193-Nm Excimer-Laser-Induced Densification Of Fused Silica

This paper reports on the densification of fused silica as a function of exposure to pulsed 193nm excimer-laser irradiation. Defining a dose as the number of pulses N times the square of fluence I per pulse, it is shown that densification follows a universal function of dose, a x (NI2)b, where a and b can vary somewhat according to glass preparation. Density 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.