Thermodynamic reversibility in polarimetry

The action of linear media on incident polarized electromagnetic waves can produce two kinds of thermodynamic irreversible effects, namely, loss of intensity, in general anisotropic, and reduction of the degree of polarization. Even though both phenomena can be described through specific properties, the overall degree of reversibility of polarimetric interactions can be characterized by means of a single parameter whose minimum and maximum values are achieved by fully irreversible and reversible polarimetric transformations, respectively. Furthermore, the sources of irreversibility associated to the entire family of Mueller matrices proportional to a given one are identified, leading to the definition of the specific reversibility as the square average of the degree of polarimetric purity and the polarimetric dimension index. The feasible values of the degree of reversibility with respect to the mean intensity coefficient and the degree of polarimetric purity are analyzed graphically, and the iso-reversibility branches are identified and analyzed. Furthermore, the behavior of the specific reversibility with respect to the achievable values of the polarimetric dimension index and the degree of polarizance is described by means of the purity figure, and it is compared to the iso-purity elliptical branches in such figure