Evolution of energy spectrum from laser-accelerated protons with a 100 fs intense prepulse
A parametric study is reported where a femtosecond prepulse is used to change the target properties before the interaction with a multi-terawatt laser pulse which accelerates protons from a foil target. The proton spectrum as function of the prepulse delay and intensity, up to 1.5 ns and up to 3x106 W/cm2, respectively, shows a global decrease of the maximum proton energy with delay and intensity.