Plasmonic terahertz lasing in an array of graphene nanocavities

We propose a novel concept of terahertz lasing based on stimulated generation of plasmons in a planar array of graphene resonant micro/nanocavities strongly coupled to terahertz radiation. Due to the strong plasmon confinement and superradiant nature of terahertz emission by the array of plasmonic nanocavities, the amplification of terahertz waves is enhanced by many orders of magnitude at the plasmon resonance frequencies. We show that the lasing regime is ensured by the balance between the plasmon gain and plasmon radiative damping.

Figure 1

Schematic view of the array of graphene micro/nanocavities. The incoming electromagnetic wave is incident from the top at normal direction to the structure plane with the polarization of the electric field across the metal grating contacts. The energy band structure of pumped graphene is shown schematically in the inset.

Figure 2

Contour map of the absorbance as a function of the quasi-Fermi energy and the frequency of incoming THz wave for the array of graphene microcavities with period $L=4$ $\mu$m and the length of a graphene microcavity $a=2$ $\mu$m. The electron scattering time in graphene is $\tau ={10}^{-12}$ s. Blue and red arrows mark the quasi-Fermi energies for the maximal absorption and for the plasmonic lasing regime, respectively, at the fundamental plasmon resonance.

Figure 3

The fundamental plasmon resonance (a) in the maximal absorption regime, (b) near the graphene transparency regime $\mathrm{Re}\left[{\sigma }_{Gr}\left(\omega \right)\right]=0$, and (c) near the self-excitation regime.

Figure 4

(a) The variation of the power amplification coefficient along the first-plasmon-resonance lobe (see Fig. 2) near the self-excitation regime. The frequency of the plasmon lasing is marked by the vertical dashed line. (b) Schematic illustration of the energy rate balance in the plasmon lasing regime. (c) The snapshot of the distribution of the normalized induced in-plane electric field at the moment of time corresponding to the maximal swing of plasma oscillations in the graphene microcavities at the fundamental plasmon amplification resonance shown in Fig. 3c.