Makovetskiy Y. Competition of spontaneous gratings on TE- and TM-modes in light-sensitive waveguide AgCl-Ag films

Object: waveguide films of AgCl containing granular silver; Aim: determination of the role of competition of gratings on TE- and TM-modes in development of spontaneous gratings in composite AgCl-Ag films, and determination of possibility of a practical use of competition of TE- and TM-gratings; Methods: a theoretical study of indicatrices of scattering in the film's modes based on Mie theory, irradiation of light-sensitive films by a laser beam, photographic registration and analysis of small-angle scattering patterns and substrate modes based on Ewald's diagrams, an optical microscopy, a computer-based modeling of grating evolution; Results: A theoretical description of azimuthal distribution of TE- and TM-mode intensities was conducted for elliptically polarized beam being scattered by a small particle in a waveguide. A dominating influence of spread of the film's optical thickness on spontaneous grating structure was found at small angles of beam incidence. A method of determining the spread of optical thickness in situ is proposed. It is based on measuring the least angle of incidence of S-polarized beam at which TM-gratings develop. It was found that TE-grating development at P-polarization and large angles of incidence changes the scattering indicatrices thus leading to development of S–-gratings of higher quality. It increases the accuracy of method of determining the dielectric substrate's refractive index by measuring the S–-grating period, from 0,002 to 0,001. It was found that at strong competi-tion of gratings on TE- and TM-modes a two-dimensional Bragg diffraction on primary gratings defines a secondary gratings' characteristics. A tertiary spontaneous grating development was found for the first time at mixed P/S-polarization and explained by two-dimensional Bragg diffraction on secondary gratings. The ranges of angle of incidence were determined at which a strong TE- and TM-grating competition takes place; Field: optics and laser physics.