Light propagation in multilayered scattering media beyond the diffusive regime.

We describe a method to solve the radiative transfer equation (RTE) in multilayered geometry with index mismatch and demonstrate its potential for modeling light propagation in biological systems. The method is compared to Monte Carlo simulations with high accuracy but is much more efficient in terms of computer time. We illustrate the potential of the method by studying a multilayered system containing a weakly scattering layer surrounded by highly scattering layers, with anisotropic scattering and index mismatched interfaces. The calculation of directional transmitted fluxes has shown that the RTE method can be used to calculate relevant quantities in realistic systems in the presence of non-diffusive behavior.

Spatial coherence in strongly scattering media.

We study the spatial coherence of an optical beam in a strongly scattering medium confined in a slab geometry. Using the radiative transfer equation, we study numerically the behavior of the transverse spatial coherence length in the different transport regimes. Transitions from the ballistic to the diffusive regimes are clearly identified.

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

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 Deff. 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 Deff in the nondiffusive region is strongly affected by internal reflections. We show that the reduction of approximately 50% of Deff 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.

Definition of the diffusion coefficient in scattering and absorbing media.

We revisit the definition of the diffusion coefficient for light transport in scattering and absorbing media. From an asymptotic analysis of the transport equation, we present a novel derivation of the diffusion coefficient, which is restricted neither to low absorption nor to a situation in which the specific intensity is quasi-isotropic. Our result agrees with previous expressions of the diffusion coefficient in the appropriate limit. Using numerical simulations, we discuss the implications of the proper choice of the diffusion coefficient for time-dependent transport.