Diffusive-to-ballistic transition in dynamic light transmission through thin scattering slabs: a radiative transfer approach

摘要

We study the deviation from diffusion theory that occurs in the dynamic transport of light through thin scattering slabs. Solving numerically the time-dependent radiative transfer equation, we obtain the decay time and the effective diffusion coefficient D_(eff). We observe a nondiffusive behavior for systems whose thickness L is smaller than 8l_(tr), where l_(tr) is the transport mean free path. We introduce a simple model that yields the position of the transition between the diffusive and the nondiffusive regimes. The size dependence of D_(eff) in the nondiffusive region is strongly affected by internal reflections. We show that the reduction of ～50% of D_(eff) that was observed experimentally [Phys. Rev. Lett. 79, 4369 (1997)] can be reproduced by the radiative transfer approach. We demonstrate that the radiative transfer equation is an appropriate tool for studying dynamic light transport in thin scattering systems when coherent effects play no significant role.