Dual-surface plasmon excitation with thin metallic nanoslits

Based on the experimental results and comparison between analytical and rigorous calculations, we have found that dual-surface plasmon (SP) waves are excited at both interfaces of a periodic array of thin metallic nanoslits: one at the grating-substrate interface and one at the grating-superstrate interface. Dual plasmons are excited for each diffraction order at two different wavelengths when the substrate differs from the superstrate. The splitting of the plasmons was investigated as a function of the refractive index difference between the substrate and superstrate. Verification of the extended nature of the double SPs is presented by comparing the rigorous calculation and analytic dispersion relation of extended SPs.