Femtosecond UV-pump/visible-probe measurements of carrier dynamics in stacked graphene films

The transient differential transmission (Delta T/T) spectra of graphene were obtained from 380 (3.3 eV) to 670 nm (1.9 eV). The intraband carrier equilibration by carrier-carrier scattering occurred within 60 fs. The subsequent carrier relaxation process was governed by carrier-optical phonon scattering and had linear dependence on the probe photon energy (E-pr); lifetimes ranged from 180 to 90 fs for E-pr from 2.1 to 2.8 eV. Negative Delta T/T signals in kinetic curves were discussed and assigned to thermal diffusion and shrinkage of band separation caused by lattice heating. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3504704]