Comparative analysis of laser-triggered proton generation from overdense and low-density targets

Based on 3D particle-in-cell (PIC) simulations a comparative analysis of laser-triggered proton generation from the interaction of short high-intensity laser pulses with ultrathin foils and dense gas jets has been performed. It has been shown that for ultra-relativistic laser intensities the use of low-density targets with near critical density (aerogel or dense gas jet) has no advantage in comparison with ultrathin foils in terms of maximum proton energy and spectrum quality. Utilization of mass-limited foils with submicron thickness demonstrates even greater superiority for overdense targets and allows one to produce monoenergetic proton beams with energies of hundreds of mega-electron-volts by using high-contrast laser pulses with energies of the order of tens of Joules.