Paramagnetic garnet-type transparent ceramics, method for producing the same, magneto-optical material, and magneto-optical device

Abstract

To provide a paramagnetic garnet-type transparent ceramic capable of being mounted on a high-power laser processing machine as designed, without quality problems caused by residual oxygen vacancies, and to provide a method for producing the paramagnetic garnet-type transparent ceramics, a magneto-optical material, and a magneto-optical device.SOLUTION: By a producing method in which, in an annealing step at 1,400°C to 1,500°C, when a material diameter of a sintered body is defined as D [mm], an annealing holding time T [hr] satisfies T≥10×D, paramagnetic garnet-type transparent ceramics can be obtained which include a sintered body containing a composite oxide represented by formula (1), wherein an outer diameter of the sintered body is 4 mm or more, a forward scattering value at a wavelength of 350 nm is 1.1% or more, and a forward scattering value at a wavelength of 430 nm is less than 1%. (Tb1-x-yYxScy)3(Al1-zScz)5O12 (1) (wherein 0.05≤x≤0.45, 0<y<0.1, 0.5<1-x-y<0.95, 0.001<z<0.15, and 0<y+z<0.2).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a paramagnetic garnet-type transparent ceramic, a manufacturing method thereof, a magneto-optical material, and a magneto-optical device, and more particularly to a terbium-containing paramagnetic garnet-type transparent ceramic suitable for constituting a magneto-optical device such as an optical isolator, a manufacturing method thereof, and a magneto-optical device using this paramagnetic garnet-type transparent ceramic as a magneto-optical material. [Background technology]

[0002] In recent years, as it has become possible to achieve higher output, the use of laser processing machines using fiber lasers has become increasingly common. However, when external light enters the laser light source built into the laser processing machine, the resonance state becomes unstable, causing the oscillation state to be disrupted. 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 significantly disrupted. To prevent this, an optical isolator is usually installed before the light source.

[0003] An optical isolator consists of a Faraday rotator, a polarizer placed on the light input side of the Faraday rotator, and an analyzer placed on the light output side of the Faraday rotator. The Faraday rotator is used by applying a magnetic field parallel to the light's direction of propagation. The polarization of the light rotates in only one direction, whether it is traveling forward or backward through the Faraday rotator. Furthermore, the Faraday rotator's length is adjusted so that the polarization of the light rotates exactly 45 degrees. If the polarization planes of the polarizer and analyzer are offset 45 degrees from the direction of rotation of the forward light, the polarization of the forward light will be transmitted because it coincides with the polarizer position and the analyzer position. On the other hand, the polarization of the backward light will be rotated 45 degrees in the opposite direction to the polarization plane of the polarizer, which is offset 45 degrees from the analyzer position. As a result, the polarization plane of the returning light at the polarizer position is shifted by 45 degrees - (-45 degrees) = 90 degrees relative to the polarization plane of the polarizer, and it cannot pass through the polarizer. In this way, it functions as an optical isolator, allowing forward light to pass through and exit, while blocking backward returning light.

[0004] As a material used for the Faraday rotator that constitutes the optical isolator, a terbium-containing paramagnetic transparent ceramic sintered body (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 For example, the composition and transparency are described in detail in JP 2019-199386 A (Patent Document 1) and WO 2022 / 054596 A (Patent Document 2).

[0005] The manufacturing method is described in detail in JP 2019-104674 A (Patent Document 3), JP 2019-207340 A (Patent Document 4), JP 2019-199078 A (Patent Document 5), JP 2019-199079 A (Patent Document 6), WO 2022 / 054593 A (Patent Document 7), WO 2022 / 054515 A (Patent Document 8), JP 2023-064774 A (Patent Document 9), JP 2023-082887 A (Patent Document 10), JP 2023-128125 A (Patent Document 11), etc.

[0006] Further details regarding quality etc. are provided in Patent Document 7, International Publication No. 2022 / 054595 (Patent Document 12), International Publication No. 2022 / 085107 (Patent Document 13), International Publication No. 2022 / 054592 (Patent Document 14), International Publication No. 2022 / 054594 (Patent Document 15), and JP 2023-128117 A (Patent Document 16).

[0007] In actual industrial applications, the diameter of the Faraday rotator material used varies depending on the output power grade of the laser processing machine. For example, for high-power laser applications up to 100 W, a thin Faraday rotator with an outer diameter of 4 mm or less can maintain sufficient optical quality, but for next-generation high-power laser applications such as 200 W and 300 W, the outer diameter must be increased to 6 mm or 8 mm in order to maintain a spot diameter change rate of the output beam of 10% or less. Those skilled in the art can easily understand that for ultra-high-power laser applications in the kW range, the outer diameter must be increased to 10 mm or more in order to maintain a spot diameter change rate of 10% or less.

[0008] However, simply increasing the diameter of the material makes it difficult to expand the practical laser power application range, because as the material diameter increases, it becomes more difficult to remove defects, especially oxygen vacancies, remaining in the material.

