Observation of coherent lattice vibrations in epitaxial graphene

We demonstrate time-resolved coherent lattice vibrations in graphene using femtosecond laser pulses. The high-frequency G-mode phonons were excited by impulsive stimulated Raman scattering, and detected via measuring induced reflectivity modulations. The dephasing time of graphene was found to be shorter than that of semiconducting carbon nanotubes (CNTs), but longer than metallic CNTs. The E2g symmetry was verified from the polarization-dependent phonon amplitudes.