Experimental dispersion of the third-order optical susceptibility of graphene oxide

We experimentally determined the dispersion of third-order optical susceptibility χ(3) of graphene oxide (GO) in the visible region (450 - 750 nm) by combining spectroscopic ellipsometry and ultrafast pump and probe spectroscopy in the femtosecond regime. In order to mitigate the damage of wide-spectrum laser to photonic devices, GO has become a promising material for optical limiting (OL) devices. However, there is no report about the χ(3) dispersion of GO, which is a complex quantity that directly corresponds to nonlinear refraction and absorption and is a crucial parameter for the manipulation and application of its OL properties. Here, we identified that the linear optical response of GO shows a flat dispersion in the visible region. In contrast, its nonlinear optical response exhibits saturable absorption (SA) at the short wavelength and reverse saturable absorption (RSA) at the long wavelength. These results propel the application of GO in the broadband OL devices based on the RSA behavior. In addition, by controlling the fraction of sp2 and sp3 hybridizations, it also provides opportunities to tailor the NLO properties and OL performance of GO.