Calcium fluoride polycrystal, method for producing same, optical element, optical system, and optical device

Abstract

Provided are a calcium fluoride polycrystal having an internal transmittance of 98% or more and an optical strain of 10 nm / cm or less per 10 mm thickness of light having a wavelength of 550 nm, a method for producing the calcium fluoride polycrystal, an optical element, an optical system, and an optical device.

Description

[0001] This application is a divisional application of the application with Chinese national application No. 202180079945.5, international application No. PCT / JP2021 / 048842, filing date of 2021 / 12 / 28, entering China date of 2023 / 05 / 29, and invention name of "Calcium fluoride sintered body, calcium fluoride particles and method for manufacturing sintered body, optical element and system, interchangeable lens, and optical device". TECHNICAL FIELD

[0002] The present application relates to a calcium fluoride polycrystal, a method for manufacturing calcium fluoride particles, a method for manufacturing calcium fluoride polycrystal, an optical element, an optical system, an interchangeable lens, and an optical device. BACKGROUND

[0003] There is a method for manufacturing a calcium fluoride sintered body by hot pressing (for example, Patent Literature 1).

[0004] However, the transmittance of the sintered body is lower than that of a single crystal, and in order to be used as an optical member, it is required to improve the transmittance.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Publication No. 2003-300777 SUMMARY

[0008] According to a first aspect, a calcium fluoride polycrystal has an internal transmittance of light of a wavelength of 550 nm of 98% or more per 10 mm of thickness.

[0009] According to a second aspect, a method for manufacturing calcium fluoride particles has: a generation step of generating a dispersion liquid containing calcium fluoride particles by reacting a calcium compound and a fluorine compound in a solution; a mixing step of mixing the calcium fluoride particles contained in the dispersion liquid and hydrofluoric acid; and a separation step of separating the calcium fluoride particles and the hydrofluoric acid after the mixing step.

[0010] According to a third aspect, a method for manufacturing calcium fluoride polycrystal has: a molding step of molding calcium fluoride particles manufactured by the method for manufacturing calcium fluoride particles of the second aspect to form a molded body; and a sintering step of sintering the molded body in an inactive atmosphere to generate a polycrystal.

[0011] According to a fourth aspect, an optical element uses the calcium fluoride polycrystal of the first aspect.

[0012] According to a fifth aspect of the present application, an optical system has the optical element of the fourth aspect.

[0013] According to a sixth aspect, the replacement lens has the optical system of the fifth aspect.

[0014] According to a seventh aspect, the optical device has the optical system of the fifth aspect. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a flowchart illustrating a method of manufacturing a calcium fluoride sintered body according to an embodiment.

[0016] Figure 2 is a view schematically showing an example of a stirring device used when reacting a calcium compound aqueous solution with a fluorine compound aqueous solution.

[0017] Figure 3 is a perspective view showing an example of an imaging device according to an embodiment.

[0018] Figure 4 is a front view showing another example of an imaging device according to an embodiment.

[0019] Figure 5 is a rear view showing another example of an imaging device according to an embodiment.

[0020] Figure 6 is a block diagram showing an example of a multi-photon microscope according to an embodiment.

[0021] Figure 7 Conditions at the time of manufacturing calcium fluoride particles according to the embodiment and measurement results of internal transmittance of a calcium fluoride sintered body with respect to light having a wavelength of 550 nm and optical strain are shown.

[0022] Figure 8 Conditions at the time of manufacturing calcium fluoride particles according to the embodiment and measurement results of internal transmittance of a calcium fluoride sintered body with respect to light having a wavelength of 550 nm and optical strain are shown.

[0023] Figure 9A is a graph showing results of measuring the spectral transmittance of a calcium fluoride sintered body in an example.

[0024] Figure 9B is a graph showing results of measuring the spectral transmittance of a calcium fluoride sintered body in an example.

[0025] Figure 10A is a graph showing results of measuring the spectral transmittance of a calcium fluoride sintered body in an example.

[0026] Figure 10B is a graph showing results of measuring the spectral transmittance of a calcium fluoride sintered body in an example.

[0027] Figure 11A is a graph showing results of measuring the spectral transmittance of a calcium fluoride sintered body in an example.

[0028] Figure 11B Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0029] Figure 12A Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0030] Figure 12B Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0031] Figure 13 Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0032] Figure 14A Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0033] Figure 14B Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0034] Figure 15A Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0035] Figure 15B Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0036] Figure 16 Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1.

[0037] Figure 17 Fig. 6 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Example 1. DETAILED DESCRIPTION

[0038] A calcium fluoride (CaF2) sintered body, a method for manufacturing calcium fluoride particles, and a method for manufacturing a calcium fluoride sintered body according to an embodiment will be described with reference to the accompanying drawings. Note that the sintered body in this specification refers to a polycrystal.

