Effect of the rising edge of ultrashort laser pulse on the target normal sheath acceleration of ions

Abstract

Laser-driven ion acceleration is theoretically/numerically mostly studied with the assumption of the idealized main ultrashort pulse of Gaussian temporal shape, where nanosecond/multi-picosecond pedestal and short prepulses preceded the main pulse can be incorporated in the form of modifications in the initial density profile of irradiated ionized targets. 
This paper shows that the relatively slowly rising edge (also called picosecond ramp) of the main ultrashort pulse, usually neglected in previous studies, can substantially change the efficiency of the target normal sheath acceleration of ions depending on laser intensity. 
The rising edge can enhance ion acceleration at mildly relativistic laser intensities, but increases divergence and reduces cutoff energy of accelerated ions at highly relativistic intensities relevant to petawatt lasers.