Asymmetric and symmetric coupling of surface-plasmon-polariton waves to planar interfaces with periodically patterned slanted columnar thin films of silver

We investigated the interaction of a periodically patterned columnar thin film (PP-CTF) of silver with light incident on it from a vacuous half space, as a function of the angle ψ between the plane of incidence and the morphologically significant plane of the PP-CTF. The chosen structure had previously been shown to be capable of showing asymmetric coupling of surface-plasmon-polariton (SPP) waves over a broad bandwidth in the visible regime with incident light when the plane of incidence coincides with the morphologically significant plane of the PP-CTF (ψ = 0°). We determined experimentally that coupling may be completely symmetric in some spectral regime, when the plane of incidence is orthogonal to the morphologically significant plane of the PP-CTF (ψ = 90°). Whereas asymmetric coupling occurs with quasilinear dispersion when ψ = 0°, completely symmetric coupling occurs with quasiparabolic dispersion.