Theoretical investigation of the spontaneous emission on graphene plasmonic antenna in THz regime

The present work deals with a theoretical research on the emission and radiation properties of a dipole emitter source close to a dimer graphene plasmonic antenna. Modification of the radiation and the quantum efficiencies resulting from varying the position of the emitter and the orientation of its dipole moment are calculated by using a rigorous electromagnetic method based on Green's second identity. Large enhancements in the emission and the radiation of the emitter occur due to the coupling with the antenna surface plasmons in the spectral region from ≈4 THz to ≈15 THz. Our results show that the radiation efficiency can be enhanced by four orders of magnitude and that the quantum efficiency reaches values close to 0.8 when the emission frequency coincides with one of the resonant dipolar frequencies. On the other hand, these quantities can be reduced in a great measure at a specific frequency for a given emitter location. We present calculations of the near-field distribution and the far field intensity which reveal the role of the plasmonic antenna resonance in the emitter enhanced radiation. We show that the spectral region where the radiation is enhanced can be chosen over a wide range by varying the chemical potential of graphene from 0.2eV to 1eV.