In this paper, we present single shot measurements of the excited carrier d
ensity in various wide band gap oxides (SiO2, MgO, and Al2O3), irradiated b
y short laser pulses (60 fs to 1.3 ps), at intensities below and above brea
kdown threshold. This is achieved with the time resolved interferometry tec
hnique in the frequency domain. This technique was successfully used to stu
dy the dynamics of photoexcited carriers in insulators. The results obtaine
d in different experimental conditions, pump intensities and durations are
discussed and compared with a model developed to explain optical breakdown.
We demonstrate that optical breakdown of dielectrics is due to multiphoton
absorption and not to the avalanche process.