Theoretical and experimental study on femtosecond laser-induced damage in MgF₂ crystals

We study single-shot damage morphology of MgF2 irradiated under 800 nm laser using scanning electronic microscope (SEM). The dependence of damage threshold on laser pulse width is measured by the linear relationship between the area of damage spot and the logarithm of laser energy. The pulse duration ranges from 55 fs to 750 fs. We develop the multiple-equation model (Phys. Rev. Lett. Vol.92, pp.187401, 2004), in which two-photon absorption in the conduction band is considered. The experimental results agree well with our model.