Rayleigh scattering of polarized photons by molecules

The scattering of polarized light by molecules is discussed in terms of a polarization density matrix. Particular attention is paid to scattering out of the direction of the incident beam, and the formalism enables the polarization characteristics of the non-forward scattered beam to be predicted for any polarization condition of the incident beam. Both Rayleigh and Raman scattering processes are contained in the formalism, although most attention is given to the former. Explicit expressions for the polarization of the scattered beams are obtained in terms of the polarizability and gyration tensors of the molecules by the application of diagrammatic perturbation theory, and it is demonstrated that a determination of the precise polarization state of the scattered beam can provide useful molecular information which is additional to that obtained from depolarization ratios alone. This is because the depolarization ratio depends on only the diagonal elements of the polarization density matrix and so does not convey all the information about the system