B. Sturman et al., POLARIZATION-DEGENERATE PARAMETRIC LIGHT-SCATTERING IN PHOTOREFRACTIVE CRYSTALS, Applied physics. B, Photophysics and laser chemistry, 56(4), 1993, pp. 193-199
Parametric scattering of two copropagating coherent light waves into c
ones of light with the same polarization is considered both experiment
ally (in photorefractive LiNbO3 : Fe) and theoretically.