Simulations of radiation pressure ion acceleration with the VEGA Petawatt laser

Abstract

The Spanish Pulsed Laser Centre (CLPU) is a new high-power laser facility for users. Its main system,VEGA, is a CPA Ti:Sapphire laser which, in itsfinal phase, will be able to reach Petawatt peak powers inpulses of 30 fs with a pulse contrast of 1:1010at 1 ps. The extremely low level of pre-pulse intensitymakes this system ideally suited for studying the laser interaction with ultrathin targets. We have usedthe particle-in-cell (PIC) code OSIRIS to carry out 2D simulations of the acceleration of ions from ultrathinsolid targets under the unique conditions provided by VEGA, with laser intensities up to 1022Wcm 2impinging normally on 20–60 nm thick overdense plasmas, with different polarizations and pre-plasmascale lengths. We show how signatures of the radiation pressure-dominated regime, such as layercompression and bunch formation, are only present with circular polarization. By passively shaping thedensity gradient of the plasma, we demonstrate an enhancement in peak energy up to tens of MeV andmonoenergetic features. On the contrary linear polarization at the same intensity level causes the targetto blow up, resulting in much lower energies and broader spectra. One limiting factor of RadiationPressure Acceleration is the development of Rayleigh–Taylor like instabilities at the interface of theplasma and photonfluid. This results in the formation of bubbles in the spatial profile of laser-acceleratedproton beams. These structures were previously evidenced both experimentally and theoretically. Wehave performed 2D simulations to characterize this bubble-like structure and report on the dependencyon laser and target parameters