CALCULATION OF NONSTATIONARY LIGHT FIELDS IN A HOMOGENEOUS 2D MEDIUM WITH A MODEL 4-DIRECTIONAL SCATTERING PHASE FUNCTION UNDER THE NORMAL INCIDENCE OF RADIATION UPON A MEDIUM SURFACE

In this paper, we consider the propagation of light fluxes in an absor bing medium with a model four-directional scattering phase function in the case of irradiation of matter by a delta-pulse light source. We i nvestigate thoroughly the intensities of descending and ascending radi ation at various depths as functions of time for an elementary two-dir ectional scattering phase function. Thus, we give a detailed analysis of the problem of random nonstationary walk of photons in 2D and 3D me dia. The expressions for the descending and ascending fluxes are obtai ned in the form of series expansions in partial fluxes, i.e., in the n umber of changes in the sign of the velocity projection on the z-axis. Time dependence of the intensity of descending and ascending radiatio n at various depths in the case of a two-directional single-scattering law is analyzed. We focus special attention on the analysis of charac teristics of reflected radiation in the most general case of a four-di rectional scattering phase function. In some particular cases, we give simple analytical expressions for the temporal dependence of the refl ection coefficient.