Phase effects in multistage fourth-harmonic generation

An analysis is made of the process of multistage fourth-harmonic generation. Use is made of the approximation of a constant intensity and an allowance is made for the reaction of the fourth harmonic on the phase of the fundamental (first-harmonic) radiation. It is shown that selection of the optimal lengths of crystals can ensure a considerable increase in the efficiency of a multistage fourth-harmonic generator.