Physical origin of directional beaming emitted from a subwavelength slit

We propose the physical origin for a directional beam of light emitting from a single subwavelength slit in metallic film that is characterized by a corrugation feature at the exiting side of the film. We theorize that the beaming phenomenon can be explained simply as surface plasmon diffraction along the corrugation as long as the multiple scattering effects are taken into account to restate the dispersion relationship of the surface plasmon. In order to prove our theory, both an experimental setup and numerical simulations were undertaken. Results obtained match well with our theory of an explanation based on a surface plasmon diffraction scheme.