Calcium fluoride sintered compact, method for manufacturing calcium fluoride particle, method for manufacturing calcium fluoride sintered compact, optical element, optical system, interchangeable lens, and optical device

Abstract

To provide a calcium fluoride sintered compact, a method for manufacturing calcium fluoride particles, a method for a manufacturing a calcium fluoride sintered compact, an optical element, an optical system, an interchangeable lens, and an optical device.SOLUTION: A calcium fluoride sintered compact has an internal transmittance of 98% or more for light at a wavelength of 550 nm per 10 mm of thickness.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a calcium fluoride sintered body, a method for producing calcium fluoride particles, a method for producing a calcium fluoride sintered body, an optical element, an optical system, an interchangeable lens, and an optical device. [Background technology]

[0002] A manufacturing method for obtaining a calcium fluoride sintered body by hot pressing has been proposed (for example, Patent Document 1). However, the transmittance of a sintered body is lower than that of a single crystal, and for use as an optical member, it is necessary to increase the transmittance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2003-300777 Summary of the Invention

[0004] According to the first aspect, the calcium fluoride sintered body has an internal transmittance of 98% or more per 10 mm thickness for light with a wavelength of 550 nm. According to a second aspect, a method for producing calcium fluoride particles includes a production step of reacting a calcium compound with a fluorine compound in a solution to produce a dispersion liquid containing calcium fluoride particles, a mixing step of mixing the calcium fluoride particles contained in the dispersion liquid with hydrofluoric acid, and a separation step of separating the calcium fluoride particles and the hydrofluoric acid after the mixing step. According to a third aspect, a method for producing a calcium fluoride sintered body includes a molding step of forming a molded body by molding calcium fluoride particles produced by the method for producing calcium fluoride particles of the second aspect, and a sintering step of sintering the molded body in an inert atmosphere to produce a sintered body. According to a fourth aspect, an optical element uses the calcium fluoride sintered body of the first aspect. According to a fifth aspect of the present invention, an optical system comprises the optical element of the fourth aspect. According to a sixth aspect, an interchangeable lens comprises the optical system of the fifth aspect. According to a seventh aspect, an optical device comprises the optical system of the fifth aspect. [Brief description of the drawings]

[0005] [Figure 1] 1 is a flowchart illustrating a method for producing a calcium fluoride sintered body according to an embodiment. [Diagram 2] FIG. 1 is a diagram showing an example of a stirring device used when reacting an aqueous calcium compound solution with an aqueous fluorine compound solution. [Diagram 3] 1 is a perspective view showing an example of an imaging device according to an embodiment. [Figure 4] FIG. 11 is a front view showing another example of an imaging device according to an embodiment. [Diagram 5] FIG. 11 is a rear view showing another example of the imaging device according to the embodiment. [Figure 6] FIG. 1 is a block diagram showing an example of a multiphoton microscope according to an embodiment. [Figure 7] 4 shows the conditions for producing calcium fluoride particles of the example, and the measurement results of the internal transmittance and optical distortion of a calcium fluoride sintered body for light with a wavelength of 550 nm. [Figure 8] 4 shows the conditions for producing calcium fluoride particles of the example, and the measurement results of the internal transmittance and optical distortion of a calcium fluoride sintered body for light with a wavelength of 550 nm. [Figure 9A] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 9B] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 10A] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 10B] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 11A] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 11B] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 12A] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 12B] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 13] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. [Figure 14A] FIG. 2 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Comparative Example 1. [Figure 14B] FIG. 2 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Comparative Example 1. [Figure 15A] FIG. 13 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Comparative Example 2. [Figure 15B] FIG. 13 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Comparative Example 2. [Figure 16] 4 shows the conditions for producing calcium fluoride particles of the example, and the measurement results of the internal transmittance and optical distortion of a calcium fluoride sintered body for light with a wavelength of 550 nm. [Figure 17] FIG. 1 is a diagram showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] A calcium fluoride (CaF2) sintered body, a manufacturing method of calcium fluoride particles, and a manufacturing method of calcium fluoride sintered body according to embodiments will be described with reference to the drawings. Note that the sintered body in this specification refers to a polycrystalline body. The calcium fluoride sintered body of this embodiment has an internal transmittance of 98% or more per 10 mm thickness for light with a wavelength of 550 nm. The calcium fluoride sintered body of this embodiment may have an internal transmittance of 90% or more per 10 mm thickness for light with a wavelength of 380 nm to 780 nm. The calcium fluoride sintered body of this embodiment may have an internal transmittance of 90% or more per 10 mm thickness for light with a wavelength of 3 μm to 7 μm. The calcium fluoride sintered body of this embodiment has an internal transmittance of 80% or more per 10 mm thickness in the infrared region at a wavelength IRλ 80 The calcium fluoride sintered body of the present embodiment may have an optical distortion of 25 nm / cm or less, 20 nm / cm or less, or 10 nm / cm or less. The calcium fluoride sintered body of the present embodiment may have a relative density of 98% or more with respect to the density of calcium fluoride single crystal.

