Enhancement and suppression of surface plasmon resonance in Ag aggregate   by optical gain and absorption in surrounding dielectric medium
  We have observed the compensation of loss in metal by gain in interfacing dielectric in the mixture of aggregated silver nanoparticles and rhodamine 6G dye. The demonstrated six-fold enhancement of the Rayleigh scattering is the evidence of the increase of the quality factor of the surface plasmon (SP) resonance. The reported experimental observation paves the road to many practical applications of nanoplasmonics. We have also predicted and experimentally observed a suppression of the surface SP resonance in metallic nanoparticles embedded in a dielectric host with absorption. 
M. A. Noginov, G. Zhu, V. M. Shalaev, V. P. Drachev, M. Bahoura, J.   Adegoke, C. Small, B. A. Ritzo