configured by using the paramagnetic garnet-type transparent ceramics described in 1 as a magneto-optical material. 4 . An optical isolator that includes the above terbium-containing paramagnetic garnet-type transparent ceramics as a Faraday rotator and has polarizing materials before and after on the optical axis of the Faraday rotator and is usable in a wavelength band of 0.9 μm or more and 1.1 μm or less 3 the magneto-optical device described in.

Advantages of the Invention

[0015] According to the terbium-containing paramagnetic garnet-type transparent ceramics of the present invention, the average value (dn(1064) / dt) of the temperature coefficients of the refractive index dn(1064,20) / dt, dn(1064,30) / dt, dn(1064,40) / dt ave is 9.0×10 -6 (K -1 ) or less, and is approximately reduced by half or less compared to that of the conventional TGG crystal. Therefore, when the terbium-containing paramagnetic garnet-type transparent ceramics of the present invention are applied to a laser device, the amount of heat lens generated due to the change in the refractive index of the material is also reduced by half. That is, it can be applied to a high-power laser device with at least twice the output compared to the existing TGG crystal.

Brief Description of the Drawings

[0016]

Figure 1

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] <Terbium-containing paramagnetic garnet-type transparent ceramics> Hereinafter, the terbium-containing paramagnetic garnet-type transparent ceramics (sometimes simply referred to as transparent ceramics) according to the present invention will be described. The transparent ceramics of the present invention are sintered bodies of complex oxides containing terbium, yttrium, and aluminum, and the volume molar concentration of the terbium is equal to or higher than the volume molar concentration of the yttrium. The Verdet constant at a wavelength of 1064 nm is 30 rad / (T·m) or higher, and the average value of the temperature coefficient of the refractive index (dn(1064) / dt) at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C ave is 9.0×10 -6 (K -1 ) or less, which is characterized by the above.

[0018] Here, the Verdet constant of the transparent ceramics of the present invention at a wavelength of 1064 nm is 30 rad / (T·m) or higher, preferably 32 rad / (T·m) or higher. In the composition constituting the garnet-type oxide sintered body, the volume molar concentration of terbium is controlled to be equal to or higher than the volume molar concentration of yttrium, and the above Verdet constant is obtained by manufacturing under appropriate conditions in each step as described later as a method for manufacturing transparent ceramics.

[0019] Also, the average value (dn(1064) / dt) of the temperature coefficients of the refractive index dn(1064,20) / dt, dn(1064,30) / dt, and dn(1064,40) / dt of the transparent ceramics of the present invention at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C ave is 9.0×10 -6 (K -1 ) or less, preferably 8.9×10 -6 (K -1)The following is the case. The composition of the transparent ceramics of the present invention is within the composition range represented by the formula (1) described later, and by being manufactured under appropriate conditions in each step as described later as a method for manufacturing transparent ceramics, the average value (dn(1064) / dt) of the temperature coefficient of the refractive index ave is obtained.

[0020] Here, the temperature coefficient of refractive index dn(λ,T) / dt is the temperature coefficient of the refractive index at the wavelength λ (nm) and temperature T (°C) of the target transparent ceramics, and is obtained by a method conforming to JIS B7071-2 (Method for measuring refractive index of optical glass - Part 2: V-block method). The average value (dn(1064) / dt) of the temperature coefficient of the refractive index at the wavelengths 1064 nm, temperatures 20, 30, and 40 °C defined in the present invention ave is obtained as follows. First, a block sample in the shape of a triangular prism with two right-angled isosceles triangle-shaped bottom surfaces of the transparent ceramics to be measured is placed on a V-block prism having a predetermined refractive index N, and four types of standard laser lights with different wavelengths (for example, laser lights with wavelengths 785.4 nm, 830.5 nm, 1310 nm, and 1550 nm) are incident from the normal line of the wall surface of the prism. At this time, the light refracted by the V-block prism and the block sample that passes through and exits from the wall surface on the opposite side of the prism, the angle of the light (deviation angle i * ), is used to calculate the refractive index n of the block sample to be measured for each wavelength using the following formula. At this time, the temperatures of the V-block prism and the block sample (sample temperature) are set to 20 °C, 30 °C, and 40 °C, and the refractive indices for each of the four wavelengths at each sample temperature are measured. n = {N 2 + sini * ·(N 2 - sin 2 i * ) 1 / 2} 1 / 2 Next, from the refractive index values at four wavelengths calculated for each of the sample temperatures of 20°C, 30°C, and 40°C, the refractive indices at a wavelength of 1064 nm for each of the sample temperatures of 20°C, 30°C, and 40°C are derived based on the Sellmeier dispersion formula of the cell, and are denoted as the temperature coefficients of the refractive index dn(1064,20) / dt, dn(1064,30) / dt, and dn(1064,40) / dt at wavelengths of 1064 nm and temperatures of 20, 30, and 40°C, respectively. The average values of these are taken as the average value (dn(1064) / dt) of the temperature coefficients of the refractive index dn(1064,20) / dt, dn(1064,30) / dt, and dn(1064,40) / dt at wavelengths of 1064 nm and temperatures of 20, 30, and 40°C for the transparent ceramics to be measured. ave Let it be so. Such measurement may be performed using a precision refractometer (for example, the Carl Zeiss Jena Precision Refractometer KPR-3000 type manufactured by Shimadzu Corporation) in the fully automatic measurement mode of the apparatus.

