Surface Plasmon Interference Device as a Source of Near-Field Power for Photoluminescence

Abstract

We theoretically demonstrate that a simple device consisting of an opaque gold layer with subwavelength slits — the so-called surface plasmon interference device — is capable of transforming the far-field optical power to the near-field one. Optimized slits yield a high conversion efficiency amounting to 45% in terms of the near-field to far-field electric intensity ratio. With a single linear slit arrangement, a propagating wave with a homogeneous field distribution is formed, attributed to surface plasmon polaritons based on its polarization properties. On the other hand, with the slit arrangement supporting interference, it is possible to obtain a standing wave with characteristic spatially modulated interference fringes and spatially separate polarization components. A circular slit can be used for focusing the near-field, with the possibility of obtaining a considerably enhanced field with respect to the excitation. We discuss the implication of the enhanced near-field for the near-field excitation of photoluminescence with the capability to bring a spatial resolution of the photoluminescence spectroscopy beyond the diffraction limit.