Two-dimensional Bragg-Ewald's dynamical diffraction and spontaneous gratings

Convincing experimental data about a complex spontaneous grating (SG) structure have been revealed under influence of a laser irradiation on thin waveguide photosensitive films. The main features of SG structures are explained in terms of two-dimensional Bragg-Ewald dynamical diffraction (TDDD). A TDDD model is founded on the well-known Sommerfeld's treatment of electromagnetic fields generated by a source near an interface as well as the well-known Ewald's self-consistent principle. TDDD equations turned out to be different in content and form compared to classical Bragg or Rayleigh diffraction on periodical structures.