Momentum distribution of accelerated ions in ultra-intense laser–plasma interactions via neutron spectroscopy

The dependence of neutron spectra on the incident laser polarization has been studied to elucidate ion acceleration processes in ultra-intense laser–plasma interactions. Obliquely incident, 50–100 TW (450–800 fs) laser pulses irradiated a deuterated plastic solid target at 1019 W/cm2 with both s- and p-polarizations. Neutron spectra from the deuteron–deuteron d(d,n)3He nuclear reactions show the ion acceleration into the target in the direction of the target normal for both polarizations. The experiment and particle-in-cell simulations indicate the ions are accelerated inside the target by an intense electrostatic field created by charge displacement at the laser focus.