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 ir radiated with intense, ultrashort laser pulses (approximate to 120 fs) at 7 80 nm, in both S and P polarized states. The measured energy spectra show t he presence of a nonthermal, high-energy (several keV) ion component accomp anying low-energy ions (tens of eV) produced by a thermal mechanism. The yi eld of the high-energy component shows a strong dependence on both laser fl uence and light polarization. For the low-energy component a higher ablatio n efficiency was observed for P polarization, and ascribed to a more effect ive absorption mechanism active during the laser-target interaction. (C) 20 00 American Institute of Physics. [S0003-6951(00)02549-3].