The impact of pump fluence on carrier relaxation dynamics in optically excited graphene

The carrier dynamics in optically excited graphene is determined by an interplay between the Coulomb- and phonon-induced scattering processes. The pump fluence of the excitation pulse plays a crucial role: for high fluences the ultrafast relaxation dynamics is determined by carrier-carrier scattering, whereas for low fluences the carrier-phonon relaxation channels are predominant. On the basis of a microscopic approach, we shed light on the influence of the pump fluence on the temporal evolution of carrier and phonon occupations as well as on the many-particle dephasing of the microscopic polarization. The new insights obtained contribute to a better understanding of the ultrafast carrier dynamics in graphene and can guide future pump-probe experiments.