Generation of hot surface plasmons in graphene by a powerful optical beam

Resonant interaction of two optical beams, with specially adjusted frequencies and wavevectors, mediated by graphene surface plasmons (SPs) and eventually leading to their all-optical generation, was demonstrated experimentally several years ago by measuring the differential reflectance of the probe beam. However, the quantitative explanation of these results requires much larger second-order optical conductivities of graphene than calculations based on standard perturbation theory approaches can yield. We suggest that the observed effect can be understood by considering, in addition to the second-order frequency-difference process, the generation of SPs via interband relaxation of hot electrons created by the powerful pump pulse. We calculate the generation rate of out-of-equilibrium plasmons by the latter mechanism and compare it to other mechanisms of hot carrier relaxation in graphene described in the literature.