193-nm excimer-laser-induced densification of fused silica

We report the densification of fused silica as a function of exposure to pulsed 193-nm excimer-laser irradiation. Defining a dose as the number of pulses N times the square of fluence I per pulse, we find that densification follows a universal function of dose, a x (NI2)(b), where a and b can vary somewhat according to glass preparation. Densification is measured with interferometry and birefringence, interpreted with a finite-element elastic model. Wave-front distortion for a typical photolithographic lens element in typical use conditions is described. (C) 1996 Optical Society of America