Low dispersion surface plasmon-polaritons on deep silver gratings

Surface plasmon modes supported by short-pitch silver gratings with different depths have been characterized by studying the reflectivity as a function of the angle of incidence and the incident wavelength (400-850 nm). Highly non-dispersive `flat' surface plasmon-polariton bands were found corresponding to localized, within the grooves, radiative resonant modes. Experimental reflectivities were compared with model calculations and to help understand the character of each of the modes, the optical magnetic field distributions at the resonant frequencies were explored.