Optical gain enhances surface-plasmon resonance

Surface plasmons (SPs; oscillations of free electrons in a metallic particle) and surface-plasmon polaritons (electromagnetic waves propagating along a metal/dielectric interface) are important to the development of plasmonic nanostructures that can act as optical nanoantennae and nanocircuits, and to surface-enhanced Raman-scattering applications; however, future development of nanoplasmonics is limited by metallic absorption of SPs. Spurred by their theoretical calculations, researchers at Norfolk State University (Norfolk, VA) and Purdue University (West Lafayette, IN) were able to experimentally demonstrate that optical gain in a dielectric medium could compensate for loss in a metal and enhance SP resonance.

In a pump-probe Rayleigh-scattering experiment, a mixture of Rhodamine 6G dye and an aggregate of silver nanoparticles was pumped with a 532 nm Nd:YAG laser and the Rayleigh scattering probed at approximately 570 nm at the peak of the gain spectrum of the dye. A sixfold increase in the Rayleigh scattering from the dye/aggregate mixture (subtracting out spontaneous emission) upon the increase of pumping energy confirmed compensation of the loss in the metal by the gain in the interfacing dielectric of the mixture. Contact Mikhail A. Noginov at [email protected].