▎ 摘　　要

We investigate the second-order optical response of graphene irradiated by two-color lights with frequencies ! and 3 !, focusing on the modulation by ellipticity and phase of the incident fields. Based on the analytical perturbation theory, it is found that the interplay between the second harmonic generation (SHG) (omega + omega) and difference frequency generation (DFG) (3 omega - omega) processes leads to nontrivial nonlinear optical properties. The interference between the two processes (SHG and DFG) results in different dependencies of the second-order response intensity I(2 omega) on ellipticity, including monotonic, nonmonotonic change of I(2 omega)with ellipticity, or even nearly independent of ellipticity under suitable conditions. The optimal incident angles for the highest I(2 omega) are found, which can be tuned by changing the ellipticity, relative phase, or field strength of the incident light. In particular, a large output enhancement with respect to a small increment of the incident field can be achieved. We have found effective methods of modulating nonlinear optical processes, which may have applications in optical devices based on two-dimensional materials. (C) 2021 Optical Society of America.