Laser Acceleration of Ultrashort Ion Bunches and Femtosecond Neutron Sources

Abstract

We have theoretically investigated the acceleration of ions in the interaction of high intensity, circularly polarized laser pulses with overdense plasmas. By using 1D and 2D particle‐in‐cell (PIC) simulations we find that high‐density, short duration ion bunches moving into the plasma are promptly generated at the laser‐plasma interaction surface. This regime is qualitatively different from ion acceleration regimes driven by fast electrons, such as sheath acceleration at the back of the target or shock acceleration at the front, which occur for linear polarization. A simple analytical model accounts for the numerical observations and provides scaling laws for the ion bunch velocity and generation time as a function of pulse intensity and plasma density. The present mechanism based on circular polarization of the laser pulse leads to moderate ion energies (in the 100 keV–1 MeV range) but very high ion densities and low beam divergence. These ion bunches might be of interest for problems of compression and...