[0007] With reference to FIG. 1, a method for producing the above-mentioned calcium fluoride sintered body and a method for producing calcium fluoride particles that are the material for the calcium fluoride sintered body will be described. In step S1, a calcium compound (e.g., high-purity calcium acetate hydrate, high-purity calcium carbonate, high-purity calcium nitrate, etc.) is dissolved in distilled water to prepare an aqueous calcium compound solution. At this time, when an organic salt such as calcium acetate is used, it is preferable to add nitric acid as an oxidizing agent. In step S2, distilled water is added to high-purity hydrofluoric acid (hydrofluoric acid) to dilute it to an appropriate concentration to prepare an aqueous solution of a fluorine compound. Note that the aqueous solution of a fluorine compound may be prepared by using ammonium fluoride instead of hydrofluoric acid and dissolving the ammonium fluoride in distilled water.

[0008] In step S3, the calcium compound aqueous solution and the fluorine compound aqueous solution are reacted (i.e., the calcium compound and the fluorine compound are reacted in the aqueous solution) to generate a dispersion liquid containing calcium fluoride particles (generation step). Specifically, while stirring the calcium compound aqueous solution, a fluorine compound aqueous solution is injected into the calcium compound aqueous solution at a molar ratio of 2.4 to 5.0. In this case, a stirring rod 31 (blade diameter 10 cm) of the stirring device 3 shown in FIG. 2 is rotated at 300 rpm, and the fluorine compound aqueous solution is slowly injected into the calcium compound aqueous solution while stirring the calcium compound aqueous solution. Inlets 33 and 34 for the fluorine compound aqueous solution are attached to the side of a plastic beaker 32 of the stirring device 3, and the fluorine compound aqueous solution is injected into the calcium compound aqueous solution from a container (not shown) containing the fluorine compound aqueous solution by a roller tube pump (not shown) for about 1 hour, for example. After the injection of the fluorine compound aqueous solution into the calcium compound aqueous solution is completed, stirring is continued for, for example, 2 to 6 hours. This makes it possible to suppress the aggregation of calcium fluoride particles and generate calcium fluoride particles with a small particle size. The stirring after pouring the aqueous solution of the fluorine compound is carried out, for example, by using a water bath while keeping the temperature at 5 to 10° C. Stirring at a low temperature can increase the transmittance of the calcium fluoride sintered body produced by using the generated calcium fluoride particles.

[0009] In step S4, the dispersion liquid containing calcium fluoride particles is heated and pressurized at the same time to promote the reaction between the calcium compound and the fluorine compound, and the calcium fluoride particles are grown large to increase the crystallinity (heating and pressurizing step). Specifically, the dispersion liquid containing calcium fluoride particles (dispersion liquid (slurry) in which calcium fluoride fine particles are suspended) is heated and pressurized in a closed container (e.g., an autoclave equipped with a Teflon (registered trademark) container) for 10 hours to 24 hours while maintaining a heating temperature of 100°C to 180°C. After the heating and pressurizing step, when the temperature of the closed container is lowered to room temperature, the supernatant liquid is sucked and removed, and the calcium fluoride particles are left behind and separated. In step S5, the separated calcium fluoride particles are mixed with, for example, 0.1 to 20% hydrofluoric acid and stirred (mixing step).

