Analysis of generation of optical harmonics in isotropic media under the self-action conditions

Solutions are obtained for the amplitudes of harmonics of focused wave beam s in the paraxial approximation taking into account the self-action effects caused by the third-order Ken nonlinearities. It is shown that the develop ment of nonlinear processes is determined by the initial curvature of the w ave front of the radiation at the fundamental frequency. As the intensity o f the fundamental radiation in the media focusing this radiation is increas ed, the harmonic signal can considerably increase in intensity for a medium initial focusing and oscillate for weak and strong focusing. For the media defocusing the fundamental radiation or changing the dielectric constant a t the harmonic frequency, the power dependence of the intensity of higher h armonics on the intensity of fundamental radiation becomes weaker. The resu lts of the present work are compared with the experimental data on harmonic generation in gases.