Stimulated emission of surface plasmon polaritons
  We have observed laser-like emission of surface plasmon polaritons (SPPs) decoupled to the glass prism in an attenuated total reflection setup. SPPs were excited by optically pumped molecules in a polymeric film deposited on the top of the silver film. Stimulated emission was characterized by a distinct threshold in the input-output dependence and narrowing of the emission spectrum. The observed stimulated emission and corresponding to it compensation of the metallic absorption loss by gain enables many applications of metamaterials and nanoplasmonic devices. 
M. A. Noginov, G. Zhu, M. F. Mayy, B. A. Ritzo, N. Noginova, and V. A.   Podolskiy