[0010] In step S6, the mixture of calcium fluoride particles and hydrofluoric acid produced in the mixing step is transferred to a centrifuge tube, and the centrifuge tube is centrifuged to separate the mixture into a solid (calcium fluoride particles) and a liquid (hydrofluoric acid) (separation step). In this case, for example, the centrifuge is rotated at 1000 rpm for 10 minutes. After the solid and liquid are separated, the supernatant liquid is removed, and then distilled water is injected into the centrifuge tube in which the calcium fluoride particles remain to thoroughly disperse the calcium fluoride particles. At this time, the inflow of foreign matter from the outside can be prevented by dispersing the calcium fluoride particles using a shaker. After shaking the calcium fluoride particles for about 30 minutes until they do not precipitate, the calcium fluoride particles are again separated into a solid and a liquid using a centrifuge, the supernatant liquid is removed, and distilled water is further injected to thoroughly disperse the calcium fluoride particles. The step of adding distilled water to disperse the calcium fluoride particles and the step of separating the solid and liquid using a centrifuge are repeated until the concentration of hydrofluoric acid in the supernatant becomes 200 ppm or less. If the number of injections of distilled water is small, the transmittance of the calcium fluoride sintered body produced using the generated calcium fluoride particles is low, and many white spots of about 0.1 mm, which are aggregates of fine bubbles, are observed inside. Also, as the number of injections of distilled water increases, the aggregates of calcium fluoride particles are loosened and the particle size becomes smaller, making it difficult to precipitate. Therefore, the rotation speed of the centrifuge is gradually increased, for example, to 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, and 2000 rpm. The separation step is not limited to the method using the shaker and centrifuge described above. For example, the separation step may be performed using a known filtration device. Examples of the filtration device include a Nutsche type filtration device. When using a Nutsche type filtration device, first, water is added to the hydrofluoric acid mixture of calcium fluoride particles generated in the mixing step and stirred to prepare a dilute slurry. Next, the dilute slurry is supplied to the Nutsche type filtration device, and filtration is performed while applying pressure to the dilute slurry. At this time, it is preferable to apply pressure while supplying water. When using such a filtration device, the separation step can be performed in a shorter time than when using a shaker and a centrifuge. The above-mentioned processes in steps S1 to S6 constitute the process for producing calcium fluoride particles in this embodiment.

[0011] In step S7, the calcium fluoride granules classified into those having a predetermined particle size or smaller among the granules obtained by pulverizing the dried body (cake) made of calcium fluoride particles produced by the above-mentioned method for producing calcium fluoride particles are molded to form a molded body (molding step). The classification is performed by placing the calcium fluoride particles produced by the above-mentioned method for producing calcium fluoride particles in a Teflon container, drying the particles at, for example, 160°C for about 10 hours, and then removing larger granules using, for example, a 1 mm sieve. There are, for example, two molding methods: In the first molding method, classified calcium fluoride particles are press-molded using a mold having a predetermined shape to form a green body. In the second molding method, a slurry containing calcium fluoride particles produced by the above-mentioned method for producing calcium fluoride particles is placed in, for example, a dish-shaped container and dried at 70 to 300°C for about 10 hours to form a green body.

[0012] In step S8, the green compact (green compact with a relative density of 35-50%) formed by the first or second forming method is sintered to produce a sintered body (white sintered body) (sintering process). In the sintering process, the white green compact is sintered (initial sintering) for 2-6 hours at, for example, 400-700°C to produce a white sintered body with a relative density of about 40-70%. If the relative density of the green compact before sintering is too high, the white sintered body will not become transparent in the subsequent process. If the sintering temperature is too high, the initial sintering will proceed, and the driving force for sintering in the subsequent process will be small, which will cause an increase in optical distortion (i.e., deterioration of optical properties). If the sintering temperature is too low, organic matter will remain in the sintered body, and high transmittance will not be obtained. Next, the mixture is kept in an inert atmosphere (eg, vacuum, argon, or nitrogen atmosphere) at, for example, 900 to 1000° C. for 1 to 2 hours to obtain a white sintered body with a relative density of about 98%.

[0013] In step S9, the white sintered body is subjected to a heating and pressurizing treatment, for example, using a hot isostatic pressing (HIP) device, to make it transparent and produce a transparent sintered body (transparentization step). Specifically, the white sintered body is heated to, for example, 1000 to 1100°C in an inert atmosphere (for example, an argon atmosphere) while maintaining a pressure of 100 MPa, so that pores remaining inside the white sintered body are pushed out to the outside, and a transparent sintered body (i.e., the calcium fluoride sintered body of this embodiment) is produced. That is, the processes of steps S7 to S9 described above are the processes in the method for producing a calcium fluoride sintered body of this embodiment.

