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.