Enhancement of high energy proton yield with a polystyrene-coated metal target driven by a high-intensity femtosecond laser

We present experimental results on protons accelerated up to 950 keV from a 3- Delta *mm thick tantalum foil with a 133-nm thick polystyrene layer on its rear surface, irradiated with a laser pulse having the duration of 70 fs and the intensity of 2.7X1018 W/cm2. The energy distribution of fast protons was measured simultaneously with that of the hot-electrons from the rear surface. The proton yield from the polystyrene-coated target is about 10 times as high as that from the uncoated metal target. This enhancement of the proton yield is roughly proportional to the increase of hydrogen atoms given by the 133-nm thick polystyrene layer, assuming a contaminant layer of ~10-nm thickness is on the metal surface without coating. This result shows that the polystyrene layer contributes to the yield enhancement.