A decrease in the damage threshold in dielectric materials induced by negatively chirped laser pulses

摘要

The threshold fluence for laser induced damage in wide band gap dielectric materials, such as fused silica and MgF_2, is observed to be lower by up to 20% for negatively (down) chirped pulses than for positively (up) chirped, at pulse durations ranging from 60 fs to 1 ps. This behavior of the threshold fluence for damage on the chirp direction was not observed in semiconductors, such as silicon and GaAs. Based on a model describing electron generation in the conduction band and Joule heating, it is suggested that the decrease in the damage threshold for negatively chirped pulse is related to the role of multiphoton ionization in wide gap materials.