| Popis: |
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 sili con 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. Short pulse laser induced optical breakdown has been a challenging research topic in the last years. It involves non-equilibrium states of matter governed by complex interactions between electrons, ions and photons and interesting phenomena such as plasma induced softening of the crystal lattice and non-thermal melting. The study of femtosecond laser pulses interaction with dielectrics and semiconductors has many technological applications, due to the deterministic nature of the breakdown and ablation threshold compared to picosecond and nanosecond pulses. Short pulse laser interaction with dielectrics and semiconductors was studied intensively as a functi on of pulse duration |
