Target normal sheath ion acceleration by fs laser irradiating metal/reduced graphene oxide targets

Target normal sheath ion acceleration is applied with a high contrast fs laser irradiating advanced targets based on thin metallic films (Al, Cu, Ag and Au) covering micrometric foils of reduced graphene oxide (rGO). The laser intensity is of about 10¹⁸ W/cm² and the laser focal position with respect to the target surface is optimized to have the maximum proton acceleration. Plasma diagnostics are investigated using time-of-flight technique employing SiC detectors, ion collectors, and gaf-chromic films. Micrometric aluminum absorbers were employed to separate the faster proton detection by other accelerated ions. At the optimized laser focal position, the maximum proton acceleration of 2.5 MeV and 3.0 MeV energy was obtained using Ag(200 nm) and Au(200 nm) covering rGO(7 μm) targets, respectively. The high proton energy is due to the high electrical and thermal conductivity and high mechanical resistance of the used rGO foils and to the high plasma electron density of the target.