Multiplexed infrared plasmonic surface lattice resonances

We demonstrate that arrays of flat gold nanodisks with rectangular lattices can support a tunable hybrid frequency gap formed by the surface lattice resonances in the substrate ((+1, 0)sub) and the superstrate ((−1, 0)sup). For a certain polarization, rotation of the arrays reduces this gap, forming a band crossing (degenerate state) wherein both surface lattice resonances happen around a single wavelength (∼1300 nm). This highlights a situation wherein hybridization of the Rayleigh anomaly with localized surface plasmon resonances with different multipolar natures happens around the same wavelength. We demonstrate that for a different polarization of the incident light the arrays support the formation of a photonic–plasmonic state at about 1650 nm. Our results show that as the projection of the wave vector of the incident light on the planes of the nanodisk arrays increases, within a given wavelength range, the (+1, 0) mode of this state becomes amplified. Under this condition, this mode can undergo a significant blue shift without broadening, while its amplitude increases.