Study of proton acceleration at the target front surface in laser-solid interactions by neutron spectroscopy

Proton acceleration inside solid LiF and CH–LiF targets irradiated by a 450-fs, 20‐J, 1053‐nm laser at an intensity of 3×1018W∕cm2 has been studied via neutron spectroscopy. Neutron spectra produced through the Li7(p,n)Be7 reaction that occurs between accelerated protons, at the front surface, and background Li7 ions inside the target. From measured and calculated spectra, by three–dimensional Monte Carlo code, the maximum energy, total number, and slope temperature of the accelerated protons are investigated. The study indicates that protons originate at the front surface and are accelerated to a maximum energy that is reasonably consistent with the calculated one due to the ponderomotive force.