Nonlinear refraction in semitransparent pyrolytic carbon films

We report on Z–scan measurements of the nonlinear refractive index of semitransparent pyrolytic carbon films. The nonlinear refractive index of the film is as high as 8.23 × 10−9 cm2/W and shows a non–monotonous dependence on the film thickness. We demonstrate that, although the linear absorption coefficient of the pyrolytic carbon films is comparable to that of crystalline graphite, the nonlinear absorption coefficient of the films is much lower than that of graphene.