We present a novel theoretical approach for modeling the resonant propertiesof transmission through subwavelength apertures penetrating metal films. Weshow that cavity mode theory applies to an effective resonant cavity whosedimensions are determined by the aperture's geometry and the evanescent decaylengths of the associated diffracted waves. This method suggests a concretephysical mechanism for the enhanced transmission observed in periodic aperturearrays, namely it is the evanescently scattered light, localized in the nearfield of metal surface, which couples into the apertures. Furthermore, itanalytically predicts the frequencies of peaks in enhanced transmission, thequality factor of the peaks, and explains their dependence on variation in thehole radius, periodicity, and the film thickness over a wide range ofgeometries. This model demonstrates strong correlation to simulation andexisting results with a high degree of accuracy.
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