Improvement of hot-electron and gamma-ray yields by selecting preplasma thickness for a target irradiated by a short laser pulse

The dependences of the temperature and the number of hot electrons on the size of the plasma corona of a thin foil target irradiated by a short relativistically intense laser pulse are investigated by three-dimensional numerical simulations. For a 30-fs long laser pulse with an energy of 300 mJ we have determined the optimal preplasma size which maximises the yield of forward-accelerated electrons capable of generating gamma-ray photons several MeV in energy. A study is made of gamma-ray generation by such laser-accelerated electrons in the bombardment of a converter target placed behind the laser target; the brightness of this gamma-ray source is shown to range up to 10¹⁵ photons s^-1 mrad^-2 mm^-2 × (0.1% BW)^-1.