Generation of higher harmonics in the constant intensity approximation

An analysis is made of higher harmonic generation in the constant intensity approximation taking into account the reaction of the harmonic on the phase of the exciting waves. It is shown that allowance for the reaction reduces the period of the spatial beats of the harmonic amplitude. An increase in the pump intensity is accompanied by a reduction in the coherence length at which the harmonic intensity reaches a maximum. Depending on the parameters of the problem, the phase shifts varying with the intensity of the fundamental-frequency radiation may either enhance or reduce the conversion efficiency, making the total phase mismatch closer to or farther away from the optimum.