抄録
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.