[0039] The calcium fluoride sintered body of the present embodiment has an internal transmittance of light of wavelength 550 nm of 98% or more per 10 mm thickness. The calcium fluoride sintered body of the present embodiment can have an internal transmittance of light of wavelength 380 nm to 780 nm of 90% or more per 10 mm thickness. In addition, the calcium fluoride sintered body of the present embodiment can have an internal transmittance of light of wavelength 3 μm to 7 μm of 90% or more per 10 mm thickness. In addition, in the infrared region, the calcium fluoride sintered body of the present embodiment has an internal transmittance of 80% or more per 10 mm thickness at a wavelength IRλ 80 may be 8 μm or more. In addition, the optical strain of the calcium fluoride sintered body of the present embodiment can be 25 nm / cm or less, can be 20 nm / cm or less, or can be 10 nm / cm or less. In addition, the relative density of the calcium fluoride sintered body of the present embodiment with respect to the density of a calcium fluoride single crystal can be 98% or more.

[0040] Reference Signs List Figure 1 The production method of the calcium fluoride sintered body described above and the production method of the calcium fluoride particles as a material of the calcium fluoride sintered body will be described.

[0041] In step S1, a calcium compound (for example, calcium acetate hydrate of high purity, calcium carbonate of high purity, calcium nitrate of high purity, or the like) is dissolved in distilled water to prepare a calcium compound aqueous solution. At this time, in the case of using an organic salt such as calcium acetate, nitric acid is preferably added as an oxidizing agent.

[0042] In step S2, distilled water is added to high-purity hydrofluoric acid (hydrofluoric acid) to dilute to an appropriate concentration to prepare a fluorine compound aqueous solution. Note that, instead of hydrofluoric acid, ammonium fluoride or the like can be used to prepare a fluorine compound aqueous solution by dissolving the ammonium fluoride in distilled water.

[0043] In step S3, the calcium compound aqueous solution is reacted with the fluorine compound aqueous solution (that is, the calcium compound is reacted with the fluorine compound in the aqueous solution) to generate a dispersion liquid containing calcium fluoride particles (generation step). Specifically, while stirring the calcium compound aqueous solution, the fluorine compound aqueous solution is injected at a molar ratio of 2.4 to 5.0 with respect to the calcium compound aqueous solution. In this case, the calcium compound aqueous solution and the fluorine compound aqueous solution are reacted at a temperature of 20°C to 100°C for 1 hour to 24 hours. Figure 2The stirring device 3 shown has a stirring rod 31 (blade diameter 10 cm) that rotates at 300 rpm, and the fluorine compound aqueous solution is slowly injected while stirring the calcium compound aqueous solution. The fluorine compound aqueous solution is injected into the calcium compound aqueous solution from a container (not shown) containing the fluorine compound aqueous solution using a roller tube pump (not shown) via an injection port 33, 34 provided on the side of a plastic beaker 32 of the stirring device 3, for example, over a period of about 1 hour. After the injection of the fluorine compound aqueous solution into the calcium compound aqueous solution is completed, stirring is continued, for example, for 2 to 6 hours. Thus, the agglomeration of the calcium fluoride particles is suppressed, and calcium fluoride particles having a small particle diameter are produced. The stirring after the injection of the fluorine compound aqueous solution is performed, for example, while maintaining the temperature at 5 to 10°C using a water bath. Performing the stirring at a low temperature makes it possible to improve the transmittance of the calcium fluoride sinter produced using the calcium fluoride particles produced.

[0044] In step S4, the dispersion liquid containing the calcium fluoride particles is simultaneously subjected to heating and pressurization, the reaction of the calcium compound and the fluorine compound is promoted, and the calcium fluoride particles are grown larger to improve the crystallinity (heating and pressurization process). Specifically, the dispersion liquid containing the calcium fluoride particles (dispersion liquid (slurry) in which calcium fluoride particles are suspended) is subjected to a heating and pressurization treatment in a closed container (for example, an autoclave provided with a Teflon (registered trademark) container) at a temperature at which the heating temperature is maintained at 100°C or higher and 180°C or lower, for example, for a period of 10 hours or more and 24 hours or less. After the heating and pressurization process, if the temperature of the closed container is lowered to room temperature, the supernatant is removed by suction, and the calcium fluoride particles are left to separate. In step S5, the separated calcium fluoride particles are mixed with, for example, 0.1 to 20% of hydrofluoric acid and stirred (mixing process).

