Time-resolved reflectivity evolution of transparent dielectrics under femtosecond-laser pulse excitation

Using the 800-nm-pump and 400-nm-probe technique, the dynamics of the electron excitation and relaxation in CaF₂ and MgO crystals was studied. A coupling model including both the multiphoton ionization (MPI) and the impact ionization (II) was applied to investigate laser propagation and conduction band electron production. The evolution of reflectivity was calculated, and the calculated results agree with the experimental results. The results indicate that both MPI and II play important roles in the generation of conduction band electrons. The relaxation dynamics was also discussed.