  We considered the set of the ordered split-ring silver resonators in the form
of nanosize horseshoes arranged in a layer at the surface of the active
dielectric medium. The size of the horseshoe resonator is much less than the
wavelength of the incident light. The plasmon nanoresonator takes energy from
the active medium and can operate as a nanolaser. We show that nanoscale laser
pumping should be treated as a random external force because of the incoherent
quantum-mechanical process of photon absorption in the active medium. The
operation of the plasmonic nanoresonator immersed in the active medium is the
response to the action of random force. We find luminescence line and predict
its evolution to the laser spectrum when inversion of the active medium is
increased to the threshold value. The resonance behavior of the horseshoe can
be conveniently tuned by variation of its size and shape. Results are compared
with the full quantum mechanical simulation.
