Ion acceleration by fs laser in target-normal-sheath-acceleration regime and comparison of time-of-flight spectra with particle-in-cell simulations

The ions acceleration through an fs laser irradiating a reduced graphene oxide foil in a target-normal-sheath-acceleration regime is investigated using a SiC detector connected in time-of-flight configuration. The experimental data indicated maximum proton energy of 1.8 MeV and a large number of carbon ions accelerated at different energies depending on their charge state. Particle-in-cell (PIC) simulations were applied to the studied target given the electron density as a function of the space and time and permitted one to evaluate the electrical field developed in the rear side of the foil driving the forward ion acceleration. The simulation indicates that the carbon ions are subjected to a lower acceleration with respect to protons, due to their slow velocity, depending on the charge-to-mass ratio. The latter does not permit carbon ions to be affected by the maximum electric field but a lower intensity due to the fast time decay of the electric field. Considering the angular emission of protons and the six carbon ions, the charge particles assume a Boltzmann energy distribution with a fixed cutoff at high energy, in agreement with the experimental measurements of ion energy.