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 frequencyω₀(where the intensity of the third order response (I(3ω₀)) decreases monotonically with the ellipticity and becomes zero for circularly polarized light),I(3ω₀) 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 highestI(3ω₀). 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.