METHOD OF SEPARATION OF FLUXES IN THE THEORY OF LIGHT-PROPAGATION IN DISORDERED MEDIA

This paper considers the problem of determination of the light-field i ntensity in conditions of plane geometry of a scattering material laye r. Discussing theoretically well-studied problems, namely, small-angle light reflection from media with sharply anisotropic scattering on se parate centers, light reflection from a semiinfinite medium in conditi ons of isotropic scattering, P-1-approximation, and others, we demonst rate considerable difficulties connected with boundary conditions in t he solution of different problems in the theory of optical radiation t ransfer. In order to overcome these difficulties, we propose an origin al method of separation of light fluxes. The essence of this method is in representing the intensities of both ascending and descending radi ation as series. According to this method, instead of expanding the in tensities in the multiplicity of collisions, we use expansions in the number of events that imply the sign reversal of the projection of the photon velocity on the direction normal to the boundaries of the scat tering medium. We derive equations for independent calculation of asce nding and descending radiation fluxes. Moreover, boundary conditions o n material surfaces are exactly fulfilled for any approximate method o f solving these equations. Taking a simple bidirectional scattering ph ase function as an example, we analytically calculate the ascending an d descending radiation in a material layer with a finite thickness and partial fluxes of various multiplicities. We analytically calculated the Green's function in a medium with isotropic scattering and the Gre en's function that corresponds to the standard small-angle approximati on in media with sharply anisotropic scattering. For the Henyey-Greens tein scattering law, we obtain a simple analytical expression for the intensity of transmitted radiation under oblique incidence of a light flux upon a material surface.