[0045] In step S6, the hydrogen fluoride acid mixed solution of the calcium fluoride particles generated by the mixing process is transferred to a centrifuge tube, the centrifuge tube is placed in a centrifuge, and the mixed solution is separated into a solid (calcium fluoride particles) and a liquid (hydrogen fluoride acid) (separation process). In this case, for example, the centrifuge is set to 1000 rpm, and centrifugal separation is performed for 10 minutes. After the solid and the liquid are separated, the supernatant is discharged, and then distilled water is injected into the centrifuge tube in which the calcium fluoride particles remain, so that the calcium fluoride particles are sufficiently dispersed. At this time, by using a shaker, the dispersion is performed, and foreign matter can be prevented from flowing in from the outside. The shaking is performed for about 30 minutes, and after the calcium fluoride particles are brought to a state in which they do not settle by the shaker, the solid and the liquid are again separated by the centrifuge, the supernatant is removed, and further distilled water is injected to sufficiently disperse the calcium fluoride particles. The process of adding distilled water to disperse the calcium fluoride particles and the process of separating the solid and the liquid by the centrifuge are repeated until the concentration of the hydrogen fluoride acid in the supernatant is 200 ppm or less. If the number of times of injection of the distilled water is small, the transmittance of the calcium fluoride sintered body manufactured using the generated calcium fluoride particles is low, and a plurality of white spots of about 0.1 mm as a collection of fine bubbles are observed inside. In addition, as the number of times of injection of the distilled water increases, the aggregation of the calcium fluoride particles is broken, and the particle diameter becomes small, and thus the particles are difficult to settle. Therefore, the rotation speed of the centrifuge is gradually increased, for example, at 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, and 2000 rpm.

[0046] Note that the separation process is not limited to the method using the shaker and the centrifuge described above. For example, the separation process can be performed using a publicly known filter device. As the filter device, a Nutsche-type filter device or the like can be given. In the case of using the Nutsche-type filter device, first, water is added to the hydrogen fluoride acid mixed solution of the calcium fluoride particles generated by the mixing process, and the mixture is stirred to prepare a thin slurry. Next, the thin slurry is supplied to the Nutsche-type filter device, and the filtration is performed while the thin slurry is subjected to pressure. At this time, it is preferable to supply water while the pressure is applied. In the case of using such a filter device, the separation process can be performed in a shorter time than in the case of using the shaker and the centrifuge.

[0047] The processes of steps S1 to S6 described above are processes in the method of manufacturing calcium fluoride particles in the present embodiment.

[0048] In step S7, among the particles obtained by pulverizing the dry body (filter cake) composed of the calcium fluoride particles manufactured by the above-described manufacturing method of calcium fluoride particles, the particles of calcium fluoride classified to be equal to or smaller than a prescribed particle diameter are molded to form a molded body (molding step). The classification is performed as follows: the calcium fluoride particles manufactured by the above-described manufacturing method of calcium fluoride particles are housed in a Teflon container, dried at, for example, 160°C for about 10 hours, and then large particles are removed using, for example, a 1 mm sieve.

[0049] As the molding method, for example, the following two methods are available.

[0050] In the first molding method, the calcium fluoride particles classified as described above are molded into a molded body by using a mold having a prescribed shape.

[0051] In the second molding method, a slurry containing the calcium fluoride particles manufactured by the above-described manufacturing method of calcium fluoride particles is housed in, for example, a disk-shaped container, and dried at 70 to 300°C for about 10 hours to mold a molded body.

[0052] In step S8, the molded body (molded body having a relative density of 35 to 50%) molded by the above-described first molding method or second molding method is sintered to produce a sintered body (white sintered body) (sintering step). In the sintering step, the white molded body is sintered (initial sintering) at, for example, 400 to 700°C for 2 to 6 hours to produce a white sintered body having a relative density of about 40 to 70%. Note that if the relative density of the molded body before sintering is too high, the white sintered body does not become transparent in the subsequent step. In addition, if the temperature at the time of sintering is too high, the initial sintering progresses, and the driving force of sintering in the subsequent step becomes small, which causes an increase in optical strain (i.e., deterioration of optical properties). In addition, if the temperature at the time of sintering is too low, organic components remain in the sintered body, and a high transmittance cannot be obtained.

[0053] Next, under a non-reactive atmosphere (for example, vacuum, argon, nitrogen atmosphere), the white sintered body is maintained at, for example, 900 to 1000°C for 1 to 2 hours to obtain a white sintered body having a relative density of about 98%.

[0054] In step S9, the white sintered body is subjected to a heating and pressurization treatment based on, for example, a hot isostatic press (HIP) to be transparent, and a transparent sintered body is produced (transparency step). Specifically, the white sintered body is maintained at a pressure of 100 MPa in a non-reactive atmosphere (for example, argon atmosphere), and, for example, heated to 1000 to 1100°C. As a result, the pores remaining in the white sintered body are extruded to the outside, and a transparent sintered body (i.e., the calcium fluoride sintered body of the present embodiment) is produced. That is, the processes of steps S7 to S9 described above are processes in the manufacturing method of the calcium fluoride sintered body in the present embodiment.

[0055] Note that, if necessary, an annealing process for annealing the transparent sintered body can be provided after the transparent process. The annealing is performed, for example, in a non-active atmosphere, at a temperature of 600°C or higher and 800°C or lower for a heating time of 40 hours or more. Thus, the optical strain of the transparent sintered body can be further reduced, for example, to 2 nm / cm or less.

