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 (10(12)-10(13) 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. (C) 2002 Elsevier Science B.V. All rights reserved.