Neutron energy spectra from the laser-induced $\mathrm{D}{\mathrm{}(d,n)\mathrm{}}^3\mathrm{He}$ reaction

Detailed neutron energy spectra were measured for the $\mathrm{D}{\mathrm{}(d,n)\mathrm{}}^3\mathrm{He}$ reaction induced in solid $({\mathrm{CD}}_2{)}_n$ targets by irradiation with 50-fs $2\times {10}^{18}\hspace{0.5em}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ light pulses from a 10-TW Ti:Sapphire laser. The neutrons were observed at two angles $5°$ and $112°$ relative to the incident laser beam. The neutron spectra at the two angles are characterized by peaks with large widths of about 700 keV full width at half maximum and a shift of 300 keV between them. Neutron energies of up to about 4 MeV were observed indicating that deuterons are accelerated up to an energy of 1 MeV in the laser produced plasma. Simulation calculations can describe qualitatively the neutron spectra by assuming isotropic deuteron acceleration and a reduction of the reaction probability by a factor of 1/3 for deuterons emitted from the front of the target. These calculations indicate in particular that it is necessary to assume deuterons moving both into and out of the front of the target in order to describe the neutron energy spectra at the two angles. The highest recorded mean neutron yield was about ${10}^4$ neutrons per pulse. The neutron yield increases with the number of electrons emitted from the front of the target and with the intensity of the prompt $\gamma$ flash induced by the bremsstrahlung of energetic electrons.