Abstract
The propagation of light through a statistically homogeneous medium is investigated using the radiative transfer theory that yields linear equations for intensities in the case where the medium has a negligible emission of its own. This condition makes it possible to decompose the total light field in a series of eigen-solutions, designated as 'beam fields', associated with eigen-values, which yield the extinction coefficients of the beam fields. The medium under test being limited by two interfaces, the coefficients to be ascribed to a given field are determined by boundary equations. The basic properties of eigen-solutions are described as well as their corresponding eigen-values. Forward and back scattering indicatrices are established for fiber layers of different thicknesses under illumination at several incidence angles. Results are rather easy to interpret, if the layers are thick enough and scatter much more light than they absorb. In that case there exists a 'beam field' which fades out very much less than all others. This gives a simple way to explain depolarization effects of the scattered light and also a clue to appreciate the validity of simplified theories, known as two-wave theories.