▎ 摘　　要

An analytical theory of the nonlinear electromagnetic response of a two-dimensional (2D) electron system in the second order in the electric field amplitude is developed. The second-order polarizability and the intensity of the second harmonic signal are calculated within the self-consistent-field approach both for semiconductor 2D electron systems and for graphene. The second harmonic generation in graphene is shown to be about 2 orders of magnitude stronger than in GaAs quantum wells at typical experimental parameters. Under the conditions of 2D plasmon resonance the second harmonic radiation intensity is further increased by several orders of magnitude.