Distance-of-flight spectra of charge density of ions generated with a low laser intensity

A charge density profile of ions emitted from a laser ion source is derived from a time-resolved current of ions collected with a time-of-flight detector. This relationship between the density profile over path of ions and an ion current observed far from the ion source is based on a similarity relationship for ion currents with "frozen" charges observed at different distances from the target. In this contribution, we present distance-of-flight spectra of the charge density of ions emitted from various plasmas driven by a Compex 205 KrF excimer laser (lambda = 248 nm, tau(FWHM)=23ns) which works at laser irradiances between 10(8) and 10(10) W/cm(2).