| 摘要 |
In order to shorten the annealing time to thereby reduce the production cost of a fluoride crystal, the method of heat treating a fluoride crystal of the present invention comprises the steps of: raising the temperature of a fluoride crystal; reducing the raised temperature of the fluoride crystal at a first temperature reducing rate; and then reducing the temperature of the fluoride crystal at a second temperature reducing rate which is larger than the first temperature reducing rate.
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