Peculiarities of the spontaneous grating formation in light-sensitive waveguide films near a magic angle of laser beam incidence

We investigated generation and competition of spontaneous gratings in thin light-sensitive AgCl-Ag films under irradiation by P-polarized laser beam. The incidence angles used were close to the “magic” angle at which a strong diffraction beam appears to propagate against the incident beam. A considerable increase of number of dominant grating types was revealed at angles close to the magic one while the strong regular S−-grating is formed at exact magic angle. It is the result of TE- and TM-mode scattering conditions favourable to various cases of double Bragg's diffraction. At the magic angle, gratings of several types merge into single S−-grating.