Observations of proton beam enhancement due to erbium hydride on gold foil targets

Recent theoretical work suggests that the conversion efficiency from laser to protons in laser irradiated thin foil experiments increases if the atomic mass of nonhydrogen atoms on the foil rear surface increases. Experiments were performed at the Lawrence Livermore National Laboratory Jupiter Laser Facility to observe the effect of thin foils coated with erbium hydride on the conversion efficiency from laser to protons. Gold foils with and without the rear surface coated with ErH3 were irradiated using the ultrashort pulse, 40 TW Callisto laser. An argon-ion etching system was used to remove naturally occurring nanometer thick surface layer contaminants from the hydride. With the etcher, gold with ErH3 showed a 25% increase in the conversion efficiency to protons above 3.4 MeV relative to contaminants, where C+4 and H+ were the dominant ion species. No difference in the ion signal was observed without first cleaning the hydrides. Simulations using the hybrid PIC code, LSP, revealed that the increase due ...