Observation of neutron spectrum produced by fast deuterons via ultraintense laser plasma interactions

We report the first precise spectral measurement of fast neutrons produced in a deuterated plastic target irradiated by an ultraintense sub-picosecond laser pulse. The 500-fs, 50-J, 1054-nm laser pulse was focused on the deuterated polystyrene target with an intensity of 2×10¹⁹W/cm². The neutron spectra were observed at 55^∘{} and 90^∘{} to the rear target normal. The neutron emission was 7×10⁴ per steradian for each detector. The observed neutron spectra prove the acceleration of deuterons and neutron production by d(d,n)³He reactions in the target. The neutron spectra were compared with Monte Carlo simulation results and the deuteron's directional anisotropy and energy spectrum were studied. We conclude that 2% of the laser energy was converted to deuterons, which has an energy range of 30 keV up to 3 MeV.