[0009] However, there have been no prior art examples that mention a manufacturing method for controlling the degree of release of material defects, particularly oxygen vacancies, depending on the thickness of the Faraday rotator. Incidentally, the oxygen vacancies can be reduced by annealing. Furthermore, the annealing process is also mentioned in the text of prior art examples such as Patent Document 1. However, these prior art examples only indicate the preferred range of annealing conditions, and do not provide any examples or suggestions regarding the accurate control of annealing conditions depending on the thickness of the Faraday rotator. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2019-199386 [Patent Document 2] International Publication No. 2022 / 054596 [Patent Document 3] Japanese Patent Application Publication No. 2019-104674 [Patent Document 4] Japanese Patent Application Publication No. 2019-207340 [Patent Document 5] Japanese Patent Application Publication No. 2019-199078 [Patent Document 6] Japanese Patent Application Publication No. 2019-199079 [Patent Document 7] International Publication No. 2022 / 054593 [Patent Document 8] International Publication No. 2022 / 054515 [Patent Document 9] Japanese Patent Application Publication No. 2023-064774 [Patent Document 10] Japanese Patent Application Publication No. 2023-082887 [Patent Document 11] Japanese Patent Publication No. 2023-128125 [Patent Document 12] International Publication No. 2022 / 054595 [Patent Document 13] International Publication No. 2022 / 085107 [Patent Document 14] International Publication No. 2022 / 054592 [Patent Document 15] International Publication No. 2022 / 054594 [Patent Document 16] Japanese Patent Application Publication No. 2023-128117 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in view of the above circumstances, and aims to provide a paramagnetic garnet-type transparent ceramics, a magneto-optical material, and a magneto-optical device, which are sintered bodies of paramagnetic garnet-type oxides containing at least yttrium, terbium, and aluminum as main components, with the volume molar concentration of terbium being equal to or higher than that of yttrium, and which are free from quality problems due to residual oxygen deficiency regardless of the size of the sintered body and can be mounted in a high-power laser processing machine as designed, as well as a manufacturing method thereof, a magneto-optical material, and a magneto-optical device. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides, as a first aspect, a method for producing a paramagnetic garnet-type transparent ceramic including a sintered body containing a composite oxide represented by the following formula (1): (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (In the formula, 0.05≦x≦0.45, 0 <y<0.1、0.5<1-x-y<0.95、0.001<z<0.15、0<y+z<0.2である。) The method includes a step of sintering the composite oxide compact to obtain a sintered body, a step of hot isostatically pressing (HIP) the sintered body, and a step of annealing the HIP-treated sintered body, wherein in the annealing step, the annealing temperature is 1400°C or higher and 1500°C or lower, and the annealing holding time T [hr] is calculated based on the following formula (2) when the material diameter of the sintered body to be annealed is D [mm]: T≧10×D (2) Meet the following.

[0013] The method may further include an outer periphery grinding step of grinding the outer periphery of the sintered body before the annealing treatment step or grinding the outer periphery of the sintered body after the annealing treatment step to process it into a cylindrical body having a desired outer diameter.

[0014] When the outer periphery grinding is carried out after the annealing treatment step, it is preferable to heat treat the outer periphery ground sintered body at a temperature of 1300° C. or higher for 5 hours or more.

[0015] In a second aspect, the present invention provides a paramagnetic garnet-type transparent ceramic including a sintered body containing a composite oxide represented by the following formula (1): (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (In the formula, 0.05≦x≦0.45, 0 <y<0.1、0.5<1-x-y<0.95、0.001<z<0.15、0<y+z<0.2である。) The sintered body has an outer diameter of 4 mm or more, a forward scattering value of 1.1% or more at a wavelength of 350 nm, and a forward scattering value of less than 1% at a wavelength of 430 nm.

[0016] The sintered body may further contain SiO2 as a sintering aid in an amount of more than 0 mass % and 0.1 mass % or less.

[0017] In a third aspect, the present invention provides a magneto-optical material, which includes the above-mentioned paramagnetic garnet-type transparent ceramics.

[0018] A fourth aspect of the present invention is a magneto-optical device that is constructed using the magneto-optical material.

[0019] The magneto-optical device of the present invention may be an optical isolator that includes the magneto-optical material as a Faraday rotator and has polarizing materials in front of and behind the optical axis of the Faraday rotator and is usable in the wavelength range of 0.9 μm or more and 1.1 μm or less. [Effects of the Invention]

