A theory of multiple photon absorption by graphene in intense laser fields

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(g cos(φp - θ0)), where g = 2νF (eF)/(ℎω2), is the Fermi-velocity, F is the peak field strength, ω is the frequency; φp and θ0 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 = ncut-off ∼ g is also predicted to occur. (copyright 2012 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)