| 摘要 |
PROBLEM TO BE SOLVED: To widen the selectivity of a substrate shape and to obtain an optical thin film of uniform quality and thickness easily by a method in which optical thin film material sol is applied on a substrate, after a gel film being deposited, the temperature and pressure of liquid for immersion are brought into a critical state or above to vaporize the liquid, and unnecessary components in the gel film are removed. SOLUTION: A double-convex fluorite lens is set in a holder, immersed in a SiO2 sol solution, pulled up at a constant speed, and a SiO2 gel film is formed. The lens with the SiO2 gel film formed is transferred quickly together with the holder into the chamber 7 of a critical drier, the chamber 7 is sealed, a valve 13b is opened, liquid carbon dioxide which was heated in advance is introduced from a liquid tank 5 into the chamber 7. Next, the temperature and pressure of the chamber are brought into the critical temperature and critical pressure of carbon dioxide or above, the liquid carbon dioxide from which unnecessary components are eluted is released into a separator 9 held at a critical point or below, the sequence of operations is repeated five times, and the SiO2 gel film is dried completely.
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