Hot carrier diffusion in graphene

We report an optical study of charge transport in graphene. Diffusion of hot carriers in epitaxial graphene and reduced graphene-oxide samples are studied using an ultrafast pump-probe technique with a high spatial resolution. Spatiotemporal dynamics of hot carriers after a pointlike excitation are monitored. Carrier-diffusion coefficients of 11 000 and 5500 cm(2) s(-1) are measured in epitaxial graphene and reduced graphene-oxide samples, respectively, with a carrier temperature on the order of 3600 K. The demonstrated optical techniques can be used for noncontact and noninvasive in situ detection of transport properties of graphene.