Mechanisms of ultra-short laser pulse ablation from ionic crystals

In ultra-short laser pulse ablation from dielectric crystals two different ablation regimes are observed: 1) At laser intensities well below the single shot damage threshold, Coulomb explosion upon multiphoton surface ionization is the dominant process, yielding electrons and fast positive ions. 2) At higher laser intensities, ablation exhibits signs of hyper-thermal emission (phase explosion) as a result of rapid hot electron thermalization. This regime is characterized by massive etching, mostly of neutral particles. The transition from regime one to two is associated with the appearance of an additional, slower group of positive ions, saturation in the positive ion yield, and the occurrence of negative ions. PACS 61.80.Ba; 61.82.Ms; 79.20.Ds