Hard x-ray and hot electron production from intense laser irradiation of wavelength-scale particles

We have examined the production of hard x-rays from the irradiation of ~1 µm diameter water droplets with a 35 fs laser at an intensity of up to 7 × 10 17 W cm -2 . We observe substantial x-ray production in the photon energy range above 100 keV and find that the implied hot electron temperatures from these micron-scale targets are significantly higher than electron temperatures observed from irradiation of solid planar plastic targets under nearly identical irradiation conditions. The observed enhancement of the hot electron temperature from droplets is consistent with hot electron spectra calculated from particle-in-cell simulations.