Various approaches to the basic physics of optical transmission through subwavelength structures have led to diverse and often conflicting interpretations of the nature of the transmission and predictions of its properties. We present a series of experimental and model studies clarifying the essential interaction between incident light, surface waves, and transmission through subwavelength slits and slit arrays. We find that many surface modes contribute to the composite surface wave within a “near zone” of ~ 2 λ from the transmitting slit. Furthermore, the surface plasmon polariton mode (spp), the only surviving surface mode beyond the “near zone,” is π out of phase with the incident light, and a minimum in transmission obtains when slit array periodicity is equal to an integer number of spp wavelengths. This minimum in transmission is due to destructive interference between the out-of-phase spp mode launched from neighboring elements and the incident wave. We also find that interaction between adjacent slit elements is very strong and effectively shields interactions with slit elements beyond nearest neighbors. We interpret these properties in terms of oscillating dipoles induced at discontinuities in the metal surface (slits and grooves) by currents within the skin depth of the metal. These currents are in turn set up by a standing-wave E-M field arising from reflection of the incident wave at the metal surface.
© 2008 Optical Society of AmericaPDF Article