[0021] Note that the average value (dn(1064) / dt) of the temperature coefficients of the refractive index dn(1064,20) / dt, dn(1064,30) / dt, and dn(1064,40) / dt at wavelengths of 1064 nm and temperatures of 20, 30, and 40°C ave is 9.0×10 -6 (K -1 ) or less. When it can be controlled to be so, since the average value (18×10 -6 (K -1 )) of the temperature coefficients of the refractive index dn(1064,20) / dt, dn(1064,30) / dt, and dn(1064,40) / dt at wavelengths of 1064 nm and temperatures of 20, 30, and 40°C for the TGG crystal becomes half or less of this value, when a high-power laser with a wavelength of 1064 nm is irradiated onto the transparent ceramics of the present invention, the amount of heat lens generation due to the refractive index change is half or less of that in the case of the TGG crystal, and the high-power application resistance becomes substantially two times or more, which is preferable.

[0022] Furthermore, as a detailed composition of the transparent ceramics of the present invention, it is preferably the one represented by the following formula (1). (Tb 1-x-y Y x Sc y )3(Al 1-z Scz )5O 12 (1) (where 0.05 ≤ x ≤ 0.4, 0 ≤ y < 0.08, 0.52 < 1 - x - y < 0.95, 0 ≤ z < 0.15, and 0.001 < y + z < 0.2.)

[0023] Here, by adding terbium (Tb) within the concentration range represented by formula (1), a sufficient Verdet constant can be ensured. By adding yttrium (Y) within the concentration range represented by formula (1), suppression of heterophase and minimization of internal strain can be ensured. Also, by adding scandium (Sc) within the concentration range represented by formula (1), complete disappearance of heterophase has been achieved. Furthermore, by adding aluminum (Al) within the concentration range represented by formula (1), a sufficient Verdet constant is ensured, and a relatively high thermal conductivity is imparted.

[0024] Note that the numerical ranges for x, y, and z in formula (1) are as follows in detail. In formula (1), the range of x is 0.05 ≤ x ≤ 0.4, preferably 0.1 ≤ x ≤ 0.4, and more preferably 0.2 ≤ x ≤ 0.4. When x is within this range, the perovskite - type heterophase can be reduced to a level where it cannot be detected by X - ray diffraction (XRD) analysis.

[0025] When x is less than 0.05, the effect of substituting part of terbium with yttrium cannot be obtained, and it becomes substantially the same as the conditions for producing TAG, so it is difficult to stably manufacture a high - quality ceramic sintered body with low scattering and low absorption, which is not preferable. Also, when x is greater than 0.4, the Verdet constant at a wavelength of 1064 nm becomes less than 32 rad / (T·m), which is not preferable. Furthermore, when the relative concentration of terbium becomes excessively thin, the total length required to rotate the laser light at a wavelength of 1064 nm by 45 degrees becomes longer than 25 mm, making manufacturing difficult, which is not preferable.

[0026] In formula (1), the range of y is 0 ≦ y < 0.08, preferably 0.001 < y < 0.004, and more preferably 0.002 < y < 0.004. When y 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 it can prevent an excessive decrease in the thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0027] When y is 0.08 or more, while the effect of suppressing the precipitation of the perovskite-type heterogeneous phase or the 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 suppression effect of scandium. As a result, a local decrease in the extinction ratio and a decrease in the average value of the thermal conductivity occur, which is not preferable.

[0028] In formula (1), the range of 1 - x - y is 0.52 < 1 - x - y < 0.95, and more preferably 0.6 ≦ 1 - x - y < 0.8. 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.

