Ablation of metals by ultrashort laser pulses

Ablation of metal targets by Ti:sapphire laser radiation is studied. The ablation depth per pulse is measured for laser pulse durations between 150 fs and 30 ps and fluences ranging from the ablation threshold $\sim 0.1 \mathrm{J}/{\mathrm{cm}}^2$ up to $10 \mathrm{J}/{\mathrm{cm}}^2.$ Two different ablation regimes are observed for the first time. In both cases the ablation depth per pulse depends logarithmically on the laser fluence. A simple theoretical model for a qualitative description of the experimental results is presented.