Effective Wavelength Scaling of and Damping in Plasmonic Helical Antennae

We report on the optical performance of metallic nanohelices as the extension of the helical antenna concept into the optical wavelength range. These helical nanoparticles exhibit a structure and material dependent optical response due to the existence of a longitudinal localized-plasmon resonance which scales linearly with the total length of the helix; thus, comprising the number of turns and the single-turn length of the nanohelix. This is in contrast with macroscopic metallic helices, where the scaling of their operational mode is only determined by the length of a single turn. We show how the plasmon damping is radiated or absorbed depending on the interband activity of the metal forming the nanohelix. This study demonstrates the ability of helical structures to control and manipulate optical fields at the nanometer scale according to their specific shape and material composition.