The structure of the Stokes' fields reflected in SBS in a light guide

The calculation of gain increments and the spatial structure of the scattered Stokes' radiation is carried out on the basis of a proposed theoretical method. The so-called rotated modes are shown to be trapped into a spatial resonance with the central reversed mode. These spatial configurations are discovered experimentally with the help of an interferometer with wavefront-reversing mirrors based on stimulated Brillouin scattering. The rotated modes are concentrated in a so-called 'background pedestal' for which the divergence theta /sub b/ increases with the gain increment at the longitudinal correlation length Gamma /sub c/. For a fixed Gamma /sub c/ the relationship between the energy of the Stokes' signal reproducing exactly the spatial structure of the pump radiation and the energy of the background pedestal varies randomly from one laser pulse to another, resulting in a strong dispersion of the energy of the Stokes' waves measured in both interferometer arms.< >