Measurement of the transport mean free path of diffusing photons

Abstract

We measure microwave intensity inside and transmission through random samples of polystyrene spheres with different output reflectors. We show that with appropriate boundary conditions diffusion theory gives an excellent description of transport from the interior to the output surface of a sample. From these measurements we determine the transport mean free path and the surface reflectivities without additional assumptions regarding the interface or the scattering form factor. From a comparison with a measurement of the diffusion coefficient we determine the transport velocity and find that it is smaller than the velocity in the high-index material.