Efficient ion acceleration by multistaged intense short laser pulses

We present a computational study of laser-driven ion acceleration that optimizes a combination of target transparency and extended field acceleration at moderate relativistic intensity. Our scheme applies two sequential laser pulses irradiating a thin target foil along the same direction: The first pulse drives a rapid expansion of the target, while the second one drives a quasistatic electric field in the expanding target with increasing electron temperature. In our particle-in-cell simulations we observe proton peak energies and numbers enhanced by factors of up to 3 compared with regular target-normal sheath acceleration.