Terahertz radiation processes in critically coupled graphene plasmonic nanostructures

Abstract

Plasmonic excitations in graphene nanostructures provide a particularly effective means to enhance light-matter interactions at THz frequencies. Here, we investigate the use of graphene nanoribbons for narrowband THz light emission based on the excitation of plasmonic oscillations under current injection and their resonant decay into free-space radiation. A detailed theoretical model of the underlying plasmon-enhanced thermal emission mechanism is presented, whose predictions are in good agreement with the recent experimental demonstration of this phenomenon. This model highlights the key role played by the nanostructure absorption efficiency to maximize the output radiation at the plasmonic resonance frequency. Based on this idea, we explore the integration of graphene nanoribbons with nearby metallic antennas in an open cavity configuration in order to promote critical coupling to free-space radiation and correspondingly enhance the absorption (and, therefore, radiation) efficiency by up to two orders of magnitude. The simulation results indicate that this approach is promising for the development of novel THz sources with technologically relevant emission characteristics.