Material Dependence of Energy Spectra of Fast Electrons Generated by Use of High Contrast Laser

Abstract

We studied the material dependence of electron acceleration with ultra-intense laser light at an intensity of 5 × 1019 W/cm2. Recent particle simulations have shown that the average energy of fast electrons stays lower than the prediction of ponderomotive scaling if intense laser light interacts directly with the target material. To control the fast electron energy spectra, we performed an experiment at the J-KAREN laser facility. The observed electron spectra show that the slope temperature for aluminum is 1.4 times higher than gold. The enhancement is strongly related to the average ioniation degree in the thin preplasma region in the PIC simulation result. The maximum proton energy reaches 10 MeV, and it shows the same values for Al, Cu and Au. The PIC simulations exhibit the values of the sheath fi eld at the target rear for Al, Cu, and Au, all of which are the same as the experiment.