Laser acceleration of ions in mass-limited multi-species targets

Abstract

Intense short laser pulses may accelerate ions in thin targets to energies of several MeV per nucleon and highly collimated ion beams may be formed. Quasi-monoenergetic ion beams were generated last year from foils with a specially treated rear surface and from the water droplets. Mass-limited targets such as water μm-sized spheres or small metal discs offer an advantage of reducing the absorbed laser energy spread in the transverse directions. Ion acceleration in targets irradiated by short ultra-intense laser pulses is studied here via two-dimensional in space and three-dimensional in velocities (2D3V) relativistic electromagnetic particle-in-cell code. Simulations were performed for plane and curved foil sections and cylindrical targets that serve as a two-dimensional model of spherical micro-droplets. Two ion species with different charge-to-mass ratios facilitate the formation of persistent peak in energy distribution of the lighter ions, while the heavier ions act like a piston.