Development of secondary and tertiary noisy gratings in light-sensitive waveguide films due to two-dimensional Bragg's diffraction

We investigated development of spontaneous (noisy) phase gratings in light-sensitive waveguide AgCl-Ag films on glass substrates at various cases of linear polarization of the single inducing He-Ne laser beam. Such gratings develop due to appearance of interference field created by summation of the incident wave and scattered waveguide TE- and TM-modes. Competition of noisy gratings is affected by two-dimensional Bragg's diffraction on primary gratings, which results in appearance of mutually amplified secondary gratings. At linear beam's polarization, deviated from P-polarization, appearance of tertiary noisy gratings becomes possible due to analogous Bragg's diffraction on secondary gratings. So a quite simple case of diffraction, combined with positive feedback, leads to a complicated step-type evolution