[0020] As described above, according to the present invention, by adjusting the annealing conditions in the annealing treatment step to correspond to the outer diameter of the sintered body, it is possible to provide a paramagnetic garnet-type transparent ceramic that can be mounted on a high-power laser processing machine as designed and that does not suffer from quality problems due to residual oxygen vacancies, regardless of the size of the Faraday rotator, whose diameter increases in proportion to the increase in laser output power, as well as a manufacturing method thereof, a magneto-optical material, and a magneto-optical device. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view schematically showing an example of an optical isolator using the paramagnetic garnet-type transparent ceramic according to the present invention as a Faraday rotator. [Figure 2]1 is a graph showing the total light transmittance versus wavelength of the paramagnetic garnet-type transparent ceramic of Example 2. [Figure 3] 1 is a graph showing forward scattering versus wavelength of the paramagnetic garnet-type transparent ceramic of Example 2. [Figure 4] 10 is a graph showing the total light transmittance versus wavelength of the paramagnetic garnet-type transparent ceramic of Comparative Example 2. [Figure 5] 10 is a graph showing forward scattering versus wavelength of the paramagnetic garnet-type transparent ceramic of Comparative Example 2. [Figure 6] 1 is a graph showing the total light transmittance versus wavelength of the paramagnetic garnet-type transparent ceramic of Example 3. [Figure 7] 10 is a graph showing forward scattering versus wavelength of the paramagnetic garnet-type transparent ceramic of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0022] [1. Manufacturing method of paramagnetic garnet-type transparent ceramics] First, one embodiment of a method for producing a paramagnetic garnet-type transparent ceramic according to the present invention will be described. This embodiment is a method for producing a paramagnetic garnet-type transparent ceramic including a sintered body containing a complex oxide represented by the following formula (1): (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (In the formula, 0.05≦x≦0.45, 0 <y<0.1、0.5<1-x-y<0.95、0.001<z<0.15、0<y+z<0.2である。) The process includes a step of molding the raw material to obtain a molded body, a step of degreasing the molded body to obtain a degreasing body, a step of sintering the degreasing body to obtain a sintered body, a step of densifying the sintered body by hot isostatic pressing (HIP), and a step of annealing the densified sintered body.

[0023] The sintered body preferably further contains SiO2 as a sintering aid in an amount of more than 0% by mass and not more than 0.1% by mass. The SiO2 content in this range is preferable because it improves the transparency of the resulting paramagnetic garnet-type ceramics to a practically acceptable level and stabilizes it. The raw materials used and each step are described below.

[0024] [1-1. Raw materials] The raw materials used in this embodiment are oxide powders of terbium, yttrium, scandium, and aluminum. The purity of the raw materials is preferably 99.9% by mass or more, and particularly preferably 99.99% by mass or more. These elements are weighed out in predetermined amounts, and silicon oxide (SiO2) is added in an amount of more than 0% by mass and 0.1% by mass or less. The mixture is then processed using a wet ball mill, bead mill, or jet mill.

[0025] Various organic additives may be added to the garnet-type oxide powder raw material used in this embodiment for the purpose of improving the quality stability and yield in the subsequent ceramic manufacturing process. In this embodiment, there is no particular limitation on these additives. That is, various dispersants, binders, lubricants, plasticizers, etc. can be suitably used. However, it is preferable to select high-purity organic additives that do not contain unnecessary metal ions. Furthermore, the order of addition of each organic additive must be properly designed so as not to interfere with the control of the properties (particle size distribution, etc.) of the raw material to be manufactured.

[0026] [1-2. Molding process] In this embodiment, the raw material powder can be press-molded into a desired shape, or the wet slurry can be cast directly to produce a green body. For press molding, conventional press molding methods can be used. Examples of suitable methods include the uniaxial press, which is a common method of filling a mold and applying pressure from a specific direction, and the cold isostatic pressing (CIP) or warm isostatic pressing (WIP) processes, which involve isostatically pressing a sealed, deformable, waterproof container. The applied pressure can be adjusted appropriately while checking the relative density of the resulting green body. For example, controlling the pressure within a pressure range of approximately 300 MPa or less, which is compatible with commercially available CIP and WIP equipment, can reduce manufacturing costs. Alternatively, hot pressing, spark plasma sintering, and microwave heating processes, which combine the molding process with sintering, can also be used. In the case of slip casting, other molding methods such as pressure slip casting, centrifugal slip casting, and extrusion molding can also be used by optimizing the shape and size of the oxide powder as the starting material and the combination of various organic additives.

[0027] In order to produce sintered bodies of various outer diameters for the paramagnetic garnet-type transparent ceramics of this embodiment, it is preferable to prepare dedicated uniaxial press molding jigs with different inner diameters. This makes it possible to obtain paramagnetic garnet-type transparent ceramics of the desired outer diameter. Note that the length of the molding jig will vary depending on the material and size of the magnet surrounding the material, so it is advisable to prepare a molding jig that is a little longer.

[0028] [1-3. Degreasing process] In the manufacturing method of this embodiment, a normal degreasing process can be suitably used. That is, a temperature-raising degreasing process using a heating furnace can be performed. The type of atmospheric gas used is not particularly limited, and air, oxygen, hydrogen, etc. can be suitably used. The degreasing temperature is preferably a temperature at which the organic components of the organic additives added can be sufficiently decomposed and removed, and is preferably kept below 1000°C.

[0029] [1-4. Sintering process] In the manufacturing method of this embodiment, a general sintering process can be suitably used. That is, a heat sintering process such as a resistance heating method or an induction heating method can be suitably used. In addition, the atmosphere at this time is preferably a reduced pressure environment (vacuum). Furthermore, the degree of vacuum is preferably 1×10 -3 Torr or less is preferable. If the degree of vacuum is controlled within this range, oxygen gas desorbed from the degreased body can be sufficiently discharged to the center of any size sintered body, from a small sintered body with a diameter of about 2 mm to a large sintered body with a diameter of 8 mm or more.

