Proton Acceleration with Double-Layer Targets in the Radiation Pressure Dominant Regime

Acceleration of protons by a circularly polarized laser pulse irradiating on a double-layer target is investigated by a theoretical model and particle-in-cell simulations. The target is made up of a heavy ion layer coated with a proton layer on the rear surface. The results show that when the first layer is transparent induced by the hole-boring effect, the whole proton layer is accelerated by the transmitted laser pulse to high energy with low energy spread. The quality of the proton beam generated from a double-layer target is better than that from a single-layer target. The improvement is attributed to the flat top structure of the electrostatic field caused by the electrons injected into the second layer. It is easier to control the spectrum quality by using a double-layer target rather than using a single-layer one when the radiation pressure acceleration is dominant.