| 摘要 |
<p>PROBLEM TO BE SOLVED: To obtain the subject optical member suppressed from transmittance drop or fluorescence generation as a result of being irradiated with radiation or high-energy beams such as excimer laser by heat treatment, in a steam-contg. non-hydrogen atmosphere at a specific temperature or higher, of a porous silica glass form produced by flame hydrolysis of a glass-forming material. SOLUTION: This optical member is obtained by heat treatment, in an atmosphere cotaining, in particular pref. >=10 vol.% of steam at >=200 deg.C. Thereby, the aimed synthetic silica glass of low chlorine content can be afforded; because of little containing defective precursors contributing to absorption band when irradiated with laser beams, the objective optical member thus obtained is slight in transmittance drop and excellent in resistance to laser beams; furthermore, by bringing the hydrogen atom content of this optical member to >=5×1016 molecules/cm3, the laser beam resistance of this optical member is further improved; moreover, by bringing the OH group content distribution on the light transmission plane to <=50 ppm, the aimed uniform synthetic silica glass with slight refractive index variance can be afforded.</p> |
