Shaping light beams in the nanometer scale: A Yagi-Uda nanoantenna in the optical domain

A Yagi-Uda-like optical nanoantenna concept using resonant core-shell plasmonic particles as its ``reflectors'' and ``directors'' is studied numerically. Such particles when placed near an optical dipole source in a certain arrangement may exhibit large induced dipole moments, resulting in shaping the far-field radiation pattern, analogous to the far field of classical Yagi-Uda antennas in the microwave regime. The variation of the ratio of radii in concentric core-shell nanostructure is used to tailor the phase of the polarizabilities of the particles and, consequently, the antenna's far-field pattern. The idea of a nanospectrum analyzer is also briefly proposed for molecular spectroscopy.