Influence of charge transfer on energy measurements of ions expanding from laser-produced plasmas

The energy distributions of ions measured at some distance from an expanding laser-produced plasma are shown to be influenced by the presence of a low-pressure (<10 -4 Torr) background gas in the target chamber. This was revealed through the development of structure in the energy distributions and the appearance of neutral particles as the pressure of a background gas in the target chamber was systematically increased. At each pressure, complete sets of energy distributions for C 4+ , C 3+ , C 2+ and C + were obtained with a t -2 analyser using only a single laser shot. The effects seen on the ion energy distributions have been attributed to charge exchange along the flight path, although direct confirmation of this process has not yet been obtained. If charge exchange is responsible then background pressures better than 10 -6 Torr would be necessary for reliable measurements of ion energy spectra in laser-produced plasma experiments.