[0056] An embodiment of an imaging device provided with an optical element composed of the calcium fluoride sintered body manufactured as described above will be described.

[0057] Figure 3 is a perspective view of an imaging device of the present embodiment. The imaging device 1 is a so-called digital single-lens reflex camera (interchangeable lens camera), and a photographic lens 103 (optical system) is provided with an optical element using the calcium fluoride sintered body of the present embodiment as a base material. The lens barrel 102 is detachably attached to a lens mount (not shown) of the camera body 101. Light from the photographic 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 back side of the camera body 101. The sensor chip 104 is a so-called CMOS image sensor or the like, and the multi-chip module 106 is, for example, a COG (Chip On Glass) type module in which the sensor chip 104 is mounted on a glass substrate 105.

[0058] Figure 4 is a front view of another example of an imaging device provided with an optical element composed of the calcium fluoride sintered body of the present embodiment, Figure 5 is a front view of another example of an imaging device provided with an optical element composed of the calcium fluoride sintered body of the present embodiment, Figure 4 is a rear view of the imaging device of

[0059] The imaging device CAM is a so-called digital still camera (non-interchangeable lens camera), and a photographic lens WL (optical system) is provided with an optical element using the calcium fluoride sintered body of the present embodiment as a base material. When a power button (not shown) is pressed, the shutter (not shown) of the photographic lens WL is opened, and light from an object is condensed by the photographic lens WL and imaged on an imaging device arranged on an image plane. An object image imaged on the imaging device is displayed on a liquid crystal monitor LM arranged behind the imaging device CAM. After a photographer decides the composition of the object image while observing the liquid crystal monitor LM, the object image is imaged by the imaging device by pressing a release button B1, and recorded and saved in a memory (not shown).

[0060] An auxiliary light emitting section EF that emits auxiliary light in a case where a subject is dark, a function button B2 for setting various conditions of the camera, and the like are provided in the camera CAM. For an optical system for such a digital camera and the like, higher resolution, weight reduction, and downsizing are required. In order to achieve these, it is effective to use a glass having a high refractive index in the optical system. In particular, a demand for a glass having a high refractive index and having a lower specific gravity (S g ), a high moldability is high. From such a viewpoint, the calcium fluoride sintered body of the present embodiment is suitable as a member of an optical device.

[0061] Note that, as the optical device that can be applied in the present embodiment, not limited to the above-described camera, for example, a projector and the like can be cited. As the optical element, not limited to the lens, for example, a prism and the like can be cited.

[0062] Next, a multi-photon microscope provided with an optical element using the calcium fluoride sintered body of the present embodiment is described.

[0063] Figure 6 is a block diagram showing an example of the configuration of a multi-photon microscope 2 of the present embodiment. The multi-photon 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 is provided with an optical element having the calcium fluoride sintered body of the present embodiment as a base material. Hereinafter, description is made focusing on the optical system of the multi-photon microscope 2.

[0064] The pulse laser device 201, for example, emits near-infrared rays (about 1000 nm) and an ultrashort pulse light having a pulse width of femtosecond units (for example, 100 femtosecond). The ultrashort pulse light immediately after being emitted from the pulse laser device 201 is generally linearly polarized light having a vibration direction of an electric field in a prescribed direction. The pulse separation device 202 divides the ultrashort pulse light, increases the repetition frequency of the ultrashort pulse light, and emits it.

[0065] The beam adjustment section 203 has a function of adjusting the beam diameter of the ultrashort pulse light incident from the pulse separation device 202 according to the pupil diameter of the objective lens 206, a function of adjusting the condensing and divergence angles of the ultrashort pulse light in order to correct the on-axis chromatic aberration (focal point difference) of the wavelength of the multi-photon excitation light emitted from the sample S and the wavelength of the ultrashort pulse light, and a pre-chirping function (group velocity dispersion compensation function) of imparting the opposite group velocity dispersion to the ultrashort pulse light in order to correct the phenomenon that the pulse width of the ultrashort pulse light is expanded during passing through the optical system due to the group velocity dispersion.

[0066] The ultra-short pulse light emitted from the pulse laser device 201 is made to have a larger repetition frequency by the pulse division device 202, and the adjustment described above is performed by the beam adjustment section 203. The ultra-short pulse light emitted from the beam adjustment section 203 is reflected by the dichroic mirror 204 toward the direction of the dichroic mirror 205 and passes through the dichroic mirror 205, is condensed by the objective lens 206, and is irradiated to the sample S. At this time, the ultra-short pulse light can also be scanned on the observation surface of the sample S by using a scanning unit (not shown).

[0067] For example, in the case of performing fluorescence observation on the sample S, the fluorescent coloring matter of the sample S dyed in the irradiated region of the ultra-short pulse light of the sample S and its vicinity is multi-photonic excited, and emits fluorescence (hereinafter, referred to as observation light) having a shorter wavelength than the ultra-short pulse light which is an infrared wavelength. The observation light emitted from the sample S toward the direction of the objective lens 206 is collimated by the objective lens 206, and is reflected by the dichroic mirror 205 or passes through the dichroic mirror 205 according to its wavelength.

