Localized surface plasmon singularities in amplifying media

The localized surface plasmon resonance of nanostructures is shown to exhibit a singularity when the surrounding medium exhibits amplification with a critical value of gain. This singularity can lead to large enhancements even when the gain is saturated. This composite medium should exhibit strong scattering within the plasmon band leading to low threshold random laser action and light localization effects. This effect could also greatly increase surface enhanced Raman scattering signals for rapid single, molecule detection, identification and sequencing. (C) 2004 American Institute of Physics.