Calcium fluoride polycrystal, calcium fluoride particle, method for manufacturing polycrystal, optical element and system, replacement lens, and optical device

Abstract

A calcium fluoride polycrystal having an internal transmittance of 98% or more for light of a wavelength of 550 nm per a thickness of 10 mm.

Description

Technical Field

[0001] The present invention relates to calcium fluoride polycrystals, a method for producing calcium fluoride particles, a method for producing calcium fluoride polycrystals, an optical element, an optical system, a replacement lens, and an optical device. Background Art

[0002] There is a proposal for a method for producing a calcium fluoride sintered body by hot pressing (for example, Patent Document 1).

[0003] However, the transmittance of a sintered body is lower than that of a single crystal, and in order to use it as an optical component, the transmittance is required to be improved.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-300777 Summary of the Invention

[0007] According to the first embodiment, the internal transmittance of the calcium fluoride polycrystal for light of a wavelength of 550 nm per a thickness of 10 mm is 98% or more.

[0008] According to a second embodiment, a method for producing calcium fluoride particles comprises: a generating step of reacting a calcium compound and a fluorine compound in a solution to generate a dispersion containing calcium fluoride particles; a mixing step of mixing the calcium fluoride particles contained in the dispersion with hydrofluoric acid; and a separating step of separating the calcium fluoride particles and the hydrofluoric acid after the mixing step.

[0009] According to a third aspect, a method for producing calcium fluoride polycrystals comprises: a molding step of molding calcium fluoride particles produced by the method for producing calcium fluoride particles according to the second aspect to form a molded body; and a sintering step of sintering the molded body in an inert atmosphere to produce a polycrystal.

[0010] According to a fourth aspect, the calcium fluoride polycrystal according to the first aspect is used in an optical element.

[0011] According to a fifth aspect of the present invention, an optical system includes the optical element according to the fourth aspect.

[0012] According to a sixth aspect, the interchangeable lens includes the optical system according to the fifth aspect.

[0013] According to a seventh aspect, an optical device includes the optical system according to the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flowchart illustrating a method for producing a calcium fluoride sintered body according to an embodiment.

[0015] Figure 2 This is a diagram schematically showing an example of a stirring device used when reacting an aqueous calcium compound solution and an aqueous fluorine compound solution.

[0016] Figure 3 It is a perspective view showing an example of an imaging device according to an embodiment.

[0017] Figure 4 This is a front view showing another example of the imaging device according to the embodiment.

[0018] Figure 5 This is a rear view showing another example of the imaging device according to the embodiment.

[0019] Figure 6 This is a block diagram showing an example of a multiphoton microscope according to an embodiment.

[0020] Figure 7 The conditions for producing the calcium fluoride particles of the examples and the measurement results of the internal transmittance and optical strain of the calcium fluoride sintered body with respect to light having a wavelength of 550 nm are shown.

[0021] Figure 8 The conditions for producing the calcium fluoride particles of the examples and the measurement results of the internal transmittance and optical strain of the calcium fluoride sintered body with respect to light having a wavelength of 550 nm are shown.

[0022] Figure 9A This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0023] Figure 9B This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0024] Figure 10A This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0025] Figure 10B This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0026] Figure 11A This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0027] Figure 11B This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0028] Figure 12A This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0029] Figure 12BThis is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0030] Figure 13 This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples.

[0031] Figure 14A This is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Comparative Example 1.

[0032] Figure 14B This is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Comparative Example 1.

[0033] Figure 15A This is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Comparative Example 2.

[0034] Figure 15B This is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body in Comparative Example 2.

[0035] Figure 16 The conditions for producing the calcium fluoride particles of the examples and the measurement results of the internal transmittance and optical strain of the calcium fluoride sintered body with respect to light having a wavelength of 550 nm are shown.

[0036] Figure 17 This is a graph showing the results of measuring the spectral transmittance of a calcium fluoride sintered body in Examples. DETAILED DESCRIPTION

[0037] The calcium fluoride (CaF2) sintered body, the method for producing calcium fluoride particles, and the method for producing a calcium fluoride sintered body according to the embodiment will be described with reference to the accompanying drawings. Note that the sintered body in this specification refers to a polycrystalline body.

