title: Optical antenna arrays in the visible range.
abstract: We report on experimental observations of highly collimated beams of radiation generated when a periodic sub-wavelength grating interacts with surface bound plasmon-polariton modes of a thin gold film. We find that the radiation process can be fully described in terms of interference of emission from a dipole antenna array and modeling the structure in this way enables the far-field radiation pattern to be predicted. The directionality, multiplicity and divergence of the beams can be completely described within this framework. Essential to the process are the surface plasmon excitations: these are the driving mechanism behind the beam formation, phase-coupling radiation from the periodic surface structure and thus imposing a spatial coherence. Detailed fitting of the experimental and modeled data indicates the presence of scattering events involving the interaction of two surface plasmon polariton modes.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Matthews
authors.forename: Huw D
authors.initials: HD
authors.lastname: Summers
authors.forename: Kerenza
authors.initials: K
authors.lastname: Njoh
authors.forename: Sally
authors.initials: S
authors.lastname: Chappell
authors.forename: Rachel
authors.initials: R
authors.lastname: Errington
authors.forename: Paul
authors.initials: P
authors.lastname: Smith