  Steady-state plasmonic lasing is studied theoretically for a system
consisting of many dye molecules arranged regularly around a gold nano-sphere.
A three-level model with realistic molecular dissipation is employed to analyze
the performance as function of the pump field amplitude and number of
molecules. Few molecules and moderate pumping produce a single narrow emission
peak because the excited molecules transfer energy to a single dipole plasmon
mode by amplified spontaneous emission. Under strong pumping, the single peak
splits into broader and weaker emission peaks because two molecular excited
levels interfere with each other through coherent coupling with the pump field
and with the dipole plasmon field. A large number of molecules gives rise to a
Poisson-like distribution of plasmon number states with a large mean number
characteristic of lasing action. These characteristics of lasing, however,
deteriorate under strong pumping because of the molecular interference effect.
