Nonlinear optical frequency mixing response of single and multilayer graphene.

It has been shown that graphene exhibits unique electronic, thermal, mechanical, and optical properties. In particular, due to its gapless band structure and linear dispersion relation around the Dirac points, graphene exhibits a strong nonlinear optical response, which has been theoretically predicted to depend on the number of graphene layers. In this Letter, we experimentally validate the theoretical predictions by probing multilayer graphene χ(3) nonlinearities. The intensity of the four-wave mixing signal is observed to grow monotonically as a function of the number of graphene layers, up to a maximum intensity corresponding to ∼32 layers, after which it decreases, well in agreement with theoretical predictions.