Comparison of optimized ion acceleration from thin foils and low-density targets for linearly and circularly polarized laser pulses

Abstract

A multiparameter comparative analysis of ion acceleration with linearly and circularly polarized relativistically intense laser pulses for solid-density thin foils and low-density planar targets was performed using 3D particle-in-cell (PIC) simulations. Ion acceleration optimization was studied with 3D PIC MANDOR over the laser energy range of three orders of magnitude from three hundred millijoules to three hundred joules in a femtosecond pulse. The optimum target thickness and density was found for a given energy of the laser pulse corresponding to the maximum energy of the accelerated ions. This allows deriving a dependence of the maximum ion energy on laser energy for the optimized solid or low-density targets. The advantage of a circularly polarized laser pulse for generating the most energetic ions was demonstrated, which happens for the regimes of volumetrically heated semitransparent solid foils (directed Coulomb explosion) and of synchronized ion acceleration by slow light from low-density targets. The dependence of the maximum ion energy on laser energy for the optimized targets and both linearly and circularly polarized femtosecond pulses demonstrates a sharper-than-square-root increase.