Theory of extraordinary light transmission through arrays of subwavelength slits

We propose a self-consistent theory of the extraordinary light transmission through periodic arrays of subwavelength holes in metals. Its basis is an expansion of the light fields in terms of exact eigenmodes-propagating, evanescent, and anomalous-investigated in our recent paper and matching at the interfaces using the exact boundary conditions. An excellent convergence of this expansion has allowed us to decompose the anomalous transmission phenomenon into elementary parts and to investigate the characteristic parametric dependences. Transmission properties of a single interface play a key role in our theory in the subwavelength range. They include the coefficient of energy transmission into the propagating mode and the phases of the reflected and transmitted waves. These key parameters possess remarkable resonant dependences on the wavelength of light; they are sensitive to the size of the holes and rather insensitive to weak losses. The surface-plasmon-related features of the above characteristics are established. Transmission properties of a slab are expressed by the single-interface parameters, the phase incursion for the propagating mode, and the propagating losses.