Spatial-temporal instability and optical turbulence upon the formation of spontaneous gratings by S-polarized light in waveguide AgCl-Ag films

Abstract

The spatial-temporal instability of the spontaneous gratings formed in waveguide AgCl-Ag films under irradiation with an S-polarized laser beam is investigated. The studies are based on the simultaneous observation of diffraction (D) patterns formed by the S− gratings and small-angle scattering (SAS). The transverse instability of D and SAS patterns was found to be associated with excitation of TE0 modes at different angles with respect to the plane of incidence by scattering centers of Rayleigh type with the following formation of microgratings by the scattered modes and with their competition. It is shown that the time evolution of the form and the dynamic shift of the D patterns is also connected with the time dependence of the effective refractive index for TE0 modes. In the case when a focused laser beam was used, the optical turbulence was found in the SAS and D patterns, caused, mainly, by the competition of S−-and S+-microgratings, which eventually leads to the destruction of the latter.