Interference and resonant cavity effects explain enhanced transmission through subwavelength apertures in thin metal films

Transmission through an opaque Au film with a single subwavelength aperture centered in a smooth cavity between linear grating structures is studied experimentally and with a finite element model. The model is in good agreement with measured results and is used to investigate local field behavior. It shows that a surface plasmon polariton (SPP) is launched along the metal surface, while interference of the SPP with the incident light along with resonant cavity effects give rise to suppression and enhancement in transmission. Based on experimental and modeling results, peak location and structure of the enhancement/suppression bands are explained analytically, confirming the primary role of SPPs in enhanced transmission through small apertures in opaque metal films. (C) 2007 Optical Society of America