NANOSECOND-TO-FEMTOSECOND LASER-INDUCED BREAKDOWN IN DIELECTRICS

We report extensive laser-induced damage threshold measurements on die lectric materials at wavelengths of 1053 and 526 nm for pulse duration s tau ranging from 140 fs to 1 ns. Qualitative differences in the morp hology of damage and a departure from the diffusion-dominated tau(1/2) scaling of the-damage fluence indicate that damage occurs from ablati on for tau less than or equal to 10 ps and from conventional melting, boiling, and fracture for tau>50 ps. We find a decreasing threshold fl uence associated with a gradual transition from the long-pulse, therma lly dominated regime to an ablative regime dominated by collisional an d multiphoton ionization, and plasma formation. A theoretical model ba sed on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in quantitative agreement wi th the experimental results.