[0029] (1) In the formula, the range of z is 0 ≦ z < 0.15, preferably 0.001 < z < 0.004 shi . 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 it can prevent an excessive decrease in the thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0030] When z is 0.15 or more, while the effect of suppressing the precipitation of the perovskite-type heterogeneous phase or the 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 suppression effect of scandium. As a result, a local decrease in the extinction ratio and a decrease in the average value of the thermal conductivity occur, which is not preferable.

[0031] In the transparent ceramics of the present invention, scandium (Sc) can be added within the ranges of y and z in the above formula (1). The addition amounts y and z of scandium each include 0 as a range when viewed individually. However, when considering the composition of the entire paramagnetic garnet-type transparent ceramics, it is preferable that y + z exceeds 0.001 and is added within the range of the formula (1) because a highly transparent sintered body can be stably manufactured.

[0032] That is, in the formula (1), the range of y + z is 0.001 < y + z < 0.2, more preferably 0.002 < y + z < 0.005, and even more preferably 0.003 < z < 0.005. 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 it can prevent excessive reduction in thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0033] When y + z is 0.001 or less, the risk of precipitation of perovskite-type heterogeneous phases and alumina heterogeneous phases increases, which is not preferable. When y + z is 0.2 or more, while the effect of suppressing the precipitation of perovskite-type heterogeneous phases or alumina heterogeneous phases saturates and does not change, sintering unevenness, residual sintering strain, or residual grain boundary scattering occurs due to the excessive sintering suppression effect of scandium. As a result, local reduction in the extinction ratio and reduction in the average value of thermal conductivity occur, which is not preferable.

[0034] In the transparent ceramics of the present invention, it is preferable that the main components of the 6-coordinate site and the 4-coordinate site in the garnet structure are aluminum (Al). When the main components of these sites can be composed of aluminum (Al), the crystal bondability is improved, and thus the average value of the temperature coefficient of refractive index (dn(1064) / dt) ave at wavelengths of 1064 nm, temperatures of 20, 30, and 40 °C can be reduced. In particular, when, as in the above formula (1), the ratio of aluminum (Al) occupying the 6-coordinate site and the 4-coordinate site is 1 - z (0 ≤ z < 0.15), the average value of the temperature coefficient of refractive index (dn(1064) / dt) avecan be controlled to be 9.0×10 -6 (K -1 ) or less.

[0035] In addition, in the transparent ceramics of the present invention, terbium (Tb) and yttrium (Y) are selected as the main components of the 8 - coordinate sites, and the concentration of terbium is preferably controlled in the range of 1 - x - y (0.52 < 1 - x - y < 0.95), and the concentration of yttrium is in the range of x (0.05 ≤ x ≤ 0.4). When the concentration of terbium is controlled within this range, the Verdet constant at a wavelength of 1064 nm can be ensured to be 32 rad / (T·m) or more. When the concentration of terbium is within the said range and the concentration of yttrium is controlled within the above range, the average value of the temperature coefficient of refractive index (dn(1064) / dt) at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C ave can be controlled to be 9.0×10 -6 (K -1 ) or less. In addition, when each of these two components Tb and Y simultaneously satisfies the above - mentioned range, these two properties (Verdet constant, the average value of the temperature coefficient of the refractive index (dn(1064) / dt) ave ) can be simultaneously satisfied.

[0036] By the way, the paramagnetic garnet - type transparent ceramics obtained in the present invention contain, as the main component, components having a composition within the range represented by the formula (1), and as the sub - component, SiO2 serving as a sintering aid is contained in a range of 0.1 mass% or less (that is, the content is more than 0 mass% and 0.1 mass% or less). When SiO2 is contained as a sintering aid within this range, the transparency of the obtained paramagnetic garnet - type ceramics is improved to a level that can withstand practical use and is stable, which is preferable.

[0037] Here, "contained as the main component" means containing 90 mass% or more of the complex oxide represented by the above formula (1). The content of the complex oxide represented by the formula (1) is preferably 99 mass% or more, more preferably 99.9 mass% or more, still more preferably 99.99 mass% or more, and particularly preferably 99.999 mass% or more.

[0038] In addition, the transparent ceramics of the present invention are composed of the above main components and sub-components, but may further contain other elements. Examples of other elements include rare earth elements such as lutetium (Lu) and cerium (Ce), or various impurity groups such as sodium (Na), calcium (Ca), magnesium (Mg), phosphorus (P), tungsten (W), molybdenum (Mo), etc.

