Dynamics of femtosecond laser pulse induced damage in multilayers

We report the single-shot damage thresholds of MgF2/ZnS omnidirectional reflector for laser pulse durations from 50 fs to 900 fs. A coupled dynamic model is applied to study the damage mechanisms, in which we consider not only the electronic excitation of the material, but also the influence of this excitation-induced changes in the complex refractive index of material on the laser pulse itself. The results indicate that this feedback effect plays a very important role during the damage of material. Based on this model, we calculate the threshold fluences and the time-resolved excitation process of the multiplayer. The theoretical calculations agree well with our experimental results.