THE DIFFUSION-COEFFICIENT DEPENDS ON ABSORPTION

The diffusion approximation is widely invoked to model the propagation of light in turbid media. When absorption is not weak in comparison w ith scattering, there is currently a controversy as to if, and how, th e diffusion coefficient depends on absorption, Here it is shown that b etter agreement with random walk simulation is obtained if the photon- diffusion coefficient is taken as D = c/(3 mu(s)' + mu(a)). One can re concile this result with recent work advocating D = c/3 mu(s)' by noti ng that the diffusion equation must be correspondingly changed to a te legrapher's equation. (C) 1998 Optical Society of America.