Scaling of proton energies in ultrashort pulse laser plasma acceleration

This paper presents a systematic investigation of an ultrashort pulse laser acceleration of protons that yields unprecedented maximum proton energies of 17MeV at a table-top Ti:sapphire laser power level of 100TW. For plain fewmicron- thick foil targets, a linear scaling of the maximum proton energy with laser power is observed and this is attributed to the short acceleration period close to the target rear surface. Although excellent laser pulse contrast was available, slight deformations of the target rear were found to lead to a predictable shift of the direction of the energetic proton emission away from the target normal that could be used for better discrimination of the low-energy part of the spectrum.