Influence of fs-laser desorption on target normal sheath accelerated ions

Abstract

We report on the effects of fs-laser desorption on the ion acceleration induced by the target normal sheath acceleration (TNSA) mechanism. The experiment was performed at the Lawrence Livermore National Laboratory (LLNL) using the 100 TW Callisto laser of the Jupiter Laser Facility (JLF). Thin metal foils (Au, Cu, and Al) with thicknesses ranging from 10 to 20 μm were irradiated by a variable number of low intensity (∼10^{12} W/cm^{2}) laser pulses, the last one arriving 100 ms before the main pulse. With these short pulses water vapor and hydrocarbon contaminations could stepwise be removed from the target surface. Substantial modifications of the TNSA-ion energy spectra were observed such as diminished proton energy and intensity, the absence of low-charged ion states, increased particle numbers for C^{4+} and O^{6+} ions in the higher energetic part of their particle spectra as well as the acceleration of target ions. The controlled application of fs-laser desorption on the laser-ion acceleration thus strongly influences the ion spectra and offers the possibility of selecting a targeted range of ion species for the acceleration to higher energies due to the systematic removal of contamination layers.