[0014] After the transparentization step, an annealing step may be performed to anneal the transparent sintered body as necessary. The annealing step is performed, for example, in an inert atmosphere, for a heating time of 40 hours or more, at a temperature range of 600° C. to 800° C. This can further reduce the optical distortion of the transparent sintered body, for example, to 2 nm / cm or less.

[0015] An embodiment of an imaging device including an optical element made of the calcium fluoride sintered body produced as described above will be described. 3 is a perspective view of the imaging device of this embodiment. The imaging device 1 is a so-called digital single-lens reflex camera (lens-interchangeable camera), and the photographing lens 103 (optical system) is provided with an optical element having the calcium fluoride sintered body according to this embodiment as a base material. A lens barrel 102 is detachably attached to a lens mount (not shown) of a camera body 101. Light passing through the photographing lens 103 of the lens barrel 102 is imaged on a sensor chip (solid-state imaging element) 104 of a multi-chip module 106 arranged on the rear side of the camera body 101. This sensor chip 104 is a bare chip such as a so-called CMOS image sensor, and the multi-chip module 106 is, for example, a COG (Chip On Glass) type module in which the sensor chip 104 is bare-chip mounted on a glass substrate 105.

[0016] FIG. 4 is a front view of another example of an imaging device including an optical element made of a calcium fluoride sintered body according to this embodiment, and FIG. 5 is a rear view of the imaging device of FIG. This imaging device CAM is a so-called digital still camera (lens non-interchangeable camera), and the photographing lens WL (optical system) includes an optical element having the calcium fluoride sintered body according to this embodiment as a base material. When the power button (not shown) of the imaging device CAM is pressed, the shutter (not shown) of the photographing lens WL is opened, and the photographing lens WL collects light from a subject (object) and forms an image on an imaging element arranged on an image plane. The subject image formed on the imaging element is displayed on a liquid crystal monitor LM arranged behind the imaging device CAM. After the photographer decides the composition of the subject image while looking at the liquid crystal monitor LM, he or she presses the release button B1 to capture the subject image with the imaging element, which is then recorded and saved in a memory (not shown).

[0017] The imaging device CAM is provided with an auxiliary light emitting section EF that emits auxiliary light when the subject is dark, and a function button B2 that is used to set various conditions for the imaging device CAM. Optical systems used in such digital cameras and the like are required to have higher resolution, lighter weight, and smaller size. In order to achieve these, it is effective to use glass with a high refractive index for the optical system. In particular, glass with a high refractive index and a low specific gravity (S g ) and thus there is a high demand for glass having high press moldability. From this viewpoint, the calcium fluoride sintered body of the present embodiment is suitable as a member of an optical device. Note that optical devices to which the present embodiment can be applied are not limited to the above-mentioned imaging device, but may also include, for example, a projector, etc. The optical elements are also not limited to lenses, but may also include, for example, a prism, etc.

[0018] Next, a multiphoton microscope including an optical element using the calcium fluoride sintered body of this embodiment will be described. 6 is a block diagram showing an example of the configuration of a multiphoton microscope 2 according to the present embodiment. The multiphoton microscope 2 includes an objective lens 206, a condenser lens 208, and an imaging lens 210. At least one of the objective lens 206, the condenser lens 208, and the imaging lens 210 includes an optical element having the calcium fluoride sintered body according to the present embodiment as a base material. The optical system of the multiphoton microscope 2 will be mainly described below.

[0019] The pulsed laser device 201 emits ultrashort pulsed light, for example, near infrared (about 1000 nm) with a pulse width in femtosecond units (for example, 100 femtoseconds). The ultrashort pulsed light immediately after being emitted from the pulsed laser device 201 is generally linearly polarized light having an electric field vibration direction in a predetermined direction. The pulse separation device 202 splits the ultrashort pulsed light, and emits the ultrashort pulsed light with a higher repetition frequency.

[0020] The beam adjusting unit 203 has a function of adjusting the beam diameter of the ultrashort pulsed light incident from the pulse splitting device 202 to match the pupil diameter of the objective lens 206, a function of adjusting the focusing and divergence angles of the ultrashort pulsed light in order to correct the on-axis chromatic aberration (focus difference) between the wavelength of the multiphoton excitation light emitted from the sample S and the wavelength of the ultrashort pulsed light, and a pre-chirp function (group velocity dispersion compensation function) of imparting inverse group velocity dispersion to the ultrashort pulsed light in order to correct the broadening of the pulse width of the ultrashort pulsed light due to group velocity dispersion while passing through the optical system.

