Using interferometric measurements and theoretical calculations, we show that a refractive index can be appropriately assigned to a thin plasmonic metafilm on a high-permittivity dielectric. A full analysis in amplitude and in phase of the composite metafilm made of metallic nanoresonators and wires is reported around the first plasmonic resonance. It reveals that contrary to solely intensity measurements, the phase behavior of the air/metafilm/dielectric system dramatically depends on both the damping effects and the dielectric index. A simple model is derived which can apply to various situations in plasmonics and optical metamaterials.

• Received 21 August 2009

DOI:https://doi.org/10.1103/PhysRevB.80.205120