We report observation results about damages on SiO2 mirror surfaces. The damages were made when the mirrors were used as a cavity reflector for the Ar and Kr excimer lasers. The surface profile, transmission and reflectance spectra, and X-ray photoelectron spectra show that bulk Si is isolated in the surface layer which was exposed to 9.8eV photons from the Ar excimer laser. The Kr excimer laser, whose photon energy is 8.5eV, does not induce such a phenomenon. The Ar excimer laser photons, surmounting the fundamental band gap of 5i02, 9eV, are considered to create high density excitons that induce the Si-0 bond breaking and Si isolation.
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