《Nanosecond-to-femtosecond laser-induced breakdown in dielectrics》.pdf

PHYSICAL REVIEW B VOLUME 53, NUMBER 4 15 JANUARY 1996-II ARTICLES Nanosecond-to-femtosecond laser-induced breakdown in dielectrics B. C. Stuart, M. D. Feit, S. Herman, A. M. Rubenchik, B. W. Shore, and M. D. Perry Lawrence Livermore National Laboratory, P.O. Box 808, L-493, Livermore, California 94550 Received 9 February 1995; revised manuscript received 4 October 1995 We report extensive laser-induced damage threshold measurements on dielectric materials at wavelengths of 1053 and 526 nm for pulse durations ranging from 140 fs to 1 ns. Qualitative differences in the morphology of damage and a departure from the diffusion-dominated 1/2 scaling of the damage fluence indicate that damage occurs from ablation for 10 ps and from conventional melting, boiling, and fracture for 50 ps. We find a decreasing threshold fluence associated with a gradual transition from the long-pulse, thermally dominated regime to an ablative regime dominated by collisional and multiphoton ionization, and plasma formation. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional avalanche ionization is in quantitative agreement with the experimental results. I. INTRODUCTION width is decreased from 10 ps to 150 fs, as reported by Du et al.23 Instead, we observe24 a continuously decreasing Theoretical and experimental investigations of the