Femtosecond laser-induced damage and ultrafast dynamics in highs reflection coating

The damage and ultrafast dynamics processes induced by 800 nm femtosecond laser in ZrO₂/SiO₂ 800 nm 45° high-reflection coating are studied. The damage morphology, and threshold fluence as a function of pulse duration and the dependence of ablation depths on the pulse fluences are measured. The damage threshold increases from 0.35 J/cm² to 1.78 J/cm² with pulse duration enlarged from 50 fs to 900 fs. The ablation depth is linearly proportional to the logarithm of pulse fluence, which suddenly reaches hundreds of nanometers once the laser fluence is above the threshold, and the layered ablation shows. By using of a pump and probe experimental system, the time-resolved reflectivity irradiated by high intensity laser pulses in the reflector ZrO₂/SiO₂ is measured. The results indicate that the optical properties of the surface layer of high-reflection coating play a very important role during the damage process.