[0038] The internal transmittance of the calcium fluoride sintered body of this embodiment for light with a wavelength of 550 nm per 10 mm thickness is 98% or more. The internal transmittance of the calcium fluoride sintered body of this embodiment for light with a wavelength of 380 nm to 780 nm per 10 mm thickness can be 90% or more. In addition, the internal transmittance of the calcium fluoride sintered body of this embodiment for light with a wavelength of 3 μm to 7 μm per 10 mm thickness can be 90% or more. In addition, in the infrared region, the internal transmittance of the calcium fluoride sintered body of this embodiment for light with a wavelength of IRλ is 80% or more per 10 mm thickness. 80 The optical strain of the calcium fluoride sintered body of this embodiment can be 25 nm / cm or less, 20 nm / cm or less, or 10 nm / cm or less. The relative density of the calcium fluoride sintered body of this embodiment relative to the density of a calcium fluoride single crystal can be 98% or more.

[0039] Reference Figure 1 A method for producing the above-mentioned calcium fluoride sintered body and a method for producing calcium fluoride particles as a material of the calcium fluoride sintered body will be described.

[0040] 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 a calcium compound aqueous solution. When an organic salt such as calcium acetate is used, nitric acid is preferably added as an oxidizing agent.

[0041] In step S2, distilled water is added to high-purity hydrofluoric acid (HF) to dilute it to an appropriate concentration to prepare a fluorine compound aqueous solution. It should be noted that ammonium fluoride or the like can also be used instead of HF to prepare the fluorine compound aqueous solution by dissolving the ammonium fluoride in distilled water.

[0042] In step S3, the calcium compound aqueous solution is reacted with the fluorine compound aqueous solution (i.e., the calcium compound and the fluorine compound are reacted in the aqueous solution) to generate a dispersion containing calcium fluoride particles (generation process). 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 relative to the calcium compound aqueous solution. In this case, Figure 2 The stirring device 3 shown has a stirring rod 31 (blade diameter 10 cm) that rotates at 300 rpm, stirring the calcium compound aqueous solution while slowly injecting the fluorine compound aqueous solution. Fluorine compound aqueous solution injection ports 33 and 34 are installed on the side of the plastic beaker 32 of the stirring device 3. 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), for example, over about 1 hour. 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. In this way, the aggregation of calcium fluoride particles can be suppressed and calcium fluoride particles with a small particle size can be generated. The stirring after the fluorine compound aqueous solution is injected is carried out, for example, in a water bath maintained at a temperature of 5 to 10°C. Stirring at a low temperature can improve the transmittance of the calcium fluoride sintered body manufactured using the generated calcium fluoride particles.

[0043] In step S4, the dispersion containing calcium fluoride particles is simultaneously heated and pressurized to promote the reaction between the calcium compound and the fluorine compound, causing the calcium fluoride particles to grow larger and improving their crystallinity (heating and pressurizing step). Specifically, the dispersion containing calcium fluoride particles (a dispersion (slurry) in which calcium fluoride microparticles are suspended) is heated and pressurized in a sealed container (e.g., an autoclave equipped with a Teflon (registered trademark) container) for a period of 10 to 24 hours, for example, while maintaining the temperature between 100°C and 180°C. After the heating and pressurizing step, when the temperature of the sealed container is lowered to room temperature, the supernatant is removed by aspiration, leaving the calcium fluoride particles and separating them. In step S5, the separated calcium fluoride particles are mixed with, for example, 0.1 to 20% hydrofluoric acid and stirred (mixing step).

[0044] In step S6, the hydrofluoric acid mixture of calcium fluoride particles generated by the mixing process is transferred to a centrifuge tube, and the centrifuge tube is placed in a centrifuge to separate the mixture into solid (calcium fluoride particles) and liquid (hydrofluoric acid) (separation process). In this case, for example, the rotation speed of the centrifuge is set to 1000 rpm, and centrifugation is performed for 10 minutes. After the solid and liquid are separated, the supernatant is removed, and then distilled water is injected into the centrifuge tube where the calcium fluoride particles remain to fully disperse the calcium fluoride particles. At this time, by using an oscillator to disperse the calcium fluoride particles, foreign matter can be prevented from entering from the outside. After oscillating for about 30 minutes until the calcium fluoride particles are in a non-precipitated state by the oscillator, the mixture is separated into solid and liquid again using a centrifuge, the supernatant is removed, and distilled water is further injected to fully 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 liquid using a centrifuge are repeated until the concentration of hydrofluoric acid in the supernatant is below 200 ppm. If the number of distilled water injections is too low, the transmittance of the calcium fluoride sintered body produced using the generated calcium fluoride particles is low, and numerous white spots of approximately 0.1 mm in diameter, representing aggregates of fine bubbles, are observed within the body. Furthermore, as the number of distilled water injections increases, the calcium fluoride particles become less agglomerated, their particle size decreases, and sedimentation becomes difficult. Therefore, the centrifuge speed is gradually increased, for example, to 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, and finally 2000 rpm.

