Ultrafast coupling of an emitter to a plasmonic antenna

Here we introduce an antenna structure consisting of a metallic nanoparticle near a stratified dielectric medium. We find that the presence of an interface significantly changes the coupling between an emitter and the antenna. In a recent realization of such a scheme, we experimentally observed that indeed the increase of fluorescence was larger than what expected without the dielectric layers by several times. Our calculations show that enhancements of spontaneous emission up to 10s and directional couplings should be possible while keeping the quantum efficiency high.