[0030] The sintering temperature in the sintering step of this embodiment is preferably 1400 to 1780° C., particularly preferably 1500 to 1750° C. A sintering temperature in this range is preferable because it promotes densification while suppressing heterophase precipitation.

[0031] In the sintering process of this embodiment, a sintering holding time of several hours is sufficient, but it is preferable to control the relative density of the sintered body in the range of 93.8% to 97.2%. Control of the sintered density can be carried out by conducting several preliminary experiments.

[0032] [1-5. Hot isostatic pressing (HIP) treatment process] In the manufacturing method of this embodiment, an additional step of hot isostatic pressing (HIP) can be added after the sintering step. The pressurizing gas medium used here can be an inert gas such as argon or nitrogen, or Ar-O2. The pressure applied by the pressurizing gas medium is preferably 50 to 300 MPa, more preferably 100 to 300 MPa. At a pressure of less than 50 MPa, the transparency improvement effect may not be obtained, while at a pressure of more than 300 MPa, further transparency improvement cannot be obtained even with increased pressure, and the load on the equipment may be excessive, potentially damaging the equipment. For simplicity, it is preferable to apply a pressure of 196 MPa or less, which can be used with commercially available HIP equipment.

[0033] The treatment temperature (predetermined holding temperature) is set in the range of 1100 to 1780°C, preferably 1200 to 1730°C, and more preferably between 1400°C and 1730°C. Heat treatment temperatures above 1780°C are undesirable because they increase the risk of oxygen vacancies. Heat treatment temperatures below 1100°C are also undesirable because they do not improve the transparency of the sintered body. Furthermore, as will be described in detail later, the annealing temperature is 1400 to 1500°C, so it is more preferable to perform the HIP treatment at a temperature higher than the annealing temperature. There are no particular restrictions on the holding time of the heat treatment temperature, but holding it for too long is undesirable because it increases the risk of oxygen vacancies. Typically, it is preferably set in the range of 1 to 3 hours.

[0034] The heater material, insulator, and processing vessel used in the HIP process are not particularly limited. Graphite, molybdenum (Mo), tungsten (W), and platinum (Pt) are suitable. Yttrium oxide and gadolinium oxide are also suitable for the processing vessel. Platinum (Pt) is particularly suitable for processing temperatures below 1500°C, as it can be used for the heater material, insulator, and processing vessel, and Ar-O can be used as the pressurized gas medium, preventing oxygen deficiency during the HIP process. Graphite is preferred for processing temperatures above 1500°C. However, in this case, selecting a graphite, molybdenum (Mo), or tungsten (W) processing vessel, and then using a double-walled container made of yttrium oxide or gadolinium oxide and filling the container with an oxygen-releasing material minimizes the amount of oxygen deficiency during the HIP process.

[0035] [1-6. Resintering process] In the manufacturing method of this embodiment, after the HIP treatment, re-sintering may be performed at a temperature higher than the HIP treatment temperature for 8 hours or more. However, it is not preferable to set the upper limit temperature above 1780°C because this increases the risk of oxygen deficiency. The re-sintering time should be longer for sintered bodies with a higher laser output grade.

[0036] [1-7. Annealing process] In the manufacturing method of this embodiment, after the re-sintering process is completed, it is preferable to perform an annealing process (oxygen deficiency recovery process) in an oxidizing atmosphere such as air at an annealing temperature that is equal to or lower than the HIP treatment temperature and is between 1400°C and 1500°C inclusive, in order to recover oxygen deficiencies in the obtained transparent ceramic sintered body. Note that it is essential that the holding time T [hr] be set within a range that satisfies the following formula, where D [mm] is the material diameter of the transparent ceramic sintered body: T≧10×D

[0037] Here, the material diameter D [mm] refers to the outer diameter of the sintered body to be annealed. The outer diameter of the transparent ceramic sintered body may be the outer diameter of the material after re-sintering, or it may be the outer diameter of the material after a peripheral grinding process, in which the sintered body is further ground to the desired outer dimensions after re-sintering, as will be described in detail later.

[0038] Setting the annealing holding time T within the range of the above formula allows oxygen vacancies in all sintered bodies to be recovered regardless of the material diameter D, which is preferable because it makes it possible to guarantee an optical effective diameter that matches the outer dimensions of the sintered body. Furthermore, ensuring an optical effective diameter that matches the outer dimensions of the sintered body makes it possible to design a high-power laser beam that matches the optical effective diameter. More specifically, the larger the beam diameter, the higher the applicable rated laser output, which is preferable.

[0039] [1-8. Periphery grinding process] In the manufacturing method of this embodiment, a peripheral grinding step may be performed before or after the annealing treatment, in which the sintered body is ground to the desired outer dimensions. In the peripheral grinding step, any widely known grinding method can be used as long as it can process the sintered body into a cylindrical body with the desired outer diameter. It is generally known that the outer diameter of a sintered body varies in finished size due to variations in the degree of shrinkage. Therefore, in order to mount the sintered body in optical equipment such as a fiber laser processing machine, it is preferable that the outer diameter be machined to a uniform size with high precision using a centerless peripheral grinding process or the like.

