Forward depolarized light scattering: heterodyne versus homodyne detection

The rotational correlation function of anisotropic colloidal particles can be measured by observing the fluctuations of the depolarized intensity scattered in the forward direction. In this work we present a theoretical treatment of forward depolarized light scattering. Our calculations show the importance of the insertion of a quarter-wave plate between the scattering cell and the analyzer. The role of the quarter-wave plate is to generate a heterodyne signal between the transmitted beam and the depolarized forward scattered field. In order to illustrate the theoretical calculations, we present experimental results obtained with dispersions of fluorinated polymer colloids and with solutions of tobacco mosaic virus.