[0068] The observation light reflected by the dichroic mirror 205 is incident to the fluorescence detection section 207. The fluorescence detection section 207 is constituted by, for example, a barrier filter, a PMT (Photo Multiplier Tube), or the like, receives the observation light reflected by the dichroic mirror 205, and outputs an electric signal corresponding to the light amount thereof. In addition, the fluorescence detection section 207 detects the observation light over the observation surface of the sample S in correspondence with the scanning of the ultra-short pulse light on the observation surface of the sample S.

[0069] Note that, by removing the dichroic mirror 205 from the optical path, the fluorescence detection section 211 can also detect all of the observation light emitted from the sample S toward the direction of the objective lens 206.

[0070] In this case, the observation light is de-scanned by the scanning unit (not shown), passes through the dichroic mirror 204, is condensed by the condenser lens 208, passes through the pinhole 209 provided at a position substantially conjugate to the focal position of the objective lens 206, and is incident to the fluorescence detection section 211 through the imaging lens 210. The fluorescence detection section 211 is constituted by, for example, a barrier filter, a PMT, or the like, receives the observation light imaged on the light-receiving surface of the fluorescence detection section 211 by the imaging lens 210, and outputs an electric signal corresponding to the light amount thereof. In addition, the fluorescence detection section 211 detects the observation light over the observation surface of the sample S in correspondence with the scanning of the ultra-short pulse light on the observation surface of the sample S.

[0071] In addition, 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 is incident on the fluorescence detection section 213. The fluorescence detection section 213 is configured by, for example, a barrier filter, a PMT, or the like, receives the observation light reflected by the dichroic mirror 212, and outputs an electric signal corresponding to the light quantity thereof. In addition, the fluorescence detection section 213 detects the observation light over the observation surface of the sample S in correspondence with the scanning of the ultrashort pulse light in the observation surface of the sample S.

[0072] The electric signals output from the fluorescence detection sections 207, 211, 213 are input, for example, to a computer (not shown). The computer can generate an observation image on the basis of the input electric signals, and display the generated observation image, or store data of the observation image.

[0073] According to the above-described embodiments, the following advantageous effects can be obtained.

[0074] (1) A method for manufacturing calcium fluoride particles includes: a generation step of generating a dispersion liquid containing calcium fluoride particles by causing a calcium compound and a fluorine compound to react 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 and a liquid component after the mixing step. Thus, it is possible to manufacture calcium fluoride particles that can be used when manufacturing a calcium fluoride sintered body having high transmittance.

[0075] (2) The concentration of hydrogen fluoride in the aqueous hydrofluoric acid solution used in the mixing step is 0.1% or more and 20% or less. Thus, it is possible to suppress the generation of white spots of about 0.1 mm that are aggregates of fine bubbles in the inside of a sintered body obtained by sintering the manufactured calcium fluoride particles.

[0076] (3) A method for manufacturing a calcium fluoride sintered body includes: a molding step of forming a molded body by molding calcium fluoride particles manufactured by the above-described method for manufacturing calcium fluoride particles; and a sintering step of generating a sintered body by sintering the molded body in an inactive atmosphere. Thus, it is possible to manufacture a calcium fluoride sintered body having high transmittance.

[0077] (4) In the molding step, calcium fluoride particles having a particle size of 20 μm or less are molded to form a molded body. Thus, it is possible to obtain a molded body of calcium fluoride particles for manufacturing a calcium fluoride sintered body having high transmittance.

[0078] (5) In a method for producing a calcium fluoride sintered body, in a sintering step, a molded body having a relative density of 35% to 50% is sintered (initial sintering) at 400°C to 700°C for 2 hours to 6 hours, and then sintered in an inert atmosphere at 900°C to 1000°C for 1 hour to 2 hours. By performing the initial sintering at 400°C to 700°C, it is possible to prevent a decrease in the driving force for sintering in subsequent steps and an increase (deterioration) in optical strain during grain growth, as would occur if the sintering temperature were too high. Furthermore, it is possible to suppress a decrease in transmittance due to residual organic components in the raw materials caused by an excessively low temperature.

[0079] (6) The method for producing a calcium fluoride sintered body includes a transparentizing step after the sintering step, wherein the sintered body is heated to 1000°C to 1100°C while applying a pressure of 100 MPa in an inert atmosphere to make the sintered body transparent. Thus, a transparent calcium fluoride sintered body can be obtained.

[0080] Examples of the calcium fluoride sintered body according to the above embodiment will be described.

[0081] [Example]

[0082] according to Figure 1 The calcium fluoride sintered body in the example was produced by the process shown in the flowchart of . In the example, calcium acetate hydrate was used as the calcium compound and hydrofluoric acid was used as the fluorine compound.

