Effect of preplasma on double pulse irradiation of targets for proton acceleration

We report on the experimental and simulated characterization of proton acceleration from double-pulse irradiation of um-scale foil targets with varying preplasma conditions. Temporally separated pulses of less than a picosecond in duration have been shown to increase the conversion efficiency of laser energy to MeV protons1. The experiment utilized two 700 fs, 1054 nm pulses, separated by 1 to 5 ps; total beam energy was 100 J, with 5–20% of the total energy contained within the first pulse. In contrast to the ultraclean beams used in previous experiments1, prepulse energies on the order of 10 mJ were present. The resulting significant preplasma appears to have a moderating effect on the double pulse enhancement. Proton beam measurements were made with radiochromic film stacks and magnetic spectrometers.