High fluence visible and ultraviolet laser ablation of metallic targets

Time of flight TOF.distributions of positive ions in nanosecond laser produced plasmas of Al targets at 532 nm and 355 nm, are reported. The investigation has been carried out in vacuum at relatively high laser fluence up to ;60 J cmy2 .. From TOF analysis, a direct characterization of both ions kinetic energy distribution and yield as a function of laser fluence has been derived. The data indicate average translational kinetic energy of the emitted ions up to ;100 eV and that all the investigated parameters strongly depend on the laser fluence until a plateau, whose onset depends on the laser wavelength, is reached. For our conditions, this phenomenon has been analysed discussing the main laser photon absorption and ionization mechanisms active in the Al plasma, at both laser wavelengths. q1998 Elsevier Science B.V.