[0040] If the outer periphery is ground after the annealing treatment, it is preferable to carry out a heat treatment for 5 hours or more at a temperature of 1300°C or higher after the outer periphery grinding in order to remove the outer periphery processing strain layer caused by the outer periphery grinding. As a result, whether the outer periphery is ground after resintering and then annealed, or the outer periphery is ground after resintering and then annealed, followed by heat treatment to remove the strain layer, it is possible to provide a high-quality paramagnetic garnet-type transparent ceramic that is free from defect absorption and strain defects.

[0041] [1-9. Optical polishing process] In the manufacturing method of this embodiment, it is preferable to optically polish both end faces on the optically utilized axis of the paramagnetic garnet-type transparent ceramics that have undergone the above-described series of manufacturing steps. The optical surface precision at this time is preferably λ / 2 or less for grades with laser powers up to 40 W (up to a practical 30 W with a safety margin) when the measurement wavelength is λ = 633 nm, and λ / 8 or less is particularly preferable for laser powers higher than this. Furthermore, regarding the optical surface roughness, it is preferable for the precision-polished surface to have an arithmetic mean height Sa ≦ 0.70 nm and a root-mean-square height Sq ≦ 0.89 nm, since this is compatible with all laser power grades. An anti-reflection coating (AR coating) tailored to the laser wavelength of the laser processing machine may be formed on the optically polished surface as described above. This allows the provision of paramagnetic garnet-type transparent ceramics compatible with all laser power grades.

[0042] [2. Paramagnetic garnet-type transparent ceramics] Next, an embodiment of the paramagnetic garnet-type transparent ceramic according to the present invention will be described. The paramagnetic garnet-type transparent ceramic according to this embodiment includes a sintered body containing a complex oxide represented by the following formula (1): (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (In the formula, 0.05≦x≦0.45, 0 <y<0.1、0.5<1-x-y<0.95、0.001<z<0.15、0<y+z<0.2である。) The outer diameter of this sintered body is 4 mm or more, and the forward scattering value at a wavelength of 350 nm is 1.1% or more, and the forward scattering value at a wavelength of 430 nm is less than 1%. Paramagnetic garnet-type transparent ceramics with such forward scattering properties can be installed in high-power laser processing machines as designed, without quality problems caused by remaining oxygen vacancies. Furthermore, paramagnetic garnet-type transparent ceramics with such forward scattering properties can be obtained by the manufacturing method for paramagnetic garnet-type transparent ceramics explained above.

[0043] [3. Magneto-optical materials and magneto-optical devices] Furthermore, an embodiment of the magneto-optical material and magneto-optical device according to the present invention will be described. The magneto-optical material of this embodiment includes the above-mentioned paramagnetic garnet-type transparent ceramic. Furthermore, the magneto-optical device of this embodiment is constructed using the above-mentioned paramagnetic garnet-type transparent ceramic. Specifically, it is preferable to construct and use a magneto-optical device by applying a magnetic field parallel to the optical axis of the above-mentioned paramagnetic garnet-type transparent ceramic, and then setting a polarizer and an analyzer so that their optical axes are shifted by 45 degrees from each other. In particular, the above-mentioned terbium-containing paramagnetic garnet-type transparent ceramic is suitable for use as a Faraday rotator in an optical isolator for a wavelength of 0.9 to 1.1 μm as a magneto-optical device.

[0044] FIG. 1 is a cross-sectional view schematically illustrating an example of an optical isolator, which is a magneto-optical device including a Faraday rotator made of the transparent ceramic of this embodiment as an optical element. As shown in FIG. 1, the optical isolator 100 includes, inside its housing 102, a Faraday rotator 110 made of the transparent ceramic, a polarizer 120 made of a polarizing material, and an analyzer 130. These are arranged in the order of polarizer 120, Faraday rotator 110, and analyzer 130 along the optical axis 104 of the Faraday rotator. The polarization vibration plane of the polarizer 120 and the polarization vibration plane of the analyzer 130 are arranged so that the relative angle is 45°. The optical isolator 100 also includes, inside the housing 102, a magnet 140 on at least one side of the Faraday rotator 110 for applying a magnetic field to the Faraday rotator 110.

[0045] Such an optical isolator 100 can be suitably used in an industrial fiber laser device (not shown). The optical isolator can 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. [Example]

[0046] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0047] [Examples 1 to 8, Comparative Examples 1 to 8] 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. We also 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.

[0048] Using the above raw materials, the mixing ratio was adjusted to prepare composite oxide raw materials with the two types of final compositions shown in Table 1. To adjust the mixing ratio, each oxide powder was weighed and mixed so that the number of moles of terbium, yttrium, aluminum, and scandium were the molar ratios of each composition shown in Table 1. Next, TEOS was weighed and added to each raw material so that the amount added, converted to SiO2, was the mass % shown in Table 1.