[0045] It should be noted that the separation process is not limited to the method using the above-mentioned oscillator and centrifuge. For example, the separation process can also be carried out using a well-known filter. As a filter, a Nutsche filter or the like can be cited. When using a Nutsche filter, first, water is added to the hydrofluoric acid mixture of calcium fluoride particles generated by the mixing process and stirred to produce a thin slurry. Then, the thin slurry is supplied to the Nutsche filter, and the thin slurry is filtered while applying pressure to the thin slurry. At this time, it is preferred to apply pressure while supplying water. When using such a filter, the separation process can be carried out in a shorter time than when using an oscillator and a centrifuge.

[0046] The processes of steps S1 to S6 described above are processes in the method for producing calcium fluoride particles in the present embodiment.

[0047] In step S7, calcium fluoride particles classified to a particle size of less than a predetermined size from among the particles obtained by pulverizing a dried body (filter cake) of calcium fluoride particles produced by the above-described 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-described method in a Teflon container, drying them at, for example, 160° C. for approximately 10 hours, and then removing large particles using, for example, a 1 mm sieve.

[0048] As the molding method, there are the following two, for example.

[0049] In the first molding method, the classified calcium fluoride particles are compression molded using a mold having a predetermined shape to form a molded body.

[0050] 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 molded body.

[0051] In step S8, the molded body (a molded body with a relative density of 35 to 50%) molded by the above-mentioned first molding method or the second molding method is sintered to generate a sintered body (white sintered body) (sintering process). In the sintering process, the above-mentioned white molded body is sintered (initial sintering) at, for example, 400 to 700°C for 2 to 6 hours to generate a white sintered body with a relative density increased to about 40 to 70%. It should be noted that if the relative density of the molded body before sintering is too high, the white sintered body will not become transparent in the subsequent process. In addition, if the temperature during sintering is too high, the initial sintering progresses, and the driving force for sintering in the subsequent process becomes smaller, which becomes a cause of increased optical strain (i.e., deterioration of optical properties). In addition, if the temperature during sintering is too low, organic components remain in the sintered body, and high transmittance cannot be obtained.

[0052] Next, the mixture is kept at 900-1000° C. for 1-2 hours in an inert atmosphere (eg, vacuum, argon, or nitrogen atmosphere) to obtain a white sintered body having a relative density of approximately 98%.

[0053] In step S9, the white sintered body is subjected to a heat and pressure treatment, for example, using a hot isostatic pressing (HIP) apparatus, to make it transparent, thereby producing a transparent sintered body (transparentization step). Specifically, the white sintered body is heated to, for example, 1000-1100°C in an inert atmosphere (for example, an argon atmosphere) while maintaining a pressure of 100 MPa. This squeezes out any pores remaining within the white sintered body, producing a transparent sintered body (i.e., the calcium fluoride sintered body of this embodiment). In other words, the processes of steps S7-S9 described above constitute the processes of the method for producing the calcium fluoride sintered body of this embodiment.

[0054] It should be noted that an annealing step may be performed after the transparentization step, if necessary, to anneal the transparent sintered body. Annealing can be performed, for example, in an inert atmosphere, at a temperature range of 600°C to 800°C, for a heating time of at least 40 hours. This can further reduce the optical strain of the transparent sintered body, for example, to below 2 nm / cm.

[0055] An embodiment of an imaging device including an optical element composed of the calcium fluoride sintered body manufactured as described above will be described.

[0056] Figure 3This is a perspective view of an imaging device according to this embodiment. Imaging device 1 is a so-called digital single-lens reflex camera (lens-interchangeable camera), and its photographic lens 103 (optical system) includes an optical element whose base material is the calcium fluoride sintered body according to this embodiment. A lens barrel 102 is detachably mounted on a lens mount (not shown) of a camera body 101. Light from the photographic lens 103 passing through the lens barrel 102 forms an image on a sensor chip (solid-state imaging element) 104 of a multi-chip module 106 disposed on the back 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 bare sensor chip 104 is mounted on a glass substrate 105.

