Resonant transmission of light through finite arrays of slits

Finite-size effects associated with the phenomenon of extraordinary optical transmission are theoretically addressed. We analyze the N dependence of the transmission resonances appearing in one-dimensional periodic arrays of N slits. For the transmission resonances located close to the period of the array, it is found that the evolution is controlled by the width of the slits. This parameter completely governs the electromagnetic coupling between slits that, in turn, is the key actor in the formation of the collective surface electromagnetic mode responsible for the enhanced transmission. On the contrary, the transmission process associated with the excitation of waveguide resonances inside the slits is almost independent of the number of slits perforated on the metallic film.