  This work analyzes the optical properties of a localized surface plasmon
(LSP) spaser made of a dielectric active wire coated with a graphene monolayer.
Our theoretical results, obtained by using rigorous electromagnetic methods,
illustrate the non-radiative transfer between the active medium and the
localized surface plasmons of the graphene. In particular, we focus on the
lasing conditions and the tunability of the LSP spaser in two cases: when the
wire is made of an infrared/THz transparent dielectric material and when it is
made of a metal-like material. We analyze the results by comparing them with
analytical expressions obtained by us using the quasistatic approximation. We
show that the studied systems present a high tunability of the spaser
resonances with the geometrical parameters as well as with the chemical
potential of the graphene.
