POYNTINGS THEOREM AND ELECTROMAGNETIC-WAVE MULTIPLE-SCATTERING IN DENSE MEDIA NEAR RESONANCE - MODIFIED RADIATIVE-TRANSFER EQUATION

A new version of nonstationary radiative transfer theory for vector el ectromagnetic wave multiple scattering in a discrete random medium is presented in which the electromagnetic energy within dielectric scatte rers may be large. The starting point is the general two frequency Bet he-Salpeter equation for the coherence tenser-function of the wave ele ctric field. In the two frequency domain it is proved that the Poyntin g's theorem can be decomposed into (1) a theorem for the spectral comp onent of the electric energy density multiplied by two and (2) a theor em for the difference between the spectral components of the electric and the magnetic energy densities. The Poynting's theorem is closely c onnected with a generalized two-frequency Ward-Takahashi identity acco rding to which the extinction of a nonsteady radiation is conditioned by the incoherent scattering, the real absorption and changing of the energy accumulation inside scatterers. As result a new radiative trans fer equation is obtained for the radiance tensor of a pulse radiation in unbounded random medium. This equation differs from the traditional one by a term with the time derivative where the inverse value of the group velocity is replaced by a tenser-operator which determines the average rate of the electromagnetic energy change within scatterers.