Expression of optical diffusion coefficient in high-absorption turbid media

The format of the diffusion coefficient in the optical diffusion equation is determined experimentally. For the diffusion coefficient D in the optical diffusion equation used for description of optical propagation in a turbid medium, two representations have been proposed, one containing the absorption coefficient μa and another without it. In the present research the scattered light is measured with steady light in a medium with large absorption in order to determine which of the diffusion coefficient expressions describes optical propagation in a turbid medium more accurately. The diffusion coefficient is found not to be affected by absorption even if the absorption varies from almost 0 to a value close to the reduced scattering coefficient μ′s, and its value agrees well with (3μ′s)−1. Hence, it is confirmed that the absorption coefficient used is not included in the diffusion coefficient used in the optical diffusion equation, and that the coefficient is given by D = (3μ′s)−1 © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(11): 34–41, 1998