We demonstrate a 13-fold increase in hard x-ray bremsstrahlung (10 - 200 keV) emitted by a copper plasma created by 100 fs, 806 nm pulses at $10^{ 14}-10^{ 15}$ Wcm$^{ -2}$. This enhancement is achieved by roughening the target surface with copper nanoparticles of ~15 nm size. A simple model that invokes local field modifications by surface plasmon excitation and `lightning rod' effects explains the observed enhancement quantitatively and provides pointers to the design of structured surfaces for maximizing the emission.
Categories: physics.plasm-ph physics.atom-ph
