Infrared resonances of local fields and ellipsometric spectra of negative-refraction metamaterials

Suitable combinations of the optical response and geometrical form of flat or curved interfaces of the constituents in nanometer-sized metamaterials can lead to a strong enhancement of local fields, seen typically as sharp spectral resonances in optical spectra. We propose a classification of the resonant phenomena in inhomogeneous systems within the effective-medium approximation, and examine their manifestation in infrared ellipsometry. We report mid-infrared ellipsometric spectra of a doped semiconductor metamaterial, exhibiting negative refraction. We provide a simple explanation for the difference in the directions of the phase- and energy propagation. The resonance responsible for a strong anisotropy and the interesting behavior of refracted light is found to lead to characteristic features in the ellipsometric spectra.