Investigation of the influence of a spatial beam profile on laser damage growth dynamics in multilayer dielectric mirrors in the near infrared sub-picosecond regime.

Laser-induced damage growth has often been studied with Gaussian beams in the sub-picosecond regime. However, beams generated by high-power laser facilities do not feature Gaussian profiles, a property that raises questions concerning the reliability of off-line laser-induced damage measurements. Here, we compare laser-induced damage growth dynamics as a function of beam profiles. Experiments on multilayer dielectric mirrors at 1053 nm have been carried out with squared top-hat and Gaussian beams. The results demonstrate that the laser-induced damage growth threshold does not depend on the incident beam profile. A higher damage growth rate, however, has been measured with the top-hat beam. In addition, three different regimes in the growth dynamics were identified above a given fluence. A numerical model has been developed to simulate a complete damage growth sequence for different beam profiles. The numerical results are in good agreement with the observations, three growth regimes were also revealed. These results demonstrate that a linear description of growth cannot be used for the whole growth domain.