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 ,J n ( g cos ( ϕ p − θ 0 ) ) , where g = 2 v Fe F ℏ ω 2, v F is the Fermi‐velocity, F is the peak field strength, ω is the frequency; ϕ p and θ 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 = n c u t − o f f ≈ g is also predicted to occur.