[0021] The repetition frequency of the ultrashort pulsed light emitted from the pulsed laser device 201 is increased by the pulse dividing device 202, and the above-mentioned adjustment is performed by the beam adjusting unit 203. The ultrashort pulsed light emitted from the beam adjusting unit 203 is reflected by the dichroic mirror 204 in the direction of the dichroic mirror 205, passes through the dichroic mirror 205, and is collected by the objective lens 206 to be irradiated onto the sample S. At this time, the ultrashort pulsed light may be scanned over the observation surface of the sample S by using a scanning means (not shown).

[0022] For example, when observing the fluorescence of the sample S, the fluorescent dye with which the sample S is stained is excited by multiphoton excitation in the region of the sample S irradiated with the ultrashort pulsed light and in the vicinity thereof, and fluorescence (hereinafter referred to as observation light) having a shorter wavelength than the ultrashort pulsed light, which is an infrared wavelength, is emitted. The observation light emitted from the sample S in the direction of the objective lens 206 is collimated by the objective lens 206, and is reflected by or passes through the dichroic mirror 205 depending on its wavelength.

[0023] The observation light reflected by the dichroic mirror 205 enters the fluorescence detection unit 207. The fluorescence detection unit 207 is composed of, for example, a barrier filter, a PMT (Photo Multiplier Tube), etc., receives the observation light reflected by the dichroic mirror 205, and outputs an electrical signal according to the amount of light. Furthermore, the fluorescence detection unit 207 detects the observation light across the observation surface of the sample S as the ultrashort pulsed light scans the observation surface of the sample S.

[0024] It is also possible to remove the dichroic mirror 205 from the optical path so that all of the observation light emitted from the sample S in the direction of the objective lens 206 is detected by the fluorescence detection unit 211 . In this case, the observation light is descanned by a scanning means (not shown), passes through a dichroic mirror 204, is collected by a collecting lens 208, passes through a pinhole 209 provided at a position approximately conjugate with the focal position of the objective lens 206, passes through an imaging lens 210, and enters a fluorescence detection unit 211. The fluorescence detection unit 211 is composed of, for example, a barrier filter, a PMT, etc., receives the observation light imaged on the light receiving surface of the fluorescence detection unit 211 by the imaging lens 210, and outputs an electrical signal according to the amount of light. In addition, the fluorescence detection unit 211 detects the observation light across the observation surface S of the sample S in accordance with the scanning of the observation surface S of the sample S with the ultrashort pulsed light.

[0025] Moreover, the observation light emitted from the sample S in the direction opposite to the objective lens 206 is reflected by the dichroic mirror 212 and enters the fluorescence detection unit 213. The fluorescence detection unit 213 is composed of, for example, a barrier filter, a PMT, etc., receives the observation light reflected by the dichroic mirror 212, and outputs an electrical signal according to the amount of light. Moreover, the fluorescence detection unit 213 detects the observation light across the observation surface of the sample S in accordance with the scanning of the observation surface of the sample S with the ultrashort pulsed light.

[0026] The electrical signals output from each of the fluorescence detection units 207, 211, and 213 are input, for example, to a computer (not shown). The computer can generate an observation image based on the input electrical signals, display the generated observation image, and store data of the observation image.

[0027] According to the above-described embodiment, the following advantageous effects can be obtained. (1) The method for producing calcium fluoride particles includes a producing step of producing a dispersion liquid containing calcium fluoride particles by reacting a calcium compound with a fluorine compound in a solution, a mixing step of mixing the calcium fluoride particles contained in the dispersion liquid with hydrofluoric acid, and a separation step of separating the calcium fluoride particles from the liquid component after the mixing step. This makes it possible to produce calcium fluoride particles that can be used for producing a calcium fluoride sintered body having high transmittance.

[0028] (2) The concentration of hydrogen fluoride in the hydrofluoric acid solution used in the mixing step is between 0.1% and 20%, which can prevent the formation of white spots of about 0.1 mm in size, which are aggregates of delicate bubbles, inside the sintered body obtained by sintering the calcium fluoride particles produced.

