Centre for Materials Research, Norfolk State University 2006

Surface plasmons — collective oscillations of free electrons that propagate along a metal/dielectric interface — have become a very hot topic because of their role in a broad range of optical phenomena. The intense fields associated with surface plasmons can enhance the optical properties of a material and have been observed on rough surfaces, in artificial nanostructures as well as in clusters and aggregates of nanoparticles. Effects attributed to surface plasmons, referred to as nanoplasmonics, include surface-enhanced Raman spectroscopy, the Kerr effect and extraordinary optical transmission.

However, strong damping of plasmons caused by metal absorption has been the major issue of most existing and potential applications of nanoplasmonics.It has been suggested that surrounding the metal in a dielectric with a high optical gain may compensate for these losses and enhance the nanoplasmonic effects. Noginov and colleagues have now shown experimentally that this is indeed possible1. They used an aggregate of silver nanoparticles suspended in a fluorescent dye, Rhodamine 6G. A laser emitting at the peak gain wavelength of the dye (558 nm) was used to probe the dye/aggregate mixture as it was pumped by a second laser (532 nm) to induce the necessary optical gain. As the intensity of the pump laser was increased, the team observed a sixfold increase in the Rayleigh scattering of the probe light, which, they claim, is a direct result of the gain in the dye compensating for the loss in the metal. The same increases were not seen using the dye or the silver aggregates alone. This work could aid the use of nanoplasmonics effects in practical optical devices.