Heavy ion acceleration using femtosecond laser pulses

TL;DR

This study uses simulations and models to explore heavy gold ion acceleration with femtosecond laser pulses, identifying key challenges and potential regimes for improved acceleration efficiency.

Contribution

It provides a detailed analysis of heavy ion acceleration mechanisms, challenges, and identifies a new regime suitable for effective heavy ion acceleration using ultrashort laser pulses.

Findings

Conversion efficiency into gold ions is 8%.

Maximum ion energy reaches 25 MeV/nucleon.

Identified challenges include low charge-to-mass ratio and high plasma reflectivity.

Abstract

Theoretical study of heavy ion acceleration from ultrathin (<200 nm) gold foils irradiated by a short pulse laser is presented. Using two dimensional particle-in-cell simulations the time history of the laser bullet is examined in order to get insight into the laser energy deposition and ion acceleration process. For laser pulses with intensity , duration 32 fs, focal spot size 5 mkm and energy 27 Joules the calculated reflection, transmission and coupling coefficients from a 20 nm foil are 80 %, 5 % and 15 %, respectively. The conversion efficiency into gold ions is 8 %. Two highly collimated counter-propagating ion beams have been identified. The forward accelerated gold ions have average and maximum charge-to-mass ratio of 0.25 and 0.3, respectively, maximum normalized energy 25 MeV/nucleon and flux . Analytical model was used to determine a range of foil thicknesses suitable for acceleration of gold ions in the Radiation Pressure Acceleration regime and the onset of the Target Normal Sheath Acceleration regime. The numerical simulations and analytical model point to at least four technical challenges hindering the heavy ion acceleration: low charge-to-mass ratio, limited number of ions amenable to acceleration, delayed acceleration and high reflectivity of the plasma. Finally, a regime suitable for heavy ion acceleration has been identified in an alternative approach by analyzing the energy absorption and distribution among participating species and scaling of conversion efficiency, maximum energy, and flux with laser intensity.