[0049] [Table 1]

[0050] The materials were then dispersed and mixed in ethanol using an alumina ball mill, taking care to prevent contamination. The processing time was 20 hours. Subsequently, spray drying was performed to produce granular raw materials with an average particle size of 20 μm. Ten compacts were fabricated for each of the two oxide raw materials using four different uniaxial press molding jigs with different inner diameters. Specifically, compacts were fabricated using uniaxial press molding jigs with inner diameters of 7 mm, 9 mm, 10.8 mm, and 12.5 mm. The raw material loading amount was adjusted so that all compacts were 30 mm long. All compacts were then subjected to isostatic pressing at a pressure of 198 MPa to obtain CIP compacts. All of the resulting compacts were degreased in a muffle furnace at 800°C for 3 hours to obtain degreased compacts.

[0051] Next, all degreased compacts were placed in a vacuum sintering furnace at a sintering temperature of 1500-1570°C for 3 hours to obtain sintered compacts with a sintered density of 93.8% to 97.2%. Each of the obtained sintered compacts was placed in a HIP furnace made of a carbon heater and subjected to HIP treatment in Ar under conditions of 200 MPa, 1600°C, and 3 hours. All of the obtained sintered compacts had a relative density of 99.9% or higher. Furthermore, they had a bluish gray appearance (oxygen deficiency absorption).

[0052] All HIP-treated sintered bodies were then heat-treated in a vacuum sintering furnace at a sintering temperature of 1730°C for 15 hours in an attempt to eliminate residual bubbles throughout the entire sintered body, including the center. As a result, the outer dimensions (outer diameter after sintering D0) of each sintered body formed using uniaxial press molding jigs of 7 mm, 9 mm, 10.8 mm, and 12.5 mm had shrunk to approximately 6 mm, 7.5 mm, 9 mm, and 10.5 mm.

[0053] Each of the resulting ceramic sintered bodies was then subjected to a peripheral grinding process using a centerless peripheral grinder to obtain the desired outer diameter. As a result, the four ceramics were ground to outer diameters of 4 mm, 6.5 mm, 8 mm, and 9.5 mm, respectively. These outer diameters after grinding were defined as the material diameter D.

[0054] Next, five of each of the obtained ceramic sintered bodies were subjected to annealing treatment at 1450°C (oxygen deficiency recovery treatment) in an atmospheric heating furnace for the holding time shown in Table 2 for each composition and outer diameter dimension (material diameter D).

[0055] [Table 2]

[0056] Afterwards, each was cut to a uniform length of 20 mm and precision-polished. The optical end faces of the samples were finished to an optical surface precision of λ / 8 or less (when the measurement wavelength λ was 633 nm), with the average roughness of the precision-polished surface being arithmetic mean height Sa ≦ 0.70 nm and root-mean-square height Sq ≦ 0.89 nm. It is known that even if the length is the same, the larger the outer diameter, the greater the applied magnetic field required to rotate the incident light 45 degrees. While we will not go into detail here, to function as an actual Faraday rotator, it is essential to adjust the material and thickness of the external magnet barrel, the magnetic field application pattern, etc., appropriately to match the outer diameter of each sintered compact.

[0057] For each sample obtained as described above, the total light transmittance and forward scattering rate were measured as follows.

[0058] (Method for measuring total light transmittance and forward scattering) The total light transmittance and forward scattering were measured with reference to JIS K7105 (ISO 13468-2:1999) and JIS K7136 (ISO 14782:1999) using a JASCO V-670 spectrophotometer at three wavelengths: 350 nm, 430 nm, and 1064 nm.

[0059] To measure total light transmittance, the spectrophotometer V-670 is irradiated with light dispersed by a spectroscope without a workpiece (sample) set on it, and this light is received by an integrating sphere that is pre-installed in the device, and the collected light is received by a detector. The obtained illuminance is designated as I0, and then the workpiece is set on 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 obtained illuminance is designated as I and is calculated using the following formula. Total light transmittance (% / 20mm)=I / I0×100

[0060] Forward scattering measurements are performed using the same measurement system as above, 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 then incident on the workpiece again, and the transmitted light is collected again by the integrating sphere and received by the detector. The obtained illuminance represents the scattered components other than the linear transmitted component, and this is called I S was calculated using the following formula: Forward scattering rate (% / 20mm)=I S / I0×100

[0061] To consider the effects of reproducibility and variation, measurements were taken for five samples under each condition, and the average values ​​were calculated to determine the total light transmittance and forward scattering values ​​for each sample.However, because this terbium-containing paramagnetic garnet-type transparent ceramic has band gap absorption in the ultraviolet region with wavelengths of 380 nm or less, the integrating sphere transmittance at a wavelength of 350 nm was <4% in all cases.

[0062] The beam diameter used was 2 mm, regardless of the diameter of the sintered body, and the incident position was adjusted to be approximately the center of the optically effective surface. The results are summarized in Table 3. For Example 2, Comparative Example 2, and Example 3, data on total light transmittance and forward scattering rate versus wavelength were also obtained for the entire wavelength range from 350 nm to 1450 nm, and these results are shown in Figures 2 to 7.

