Time-of-flight profile of multiply-charged ion currents produced by a pulse laser

Abstract

The ion emission from a Cu-plasma produced by a 308 nm excimer laser is analysed by time-of-flight spectroscopy and by deconvolution of measured ion currents. The ion current signals recorded by an ion collector outside the critical zone, where the charge-states of ions of the expanding plasma are frozen, have been deconvoluted by the use of the Kelly and Dreyfus equation. The meaningful recovered currents recorded for Cu+ and Cu2+ ions have been compared with the current signals reconstructed from the ion energy analyser spectra. A velocity distribution and the abundance of the above ions are presented. A time-resolved average charge-state of ions is also determined. The application of the law Q ∝ l−2, based on the dilution of the total charge, Q, carried out by ions at long distances, l, from the target, is shown to be fundamental for a characterization of the laser-produced plasma.