  Plasmonic nanoresonators consisting of a gold nanorod and a spherical
silica-core and gold-shell, both coated by a gain layer, were optimized to
maximize the near-field enhancement (NF-type) and far-field outcoupling
(FF-type), and to enter into the spasing operation region (NF-c*-type). It was
shown that in case of moderate concentration the nanorod has more advantages:
smaller lasing threshold, larger slope efficiency and achieved intensities in
the near-field, in addition in FF-type system smaller gain and outflow
threshold, earlier flipping and larger far-field out-coupling efficiency.
However, the near-field (far-field) bandwidth is smaller in for NF-type
(FF-type) core-shell nanoresonators. In case of larger concentration although
the slope efficiency and near-field intensity remain larger and the far-field
redistribution is more efficient in case of the nanorod, the core-shell
nanoresonator is more advantageous, taking into account the smaller lasing,
outflow, absorption and extinction cross-section thresholds, as well as the
larger internal and external quantum efficiencies. In addition to this the
bandwidth of core-shell nanoresonator is also smaller. It was also shown that
the strong-coupling of time-competing plasmonic modes accompanies the
transition from lasing to spasing.
