UV-VUV laser induced phenomena in SiO₂ glass

Creation and annihilation of point defects were studied for SiO₂ glass exposed to ultraviolet (UV) and vacuum UV (VUV) lights to improve transparency and radiation toughness of SiO₂ glass to UV-VUV laser light. Topologically disordered structure of SiO₂ glass featured by the distribution of Si-O-Si angle is a critical factor degrading transmittance near the fundamental absorption edge. Doping with terminal functional groups enhances the structural relaxation and reduces the number of strained Si-O-Si bonds by breaking up the glass network without creating the color centers. Transmittance and laser toughness of SiO₂ glass for F₂ laser is greatly improved in fluorine-doped SiO₂ glass, often referred as "modified silica glass". Interstitial hydrogenous species are mobile and reactive at ambient temperature, and play an important role in photochemical reactions induced by exposure to UV-VUV laser light. They terminate the dangling-bond type color centers, while enhancing the formation of the oxygen vacancies. These findings are utilized to develop a deep-UV optical fiber transmitting ArF laser photons with low radiation damage.