Statistical relationship governing the surface damage of optical glass by wide laser radiation beams

An investigation was made of the dependence of the surface optical strength of K-8 glass on the dimensions of the illuminated spot whose area was varied from 2 to 120 mm². A neodymium laser system emitting pulses of 200 J energy and 10^–7 sec duration was used. For a fixed pulse duration the optical strength of the surface was not a single-valued function of the threshold power (energy) density but was characterized by a damage probability which depended on the radiation intensity and the size of the illuminated spot. The optical strength of parts of the surface illuminated with a series of light pulses of subthreshold intensity was higher than the strength of other parts. The experimental results were accounted for by a probabilistic mechanism of the damage due to the presence of absorbing inclusions distributed at random on the glass surface.