[0039] When the total amount of Tb and Y is 100 parts by mass, 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).

[0040] The transparent ceramics of the present invention can be finished with a thermal conductivity of 4.8 W / m·K or more by manufacturing with the composition under the above-mentioned conditions. The measurement of the thermal conductivity can be evaluated by the laser flash method in accordance with JIS R1611.

[0041] <Method for manufacturing terbium-containing paramagnetic garnet-type transparent ceramics> [Raw materials] As raw materials used in the present invention, oxide powders of terbium, yttrium, scandium, and aluminum are used as starting materials. At this time, the raw material purity is preferably 99.9% by mass or more, and particularly preferably 99.99% by mass or more. Weigh a predetermined amount of these elements, and further contain silicon oxide (SiO2) in an amount exceeding 0% by mass and not exceeding 0.1% by mass, and process them appropriately by a wet ball mill or a bead mill.

[0042] 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, as these organic additives, it is preferable to select high-purity types that do not contain unnecessary metal ions. Also, the addition order of each organic additive needs to be appropriately designed so as not to inhibit the control of the properties (such as particle size distribution) of the raw material to be manufactured.

[0043] [Manufacturing Process] In the present invention, using the above raw material powder, it is possible to produce a molded body by press-molding it into a predetermined shape or by directly casting and molding a wet slurry as it is. The obtained molded body is sufficiently degreased, and then sintered to produce a sintered body with a relative density densified to at least 94% or more. As a subsequent process, it is preferable to perform a hot isostatic pressing (HIP) treatment. If the hot isostatic pressing (HIP) treatment is performed as it is, the paramagnetic garnet-type transparent ceramics will be reduced and some oxygen deficiencies will occur. Therefore, it is preferable to recover the oxygen deficiencies by performing a slightly oxidized HIP treatment or an annealing treatment (oxidation annealing treatment) in an oxidizing atmosphere after the HIP treatment. Thereby, transparent garnet-type oxide ceramics without defect absorption can be obtained.

[0044] (Molding) In the present invention, ordinary pressing processes can be preferably utilized. That is, a uniaxial pressing process, which is very common and involves filling a mold and applying pressure from a certain direction, or a cold isostatic pressing (CIP) process or a warm isostatic pressing (WIP) process, where the material is hermetically stored in a deformable waterproof container and pressurized by hydrostatic pressure, can be preferably utilized. The applied pressure may be appropriately adjusted while checking the relative density of the obtained molded body, and is not particularly limited. However, for example, if it is managed within a pressure range of about 300 MPa or less that can be handled by commercially available CIP devices or WIP devices, the manufacturing cost may be suppressed. Alternatively, a hot pressing process, a spark plasma sintering process, a microwave heating process, etc., which not only perform the forming process but also sinter in one go during forming, can also be preferably utilized. Furthermore, it is also possible to produce a molded body by a casting method instead of the pressing method. Forming methods such as pressure casting, centrifugal casting, and extrusion molding can also be adopted by optimizing the shape and size of the oxide powder as the starting material and the combination with various organic additives.

[0045] (Debinding) In the present invention, ordinary debinding processes can be preferably utilized. That is, it is possible to go through a temperature-raising debinding process using a heating furnace. Also, the type of the atmosphere gas at this time is not particularly limited, and air, oxygen, hydrogen, etc. can be preferably utilized. The debinding temperature is not particularly limited either. However, if a raw material mixed with an organic additive is used, it is preferable to raise the temperature to a temperature at which the organic component can be decomposed and removed.

[0046] (Sintering) In the present invention, general sintering processes can be preferably utilized. That is, heating sintering processes such as a resistance heating method and an induction heating method can be preferably utilized. The atmosphere at this time is not particularly limited, and various atmospheres such as an inert gas, an oxygen gas, a hydrogen gas, a helium gas, or sintering under reduced pressure (in a vacuum) is also possible. However, since it is preferably finally possible to prevent the occurrence of oxygen deficiency, more preferable atmospheres include an oxygen gas and a reduced-pressure oxygen gas atmosphere.

[0047] In the sintering process of the present invention, the sintering temperature is preferably 1440 to 1780 °C, and particularly preferably 1470 to 1730 °C. When the sintering temperature is within this range, it is preferable because densification is promoted while suppressing heterogeneous precipitation.

