Analytical treatment of anomalous transparency of a modulated metal film due to surface plasmon-polariton excitation

The detailed theoretical analysis of the fine optical phenomena caused by surface plasmon polariton (SPP) excitation in a metallic film with a weakly modulated dielectric permittivity is made for both symmetric and nonsymmetric dielectric arrangements. The advantage of the approach used (which is valid both for normal and oblique incidence) is that we present the most interesting results in a simple analytical form. SPP modes of the film, in the framework of our approach, are close to those existing on a metal half-space and correspond to weakly coupled states of the latter. With nonsymmetrical dielectric arrangements these SPP's are in general single-boundary localized, but under specific conditions (for instance, for the symmetric arrangements) they are double-boundary localized. Excitation of the film SPP's due to the diffraction on a grating results in the effect of enhanced light transmission. It is shown that for the nonsymmetric case, under single-boundary localized state excitation, the light tunneling process may be no less effective than that under double-boundary localized state excitation. The parameters of the problem (optimal film thickness, optimal modulation amplitude) responsible for the total suppression of the zeroth-order reflected wave and maximal transmittance are found. The dispersion relation for SPP's of the modulated film is investigated.