| 摘要 |
PROBLEM TO BE SOLVED: To obtain an optical material for a stable excimer laser generating no absorption band despite its long-time irradiation, based upon the production of synthetic silica glass by hydrolyzing silicon tetrachloride in oxyhydrogen flame, by using an excess amount of hydrogen over that resulted from the stoichiometrical ratio of hydrogen and oxygen in the oxyhydrogen flame and specifying the OH group to be contained and the transmissivity in the material. SOLUTION: This material of synthetic silica glass is obtained, e.g. based upon a direct deposition vapor phase synthetic method, by controlling the concentration of the OH group by hydrolyzing in such oxyhydrogen flame as to have an excess amount of hydrogen over the stoichiometrically necessary moler ratio of hydrogen and oxygen and regulating the conditions of reaction in the burner containing an inert gas and the conditions of exhaustion of the exhaust gas. Specifically, the oxyhydrogen flame has >=2.2 moler ratio of hydrogen to oxygen, and the resulting optical material for an stable excimer laser avoiding any absorption band even in a high pulse number irradiation contains <=50ppb alkali metal impurities and >=1,000p.p.m. OH groups and has >=89% transmissivity in its 10mm thickness and 200nm wavelength. |