[0048] In the sintering process of the present invention, a sintering holding time of about several hours is sufficient, but the relative density of the sintered body must be densified to at least 94% or more. Further, if the holding time is longer than 10 hours to densify the relative density of the sintered body to 99% or more, the final transparency is improved, which is more preferable.

[0049] (Hot Isostatic Pressing (HIP)) In the present invention, a step of further performing a hot isostatic pressing (HIP) treatment can be provided after the sintering process. At this time, as the type of pressurized gas medium, an inert gas such as argon or nitrogen, or Ar - O2 can be preferably used. The pressure applied by the pressurized gas medium is preferably 50 to 300 MPa, and more preferably 100 to 300 MPa. If the pressure is less than 50 MPa, the transparency improvement effect may not be obtained. If it exceeds 300 MPa, further transparency improvement cannot be obtained even if the pressure is increased, and the load on the device becomes excessive, which may damage the device. It is convenient and preferable that the applied pressure is 196 MPa or less, which can be processed by a commercially available HIP device.

[0050] Also, the treatment temperature (predetermined holding temperature) at that time 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 deficiency generation increases, which is not preferable. Also, if the heat treatment temperature is less than 1100 °C, almost no transparency improvement effect of the sintered body can be obtained. Regarding the holding time of the heat treatment temperature, there is no particular limitation, but if it is held for too long, the risk of oxygen deficiency generation increases, which is not preferable. Typically, it is preferably set in the range of 1 to 3 hours.

[0051] Incidentally, the heater material, heat insulating material, and processing container for HIP processing are not particularly limited, but graphite, or molybdenum (Mo), tungsten (W), or platinum (Pt) can be preferably used. As the processing container, yttrium oxide or gadolinium oxide can also be preferably used. Particularly when the processing temperature is 1500°C or lower, platinum (Pt) can be used as the heater material, heat insulating material, and processing container, and since the pressurized gas medium can be Ar-O2, it is preferable because it can prevent the generation of oxygen deficiency during HIP processing. When the processing temperature exceeds 1500°C, graphite is preferable as the heater material and heat insulating material. In this case, any one of graphite, molybdenum (Mo), or tungsten (W) is selected as the processing container, and further, after selecting either yttrium oxide or gadolinium oxide as a double container inside thereof, if the inside of the container is filled with an oxygen releasing material, it is preferable because the amount of oxygen deficiency generated during HIP processing can be suppressed to be as small as possible.

[0052] (Annealing) In the present invention, after the HIP processing, oxygen deficiency may occur in the obtained transparent ceramic sintered body, and it may exhibit a slightly light gray appearance. In that case, it is preferable to perform oxidation annealing treatment (oxygen deficiency recovery treatment) in an oxygen atmosphere or in the air at a temperature equal to or lower than the HIP processing temperature, typically 1000 to 1500°C, preferably 1400°C or higher, more preferably 1450°C or higher and 1500°C or lower. The holding time in this case is not particularly limited, but it is preferably selected to be a time sufficient for recovering oxygen deficiency and within a time that does not wastefully consume electricity by performing the treatment for an excessively long time. By this oxygen annealing treatment, even a transparent ceramic sintered body that exhibits a slightly light gray appearance in the HIP processing step can be made into a colorless and transparent paramagnetic garnet-type transparent ceramic body without defect absorption.

[0053] (Optical polishing) In the manufacturing method of the present invention, for the paramagnetic garnet-type transparent ceramics that have undergone the above series of manufacturing steps, it is preferable to optically polish both end faces on the axis that is optically utilized. At this time, when the measurement wavelength λ = 633 nm, the optical surface accuracy is preferably λ / 2 or less, and particularly preferably λ / 8 or less. It is also possible to further reduce optical loss by appropriately forming an antireflection film on the optically polished surface.

[0054] As described above, the terbium-containing paramagnetic garnet-type transparent ceramics of the present invention can be provided. The transparent ceramics can be used as a Faraday rotator operable in the wavelength band of 0.9 μm or more and 1.1 μm or less.

[0055] [Magneto-optical device] Furthermore, since the terbium-containing paramagnetic garnet-type transparent ceramics of the present invention are assumed to be used as a magneto-optical material, after applying a magnetic field parallel to the optical axis to the transparent ceramics, it is preferable to configure and use a magneto-optical device by setting a polarizer and an analyzer such that their optical axes are shifted by 45 degrees from each other. That is, the transparent ceramic material of the present invention is suitable for use in magneto-optical devices, and is particularly preferably used as a Faraday rotator of an optical isolator having a wavelength of 0.9 to 1.1 μm.

