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US-12625299-B2 - Calcium fluoride polycrystalline substance, production method of calcium fluoride particle, production method of calcium fluoride polycrystalline substance, optical element, optical system, interchangeable lens and optical device

US12625299B2US 12625299 B2US12625299 B2US 12625299B2US-12625299-B2

Abstract

A calcium fluoride polycrystalline substance, in which the internal transmittance of light having a wavelength of 550 nm per thickness of 10 mm is 98% or more.

Inventors

  • Mariko HIRAYAMA
  • Hitoshi Ishizawa
  • Takuro Nakamura
  • Yoshinobu EZURA
  • Yuya Yamamoto

Assignees

  • NIKON CORPORATION

Dates

Publication Date
20260512
Application Date
20230616
Priority Date
20201228

Claims (20)

  1. 1 . A calcium fluoride polycrystalline substance, wherein an internal transmittance of light having a wavelength of 550 nm per thickness of 10 mm is 98% or more.
  2. 2 . The calcium fluoride polycrystalline substance according to claim 1 , wherein an internal transmittance of light having wavelengths of 380 nm to 780 nm per thickness of 10 mm is 90% or more.
  3. 3 . The calcium fluoride polycrystalline substance according to claim 1 , wherein an internal transmittance of light having a wavelength of 3 μm to 7 μm per thickness of 10 mm is 90% or more.
  4. 4 . The calcium fluoride polycrystalline substance according to claim 1 , wherein, in an infrared region, a wavelength IRλ 80 at which an internal transmittance per thickness of 10 mm becomes 80% or more is 8 μm or longer.
  5. 5 . The calcium fluoride polycrystalline substance according to claim 1 , wherein an optical strain is 25 nm/cm or less.
  6. 6 . The calcium fluoride polycrystalline substance according to claim 1 , wherein an optical strain is 10 nm/cm or less.
  7. 7 . The calcium fluoride polycrystalline substance according to claim 1 , wherein a relative density is 98% or higher.
  8. 8 . An optical element, wherein the calcium fluoride polycrystalline substance according to claim 1 is used.
  9. 9 . An optical system comprising: the optical element according to claim 8 .
  10. 10 . An interchangeable lens comprising: the optical system according to claim 9 .
  11. 11 . An optical device comprising: the optical system according to claim 9 .
  12. 12 . A calcium fluoride polycrystalline substance according to claim 1 , wherein composed of calcium and fluorine.
  13. 13 . A production method of a calcium fluoride particle, comprising: 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 obtained calcium fluoride particles and hydrofluoric acid which is different from the fluorine compound used in the generation step; and a separation step of separating the calcium fluoride particles and the water after adding water to the calcium fluoride particles after the mixing step.
  14. 14 . The production method of a calcium fluoride particle according to claim 13 , wherein a concentration of hydrogen fluoride in the hydrofluoric acid is 0.1% or higher and 20% or lower.
  15. 15 . The production method of a calcium fluoride particle according to claim 13 , wherein a mole ratio of the fluorine compound to the calcium compound in the generation step is 2.4 or more and 5.0 or less.
  16. 16 . The production method of a calcium fluoride particle according to claim 13 , further comprising: a heating and pressurization step of heating and pressurizing the dispersion liquid after the generation step.
  17. 17 . The production method of a calcium fluoride particle according to claim 16 , wherein a heating temperature in the heating and pressurization step is 100° C. or higher and 180° C. or lower.
  18. 18 . The production method of a calcium fluoride particle according to claim 16 , wherein a heating time in the heating and pressurization step is 10 hours or longer and 24 hours or shorter.
  19. 19 . A production method of a calcium fluoride polycrystalline substance comprising: a molding step of molding calcium fluoride particles produced by the production method of a calcium fluoride particle according to claim 13 to form a compact; and a sintering step of sintering the compact in an inert atmosphere to generate a polycrystalline substance.
  20. 20 . The production method of a calcium fluoride polycrystalline substance according to claim 19 , wherein, in the molding step, the calcium fluoride particles having a predetermined particle diameter or smaller are molded to form the compact.

Description

CROSS-REFERENCE TO RELATED APPLICATION This is a Continuation Application of International Application No. PCT/JP2021/048842, filed on Dec. 28, 2021 which claims priority to International Application No. PCT/JP2020/049265, filed on Dec. 28, 2020. The contents of the aforementioned applications are incorporated herein by reference. BACKGROUND Field of the Invention The present invention relates to a calcium fluoride polycrystalline substance, a production method of a calcium fluoride particle, a production method of a calcium fluoride polycrystalline substance, an optical element, an optical system, an interchangeable lens and an optical device. Background A production method for obtaining a calcium fluoride sintered body by hot pressing has been proposed (for example, Japanese Unexamined Patent Application, First Publication No. 2003-300777). However, the transmittance of the sintered body is low compared with the transmittance of a single crystal, and there is a demand for increasing the transmittance in order to use the sintered body as an optical member. SUMMARY According to a first aspect, in a calcium fluoride polycrystalline substance, an internal transmittance of light having a wavelength of 550 nm per thickness of 10 mm is 98% or more. According to a second aspect, a production method of a calcium fluoride particle 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 that are 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. According to a third aspect, a production method of a calcium fluoride polycrystalline substance includes a molding step of molding calcium fluoride particles produced by the production method of a calcium fluoride particle of the second aspect to form a compact and a sintering step of sintering the compact in an inert atmosphere to generate a polycrystalline substance. According to a fourth aspect, in an optical element, the calcium fluoride polycrystalline substance of the first aspect is used. According to a fifth aspect of the present invention, an optical system has the optical element of the fourth aspect. According to a sixth aspect, an interchangeable lens includes the optical system of the fifth aspect. According to a seventh aspect, an optical device includes the optical system of the fifth aspect. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a flowchart showing a production method of a calcium fluoride sintered body according to an embodiment. FIG. 2 is a view schematically showing an example of a stirring device that is used at the time of reacting a calcium compound aqueous solution and a fluorine compound aqueous solution. FIG. 3 is a perspective view showing an example of an image capturing device according to an embodiment. FIG. 4 is a front view showing another example of the image capturing device according to the embodiment. FIG. 5 is a rear view showing the other example of the image capturing device according to the embodiment. FIG. 6 is a block diagram showing an example of a multiphoton microscope according to an embodiment. FIG. 7 shows conditions for the production of calcium fluoride particles of examples and the measurement results of the internal transmittances with respect to light having a wavelength of 550 nm and optical strains of calcium fluoride sintered bodies. FIG. 8 shows conditions for the production of calcium fluoride particles of examples and the measurement results of the internal transmittances with respect to light having a wavelength of 550 nm and optical strains of calcium fluoride sintered bodies. FIG. 9A is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 9B is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 10A is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 10B is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 11A is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 11B is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 12A is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 12B is a view showing the measurement results of the spectral transmittances of the calcium fluoride sintered bodies in the examples. FIG. 13 is a view showing the measurement results of the spectral tr