Optical breakdown under strong ultrafast laser field

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.