[0056] 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 terbium-containing paramagnetic garnet-type transparent ceramics of the present invention as an optical element. In FIG. 1, the optical isolator 100 includes a Faraday rotator 110 made of the terbium-containing paramagnetic garnet-type transparent ceramics of the present invention, and a polarizer 120 and an analyzer 130, which are polarizing materials, are provided before and after the Faraday rotator 110. Further, the optical isolator 100 is preferably arranged in the order of the polarizer 120, the Faraday rotator 110, and the analyzer 130, and a magnet 140 is placed on at least one of their side surfaces.

[0057] In addition, the optical isolator 100 can be suitably used in an industrial fiber laser device. That is, it is suitable for preventing the reflected light of the laser light emitted from the laser light source from returning to the light source and causing unstable oscillation.

Examples

[0058] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples.

[0059] [Examples 1 to 6, Comparative Examples 1 to 6] Terbium oxide powder, yttrium oxide powder, scandium oxide powder manufactured by Shin-Etsu Chemical Co., Ltd., and aluminum oxide powder manufactured by Dainippon Chemical Co., Ltd. were obtained. Further, a liquid of tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. was obtained. The purity of the powder raw materials was all 99.95% by mass or more, and the purity of the liquid raw material was 99.999% by mass or more. Using the above raw materials, the mixing ratio was adjusted to prepare composite oxide raw materials having the 12 final compositions shown in Table 1. As a method for adjusting the mixing ratio, each oxide powder was weighed and mixed so that the number of moles of terbium, yttrium, aluminum, and scandium was the molar ratio of each composition in Table 1. Subsequently, TEOS was weighed so that the added amount thereof was the mass% (wt%) in Table 1 in terms of SiO2 and added to each raw material.

[0060]

Table 1

[0061] Then, while taking care to prevent mutual contamination, dispersion and mixing treatment was performed using an alumina ball mill apparatus in ethanol. The treatment time was 15 hours. Subsequently, spray drying was performed to produce granular raw materials with an average particle size of 20 μm in each case. For each of the obtained 12 types of oxide raw materials, uniaxial pressing and isostatic pressing treatment at a pressure of 198 MPa were performed to obtain CIP compacts. In addition, to confirm production stability, three rod-shaped samples were prepared under each condition, and separately, one block-shaped sample was also molded. All of the obtained compacts were degreased in a muffle furnace under the conditions of 1000 °C for 3 hours to obtain degreased compacts.

[0062] Subsequently, the degreased compacts were charged into a vacuum sintering furnace and treated at 1500 - 1600 °C for 3 hours under a reduced pressure of less than 1.0×10 -3 Pa to obtain 12 types (three rod-shaped and one block-shaped for each type) of sintered compacts. At this time, the processing temperature was adjusted so that the sintered relative density of the samples was within the range of 94 - 98% in each case.

[0063] Each of the obtained sintered compacts was charged into 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 Ar. Almost no graying (oxygen deficiency absorption) was confirmed in appearance for any of the obtained HIP compacts (hot isostatic pressed compacts). However, as a precaution, each of the obtained HIP compacts (hot isostatic pressed compacts) was annealed at 1450 °C for 30 hours in an air heating furnace while performing lot control for each to take measures to sufficiently recover oxygen deficiency. Thus, a total of 12 types of ceramic samples for the examples and comparative examples were prepared.

[0064] Subsequently, among each of the obtained ceramic samples, first, for the rod-shaped samples, each was ground and polished so as to have a uniform rod shape with a diameter of 5 mm and a length of 25 mm, and the optical both end faces of each sample were finally optically polished with an optical surface accuracy of λ / 8 (when the measurement wavelength λ = 633 nm).

[0065] For each of the samples obtained as described above, the total light transmittance and the forward scattering rate were measured as follows. (Measurement methods for total light transmittance and forward scattering rate) The total light transmittance and forward scattering rate were measured with reference to JIS K7105 (ISO 13468-2:1999) and JIS K7136 (ISO 14782:1999). Using a spectrophotometer V-670 manufactured by JASCO Corporation, the measurement was carried out at a wavelength of 1064 nm. First, for the measurement of the total light transmittance, the light dispersed by the spectroscope without setting a work (sample) in the spectrophotometer V-670 was irradiated, the light was received by an integrating sphere pre-set in the apparatus, and the collected light was received by a detector. The obtained illuminance was designated as I0. Subsequently, the work was set in the apparatus, and this time the dispersed light was incident on the work, and the transmitted light was collected again by the integrating sphere and received by the detector. The obtained illuminance was designated as I and calculated by the following formula. Total light transmittance (% / 25 mm) = I / I0 × 100 Next, for the measurement of the forward scattering rate, from the state where the above-mentioned work was set, except that the reflector on the back surface of the integrating sphere was removed, the same measurement system was used. The dispersed light was again incident on the work, and the transmitted light was collected again by the integrating sphere and received by the detector. The obtained illuminance represents the scattering component other than the direct transmission component, and this was designated as I S and calculated by the following formula. Forward scattering rate (% / 25 mm) = I S / I0 × 100

