Mueller matrix measurements on absorbing turbid medium.

Polarization parameters of diffuse backscattered light from a turbid sample are sensitive to its structural properties and can, therefore, be used to probe morphological features of tissue and, thus, monitor changes that arise due to a disease. Extraction of morphological information from measured polarization parameters, however, requires a careful understanding of the dependence of these on factors such as size, size distribution, shape, and dielectric constant of the scatterers, which are often quite involved. In particular, the presence of absorption complicates the dependence of polarization parameters on tissue morphological features. We have found that, while for medium comprising small size scatterers (Rayleigh scatterers), the depolarization shows the expected decrease with an increase in the absorption of the scattering medium, a counterintuitive behavior was observed for larger size (>lambda) scatterers. Further analysis of the results suggests that the observed behavior might arise due to the relative contribution of two depolarizing processes, one resulting from a series of out-of-plane scattering and the other due to the angular variation of the state of polarization in a single scattering event.