Ultra-short laser ablation of metals and semiconductors: evidence of ultra-fast Coulomb explosion

We have studied ultra-fast laser ablation of Si and a metal via the neutral and ion yield, the energy distribution of emitted neutrals and the charge distribution as a function of the laser pulse width. Two processes, one leading to the ejection of fast (3-7 eV), the other to slow thermal particles, can be identified. The origin of the first process can be correlated with laser pulse widths (or pump-probe delays) and processes on a time scale below 100 fs. Results for Si confirm recent findings for Coulomb explosion (CE) and we show for the first time that CE exists as a mechanism of material removal from metals for ultra-short laser pulses.