Extraordinary Optical Transmission through Sub-wavelength Hole Arrays.

We highlight the surprising features of the transmission of light through arrays of submicron cylindrical cavities in a metallic film. The holes, which have diameter d=150nm, are fabricated in an optically thick metallic film, in either a square or a triangular lattice. The zero-order transmission, measured in the far field, shows sharp modulation as a function of both the wavelength and the orientation of the film with respect to the incident light. The maxima occur even at wavelengths larger than the array period, the highest transmission occurring at wavelengths of order ten times the hole diameter. At the peaks the transmitted intensity can exceed unity when normalised to the area of the holes.