Investigation of ion characteristics in CO2laser irradiating preformed tin-droplet plasma

Abstract

AbstractComparative study of CO2laser-produced tin-droplet plasma with and without pre-pulse laser has been presented. A pre-pulse laser and the CO2laser was combined and focused to tin-droplet with a diameter of 180 µm. The emitted Sn ions were detected by several Faraday cups to obtain angular distribution of ions in the laser-produced tin-droplet plasma. The influence of pre-pulse laser energy and delay time between pumping laser and pre-pulse laser on the ion characteristics was investigated. It is illustrated that ion average kinetic energy from CO2laser-produced plasma (LPP) can be reduced when the tin-droplet target has been replaced by the preformed Sn plasma. The obtained optimal delay time with the lowest ion average kinetic energy is about hundreds of nanoseconds. The ion time-of-flight spectra show a twin peak structure in laser-irradiating preformed Sn plasma. And a superimposed Maxwell–Boltzmann (MB) distribution is proposed to describe this twin peak ion time-of-flight spectra. The fitting results quite agree with the raw ion time-of-flight spectra in current experiment. Then, the fitted plasma temperatures and mass-center velocities with various delay times in laser-irradiating preformed plasma are obtained, and the fitted plasma temperatures can be comparable with ion average kinetic energy in double-pulse LPP, which justified the rationality using this superimposed MB distribution.