| 摘要 |
PROBLEM TO BE SOLVED: To solve such a problem that light transmission property (initial light transmittance) is deteriorated due to the appearance of plural kinds of absorption in the ultraviolet or vacuum ultraviolet region when the lead of lead fluoride which is a fluoridizing agent remains in calcium fluoride crystal. SOLUTION: This manufacturing method of calcium fluoride features that, when a metal element which is a major component of the fluoridizing agent is the element to be quantitatively determined, (1) the element to be quantitatively determined in calcium fluoride blank is quantitatively analyzed and the content of the element is controlled to be 3 ppm or less. (2) the element to be quantitatively determined in the pretreated sample is quantitatively analyzed and the content of the element is controlled to be 3 ppm or less. (3) the element to be quantitatively determined in ingot is quantitatively analyzed and the content is controlled to be 3 ppm or less.
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