Brian Soller and Dennis Hall of the University of Rochester (Rochester, NY) have observed the propagation of guided light waves confined to the surface of a discontinuous film of silver (Ag) nanoparticles. The 457.9-nm light, which was p-polarized, was confined by a two-dimensional disordered array of particles with average diameter of 400 nm and average height of 150 nm. The finding has significance for the design of nanocomposite optical materials.
The mode propagates at frequencies close to the strong plasma-resonance absorption in the film and is least-lossy at frequencies where the nanoparticle layer has a large absorption. The mode is likely the result of coupling between incident light and the particle plasma resonances of the nanoparticle layer, say the researchers. The Ag particles themselves were formed on top of a 30-nm-thick layer of lithium fluoride (LiF) by evaporation in vacuum; surface irregularities in the LiF aided in the production of evenly sized Ag particles. No signs of surface waves were observed for s-polarized radiation. By comparing theoretical calculations with reflectivity data, the researchers determined that the TM2 mode is responsible for the excitation driving the surface-mode propagation. Contact Brian Soller at [email protected].