A unifying polarization formalism for electric and magnetic multipole interactions

We rely on the spherical-wave expansion to derive the tensor form of the operator describing the interaction of the atomic system with a polarized radiation field, which naturally leads to the introduction of spherical tensors describing the polarization properties of the interacting field.

As a direct application, the formalism is used to model the radiation anisotropy affecting the scattering of radiation in an electric quadrupole transition and the associated Hanle effect in the presence of a magnetic field.