Temporal dependency in the picosecond regime of laser damage growth.

Based on squared top-hat beam irradiations, we investigate how a change of the pulse duration in the picosecond regime affects the phenomenon of laser damage growth on dielectric mirrors. We first confirm two major previously reported experimental results with a Gaussian beam that are the existence of a growth threshold fluence smaller than the laser-induced damage threshold (LIDT) and the linear evolution, characterized by a growth coefficient, of the damage area with the number of irradiations when growth occurs. We then express the growth coefficient with the fluence and the growth threshold in particular. Changing the pulse duration ultimately allows us to refine this expression a step further which leads us to establish an empirical growth law for the damage area. The temporal dependency displayed within this law appears to be very close to the one found for the LIDT which evidences the deterministic nature of laser damage growth in short pulse regimes.