This chapter is aimed at understanding how nature and laboratory devices may change the polarization state of light. The transformations of the Stokes parameters are assumed to be linear, i.e., in terms of addition and multiplication by scalars. This is why we are restricted to linear optical systems. The qualifiers quasi-monochromatic and plane will be omitted from now on under the assumption that we are in fact dealing with this type of electromagnetic wave.

Propagation of light through anisotropic media

Changing the polarization state of light means modifying the coherency matrix elements, which in turn require that different components of the electric field vector are acted on differently by the medium. If Ex and Ey suffer the same alteration, a scaling of C is effected, so that the polarization state is unchanged. As a matter of fact, we have seen in the previous chapter how both the linear analyzer and the linear retarder act differently on given components of E. The wave equation (2.1), however, predicts no different behavior for the orthogonal components.