Ultraviolet-induced densification of fused silica

A number of fused silica samples were evaluated for their resistance to densification by deep UV radiation at 193 nm wavelength. Density changes for all the samples equal the product of a material dependent constant and the absorbed two-photon dose to a sublinear power of about 2/3. This dose dependence is consistent with earlier compaction studies using UV, electron, and gamma radiation. We also studied the isothermal-annealing behavior of UV-induced compaction in fused silica and found a correlation between thermal recovery of compaction and the compaction rates for different fused silica samples. Preheat-treatment at 950 degrees C for 1 h increased the UV-induced compaction rate of two types of fused silica samples, but did not affect that of the other two types of samples. Based on these experimental observations and the well-accepted network structure model of glasses, we propose a model to explain the sublinear power dependence on absorbed radiation dose for the ionization-induced compaction. (C) 2000 American Institute of Physics. [S0021-8979(00)06306-4].