[0057] Figure 4 FIG. 1 is a front view of another example of an imaging device including an optical element composed of a calcium fluoride sintered body according to this embodiment. Figure 5 yes Figure 4 Rear view of the camera device.

[0058] This imaging device CAM is a so-called digital still camera (non-lens-replaceable camera). Its photographic lens WL (optical system) includes an optical element whose base material is the calcium fluoride sintered body of this embodiment. When the power button (not shown) of the imaging device CAM is pressed, the shutter (not shown) of the photographic lens WL opens, and light from the subject (object) is focused by the photographic lens WL, forming an image on the imaging element disposed on the imaging plane. The subject image formed on the imaging element is displayed on the liquid crystal monitor LM disposed behind the imaging device CAM. After the photographer determines the composition of the subject image while observing the liquid crystal monitor LM, they press the release button B1, causing the subject image to be captured by the imaging element and recorded and stored in a memory (not shown).

[0059] The camera CAM is provided with an auxiliary light emitting unit EF for emitting auxiliary light when the subject is dark, a function button B2 for setting various conditions of the camera CAM, etc. The optical system used in such a digital camera is required to have a higher resolution, be lightweight, and be miniaturized. In order to achieve these, it is effective to use glass with a high refractive index in the optical system. In particular, glass with a high refractive index and a lower specific gravity (S g ), there is a high demand for glass with high moldability. From this point of view, the calcium fluoride sintered body of this embodiment is suitable as a component of an optical device.

[0060] It should be noted that the optical device applicable to this embodiment is not limited to the above-mentioned imaging device, and may include, for example, a projector, etc. The optical element is not limited to a lens, and may include, for example, a prism, etc.

[0061] Next, a multiphoton microscope including an optical element using the calcium fluoride sintered body of this embodiment will be described.

[0062] Figure 6 This is a block diagram illustrating an example of the configuration of a multiphoton microscope 2 according to this 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 comprises an optical element whose base material is the calcium fluoride sintered body according to this embodiment. The following description focuses on the optical system of the multiphoton microscope 2.

[0063] The pulse laser device 201 emits, for example, near-infrared light (approximately 1000 nm) with ultrashort pulses of light with a pulse width in the femtosecond unit (e.g., 100 femtoseconds). Immediately after emitting from the pulse laser device 201, the ultrashort pulses are generally linearly polarized light with the electric field oscillating in a predetermined direction. The pulse splitting device 202 splits the ultrashort pulses, increases the repetition frequency, and emits them.

[0064] The beam adjustment unit 203 has: a function of adjusting the beam diameter of the ultrashort pulse light incident from the pulse splitting device 202 according to the pupil diameter of the objective lens 206; a function of adjusting the focusing and divergence angles of the ultrashort pulse light in order to correct the axial chromatic aberration (focal difference) between the wavelength of the multi-photon excitation light emitted from the sample S and the wavelength of the ultrashort pulse light; and a pre-frequency modulation function (group velocity dispersion compensation function) of giving the ultrashort pulse light an opposite group velocity dispersion in order to correct the phenomenon that the pulse width of the ultrashort pulse light expands due to group velocity dispersion during passing through the optical system.

[0065] The ultrashort pulse light emitted from the pulse laser device 201 passes through the pulse splitting device 202 to increase its repetition frequency, and the beam adjustment unit 203 performs the aforementioned adjustment. The ultrashort pulse light emitted from the beam adjustment unit 203 is reflected by the dichroic mirror 204 toward the dichroic mirror 205, passes through the dichroic mirror 205, and is focused by the objective lens 206 to irradiate the sample S. At this time, the ultrashort pulse light can also be scanned on the observation surface of the sample S using a scanning unit (not shown).

[0066] For example, when fluorescence observation is performed on a sample S, the fluorescent dye dyed with the sample S undergoes multiphoton excitation in and near the area illuminated by the ultrashort pulse light of the sample S, emitting fluorescence (hereinafter referred to as observation light) having a wavelength shorter than the infrared wavelength of the ultrashort pulse light. The observation light emitted from the sample S toward the objective lens 206 is collimated by the objective lens 206 and, depending on its wavelength, is reflected by or passes through the dichroic mirror 205.

