Complex polarizability of an isolated subwavelength plasmonic hole in a thin metal film

Because of the ability to concentrate light into subwavelength dimensions, plasmonic nanostructures have become a new frontier of nano-photonics, with promising applications for energy transport and conversion. In this work, we experimentally measure the near field intensity distribution of light squeezed through a subwavelength plasmonic hole in a thin metal film. Both transmission coefficient and phase shift of an in-plane electric dipole moment, which is excited near the isolated subwavelength hole, are retrieved based on the interference model of a plane and spherical wave. Strong transmission enhancement is achieved through the subwavelength hole due to the surface plasmon resonance via a model which is not predicted by the classical theory. The opposite phases of the excited dipoles in the subwavelength dent and protrusion are observed.