PUB - Publikationen an der Universität Bielefeld

A theoretical analysis of multiple photon absorption by Dirac fermions in graphene subjected to intense laser fields is made. An analytic expression for the probability of n-photon absorption is derived. It shows that the fundamental functional dependence of n photon absorption rate is governed by a Bessel function of order n, Jn(gcos(phi p0)), where g=2vFeF2, vF is the Fermi-velocity, F is the peak field strength, is the frequency; phi p and 0 are the polar angles of the fermion momentum and the laser polarization, respectively. The result is used to investigate the rate of n photon absorption in the THz and the near-infrared domains and both in the weak-field perturbative, and the strong-field non-perturbative intensity regimes. Formation of an n-photon absorption plateau followed by an exponential cut-off beyond n=ncutoff approximate to g is also predicted to occur.