• Theory;
  • intense laser;
  • multiple photon absorption;
  • Dirac fermions;
  • graphene;
  • THz;
  • near-infrared;
  • few cycles;
  • absorption plateau;
  • “cut-off” order

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, inline image, where inline image, inline image is the Fermi-velocity, F is the peak field strength, ω is the frequency; inline image 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 inline image is also predicted to occur.