Nonlinear interaction of light waves in the course of generation of a second-harmonic wave in an isotropic noncentrosymmetric medium

A theoretical investigation is reported of the propagation of light waves in the course of frequency doubling as a result of a fourth-order dipole nonlinearity of an isotropic noncentrosymmetric weakly nonlinear and weakly absorbing medium characterised by a slight spatial dispersion in the case of noncollinear interaction between the waves. Calculations are carried out by expansion into normal waves, taking account of the self-interaction of a strong wave and of its influence on a weak one. The equations describing propagation of the second-harmonic wave in the noncollinear interaction configuration are derived by the method of slowly varying amplitudes. It is shown that an interference field is formed as a result of the interaction between the strong and weak waves. Consequently, the amplitude of the second-harmonic wave acquires a complex spatial distribution along transverse coordinates and this distribution depends on the wave mismatch. An analysis of the angular spectrum of the second-harmonic wave is given.