Abstract

It was expected that the bleaching of the 240-260 nm absorption band and creation of others were sufficient to explain all part of the index change through Kramers-Kronig conjugation. However, Williams et al. [1] taking into account the UV absorption change showed that at most 20% of the index change can be accounted for by this effect. This statement was confirmed also by Eric Fertein [2] in various type of fibers and in taking into account the VUV absorption change. In addition, some recent experiments by Albert et al. [3] using 193 nm light indicates that the bleaching of absorption bands near 242 nm is not essential to induce refractive index changes. A second phase of the process may be that transformed defects lead to a change in the microstructure of the silica. The first idea is a change of volume and so we can expect to see corrugations at the surface of irradiated flat substrate close as the ones of preform slices.

© 1995 Optical Society of America