Measuring the Nonlinear Refractive Index of Graphene using the Optical   Kerr Effect Method
  By means of the ultrafast optical Kerr effect method coupled to optical heterodyne detection (OHD-OKE), we characterize the third order nonlinear response of graphene at telecom wavelength, and compare it to experimental values obtained by the Z-scan method on the same samples. From these measurements, we estimate a negative nonlinear refractive index for monolayer graphene, $n_2 = - 1.1\times 10^{-13} m^2/W$. This is in contradiction to previously reported values, which leads us to compare our experimental measurements obtained by the OHD-OKE and the Z-scan method with theoretical and experimental values found in the literature, and to discuss the discrepancies, taking into account parameters such as doping. 
Evdokia Dremetsika, Bruno Dlubak, Simon-Pierre Gorza, Charles Ciret,   Marie-Blandine Martin, Stephan Hofmann, Pierre Seneor...
physics.optics