[0083] In the examples, 20 calcium fluoride sintered body (transparent sintered body) samples were prepared under different production and sintering conditions for the calcium fluoride particles. Each double-sided polished sample was then measured for internal transmittance and optical strain at a wavelength of 550 nm. Optical strain was measured using an automatic strain gauge, the LSM-9000s (manufactured by Luceo Co., Ltd.).

[0084] Figure 7 The following shows the conditions for producing and sintering calcium fluoride particles used in samples 1 to 12 of the calcium fluoride sintered bodies of the examples, and the measurement results of the internal transmittance of light at a wavelength of 550 nm and the optical strain of the calcium fluoride sintered bodies. Figure 8 The following shows the conditions for producing and sintering calcium fluoride particles used in samples 13 to 24 of the calcium fluoride sintered bodies of the examples, as well as the measurement results of the internal transmittance and optical strain of the calcium fluoride sintered bodies at a wavelength of 550 nm. Figure 7 and Figure 8 The "transmittance" in the sample is the internal transmittance of light with a wavelength of 550nm per 10mm thickness of the sample. In other words, it is the internal transmittance of light per 10mm of actual travel distance in the sample. The "F / Ca ratio" is Figure 1In the production process of Step S3, the molar ratio of the aqueous fluorine compound solution (hydrofluoric acid) injected into the aqueous calcium acetate solution with respect to the aqueous calcium compound solution (aqueous calcium acetate solution). The "hydrofluoric acid concentration" is the concentration of the hydrofluoric acid in the aqueous calcium acetate solution at the time of the production process of Step S3. Figure 1 In the mixing process of Step S5, the concentration of the hydrofluoric acid in which the calcium fluoride particles are mixed. The "hydrothermal temperature" is the temperature at which the crystal grain growth and crystallization of the calcium fluoride particles are performed in the heating and pressurizing process of Step S4. Figure 1 In the heating and pressurizing process of Step S4, the temperature at which the crystal grain growth and crystallization of the calcium fluoride particles are performed. The "number of water washing" is the number of times of repeating the process of mixing the calcium fluoride particles and distilled water, stirring, separating the solid and the liquid, and removing the supernatant in Step S6. Figure 1 In Step S6, the number of times of repeating the process of mixing the calcium fluoride particles and distilled water, stirring, separating the solid and the liquid, and removing the supernatant. The "drying temperature" is the temperature at which the calcium fluoride particles are dried in Step S7. Figure 1 In the sintering process of Step S8, the sintering temperature at which the sintered body is generated by sintering the molded body to have a relative density of about 40 to 70%. The "non-active atmosphere sintering temperature" is the sintering temperature at which the white sintered body is generated in the sintering process of Step S8. Figure 1 In the sintering process of Step S8, the sintering temperature at which the white sintered body is generated to have a relative density of 98%. The "HIP temperature" is the heating temperature at which the HIP treatment is performed in the "transparency process" of Step S9. Figure 1 In the "transparency process" of Step S9, the heating temperature at which the HIP treatment is performed.

[0085] As shown in Figure 7 and Figure 8 , the internal transmittance of the light of wavelength 550 nm of the calcium fluoride sintered body of Samples 1 to 24 in the examples was 98% or more. In addition, the optical strain of the calcium fluoride sintered body of Samples 1 to 22 was 10 nm / cm or less.

[0086] Figure 9A , Figure 9B to Figure 13 is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body of Samples 1 to 24. Figure 9A , Figure 9B to Figure 13 The transmittance shown in the graph is the internal transmittance of each 10 mm thickness of the sample. In other words, it is the internal transmittance of the light actually advancing every 10 mm in the sample. Figure 9A L1 to L6 represent the measurement results of the spectral transmittance of the light of wavelengths 200 nm to 800 nm of Samples 1 to 6, Figure 9B L7 to L12 represent the measurement results of the spectral transmittance of the light of wavelengths 200 nm to 800 nm of Samples 7 to 12. Figure 10A L13 to L17 represent the measurement results of the spectral transmittance of the light of wavelengths 200 nm to 800 nm of Samples 13 to 17, Figure 10B L18 to L22 represent the measurement results of the spectral transmittance of the light of wavelengths 200 nm to 800 nm of Samples 18 to 22.

