Generation of high-order harmonics in the photoionisation of a gas

For a photoionised gas in the mode of suppression of the ionisation barrier, it is shown how the photoelectron distribution function in the field of high-intensity radiation is determined by the distribution of intra-atomic electrons prior to their ionisation. The partial nonlinear conductivities of the current of the harmonic generation source are determined. It is established how the harmonic intensities scale up with the harmonic order number and the intensity of the pump radiation field. (nonlinear optical phenomena)