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 with scattering, there is currently a controversy as to if, and how, the diffusion coefficient depends on absorption. Here it is shown that better agreement with random walk simulation is obtained if the photon-diffusion coefficient is taken as D=c/(3micro(s)(')+micro(a)) . One can reconcile this result with recent work advocating D=c/3micro(s)(') by noting that the diffusion equation must be correspondingly changed to a telegrapher's equation.