[0029] (3) A method for producing a calcium fluoride sintered body includes a molding step of forming a molded body by molding the calcium fluoride particles produced by the above-mentioned method for producing calcium fluoride particles, and a sintering step of sintering the molded body in an inert atmosphere to produce a sintered body, thereby making it possible to produce a calcium fluoride sintered body having high transmittance.

[0030] (4) In the molding step, calcium fluoride particles having a predetermined particle size or less are molded to form a molded body, which can be used to produce a calcium fluoride sintered body having high transmittance.

[0031] (5) In the manufacturing method of calcium fluoride sintered body, in the sintering step, a molded body having a relative density of 35% to 50% is sintered at 400°C to 700°C for 2 to 6 hours (initial sintering), and then sintered in an inert atmosphere at 900°C to 1000°C for 1 to 2 hours. By performing initial sintering at 400°C to 700°C, it is possible to prevent the driving force of sintering in the later step from decreasing, which is the case when sintering is performed at an excessively high temperature, and to prevent the optical distortion from increasing (worsening) during grain growth, and also to prevent the organic matter in the raw material from remaining and the transmittance from decreasing due to a temperature that is too low.

[0032] (6) The method for producing a calcium fluoride sintered body includes a transparentizing step in which the sintered body is heated to 1000°C or higher and 1100°C or lower while applying a pressure of 100 MPa to the sintered body in an inert atmosphere after the sintering step to make the sintered body transparent. This makes it possible to obtain a transparent calcium fluoride sintered body.

[0033] An example of the calcium fluoride sintered body according to the above-mentioned embodiment will be described. [Example] The calcium fluoride sintered body in the examples was produced according to the process shown in the flow chart of Figure 1. In the examples, calcium acetate hydrate was used as the calcium compound, and hydrofluoric acid was used as the fluorine compound. In the examples, 20 samples of calcium fluoride sintered bodies (transparent sintered bodies) were prepared by varying the conditions for producing calcium fluoride particles and sintering, and the internal transmittance of light with a wavelength of 550 nm and the optical distortion of each sample that was polished on both sides were measured. The optical distortion was measured using a fully automatic strain eye LSM-9000s (manufactured by Luceo Co., Ltd.).

[0034] FIG. 7 shows the conditions for producing and sintering calcium fluoride particles used for samples 1 to 12 of calcium fluoride sintered body of the embodiment, and the measurement results of the internal transmittance and optical distortion of the calcium fluoride sintered body of light with a wavelength of 550 nm. FIG. 8 shows the conditions for producing and sintering calcium fluoride particles used for samples 13 to 24 of calcium fluoride sintered body of the embodiment, and the measurement results of the internal transmittance and optical distortion of the calcium fluoride sintered body of light with a wavelength of 550 nm. In addition, in FIG. 7 and FIG. 8, "transmittance" is the internal transmittance of light with a wavelength of 550 nm per 10 mm of the thickness of the sample, in other words, the internal transmittance per 10 mm of the distance that the light actually travels through the sample. "F / Ca ratio" is the molar ratio of the fluorine compound aqueous solution (hydrofluoric acid) injected into the calcium acetate aqueous solution to the calcium compound aqueous solution (calcium acetate aqueous solution) in the generation process of step S3 in FIG. 1. The "hydrofluoric acid concentration" is the concentration of hydrofluoric acid mixed with calcium fluoride particles in the mixing process of step S5 in FIG. 1. The "hydrothermal temperature" is the temperature at which calcium fluoride particles grow and crystallize in the heating and pressurizing process of step S4 in FIG. 1. The "number of water washings" is the number of times the process of mixing and stirring calcium fluoride particles with distilled water, separating the solid from the liquid, and removing the supernatant is repeated in step S6 in FIG. 1. The "drying temperature" is the sintering temperature at which the green body is sintered to produce a white sintered body with a relative density of about 40 to 70% in the sintering process of step S8 in FIG. 1. The "inert atmosphere sintering temperature" is the sintering temperature at which a white sintered body with a relative density of 98% is produced in the sintering process of step S8 in FIG. 1. The "HIP temperature" is the heating temperature at which HIP treatment is performed in the "clarification process" of step S9 in FIG. 1.

[0035] 7 and 8, the calcium fluoride sintered bodies of Samples 1 to 24 in the examples had an internal transmittance of 98% or more for light with a wavelength of 550 nm. Furthermore, the calcium fluoride sintered bodies of Samples 1 to 22 had an optical distortion of 10 nm / cm or less.

