Quantum-Enhanced Second-Order Nonlinearity in Graphene: The Role of Wave Momentum and DC Biasing

A comprehensive and rigorous analysis is presented for the study of terahertz photomixing process in a biased graphene layer, when two obliquely incident waves are used as primary excitation. The second-order nonlinearity tensor of graphene associated with the difference frequency generation (DFG) is calculated to evaluate the amount of induced terahertz current density. In this analysis, we are calculating the significant contribution of the photon drag effect to the DFG and consequently to the terahertz wave generation. We also examine the effect of DC current biasing on the DFG as the Fermi energy level of graphene changes. Our results show that the DFG in graphene can be enhanced by at least two orders of magnitude when the Fermi energy level of graphene becomes equal to the energy of incident photon. This paper provides more insight into the contributing factors in the DFG process and allows the realization of more optimal graphene-based photomixing devices.