sentences:  Alternatively, a source of polarized light may be used to probe a media; in this case, the changes in the light polarization (comparing to the incidental one) allow to infer the media properties.In general, any kind of anisotropy in the media results in some sort of change in polarization.Such an anisotropy can be either inherent to the media (e.g., in the case of a crystal substance), or imposed externally (e.g., in the presence of magnetic field in plasma).