Ultrafast carrier kinetics in exfoliated graphene and thin graphite films

Time-resolved transmissivity and reflectivity of exfoliated graphene and thin graphite films on a 295 K SiO2/Si substrate are measured at 1300 nm following excitation by 150 fs, 800 nm pump pulses. From the extracted transient optical conductivity we identify a fast recovery time constant which increases from similar to 200 to 300 fs and a longer one which increases from 2.5 to 5 ps as the number of atomic layers increases from 1 to similar to 260. We attribute the temporal recovery to carrier cooling and recombination with the layer dependence related to substrate coupling. Results are compared with related measurements for epitaxial, multilayer graphene. (C) 2009 Optical Society of America