| 摘要 |
PROBLEM TO BE SOLVED: To improve the yield of a fluoride single crystal and moreover to suitably exclude the fluoride single crystal having insufficient characteristics. SOLUTION: The fluoride single crystal, used for an optical member for transmitting a light having the specific wavelength of 200 nm or shorter is an object to be inspected. A first wavelengthα(nm) and a second wavelengthβ(nm) are set so as to satisfyα<=200<=βand (β-α)>=15. C=A+(100-B) is obtained from an internal transmittance A (%/cm) at the wavelengthαof the single crystal, and an internal transmittance B (%/cm) at the wavelengthβof the single crystal. Whether a value C is 99.8% or higher is decided, and when the value C is 99.8%/cm or larger, the single crystal is evaluated as being suitable for the material of the member.
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