[0063] [Table 3]

[0064] From the results in Table 3, in the groups of Examples 1 to 8, in which the annealing holding time T [hr], where D [mm] is the material diameter after the peripheral grinding of the sintered body, satisfies the range of T≧10×D, the forward scattering value at a wavelength of 350 nm was 1.1% or more in all cases. On the other hand, in the groups of Comparative Examples 1 to 8, in which the relationship between the material diameter D [mm] and the annealing holding time T [hr] was outside the range of T≧10×D, the forward scattering value at a wavelength of 350 nm was less than 1% in all cases.

[0065] The significance of these differences will be considered in more detail using Figures 2 to 7. First, regarding the total light transmittance, in all cases shown in Figure 2 (Example 2), Figure 4 (Comparative Example 2), and Figure 5 (Example 3), the total light transmittance drops to <4% in the wavelength range of 380 nm or less due to band gap absorption. On the other hand, looking at the forward scattering graphs in Figures 3 (Example 2) and 7 (Example 3), it can be seen that the apparent forward scattering rate increases in the wavelength range of 390 nm or less. It is generally known that trivalent terbium ions emit fluorescence at wavelengths of around 545 nm due to ff excitation transitions when irradiated with ultraviolet light of 390 nm or less. Therefore, it is reasonable to assume that the increase in apparent forward scattering rate at wavelengths of 390 nm or less in Examples 2 and 3 is due to the detection of this terbium fluorescence by the device. However, the forward scattering rate graph in Figure 5 (Comparative Example 2) does not confirm an increase in apparent forward scattering rate in the wavelength range of 390 nm or less. It is reasonable to consider that this is because the annealing holding time was insufficient, leaving a small amount of defects such as oxygen vacancies, which resulted in the energy from the ff excited transition being trapped by the defects and causing non-radiative recombination.

[0066] The above consideration can be rephrased as meaning that by checking whether or not there is an increase in the apparent forward scattering rate in the wavelength range of 390 nm or less, it is possible to determine whether or not there are residual defects in the manufactured transparent ceramic sintered body.

[0067] In addition, in all of the graphs in Figures 2, 4, and 6, it can be seen that the total light transmittance at a wavelength of 488 nm drops significantly. It is generally known that trivalent terbium ions have a large excitation wavelength at a wavelength of 488 nm. Therefore, it is reasonable to consider that the drop in the total light transmittance at a wavelength of 488 nm is also due to excitation absorption by the trivalent terbium ions. On the other hand, the forward scattering graphs in Figures 3, 5, and 7 show that the apparent forward scattering rate increases even at a wavelength of 488 nm, and that the presence or degree of this increase is linked to that of the apparent forward scattering rate at wavelengths of 390 nm or less. This is likely due to the fact that the excitation transition energy at a wavelength of 488 nm, like the excitation transition energy in the ultraviolet region below 390 nm, also emits fluorescence at a wavelength of around 545 nm, and that the intensity of the fluorescence emission depends on the concentration of point defects (mainly oxygen vacancies in the present invention) caused by the material. That is, the higher the concentration of defects such as oxygen vacancies, the more excitation energy is trapped in the defect sites and recombines non-radiatively, resulting in a decrease in the fluorescence intensity.

[0068] Furthermore, as shown in Table 3, the forward scattering values ​​at a wavelength of 430 nm were comparable, less than 1%, for both the groups of Examples 1 to 8 and the groups of Comparative Examples 1 to 8. This is likely due to the absence of an ff excitation window for trivalent terbium ions in the wavelength range of 400 nm to 470 nm, which means that only the scattering amount specific to the sintered ceramic material is revealed. As shown in Figures 3, 5, and 7, there is no difference in the degree of scattering between the Examples and Comparative Examples. This indicates that if the manufacturing method for sintered ceramics is the same, the degree of forward scattering should be comparable. Furthermore, it can be concluded that the difference in the annealing time results in differences in the remaining amount of finer point defects, such as oxygen defects, that do not appear in forward scattering information, and this is reflected in the increase in the apparent forward scattering rate (fluorescence emission amount of trivalent terbium ions) in the wavelength range of 390 nm or less.

[0069] Next, a series of evaluation samples were prepared by applying an AR coating (anti-reflection film) with a wavelength of 1064 nm to both end faces of all the samples (Examples 1 to 8, Comparative Examples 1 to 8) shown in Table 3. For all the obtained samples, the rate of change in beam diameter when a high-power laser beam with a wavelength of 1070 nm and a beam diameter of 1.6 mm was irradiated was evaluated. However, for the composition 1 group (Examples 1 to 4, Comparative Examples 1 to 4), an incident power of a high-power laser beam was irradiated and evaluated, and for the composition 2 group (Examples 5 to 8, Comparative Examples 5 to 8), an incident power of a high-power laser beam was irradiated and evaluated.

