Improvement of laser-driven proton beam quality by optimized intense chirped laser pulses

Abstract

The effect of pulse shaping on the intense laser-driven proton beam produced through radiation pressure acceleration as a highly efficient mechanism is investigated. In this regard, the interaction of pulses with modified frequencies, including positive and negative chirped pulses with plasma, is simulated using particle-in-cell code. The simulation results indicate that the proton acceleration could be significantly enhanced for both negative and positive chirped pulses. As a consequence of the acceleration time extension as well as the electron heating suppression, a sharper and narrower proton beam could be achieved for negative chirped pulses. The same trend is observed for all negative chirp parameter values at different pulse durations. Furthermore, for positive chirped pulses, the generated proton spectrum is also considerably improved. However, the enhancement trend is strongly dependent on the value of the chirp parameter. Each different positive chirp parameter can alter the shape of the generated proton spectrum to a sharper, narrower, or more energetic one although, for an appropriate choice of the chirp parameter value, all three features could be simultaneously present in a single spectrum. The results showed that in the case of negative chirped pulses, the number of accelerated protons was increased to 2.35 times of its initial value and the energy spread of the proton beam was decreased by a factor of 0.677. For positive chirped pulses, the results showed up to a 51.18% improvement in the energy spread and a 22.47% increase in the accelerated beam density.