Fluorine-doped SiO₂ glasses for F₂ excimer laser optics: Fluorine content and color-center formation

Color-center formation in F-doped, OH-free synthetic SiO₂ glasses by irradiation with F₂ excimer lasers (157 nm) was examined as a function of the F content. The concentration of photoinduced E′ centers was reduced to ∼1/20 by 1 mol.% F₂ doping and remained almost constant on further doping to 7.3 mol. %. The absorption edge was considerably shifted to a lower wavelength (157.4 nm → 153 nm for a 5-mm-thick sample) by 1-mol. % doping and decreased only slightly on further doping. The intensities of the Raman bands that are due to three- and four-membered ring structures were significantly reduced by 1-mol. % F doping. These results strongly suggest that elimination of strained Si - O - Si bonds by F doping plays a central role in the improvement of radiation resistance of SiO₂ glasses to F₂ laser light.