[0087] Figure 11AThe measurement results of the spectral transmittance of light of wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) of the calcium fluoride sintered bodies of samples 1 to 6 are shown by Ml to M6. Figure 11B The measurement results of the spectral transmittance of light of wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) of the calcium fluoride sintered bodies of samples 7 to 12 are shown by M7 to M12. Figure 12A The measurement results of the spectral transmittance of light of wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) of the calcium fluoride sintered bodies of samples 13 to 17 are shown by M13 to M17. Figure 12B The measurement results of the spectral transmittance of light of wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) of the calcium fluoride sintered bodies of samples 18 to 22 are shown by M18 to M22. Figure 13 The measurement results of the spectral transmittance of light of wavelengths from 3000 nm (3 μm) to 13000 nm (13 μm) of the calcium fluoride sintered bodies of samples 23 and 24 are shown by M23 and M24. As Figure 9A , Figure 9B , Figure 10A , Figure 10B As shown in Table 1, the internal transmittance of the calcium fluoride sintered bodies of the examples was 90% or more for light of wavelengths from 380 nm to 780 nm. As Figure 11A , Figure 11B , Figure 12A , Figure 12B , Figure 13 As shown in Table 2, the internal transmittance of the calcium fluoride sintered bodies of the examples was 90% or more for light of wavelengths from 3000 nm (3 μm) to 7000 nm (7 μm). Further, as Figure 11A , Figure 11B , Figure 12A , Figure 12B , Figure 13 As shown in Table 3, in the infrared region, the internal transmittance of the calcium fluoride sintered bodies was 80% or more for wavelengths IRλ 80 or more.

[0088] Further, for the calcium fluoride sintered bodies of samples 23 and 24, the annealing process was performed under conditions of a start temperature of 800°C, a temperature decrease rate of 5°C / h, and an end temperature of 600°C. As a result, the optical strain of the calcium fluoride sintered bodies of samples 23 and 24 was 1.5 nm / cm, respectively.

[0089] In the above-described samples 1 to 24, the calcium fluoride sintered bodies were produced using calcium acetate hydrate as the calcium compound, but as sample 25, a calcium fluoride sintered body was prepared using calcium nitrate as the calcium compound. Figure 16The following table shows the conditions for producing and sintering the calcium fluoride particles used in the calcium fluoride sintered body of Sample 25, and the measurement results of the internal transmittance of light of a wavelength of 550 nm and the optical strain of the calcium fluoride sintered body. Figure 16 The "transmittance" in the sample is the internal transmittance of light with a wavelength of 550nm per 10mm thickness of the sample. In other words, it is the internal transmittance of light per 10mm of actual travel distance in the sample. The "F / Ca ratio" is Figure 1 In the step S3 of the production process, the molar ratio of the fluorine compound aqueous solution (hydrofluoric acid) to the calcium compound aqueous solution (calcium carbonate aqueous solution) injected into the calcium carbonate aqueous solution is calculated. Figure 1 The concentration of hydrofluoric acid in the mixing process of step S5 is the concentration of the hydrofluoric acid in the mixing process of step S5. Figure 1 The temperature at which the calcium fluoride particles grow and crystallize in the heating and pressing process of step S4 is used. Figure 1 In step S6, the process of mixing and stirring the calcium fluoride particles and distilled water, separating the solid and the liquid, and removing the supernatant is repeated for a certain number of times. Figure 1 The sintering temperature at which the compact is sintered in the sintering process of step S8 to produce a white sintered compact having a relative density of about 40 to 70%. Figure 1 The sintering temperature when a white sintered body with a relative density of 98% is generated in the sintering process of step S8. Figure 1 The heating temperature during the HIP treatment in the "transparentizing step" of step S9.

[0090] like Figure 16 As shown, the internal transmittance of light with a wavelength of 550 nm of the calcium fluoride sintered body of Sample 25 is 98% or higher. In addition, the optical strain of the calcium fluoride sintered body of Sample 25 is 25 nm / cm or less.

[0091] Figure 17 This is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body of Sample 25. Figure 17 The transmittance shown is the internal transmittance per 10mm thickness of the sample. In other words, it is the internal transmittance per 10mm actual distance traveled by light in the sample. Figure 17 As shown, the internal transmittance of the calcium fluoride sintered body of Sample 25 for light with a wavelength of 380 nm to 780 nm is 90% or more.

[0092] As described above, it was shown that the calcium fluoride sintered body of this example is polycrystalline and has high transmittance.

[0093] [Comparative Example 1]

[0094] The calcium fluoride sintered body in Comparative Example 1 was manufactured using calcium acetate hydrate as the calcium compound and hydrofluoric acid as the fluorine compound, similarly to the Examples. The calcium fluoride sintered body of Comparative Example 1 was manufactured using calcium fluoride particles generated without the mixing process described as Step S5 above. In the calcium fluoride sintered body of Comparative Example 2, foreign matter was generated.

[0095] Figure 14A 、 Figure 14B is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body of Comparative Example 1. Figure 14A 、 Figure 14B The transmittance shown is the internal transmittance per 10 mm thickness of the sample. In other words, the internal transmittance per actual distance of 10 mm that light travels in the sample. Figure 14A shows the results of measuring the spectral transmittance of light having a wavelength of 200 nm to 800 nm, Figure 14B shows the results of measuring the spectral transmittance of light having a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm). The internal transmittance per 10 mm thickness of the calcium fluoride sintered body of Comparative Example 1 for light having a wavelength of 550 nm was 97.7%, which is less than 98%.

