ABSTRACT
This chapter deals with an appropriate approach for the general description of the polarization properties, applicable even when the direction of propagation is not stable in time at the considered point r. It analyses the three-dimensional (3D) coherency matrix, the 3D Stokes parameters, and some other mathematical structures and physical quantities characterizing the 3D states of polarization. The 3D description of states of polarization has attracted the interest of a number of researchers for a long time. An appropriate way to study and interpret the main features and types of 3D states of polarization is provided by the decomposition of the coherency matrix into coherency matrices with simple forms. The chapter describes mathematically all the physically achievable incoherent compositions and decompositions of 3D states of polarization. Prior to introducing the concept of intrinsic coherency matrix, it is worth stressing again the difference between the roles played by unitary transformations in coherence theory and polarization theory.
