Generation of second optical harmonic in the nonlinear regime

The second harmonic in the nonlinear regime is considered in the constant intensity approximation. This method has allowed to take into account reverse reaction of generated wave on the phase of fundamental one. In contrast to constant field approximation there is dependence of spatial beats of amplitude of harmonic wave versus intensity of powerful wave. It is shown that with increase in intensity of the incident pump wave, the period of spatial beats reduces and hence the width of central maximum is narrowed. The value of phase-mismatch at which the harmonic amplitude reaches maximum is a function of intensity of fundamental wave.