Excitation of eigenmodes at uniaxial crystal-metal-isotropic films

Abstract

We perform a theoretical study about the interaction between light and the eigenmodes of a metallic film that separates a uniaxial crystal from an isotropic medium. These structures support two different eigenmodes: a surface mode at the isotropic medium-metal interface and another mode at the crystal-metal interface. We show that, contrary to what happens in isotropic configurations, these two modes can couple to incident radiation without corrugating the surface or adding another interface. We give conditions to obtain zero reflected power and a strong enhancement of the fields at both interfaces. We also show that, owing to the different characteristics of the modes supported by each interface, the relative position of their propagation constants in the complex plane can be selected rather arbitrarily by tuning the film parameters. We give examples in which both couplings occur for angles of incidence either very different (separate resonances) or very close (almost double resonances). In the latter case we observe the phenomenon of “reluctance” between resonances.