Ultra-fast laser absorption and ablation dynamics in wide-band-gap dielectrics

The highly nonlinear laser-matter interaction conditions produced by high-intensity amplified ultra-fast laser pulses have proven to be beneficial in the processing of normally transparent wide-band-gap dielectric materials. This article presents experimental studies of the ultra-fast laser absorption process in three wide-band-gap dielectrics: fused silica, calcium fluoride, and sapphire. Time-resolved measurements of the probe transmissivity and reflectivity show both the formation of dense free-electron plasma at the surface due to nonlinear absorption of the laser pulses and rapid structural damage on the order of a few picoseconds. Pump-probe data with intense pump and probe pulses was also correlated to atomic force microscopy measurements of the ablated volume. It was observed that the material removal peaked near zero delay between the pulses and decreased within a temporal separation of about 1 ps.