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 LSPs of 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/terahertz 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 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 graphene.

There is increasing interest in filling the gap of miniaturized terahertz/mid-infrared radiation sources and, particularly, in incorporating these sources into micro/nanophotonic circuits. By using rigorous electromagnetic methods, we investigate the lasing conditions and the electric-tunability of radiative and nonradiative propagating surface plasmon modes in cylinders made of active materials coated with a graphene layer. A detailed analysis of the lasing condition of different surface plasmon modes shows that there is an abrupt change in the gain required when modes become nonradiative. Although radiative modes, subject to both radiation and ohmic losses, are expected to require more gain compensation than nonradiative modes, we find that, counterintuitively, gain compensation is greater for nonradiative modes. This is explained in terms of a change in the distribution of fields that occurs when the character of modes switches from plasmonic to photonic. Finally, we assess the feasibility of our proposal by using a realistic gain medium and showing that a relatively low population inversion is required for the stimulated emission of the studied system.

There is increasing interest in filling the gap of miniaturized terahertz/mid-infrared radiation sources and, particularly, in incorporating these sources into micro/nanophotonic circuits. By using rigorous electromagnetic methods, we investigate the lasing conditions and the electric-tunability of radiative and non radiative propagating surface-plasmon modes in cylinders made of active materials coated with a graphene layer. A detailed analysis of the lasing condition of different surface-plasmon modes shows that there is an abrupt change in the gain required when modes become nonradiative. Although radiative modes, subject to both radiation and ohmic losses, are expected to require more gain compensation than nonradiative modes, we find that, counterintuitively, gain compensation is greater for nonradiative modes. This is explained in terms of a change in the distribution of fields that occurs when the character of modes switches from plasmonic to photonic. Finally, we assess the feasibility of our proposal by using a realist gain medium and showing that a relatively low population inversion is required for the stimulated emission of the studied system.

We consider a dielectric active wire coated with a graphene monolayer. Using rigorous electromagnetic methods, we present theoretical results which illustrate the non-radiative transfer between the active medium and the graphene localized surface plasmons.