Leaky surface-plasmon theory for dramatically enhanced transmission through a sub-wavelength aperture, Part II: Leaky-wave antenna model

The optical transmission through an aperture punched in an opaque metal (usually silver) film is extremely small when the aperture diameter d is much smaller than the wavelength, d/spl Lt//spl lambda//sub 0/. The optical transmission can be enhanced greatly when one or both surfaces of the metal film have periodic corrugations, provided the corrugations are chosen properly, as described in various papers, and discussed in the companion paper, Part 1. The best explanation to date for the dramatically enhanced transmission effect has been in terms of a resonance associated with a surface plasmon mode that exists on the metal film. The purpose of this paper is to demonstrate, for the first time, that the enhanced optical transmission effect is indeed due to the excitation of a leaky mode. In particular, the periodic structure (corrugations) causes the normally bound (non-leaky) surface plasmon mode to become a leaky plasmon mode. By properly choosing the periodicity, the leaky mode radiates at broadside, giving an increased field in this direction, and hence an enhanced optical transmission.