Ellipticity dependence of the third-order nonlinear optical response of graphene irradiated by two-color lights.

We theoretically investigate the third-order optical response of graphene irradiated by two-color lights, paying special attention to the quantum interference. Our studies reveal that the interplay between harmonic generation and four-wave mixing leads to unusual nonlinear optical properties with nontrivial ellipticity dependence. It is shown that, unlike the case of monochromatic light with frequency(where the intensity of the third order response ((3)) decreases monotonically with the ellipticity and becomes zero for circularly polarized light),(3) may increase monotonically with the ellipticity, or be nearly independent on the ellipticity. In particular, under suitable condition, there exists an optimal nonzero ellipticity for the highest(3). Moreover, circularly polarized third-order optical response can be generated. We have found effective methods of modulating the nonlinear optical processes, which may have various applications in optical devices based on two dimensional materials.