Spontaneous grating formation in thin light-sensitive AgCl–Ag films at linear P/S-polarization of a laser beam

We investigated the development of spontaneous gratings arising in light-sensitive waveguide AgCl–Ag films on glass substrates at various cases of linear polarization of the single inducing laser beam. The cause of such a grating development is the appearance of an interference field created by the summation of the incident beam and scattered waveguide TEand TM-modes. Positive feedback in grating growth is provided by Wood’s anomalies taking place for all the gratings, and the simultaneous development of many microgratings results in their competition. Earlier we found that two-dimensional Bragg’s diffraction seriously affects this competition. This kind of diffraction results in the appearance of secondary dominant gratings. Now we found that at the beam’s polarization, deviated from P-polarization, the appearance of tertiary gratings becomes possible due to the Bragg’s diffraction on secondary dominant gratings instead of this diffraction on primary gratings. The influence of the existence of the first and second steps in two-dimensional diffraction on grating growth is proved by both optical microscopy and complete identification of the modes excited in the substrate and in air (radiative modes in small-angle scattering pattern).