Measurements of structure-induced polarization features in forward scattering from collections of cylindrical fibers

Many applications in remote sensing, material sciences and biomedical field are characterized by a transition domain between single scattering and mul tiple-scattering regimes. This regime is described by typical polarization features which can be used to retrieve structural information. An electroni cally agile technique was used for measuring in real time the Stokes vector s of light incident on and emerging from an inhomogeneous medium. Subsequen tly. the Mueller matrix associated with the scattering medium is determined . We focus our attention on forward scattering from systems consisting of r andom as well as partially oriented long cylindrical fibers. We discuss the effects of: (1) shape of individual scattering centers, (2) structure para meter, and (3) optical density of the scattering medium. The anisotropic be havior of the structure function at different packing fractions determines nontrivial characteristics of the polarization transfer. The complex effect ive index of refraction can be polarization dependent as a result of the op tical anisotropy due to both the shape of the individual scatterers and the structure characteristics of the scattering system. Some of the Mueller ma trix elements are shown to be related to the optical anisotropy of the syst em for the case of long cylindrical fibers. The polarization efficiency, th e structure parameter, and the packing fraction are used to quantify this r elationship. We also found that some of the matrix elements are more sensit ive to the degree of structural anisotropy and the packing fraction, while other elements are sensitive to structural non-uniformities across the inve stigated area. (C) 2001 Elsevier Science Ltd. All rights reserved.