[0066] In consideration of the influence of reproducibility and variation, three measurements were made for each condition, and the average value was calculated as the total light transmittance and forward scattering rate values of each sample. Also, when the beam diameter was made thicker than 3 mmφ, the beam skirt began to be kicked at the outer periphery of the 5 mmφ diameter sample, so this beam diameter of 3 mmφ was defined as a state where light was incident on almost the entire surface of the work.

[0067] For each of the rod-shaped samples (three sets each) of the conditions of the examples and comparative examples prepared by final optical polishing in the above manner, an antireflection film (AR coat) designed so that the central wavelength was 1064 nm was coated on both optical end faces. The Verdet constant was measured for each of the obtained rod-shaped samples in the following manner. (Method for Measuring Verdet Constant) The Verdet constant V was determined based on the following formula. The magnitude (H) of the magnetic field applied to the sample was a value calculated by simulation from the dimensions of the above 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 (in this case, 0.025 m).) The average value of the Verdet constants of three samples prepared under each condition was taken as the Verdet constant under each condition.

[0068] Subsequently, the block-shaped samples of each condition of the examples and comparative examples prepared earlier were cut and ground to produce samples in the shape of a triangular prism with a side length of 20 mm, a thickness of 10 mm, and two right-angled isosceles triangles on the bottom surface. At this time, the angle of the right-angled part of the triangular prism was controlled to be 90 degrees ± 0.1 degrees. Then, the two surfaces constituting the right-angled part of the triangular prism were lapped and polished to form flat surfaces. Using the right-angled isosceles triangular prism block-shaped samples of each condition of the examples and comparative examples thus obtained, the average value (dn(1064) / dt) of the temperature coefficient of refractive index at wavelengths of 1064 nm and temperatures of 20, 30, and 40 °C ave was measured in the following manner. ((dn(1064) / dt) ave (Measurement method) The average value (dn(1064) / dt) of the temperature coefficient of refractive index of terbium-containing paramagnetic garnet transparent ceramics at wavelengths of 1064 nm and temperatures of 20, 30, and 40 °C ave was measured in accordance with JIS B7071-2 (Method for Measuring Refractive Index of Optical Glass - Part 2: V-Block Method). The measuring device selected was a precision refractometer, the Carl Zeiss KPR-3000 type manufactured by Shimadzu Corporation, and the measurement was carried out in the fully automatic measurement mode of the device. Specifically, a V-block prism made of optical glass with a known refractive index N for high refractive index samples was selected and set in the device, and each block-shaped sample prepared as described above was placed on it. Four types of standard laser lights with different wavelengths (laser lights with wavelengths of 785.4 nm, 830.5 nm, 1310 nm, and 1550 nm (standard equipment of the device)) were incident from above the normal of the wall surface of the prism, and at this time, the light refracted by the V-block prism and the block-shaped sample that passed through was emitted from the wall surface on the opposite side of the prism. The refractive index n of the block-shaped sample to be measured for each wavelength was calculated using the following formula from the angle (deviation angle i * ). At this time, the temperatures of the V-block prism and the block sample (sample temperature) were set to 20 °C, 30 °C, and 40 °C, and the refractive indices for each of the four wavelengths at each sample temperature were measured. The sample temperature was controlled to 20 °C, 30 °C, and 40 °C for the sample stage on which the prism and the block-shaped sample were placed, and the samples were left stationary while monitoring the temperature of the samples themselves. Furthermore, the surface temperatures of the samples after 5 minutes had elapsed when the temperature had stabilized were counted as 20 °C, 30 °C, and 40 °C, respectively. n = {N 2 + sin i * · (N 2 - sin 2 i * ) 1 / 2} 1 / 2 Next, from the values of the refractive indices at the four wavelengths calculated for each of the sample temperatures of 20 °C, 30 °C, and 40 °C, the refractive indices for each of the sample temperatures of 20 °C, 30 °C, and 40 °C at a wavelength of 1064 nm were derived based on the Sellmeier dispersion formula. The temperature coefficients of the refractive indices dn(1064,20) / dt, dn(1064,30) / dt, and dn(1064,40) / dt at wavelengths of 1064 nm and temperatures of 20, 30, and 40 °C were obtained respectively, and the average value of these was taken as the average value (dn(1064) / dt) of the temperature coefficients of the refractive indices dn(1064,20) / dt, dn(1064,30) / dt, and dn(1064,40) / dt of the transparent ceramics to be measured at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C avewas used. The above results are summarized in Table 2.

