On the influence of a strong pump-field ellipticity on the third harmonic generation

The third harmonic generation in plasma ionised by a high-power pump field is theoretically studied. The dependences of the harmonic generation efficiency on the electric pump-field strength and polarisation are found. It is assumed that the observation of the maximum of generation efficiency at the nonzero pump-field ellipticity is the universal property of the harmonic generation. This effect is nonlinear and has a threshold.