[0067] The observation light reflected by the dichroic mirror 205 enters the fluorescence detection unit 207. The fluorescence detection unit 207, which is composed of, for example, a barrier filter and a PMT (Photo Multiplier Tube), receives the observation light reflected by the dichroic mirror 205 and outputs an electrical signal corresponding to the light intensity. Furthermore, as the ultrashort pulse light scans the observation surface of the specimen S, the fluorescence detection unit 207 detects the observation light across the observation surface of the specimen S.

[0068] Note that, by removing the dichroic mirror 205 from the optical path, all observation light emitted from the sample S toward the objective lens 206 may be detected by the fluorescence detection unit 211 .

[0069] In this case, the observation light is scanned by a scanning unit (not shown), passes through a dichroic mirror 204, is focused by a condenser lens 208, passes through a pinhole 209 positioned approximately conjugate with the focal position of the objective lens 206, and then passes through an imaging lens 210 before entering a fluorescence detection unit 211. The fluorescence detection unit 211, comprised of, for example, a barrier filter or a PMT, receives the observation light formed on its light-receiving surface by the imaging lens 210 and outputs an electrical signal corresponding to the light intensity. Furthermore, as the ultrashort pulse light scans the observation surface of the specimen S, the fluorescence detection unit 211 detects the observation light across the observation surface S of the specimen S.

[0070] Furthermore, observation light emitted from the specimen S in a 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., and receives the observation light reflected by the dichroic mirror 212 and outputs an electrical signal corresponding to the light intensity. Furthermore, as the ultrashort pulse light scans the observation surface of the specimen S, the fluorescence detection unit 213 detects the observation light across the observation surface of the specimen S.

[0071] The electrical signals outputted from the fluorescence detection units 207, 211, and 213 are inputted to a computer (not shown), for example. The computer can generate an observation image based on the input electrical signals, and display the generated observation image or store observation image data.

[0072] According to the above-described embodiment, the following effects can be obtained.

[0073] (1) A method for producing calcium fluoride particles includes: a generation step of reacting a calcium compound and a fluorine compound in a solution to produce a dispersion containing calcium fluoride particles; a mixing step of mixing the calcium fluoride particles contained in the dispersion with hydrofluoric acid; and a separation step of separating the calcium fluoride particles from the liquid component after the mixing step. This method can produce calcium fluoride particles that can be used to produce a calcium fluoride sintered body having high transmittance.

[0074] (2) The concentration of hydrogen fluoride in the hydrofluoric acid aqueous solution used in the mixing step is 0.1% to 20%. This can suppress the generation of white spots of about 0.1 mm, which are aggregates of fine bubbles, inside the sintered body obtained by sintering the produced calcium fluoride particles.

[0075] (3) A method for producing a calcium fluoride sintered body comprises: a molding step of molding calcium fluoride particles produced by the above-described method for producing calcium fluoride particles to form a molded body; and a sintering step of sintering the molded body in an inert atmosphere to produce a sintered body. This method enables the production of a calcium fluoride sintered body having high transmittance.

[0076] (4) In the molding step, calcium fluoride particles having a predetermined particle size or less are molded into a molded body. This allows the production of a molded body of calcium fluoride particles for producing a calcium fluoride sintered body having high transmittance.

[0077] (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 excessively low temperatures.

[0078] (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.

[0079] Examples of the calcium fluoride sintered body according to the above embodiment will be described.

[0080] [Example]

[0081] 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.

[0082] 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.).

[0083] 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 distance traveled 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 acetate aqueous solution) injected into the calcium acetate aqueous solution. 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 molded body is sintered in the sintering process of step S8 to produce a white sintered body with 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 produced in the sintering process of step S8. Figure 1 The heating temperature during the HIP treatment in the "transparentizing step" of step S9.

[0084] like Figure 7 and Figure 8 As shown, the internal transmittance of the calcium fluoride sintered bodies of Samples 1 to 24 in the Examples for light with a wavelength of 550 nm was 98% or higher. In addition, the optical strain of the calcium fluoride sintered bodies of Samples 1 to 22 was 10 nm / cm or less.

