Frequency dependence of optical third-harmonic generation from doped graphene

•The controversial question about the frequency dependence of the THG from doped graphene.•The major mechanism that contributes to the third-harmonic generation (THG) from doped graphene.•The resonant structure of the THG spectrum of doped graphene.

In connection with the controversial question about the frequency dependence of the optical third-harmonic generation (THG) from doped graphene, which has recently been discussed in the literature, we develop an analytical theory for the THG susceptibility of doped graphene by using the original Genkin–Mednis nonlinear-conductivity-theory formalism including mixed intra- and interband terms. The theory is free of any nonphysical divergences at zero frequency, and it predicts the main resonant peak in the THG spectrum to be located at the photon energy ħω   equal to two thirds of the Fermi energy EFEF of charge carriers in doped graphene.