We present femtosecond differential reflectivity studies of few-layer graphene from weak to strong excitation regime. Temporal profiles of the differential reflectivity exhibit strong non-exponential decay. A nonlinear, cubic root dependence of their peak amplitudes on the pump fluence is clearly observed under relatively high intensity excitation, which indicates three-particle decay of transient carrier population via Auger scattering. Our results identify the critical role of such three-particle scattering in the initial electronic relaxation in photo-excited graphene with increasing phase-space filling of the correlated Dirac Fermions.
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