[0085] Figure 9A 、 Figures 9B to 13 This is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered bodies of Samples 1 to 24. Figure 9A 、 Figures 9B to 13 The transmittance shown is the internal transmittance per 10mm of sample thickness. In other words, it is the internal transmittance per 10mm of actual distance light travels in the sample. Figure 9A L1 to L6 represent the measurement results of the spectral transmittance of samples 1 to 6 for light with a wavelength of 200 nm to 800 nm. Figure 9B The measurement results of the spectral transmittance of samples 7 to 12 for light with a wavelength of 200 nm to 800 nm are shown as L7 to L12. Figure 10A L13 to L17 represent the measurement results of the spectral transmittance of samples 13 to 17 for light with a wavelength of 200 nm to 800 nm. Figure 10B The measurement results of the spectral transmittance of samples 18 to 22 for light with a wavelength of 200 nm to 800 nm are represented by L18 to L22.

[0086] Figure 11A M1 to M6 represent the measurement results of the spectral transmittance of samples 1 to 6 for light with a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm). Figure 11B The measurement results of the spectral transmittance of samples 7 to 12 for light with a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm) are represented by M7 to M12. Figure 12A M13 to M17 represent the measurement results of the spectral transmittance of samples 13 to 17 for light with a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm). Figure 12B The measurement results of the spectral transmittance of light with a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm) of Samples 18 to 22 are shown as M18 to M22. Figure 13 M23 and M24 represent the measurement results of the spectral transmittance of samples 23 and 24 for light with a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm). Figure 9A 、 Figure 9B 、 Figure 10A 、 Figure 10B As shown in FIG. 1 , the internal transmittance of the calcium fluoride sintered body of the embodiment for light with a wavelength of 380 nm to 780 nm is 90% or more. Figure 11A 、 Figure 11B 、 Figure 12A 、 Figure 12B 、 Figure 13 As shown in FIG. 1 , the internal transmittance of the calcium fluoride sintered body of the embodiment is 90% or more for light with a wavelength of 3000 nm (3 μm) to 7000 nm (7 μm). Figure 11A 、 Figure 11B 、 Figure 12A 、 Figure 12B 、 Figure 13 As shown, in the infrared region, the internal transmittance of the calcium fluoride sintered body is 80% or more at a wavelength IRλ 80 It is 8000nm (8μm) or more.

[0087] The calcium fluoride sintered bodies of Samples 23 and 24 were annealed at a starting temperature of 800° C., a cooling rate of 5° C. / h, and a finishing 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.

[0088] In the above-mentioned samples 1 to 24, calcium acetate hydrate was used as the raw material calcium compound to produce the calcium fluoride sintered body. However, in sample 25, calcium nitrate was used as the raw material calcium compound to produce the calcium fluoride sintered body. Figure 16 The 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 molded body is sintered in the sintering process of step S8 to produce a white sintered body with 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 produced in the sintering process of step S8. Figure 1 The heating temperature during the HIP treatment in the "transparentizing step" of step S9.

[0089] like Figure 16As shown, the internal transmittance of light with a wavelength of 550 nm of the calcium fluoride sintered body of Sample 25 is 98% or more. In addition, the optical strain of the calcium fluoride sintered body of Sample 25 is 25 nm / cm or less.

[0090] 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.

[0091] As described above, it was shown that the calcium fluoride sintered body of this example is polycrystalline and has high transmittance.

[0092] [Comparative Example 1]

[0093] The calcium fluoride sintered body in Comparative Example 1 used calcium acetate hydrate as the calcium compound and hydrofluoric acid as the fluorine compound, similarly to the examples. The calcium fluoride sintered body in Comparative Example 1 was produced without the process described as step S6. Specifically, the steps of stirring calcium fluoride particles and distilled water, separating the solid and liquid, removing the supernatant, and then adding distilled water for stirring were omitted. Instead, the calcium fluoride particles produced in this manner were used. In Comparative Example 1, a transparent calcium fluoride sintered body was obtained through HIP treatment. However, numerous white spots approximately 0.1 mm in diameter, representing aggregates of fine bubbles, were observed in the sintered body.

[0094] Figure 14A 、 Figure 14B This 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 10mm thickness of the sample. In other words, it is the internal transmittance per 10mm of actual distance light travels in the sample. Figure 14A The results of measuring the spectral transmittance of light with a wavelength of 200 nm to 800 nm are shown. Figure 14B The results of the measurement of the spectral transmittance of light with a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm) are shown. The internal transmittance of the calcium fluoride sintered body of Comparative Example 1 for light with a wavelength of 550 nm per 10 mm thickness is 97.7%, which is less than 98%.

