Velocity distribution of ions in UV laser induced plasma plumes

Plasmas induced by UV laser ablation have been studied and analysed using time-of-flight measurements. A KrF laser beam of 23 ns FWHM time duration was focused into Si and Nb targets with a moderate laser fluence of 2 J/cm(2). A suitable theoretical expressions were derived for fitting the recorded ion current under the assumption of a "shifted" Maxwell-Boltzmann velocity distribution. The deconvolution of time resolved ion current signals, taking into account a multi-mode velocity distribution has revealed that the contribution of the different charge states of ions in the plasma induces electric field which accelerate the expanding plasma along the target normal.