Charge separation effects in solid targets and ion acceleration with a two-temperature electron distribution

The electrostatic field at the solid-vacuum interface generated by two electron populations with different thermal energies, each following a Boltzmann distribution, is analytically derived from the Poisson equation and studied in terms of plasma parameters. In particular, the effect of the pressure of each of the two populations on the amplitude of the electric field and on its spatial extension is described. In order to evaluate the cold electron temperature, an analytical model for the Ohmic heating of the background electron population by laser generated fast electrons is developed and the consequences on ion detachment, ionization, and acceleration processes in laser-solid experiments are discussed. The efficiency of ion acceleration is shown to be controlled by the heating rate of the background electrons.