Material removal dynamics after femtosecond laser pulse excitation of dielectrics

Summary form only given. An important question for laser-solid interaction is: when does the material removal after the excitation begin, and what are the reasons for the observed material dependencies? To avoid added problems of dealing with the laser-plume interactions, either for fundamental studies or for material processing, the laser pulse width must be shorter than the time necessary for the ablation to develop. In early studies the temporal development of the reflectivity of the surface after strong excitations was investigated by pump-probe technique with fs laser pulses. Recent time-resolved measurements of the carrier dynamics have demonstrated a significant material dependency in the lifetime of excited electrons in the conduction band of dielectrics. While the electrons remain in or closely below the conduction band for over 50 ps in MgO and sapphire, they are trapped deep into the bandgap after only 150 fs in amorphous and crystalline quartz. To determine the onset of the ablation from the surface after intensive laser excitation, we examine the time development of changes in the scattered light from the surface.