Measurement of the transmitted intensity from a coherent monomode light source through a series of subwavelength slit arrays in Ag films, with varying array pitch and number of slits, demonstrates enhancement (suppression) by factors of as much as 6 (9) when normalized to the transmission efficiency of an isolated slit. Pronounced minima in the transmitted intensity are observed at array pitches corresponding to ${\lambda }_{\mathrm{SPP}}$, $2{\lambda }_{\mathrm{SPP}}$, and $3{\lambda }_{\mathrm{SPP}}$, where ${\lambda }_{\mathrm{SPP}}$ is the wavelength of the surface plasmon polariton (SPP). The position of these minima arises from destructive interference between incident propagating waves and pi-phase-shifted SPP waves. Increasing the number of slits to four or more does not increase appreciably the per-slit transmission intensity. A simple interference model fits well the measured transmitted intensity profile.

• Received 11 February 2008

DOI:https://doi.org/10.1103/PhysRevB.77.115411