Subwavelength hole array enhanced light transmission

An electromagnetic analysis of a two-dimensional metallic grating is used to explain the extraordinary optical transmission of a metallic film pierced by a two-dimensional subwavelength hole array, observed three years ago (T. Ebbesen et al., Nature, London, 391, 667, 1998). The analysis is based on the Fourier-modal method extended to crossed gratings (L. Li, J. Opt. Soc. Am. A 14, 2738, 1997), which reduces the diffraction problem to the search of eigenvalues and eigenvectors of a particular matrix. The computation of the eigenvalues allows finding 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.