Enhanced light transmission by hole arrays

The extraordinary optical transmission of a metallic film pierced by a two-dimensional subwavelength hole array, observed by Ebbesen et al, is explained using rigorous electromagnetic analysis and a phenomenological approach. The analysis is based on Li's Fourier-modal method extended to crossed gratings, which reduces the diffraction problem to the search for eigenvalues and eigenvectors of a particular matrix. The computation of the eigenvalues allows us to find a new channel for light transmission through the subwavelength holes, which differs from the transmission channel in the one-dimensional case (lamellar or rectangular-rod grating). It is demonstrated that the enhanced transmission is due to the excitation of a surface plasmon on the lower metallic surface.