Excimer laser-induced expansion in hydrogen-loaded silica

High-purity silica that contains a high concentration of dissolved molecula r hydrogen is found to undergo expansion, rather than densification, as a c onsequence of exposure to deep ultraviolet irradiation. Concurrent with the decreased density, we suggest that a positive photorefractive effect occur s, which increases the index. The contributions of the density change and t he photorefractive effect can be observed by comparison of the birefringenc e and the wave front change obtained through interferometry. Expansion and the photorefractive effect are interpreted in terms of the photolytic forma tion of SiOH. (C) 2001 American Institute of Physics.