Large nonlinear Kerr effect in graphene
  Under strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift. Here, we unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene. We show that graphene possesses a giant nonlinear refractive index n2=10-7cm2W-1, almost nine orders of magnitude larger than bulk dielectrics. We find that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption. This suggests that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics. 
Han Zhang, Stephane Virally, Qiaoliang Bao, Kian Ping Loh, Serge   Massar, Nicolas Godbout, and Pascal Kockaert
physics.optics cond-mat.mes-hall