Thermal and nonthermal ion emission during high-fluence femtosecond laser ablation of metallic targets

We have investigated the emission of positive ions from metallic targets irradiated with intense, ultrashort laser pulses (approximate to 120 fs) at 780 nm, in both S and P polarized states. The measured energy spectra show the presence of a nonthermal, high-energy (several keV) ion component accompanying low-energy ions (tens of eV) produced by a thermal mechanism. The yield of the high-energy component shows a strong dependence on both laser fluence and light polarization. For the low-energy component a higher ablation efficiency was observed for P polarization, and ascribed to a more effective absorption mechanism active during the laser-target interaction. (C) 2000 American Institute of Physics. [S0003-6951(00)02549-3].