Coherent and incoherent radiation from ultra-intense laser interaction with nanostructured nickel nanowire (`velvet') targets

Nickel nanowires (`velvet') are a pure metallic anisotropic nanostructured material, averaging as much as one-quarter of solid density, that does not support material polarization- or current-densities required for Fresnel reflection. Since they present $>90\%$ absorption and an effective skin-depth on the order of $1 \mu$m for intense laser light, they have been shown to be efficient x-ray converters. We show theoretical and experimental results of their behaviour under a range of irradiation conditions, from small-signal up to very clean pulses of relativistic-intensity laser light, including their transition from an effective dielectric to an effective metal, as the result of the generation of relativistic Brunel electrons.