Sodium Surface Lattice Plasmons

Metallic nanostructures can source, detect and control light through surface plasmons with applications ranging from photocatalysis, biochemical sensors, to light trapping in thin-film solar cells. Although the commonly used plasmonic materials such as gold and silver have shown great optical properties, they experience significant ohmic losses that severely limit the device performances. Sodium is predicted to be an ideal plasmonic material with much lower loss than gold and silver across the whole ultraviolet to near-infrared wavelength regime. Here we describe how sodium nanoparticles can exhibit high-quality plasmonic resonances through the excitation of surface lattice plasmons. We investigate both the sodium nanoparticles (size, array period, unit structure) and the excitation light (polarization, angle of incidence) to manipulate how light interacts with sodium nanoparticles. Specifically, by exciting in-plane and out-of-plane surface lattice plasmons, we obtain resonances with extremely narrow linewidths and localized electromagnetic field with amplified intensities for sodium nanoparticles. Sodium, as a low-cost and low-loss plasmonic material, provides an affordable alternative in a range of plasmon-enhanced applications such as chemical sensing, thin-film solar cells, and photonic circuits.