Surface plasmons enhance optical transmission through subwavelength holes

TLDR

Optically thick metal films perforated with a periodic array of subwavelength holes exhibit exceptional transmission properties. The authors show that transmission minima correspond to Wood's anomalies when a diffracted beam becomes tangent to the film, while maxima arise from resonant excitation of surface plasmons. Surface plasmons from both sides of the film appear in the dispersion diagram, revealing strong coupling that yields wavelength‑selective transmission with efficiencies roughly 1000 times higher than expected for subwavelength holes.

Abstract

Optically thick metal films perforated with a periodic array of subwavelength holes show exceptional transmission properties. The zero-order transmission spectra exhibit well-defined maxima and minima of which the positions are determined by the geometry of the hole array. We show that the minima are the collection of loci for Wood's anomaly, which occurs when a diffracted beam becomes tangent to the film, and that the maxima are the result of a resonant excitation of surface plasmons (SP's). SP's from both surfaces of the metal film are apparent in the dispersion diagram, independent of which side of the film is illuminated, indicating an anomalously strong coupling between the two sides. This leads to wavelength-selective transmission with efficiencies that are about 1000 times higher than that expected for subwavelength holes.