2D particle-in-cell simulations of ion acceleration in laser irradiated submicron clusters including field ionization

Abstract

The interaction of femtosecond laser pulses with submicron water clusters is studied here by two-dimensional particle-in-cell simulations. Field ionization is included in our simulations using Ammosov–Delone–Krainov ionization rate. We search for optimum laser and cluster parameters to obtain quasimonoenergetic beam of protons accelerated from the cluster. For the laser amplitude a0≈3 used in recent experiments, the optimum cluster size is about 150 nm for the generation of pronounced peak in proton energy distribution function at maximum energy and the optimum laser pulse duration is about 40–80 fs. Various initial density profiles of cluster plasma, formed due to insufficient laser pulse contrast and prepulses, are involved in this study, including underdense clusters.