Simulations of hard X-ray generation by hot electrons in a silver target

A semi-analytical model is developed for the generation of X-ray bremsstrahlung in metallic targets with the inclusion of hot electron recirculation (refluxing). The hard bremsstrahlung and characteristic X-ray yields are calculated in relation to the thickness of a silver target for an s-polarised subpicosecond laser pulse intensity of 2 × 10¹⁹ W cm^-2. The effect of hot electron recirculation in thin foils is shown to significantly improve the K_α radiation and bremsstrahlung yields in a photon energy of 10–100 keV. By contrast, the 0.1–1 MeV bremsstrahlung photon yield from thin foils with hot electron recirculation corresponds approximately to the highest photon yield from those targets in which recirculation is insignificant. We make a comparative analysis of the highest laser-to-X-ray energy conversion efficiencies obtained to date.