Fast ion generation in femtosecond laser ablation of a metallic target at moderate laser intensity

The generation of ions during laser ablation of a metallic target (copper) with approximate to 50 fs Ti:Sa laser pulses of moderate intensity (approximate to 10(14) W cm(-2)) is studied by simultaneous fast-imaging and ion-probe techniques. The spatiotemporal distribution of excited ions and neutrals in the laser-produced plasma plume is analyzed by exploiting appropriate band-pass filters in the imaging set-up, while the ion flux angular distribution is characterized by angle-resolved ion probe measurements. An interesting feature of our results is the generation of a fast ion population separated from the neutral component of the atomic plasma plume and characterized by sub-keV kinetic energies, which is interpreted in the frame of a simple model of ambipolar diffusion.