[0096] [Comparative Example 2]

[0097] The calcium fluoride sintered body in Comparative Example 2 was manufactured using calcium acetate hydrate as the calcium compound and hydrofluoric acid as the fluorine compound, similarly to the Examples. The calcium fluoride sintered body of Comparative Example 2 was manufactured using calcium fluoride particles generated without the mixing process described as Step S5 above. In the calcium fluoride sintered body of Comparative Example 2, foreign matter was generated.

[0098] Figure 15A 、 Figure 15B is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body of Comparative Example 2. Figure 15A 、 Figure 15B The transmittance shown is the internal transmittance per 10 mm thickness of the sample. In other words, the internal transmittance per actual distance of 10 mm that light travels in the sample. Figure 15A shows the results of measuring the spectral transmittance of light having a wavelength of 200 nm to 800 nm, Figure 15B shows the results of measuring the spectral transmittance of light having a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm). As Figure 15A 、 Figure 15BAs shown, the range of wavelengths of light for which the internal transmittance is 90% or more is narrower than in the case of the example. In addition, the internal transmittance of light of wavelength 550 nm per 10 mm thickness of the calcium fluoride sintered body of Comparative Example 2 was 87.7%, which is less than 98%.

[0099] The present application is not limited to the above-described embodiments, and other modes that can be conceived within the scope of the technical idea of the present application are also included in the scope of the present application, as long as the features of the present application are not impaired.

[0100] Symbol explanation

[0101] 1 camera

[0102] 2 multiphoton microscope

[0103] 103 photographic lens

[0104] 206 objective lens

[0105] 208 condenser lens

[0106] 210 imaging lens

[0107] CAM... camera

[0108] WL... photographic lens

Claims

1. A calcium fluoride polycrystal, wherein: The internal transmittance of light with a wavelength of 550 nm per 10 mm thickness is 98% or higher, and the optical strain is 10 nm / cm or less.

2. The calcium fluoride polycrystal according to claim 1, wherein The internal transmittance of light with a wavelength of 380nm to 780nm per 10mm thickness is 90% or more.

3. The calcium fluoride polycrystal according to claim 1 or 2, wherein: The internal transmittance of light with a wavelength of 3μm to 7μm per 10mm thickness is over 90%.

4. The calcium fluoride polycrystalline according to any one of claims 1 to 3, wherein In the infrared region, the wavelength IRλ at which the internal transmittance per 10mm thickness is 80% or more 80 It is 8μm or more.

5. The calcium fluoride polycrystal according to any one of claims 1 to 4, wherein The relative density is above 98%.

6. The calcium fluoride polycrystalline according to any one of claims 1 to 5, wherein Only calcium fluoride produced from a calcium compound and a fluorine compound is contained as the fluorine compound.

7. A method for producing calcium fluoride polycrystals, comprising: A first heating step comprises heating the molded body of calcium fluoride particles having a relative density of 35% or more in an inert atmosphere at a temperature of 900° C. or more for 1 hour or more; and The second heating step is performed after the first heating step, and is performed by heating the molded body to 1000° C. or higher while applying pressure in an inert atmosphere.

8. The method for producing calcium fluoride polycrystals according to claim 7, wherein: Before the first heating step, the method further comprises heating the molded body at 400° C. or higher for 2 hours or longer.

9. The method for producing calcium fluoride polycrystals according to claim 7 or 8, wherein: In the first heating step, the molded body is heated at 1000° C. or lower for 2 hours or lower.

10. The method for producing a calcium fluoride polycrystal according to any one of claims 7 to 9, wherein: In the second heating step, the molded body is heated at 1100° C. or lower.

11. The method for producing a calcium fluoride polycrystal according to any one of claims 7 to 10, wherein: The production method further includes a molding step of molding the calcium fluoride particles having a particle size of 1 mm or less to form the molded body.

12. The method for producing calcium fluoride polycrystals according to claim 11, wherein: In the molding step, the calcium fluoride particles are compression molded at a pressure of 1 kN or more to form the molded body.

13. The method for producing calcium fluoride polycrystals according to claim 11, wherein: In the molding step, the calcium fluoride particles are placed in a container of a predetermined shape and dried at 300° C. or lower to form the particles.

14. The method for producing a calcium fluoride polycrystal according to any one of claims 7 to 13, wherein: The manufacturing method includes a third heating step after the second heating step, wherein the formed body is heated in an inert atmosphere at a temperature lower than that in the second heating step.

15. The method for producing calcium fluoride polycrystals according to claim 14, wherein: In the third heating step, the molded body is heated at 600° C. or higher for 40 hours or longer. 16 . A calcium fluoride polycrystal produced by the method for producing a calcium fluoride polycrystal according to claim 7 .

17. An optical element using the calcium fluoride polycrystal according to any one of claims 1 to 6 or 16.

18. An optical system comprising the optical element according to claim 17. An optical device comprising the optical system according to claim 18 .

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