[0070] (Evaluation of beam diameter change rate) The beam diameter change rate was measured using a collimated CW laser beam manufactured by IPG Co., Ltd. with a wavelength of 1070 nm and a beam diameter of 1.6 mm, and the output power was set to 120 W or 180 W. The beam diameter change rate was measured using a ModeMaster PC M manufactured by Coherent Co., Ltd. 2 The beam diameter at the reference plane (full bezel) of the profiler was measured using a beam propagation analyzer. However, because the output power after passing through the sample was very high, the output laser light was first attenuated to less than 1 / 1000 using a beam separator before being introduced into the beam profiler. The distance between the reference plane (full bezel) of the beam profiler and the sample holder was 1.9 m, and the distance between the reference plane and the collimator was 2.1 m. First, the beam diameter of the original beam was measured, and this value was designated as r0. Next, each of the above 20 mm-long samples was placed in the optical path, and the beam diameter of each transmitted light was measured and designated as r. The beam diameter change rate in this invention was calculated by |(1-r / r0)| × 100, and a value of 10% or less was considered acceptable, while a value greater than 10% was considered unacceptable. The results are shown in Table 4.

[0071] [Table 4]

[0072] From the results in Table 4, in all of the groups of Examples 1 to 8, in which the annealing holding time T [hr] when the material diameter of the sintered body is D [mm] satisfies the range of T≧10×D, the rate of change in beam diameter when high-power laser is applied was 10% or less. On the other hand, in all of the groups of Comparative Examples 1 to 8, in which the relationship between the material diameter D [mm] and the annealing holding time T [hr] is outside the range of T≧10×D, the rate of change in beam diameter when high-power laser is applied was more than 10%.

[0073] From the above results, it was found that when the annealing holding time T [hr], where D [mm] is the material diameter of the sintered body, satisfies the range of T≧10×D, the forward scattering value at a wavelength of 350 nm exceeds 1.1% and, furthermore, when an AR coating is applied and a high-power laser is incident, the beam diameter change rate can be suppressed to 10% or less, making it possible to produce paramagnetic garnet-type transparent ceramics with truly low absorption and high applicable power resistance.

[0074] In this evaluation, a high-power laser beam with a beam diameter of 1.6 mm was used for all samples, regardless of material diameter. However, it is possible to increase the incident beam diameter in proportion to the material diameter. It is also known that the incident beam intensity is inversely proportional to the beam diameter. For example, if the laser powers applied in Examples 1 and 5, where the material diameter after grinding is 4 mm, are 120 W and 180 W, respectively, then the applied power can be increased by 9.5 / 4 times for Examples 4 and 8, where the material diameter after grinding is 9.5 mm. In other words, powers up to 285 W and 428 W are guaranteed, respectively.

[0075] Although the present invention has been described using the above-mentioned embodiment, the present invention is not limited to this embodiment, and can be modified within the scope of what a person skilled in the art can conceive, such as other embodiments, additions, changes, deletions, etc., and any aspect is included in the scope of the present invention as long as it achieves the effects of the present invention. [Explanation of symbols]

[0076] 100 Optical isolator 102 Case 104 Optical axis 110 Faraday rotator 120 Polarizer 130 Analyzer 140 Magnet

Claims

1. A method for producing a paramagnetic garnet-type transparent ceramic including a sintered body containing a composite oxide represented by the following formula (1), (Tb １-ｘ-ｙ Y ｘ Sc ｙ ) ３ (Al １－ｚ Sc ｚ ) ５ O １２ (1) (In the formula, 0.05≦x≦0.45, 0<y<0.1, 0.5<1−x−y<0.95, 0.001<z<0.15, and 0<y+z<0.2.) sintering the composite oxide compact to obtain a sintered body; a step of subjecting the sintered body to hot isostatic pressing (HIP); annealing the HIP-treated sintered body; Including, In the annealing treatment step, the annealing temperature is 1400° C. or higher and 1500° C. or lower, and the annealing holding time T [hr] is determined by the following formula (2) when the material diameter of the sintered body to be annealed is D [mm]: T≧10×D (2) A method for producing paramagnetic garnet-type transparent ceramics that satisfies the above requirements.

2. 2. The method for producing a paramagnetic garnet-type transparent ceramic according to claim 1, further comprising a peripheral grinding step of grinding the outer periphery of the sintered body before the annealing treatment step or grinding the outer periphery of the sintered body after the annealing treatment step to process it into a cylindrical body having a desired outer diameter.

3. 3. The method for producing a paramagnetic garnet-type transparent ceramic according to claim 2, wherein when the outer periphery grinding is carried out after the annealing treatment step, the outer periphery ground sintered body is heat treated at a temperature of 1300°C or higher for 5 hours or more.

4. A paramagnetic garnet-type transparent ceramic comprising a sintered body containing a composite oxide represented by the following formula (1): (Tb １-ｘ-ｙ Y ｘ Sc ｙ ) ３ (Al １－ｚ Sc ｚ ) ５ O １２ (1) (In the formula, 0.05≦x≦0.45, 0<y<0.1, 0.5<1−x−y<0.95, 0.001<z<0.15, and 0<y+z<0.2.) The sintered body has an outer diameter of 4 mm or more, and has a forward scattering value of 1.1% or more at a wavelength of 350 nm and a forward scattering value of less than 1% at a wavelength of 430 nm.

5. The sintered body contains SiO ２ 5. The paramagnetic garnet-type transparent ceramic according to claim 4, further comprising more than 0 mass % and 0.1 mass % or less of:

6. A magneto-optical material comprising the paramagnetic garnet-type transparent ceramic according to claim 4 or 5.

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

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

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