[0036] 9A, B to 13 are diagrams showing the results of measuring the spectral transmittance of calcium fluoride sintered bodies of samples 1 to 24. The transmittances shown in FIGS. 9A, B to 13 are all internal transmittances per 10 mm of sample thickness. In other words, they are internal transmittances per 10 mm of distance that light actually travels through the sample. FIG. 9A shows the results of measuring the spectral transmittance of light with wavelengths of 200 nm to 800 nm of samples 1 to 6 with L1 to L6, and FIG. 9B shows the results of measuring the spectral transmittance of light with wavelengths of 200 nm to 800 nm of samples 7 to 12 with L7 to L12. FIG. 10A shows the results of measuring the spectral transmittance of light with wavelengths of 200 nm to 800 nm of samples 13 to 17 with L13 to L17, and FIG. 10B shows the results of measuring the spectral transmittance of light with wavelengths of 200 nm to 800 nm of samples 18 to 22 with L18 to L22. Fig. 11A shows the measurement results of the spectral transmittance of samples 1 to 6 with wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) as M1 to M6, and Fig. 11B shows the measurement results of the spectral transmittance of samples 7 to 12 with wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) as M7 to M12. Fig. 12A shows the measurement results of the spectral transmittance of samples 13 to 17 with wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) as M13 to M17, and Fig. 12B shows the measurement results of the spectral transmittance of samples 18 to 22 with wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) as M18 to M22. FIG. 13 shows the measurement results of the spectral transmittance of samples 23 and 24 from 3000 nm (3 μm) to 13000 nm (13 μm) in M23 and M24. As shown in FIGS. 9A and 9B and 10A and 10B, the calcium fluoride sintered body of the embodiment has an internal transmittance of 90% or more for light from 380 nm to 780 nm. As shown in FIGS. 11A and 11B, 12A and 12B, and 13, the calcium fluoride sintered body of the embodiment has an internal transmittance of 90% or more for light from 3000 nm (3 μm) to 7000 nm (7 μm). Furthermore, as shown in FIGS. 11A and 11B, 12A and 12B, and 13, the calcium fluoride sintered body of the embodiment has an internal transmittance of 90% or more for light from 3000 nm (3 μm) to 7000 nm (7 μm). 80 is greater than or equal to 8000 nm (8 μm).

[0037] In addition, the calcium fluoride sintered bodies of Samples 23 and 24 were subjected to an annealing process under the conditions of a starting temperature of 800° C., a temperature drop rate of 5° C. / h, and a finishing temperature of 600° C. As a result, the optical distortion of the calcium fluoride sintered bodies of Samples 23 and 24 was 1.5 nm / cm, respectively.

[0038] In the above-mentioned samples 1 to 24, calcium fluoride sintered bodies were prepared using calcium acetate hydrate as the calcium compound of the raw material, but calcium nitrate was used as the calcium compound to prepare a calcium fluoride sintered body as sample 25. FIG. 16 shows the conditions of manufacturing and sintering calcium fluoride particles used for the calcium fluoride sintered body of sample 25, and the measurement results of the internal transmittance of light with a wavelength of 550 nm and the optical distortion of the calcium fluoride sintered body. Note that the "transmittance" in FIG. 16 is the internal transmittance of light with a wavelength of 550 nm per 10 mm of the thickness of the sample, in other words, the internal transmittance per 10 mm of the distance that the light actually travels through the sample. The "F / Ca ratio" is the molar ratio of the fluorine compound aqueous solution (hydrofluoric acid) injected into the calcium carbonate aqueous solution to the calcium compound aqueous solution (calcium carbonate aqueous solution) in the generation process of step S3 in FIG. 1. The "hydrofluoric acid concentration" is the concentration of hydrofluoric acid mixed with the calcium fluoride particles in the mixing process of step S5 in FIG. 1. The "hydrothermal temperature" is the temperature at which the calcium fluoride particles grow and crystallize in the heating and pressurizing process in step S4 in FIG. 1. The "number of water washings" is the number of times the process of mixing and stirring the calcium fluoride particles and distilled water to separate the solid from the liquid and remove the supernatant is repeated in step S6 in FIG. 1. The "drying temperature" is the sintering temperature at which the green body is sintered to produce a white sintered body with a relative density of about 40 to 70% in the sintering process in step S8 in FIG. 1. The "inert atmosphere sintering temperature" is the sintering temperature at which a white sintered body with a relative density of 98% is produced in the sintering process in step S8 in FIG. 1. The "HIP temperature" is the heating temperature at which the HIP treatment is performed in the "clarification process" in step S9 in FIG. 1.

