Problem of light diffusion in strongly scattering media

Abstract

Recently, in connection with the problem of Anderson localization of light, a new physical mechanism was considered for the decreasing of the diffusion coefficient, in which it is supposed that the velocity of energy transport, which appears in the diffusion constant D=${\mathit{v}}_{\mathit{E}}$ ${\mathit{l}}_{\mathrm{tr}}$/3, may be much smaller than the phase velocity. Using an exact definition of the diffusion coefficient and generalized Ward identity, we, however, show that in the low-density approximation ${\mathit{v}}_{\mathit{E}}$ coincides with the phase velocity.