[0095] [Comparative Example 2]

[0096] The calcium fluoride sintered body in Comparative Example 2 used calcium acetate hydrate as the calcium compound and hydrofluoric acid as the fluorine compound, similarly to the examples. The calcium fluoride sintered body in Comparative Example 2 was produced using calcium fluoride particles generated without performing the mixing step described above as step S5. Foreign matter was present in the resulting calcium fluoride sintered body of Modification Example 2.

[0097] Figure 15A 、 Figure 15B This is a graph showing the results of measuring the spectral transmittance of the calcium fluoride sintered body of Comparative Example 2 that was double-sided polished. Figure 15A 、 Figure 15B The transmittance shown is the internal transmittance per 10mm thickness of the sample. In other words, it is the internal transmittance per 10mm of actual distance light travels in the sample. Figure 15A The results of measuring the spectral transmittance for light with a wavelength of 200 nm to 800 nm are shown. Figure 15B The results of the measurement of the spectral transmittance for light with a wavelength of 3000 nm (3 μm) to 13000 nm (13 μm) are shown. Figure 15A 、 Figure 15B As shown, the wavelength range of light with an internal transmittance of 90% or more is narrower than that of the example. In addition, the internal transmittance of the calcium fluoride sintered body of Comparative Example 2 for light with a wavelength of 550 nm per 10 mm thickness is 87.7%, which is less than 98%.

[0098] The present invention is not limited to the above-described embodiments as long as the characteristics of the present invention are not impaired, and other embodiments that can be conceived within the scope of the technical concept of the present invention are also included in the scope of the present invention.

[0099] Explanation of symbols

[0100] 1 Camera device

[0101] 2 Multiphoton Microscopy

[0102] 103 camera lens

[0103] 206 objective lens

[0104] 208 focusing lens

[0105] 210 imaging lens

[0106] CAM…Camera

[0107] WL…Photographic lens

Claims

1. A method for producing calcium fluoride polycrystals, comprising: a generation step of reacting a calcium compound with a fluorine compound in a solution to generate a dispersion containing calcium fluoride particles; a heating and pressurizing step of heating and pressurizing the dispersion; a mixing step of mixing the calcium fluoride particles contained in the heated and pressurized dispersion with hydrofluoric acid different from the fluorine compound used in the generating step to obtain a mixed solution; and a separation step, after the mixing step, adding water to the mixed solution to reduce the concentration of the hydrofluoric acid in the liquid of the mixed solution, and then separating the mixed solution into the calcium fluoride particles and the liquid; a molding step of molding the calcium fluoride particles produced above into a molded body; a sintering step of sintering the molded body having a relative density of 35% to 50% at a temperature of 400° C. to 700° C. for 2 to 6 hours, and then sintering the molded body at a temperature of 900° C. to 1000° C. in an inert atmosphere for 1 to 2 hours; and A transparentizing step of transparentizing the polycrystal by heating the polycrystal to a temperature of 1000° C. to 1100° C. in an inert atmosphere while applying a pressure of 100 MPa to the polycrystal after the sintering step.

2. The method for producing calcium fluoride polycrystals according to claim 1, wherein: In the molding step, the calcium fluoride particles having a predetermined particle size or less are molded to form the molded body.

3. The method for producing calcium fluoride polycrystals according to claim 2, wherein: In the molding step, the calcium fluoride particles having a particle size of 1 mm or less are molded to form the molded body.

4. The method for producing a calcium fluoride polycrystal according to any one of claims 1 to 3, 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.

5. The method for producing a calcium fluoride polycrystal according to any one of claims 1 to 3, wherein: In the molding step, the calcium fluoride particles are placed in a container of a predetermined shape and dried at a temperature of 70° C. to 300° C. to be molded.

6. The method for producing a calcium fluoride polycrystal according to any one of claims 1 to 3, wherein: After the transparentizing step, there is an annealing step of annealing the polycrystal in an inert atmosphere.

7. The method for producing calcium fluoride polycrystals according to claim 6, wherein: The annealing step is performed at a temperature range of 600° C. to 800° C. for a heating time of 40 hours or more. 8 . A calcium fluoride polycrystal obtained by the method for producing a calcium fluoride polycrystal according to claim 1 .

9. The calcium fluoride polycrystal according to claim 8, 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. 10 . An optical element using the calcium fluoride polycrystal according to claim 8 . An optical system comprising the optical element according to claim 10 . 12 . A replacement lens comprising the optical system according to claim 11 . 13 . An optical device comprising the optical system according to claim 11 .

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