[0039] 16, the calcium fluoride sintered compact of Sample 25 had an internal transmittance of 98% or more for light with a wavelength of 550 nm. Furthermore, the calcium fluoride sintered compact of Sample 25 had an optical distortion of 25 nm / cm or less.

[0040] Fig. 17 shows the results of measuring the spectral transmittance of the calcium fluoride sintered compact of sample 25. The transmittance shown in Fig. 17 is the internal transmittance per 10 mm of sample thickness. In other words, it is the internal transmittance per 10 mm of the distance that light actually travels in the sample. As shown in Fig. 17, the calcium fluoride sintered compact of sample 25 has an internal transmittance of 90% or more for light with wavelengths from 380 nm to 780 nm.

[0041] As described above, it was shown that the calcium fluoride sintered body of this example has high transmittance despite being a polycrystalline body.

[0042] [Comparative Example 1] The calcium fluoride sintered body in Comparative Example 1 uses calcium acetate hydrate as the calcium compound and hydrofluoric acid as the fluorine compound as in the Examples. The calcium fluoride sintered body in Comparative Example 1 was produced without the step S6 described above. That is, the calcium fluoride sintered body was produced without the step of stirring calcium fluoride particles and distilled water to separate solid from liquid, removing the supernatant, and then injecting distilled water and stirring. In Comparative Example 1, a transparent calcium fluoride sintered body was obtained by HIP treatment, but many white spots of about 0.1 mm, which were aggregates of fine bubbles, were observed in the sintered body.

[0043] 14A and 14B are diagrams showing the results of measuring the spectral transmittance of the calcium fluoride sintered compact of Comparative Example 1. The transmittances shown in Figs. 14A and 14B are internal transmittances per 10 mm of sample thickness. In other words, they are internal transmittances per 10 mm of distance that light actually travels in the sample. Fig. 14A shows the results of measuring the spectral transmittance of light with wavelengths from 200 nm to 800 nm, and Fig. 14B shows the results of measuring the spectral transmittance of light with wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm). The calcium fluoride sintered compact of Comparative Example 1 had an internal transmittance of 97.7% for light with a wavelength of 550 nm per 10 mm of thickness, which was less than 98%.

[0044] [Comparative Example 2] The calcium fluoride sintered body in Comparative Example 2 uses calcium acetate hydrate as the calcium compound and hydrofluoric acid as the fluorine compound as in the Example. The calcium fluoride sintered body in Comparative Example 2 was produced using calcium fluoride particles produced without carrying out the mixing step described as step S5 above. Foreign matter was generated in the obtained calcium fluoride sintered body of Modification Example 2.

[0045] 15A and 15B are diagrams showing the results of measuring the spectral transmittance of the calcium fluoride sintered compact of Comparative Example 2, which was polished on both sides. The transmittances shown in FIGS. 15A and 15B are the internal transmittance per 10 mm of the thickness of the sample. In other words, they are the internal transmittance per 10 mm of the distance that the light actually travels through the sample. FIG. 15A shows the results of measuring the spectral transmittance for light with wavelengths of 200 nm to 800 nm, and FIG. 15B shows the results of measuring the spectral transmittance for light with wavelengths of 3000 nm (3 μm) to 13000 nm (13 μm). As shown in FIGS. 15A and 15B, the range of wavelengths of light in which the internal transmittance is 90% or more is narrower than that in the case of the embodiment. Moreover, the calcium fluoride sintered compact of Comparative Example 2 had an internal transmittance of 87.7% for light with a wavelength of 550 nm per 10 mm of thickness, which was less than 98%.

[0046] As long as the characteristics of the present invention are not impaired, the present invention is not limited to the above-described embodiments, and other forms that are conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of symbols]

[0047] 1. Imaging device 2. Multiphoton Microscopy 103 Photographic Lens 206 Objective Lens 208 Condenser Lens 210 Imaging Lens CAM: Imaging device WL: Shooting lens

Claims

[Claim 1] A calcium fluoride sintered body, A calcium fluoride sintered body having an internal transmittance of 98% or more for light with a wavelength of 550 nm per 10 mm thickness.

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