Light scattering from mesoscopic objects in diffusive media

TL;DR

This paper investigates how mesoscopic objects embedded in diffusive media affect light scattering, using diffusion and radiative transfer theories to characterize their properties based on object size and type.

Contribution

It develops a detailed framework combining diffusion approximation and radiative transfer theory to analyze scattering by mesoscopic objects of various shapes and properties.

Findings

Intrinsic characteristics like capacitance and polarizability can be evaluated within the diffusion approximation.

Radiative transfer theory is necessary for objects comparable to the mean free path.

Formalism is explicitly worked out for spheres and cylinders of different optical properties.

Abstract

The diffuse intensity propagating in turbid media is sensitive to the presence of any kind of object embedded in the medium, e.g. obstacles or defects. The long-ranged effects of isolated objects can be described by a stationary diffusion equation, the effect of any single object being parametrized in terms of a multipole expansion. An absorbing object is chiefly characterized by a negative charge, while the leading effect of a non-absorbing object is due to its dipole moment. The associated intrinsic characteristics of the object (capacitance $Q$ or effective radius $R_{\rm eff}$, polarizability $P$) can be evaluated within the diffusion approximation for large enough objects. The situation of mesoscopic objects, with a size comparable to the mean free path, requires a more careful treatment, for which the appropriate framework is radiative transfer theory. This formalism is worked out in detail for spheres and cylinders of the following kinds: totally absorbing (black), transparent, and totally reflecting.