Double-peak distribution of electron and ion emission profile during femtosecond laser ablation of metals

Femtosecond laser ablation of metals with a Ti:sapphire laser system has been investigated by a time-of-flight mass spectroscopy technique. Ion mass spectra show a double-peak distribution, evidencing the presence of a high-energy component (up to few keV), even at moderate laser intensities (1012–1013 W cm−2). Two different ablation regimes were identified for the less energetic component, and explained in the framework of the two-temperature modeling of ultrashort laser pulse–solid target interactions. Ambipolar diffusion has been identified as the probable mechanism giving rise to the observed high-energy plasma plume component.