Ultrafast carrier dynamics in laser-excited materials: subpicosecond optical studies

In this paper, we present measurements of the excited carrier density in va rious wide-band-gap oxides (SiO2, MgO and Al2O3) irradiated by short laser pulses (70 fs to 1.3 ps) at intensities below and above breakdown threshold . This is achieved with the help of time-resolved interferometry in the fre quency domain, which was successfully used to study the dynamics of photoex cited carriers in insulators. The results obtained under different experime ntal conditions, distance from the surface, pump intensities and duration, during or after the pump pulse, are discussed and compared to the models re cently developed to explain optical breakdown.