Ultraviolet-induced densification of fused silica

A number of fused silica samples were evaluated for their resistance to den sification by deep UV radiation at 193 nm wavelength. Density changes for a ll the samples equal the product of a material dependent constant and the a bsorbed two-photon dose to a sublinear power of about 2/3. This dose depend ence is consistent with earlier compaction studies using UV, electron, and gamma radiation. We also studied the isothermal-annealing behavior of UV-in duced compaction in fused silica and found a correlation between thermal re covery of compaction and the compaction rates for different fused silica sa mples. 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 th at of the other two types of samples. Based on these experimental observati ons 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 Physi cs. [S0021-8979(00)06306-4].