The temporal evolution of spontaneous periodic structures was studied under successive action of circularly and linearly polarized laser radiation in light-sensitive waveguide AgCl–Ag films. The essential role of positive feedback in the growth of periodic structures is established by measuring the differential diffraction efficiency. An asymmetry in the azimuthal distribution of diffraction efficiency is found due to gyrotropy induced by circularly polarized radiation. The existence of induced gyrotropy in the AgCl–Ag films was determined directly by measuring circular dichroism and optical rotatory dispersion. It is established that TE 0 mode scattering on anisotropic Ag particles leads to amplification of the gyrotropy influence on spontaneous grating growth at initial stages of irradiation by the linearly polarized laser beam.