Optimal conditions for the generation of the third harmonic of focused radiation in a self-interaction regime

A method developed for the analysis of the interaction of wave beams in a s elf-interaction regime is used to determine the changes in the optimal cond itions for third-harmonic generation with changes in the degree of focusing of the fundamental-frequency radiation in isotropic media. Conditions unde r which a redistribution of the intensities and phases of the interacting w ave beams reduces the efficiency of third-harmonic generation are identifie d. It is shown that, under strong focusing conditions, there may be additio nal extrema in the dependence of the intensity of the harmonic on the densi ty of the medium.