Proton acceleration from thin foils by extremely short PW laser pulse

Abstract

In the context of current efforts to compress PW-level laser pulses to an order of 10 fs, the 3D optimization particle-in-cell (PIC) simulations of proton acceleration have been performed to maximize the proton energy cutoffs using CH2 foils as an example. This was complemented by a simple theoretical model to which PIC simulation results were qualitatively compared. Such a model accounted for a fast increase in a backside surface hot spot, transition of plasma expansion from isothermal regime to the adiabatic one, and effect of target semitransparency that is important for the considered extremely short pulses. It was found that the twofold increase in a shortened laser pulse focal spot size is fraught with a loss in the maximum energy of accelerated protons even when the pulse energy is the same. The PIC simulation optimization study revealed the optimal target thicknesses and the corresponding maximum energies of accelerated protons for shortened PW pulses, and also showed that advantage from their use to increase the proton energy occurs only if the focusability at the target is not worsened.