[0069]

Table 2

[0070] From the results in Table 2, when fabricating the transparent ceramics of the present invention, first, in Comparative Example 1 and Comparative Example 4 that do not contain any yttrium, the total light transmittance was less than 84%, and the value of the forward scattering rate also exceeded 1.0%. This means that a large number of scattering sources were generated in the transparent ceramics, indicating that when a high-power laser was incident, the thermal lens effect was enhanced and it was difficult to use for industrial applications. Conversely, in each sample of Comparative Example 2, 3, 5, and 6 where the ratio of yttrium (x in Equation (1)) was more than 0.59 (i.e., the ratio of terbium 1 - x - y was 0.4 or less), the Verdet constant was less than 32 rad / (T·m). In this case, since it was necessary to make the size larger than that of an optical isolator using a TGG crystal, which is a conventional Faraday rotator material, it could not be mounted on a future high-power laser system aiming for miniaturization, which became a problem. For Examples 1 to 6, in all cases, the total light transmittance was 84% or more, the forward scattering rate was 1.0% or less, and the Verdet constant was 32 rad / (T·m) or more, ensuring that it could be mounted on a high-power laser system. Furthermore, all the samples of these Examples 1 to 6 had an average value of the temperature coefficient of refractive index (dn(1064) / dt) at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C ave was 9.0×10 -6 (K -1 ) or less, and it was confirmed that this was approximately half of (dn(1064) / dt) of a conventional material, the TGG crystal. ave The average value of the temperature coefficient of refractive index (dn(1064) / dt) at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C ave ​When the terbium-containing ferromagnetic garnet-type transparent ceramics of the present invention, which is less than half of the existing materials, is mounted on a high-power laser system, the resistance to high-power application is improved by more than twice in essence, making it possible to provide a higher-density high-power laser system that could not be achieved conventionally.

[0071] Although the present invention has been described so far with the above-described embodiments, the present invention is not limited to these embodiments and can be changed within the scope that those skilled in the art can conceive, such as other embodiments, additions, changes, deletions, etc. As long as the effects of the present invention are achieved in any aspect, it is included in the scope of the present invention.

Explanation of Reference Numerals

[0072] 100 Optical isolator 110 Faraday rotator 120 Polarizer 130 Analyzer 140 Magnet

Claims

【Claim 1】 A sintered body of a composite oxide represented by the following formula (1), having a Verdet constant at a wavelength of 1064 nm of 30 rad / (T·m) or more, and an average value (dn(1064) / dt) of the temperature coefficient of refractive index at a wavelength of 1064 nm and temperatures of 20, 30, and 40 °C ave is 9.0×10 -6 (K -1 ) or less, characterized by being terbium-containing paramagnetic garnet-type transparent ceramics. (Tb1-x-yYxScy)3(Al1-zScz)5O12 (1) (where 0.05 ≤ x ≤ 0.4, 0.0005 ≤ y < 0.08, 0.6 < 1 - x - y < 0.95, 0.0004 ≤ z < 0.15, 0.0009 ≤ y + z < 0.2.) Claim 2 Furthermore, the terbium-containing paramagnetic garnet-type transparent ceramics according to claim 1 contain SiO 2 in an amount of more than 0% by mass and 0.1% by mass or less as a sintering aid. Claim 3 A magneto-optical device configured by using the paramagnetic garnet-type transparent ceramics according to Claim 1 or 2 as a magneto-optical material. Claim 4 The magneto-optical device according to Claim 3, which includes the above terbium-containing paramagnetic garnet-type transparent ceramics as a Faraday rotator, and has polarizing materials before and after on the optical axis of the Faraday rotator, and is an optical isolator usable in a wavelength band of 0.9 μm or more and 1.1 μm or less.

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