Influence of two-dimensional Bragg´s diffraction on competition of TE0and TM0-modes at spontaneous grating formation in thin AgCl-Ag films

This study investigates spontaneous structures arising in waveguide AgCl films doped by Ag. When the film is irradiated by single laser beam with a wavelength in the visible light range (He-Ne laser, λ = 632.8 nm), Ag granules scatter the beam (Rayleigh scattering). AgCl is a dielectric with large forbidden gap, so it does not absorb visible light and therefore does not participate in scattering. Furthermore, this spontaneous structure acts as an imperfect diffraction grating and may be characterised by a set of micrograting vectors determined as differences between mode vector and tangential component of incident wave. The main result of this work is the discovery of the two-dimensional Bragg´s diffraction influence on micrograting interaction in their development. This diffraction on a dominant grating simultaneously amplifies two other microgratings which can also become dominant.