Femtosecond laser pulse induced damage in thin films

We have investigated the damage for ZrO 2 /SiO 2 800 nm 45° high-reflection mirror and MgF 2 /ZnS 800 nm interference filter with femtosecond pulses. The damage morphologies and evolution of ablation crater depths with laser fluences are dramatically different from that with pulse longer than a few tens of picoseconds. We also report their single-short damage thresholds for pulse durations ranging from 50 fs to 900 fs, which depart from the diffusion-dominated τ 1/2 scaling. A developed avalanche model, including the production of conduction band electrons (CBE) and laser energy deposition, is applied to study the damage mechanisms. The theoretical results agree well with our measurements.