An anomalous diffraction theory of linear birefringence and dichroism in colloidal dispersions

Abstract

Integral expressions are derived for the linear birefringence and dichroism induced in dispersions of colloidal particles by an electric or a magnetic field. The particle is taken to be of spheroidal shape and to be composed of a nonabsorbing, anisotropic dielectric. The birefringence and dichroism originate from the preferential orientation on these particles by the electric or magnetic field, which exerts a couple through an induced electric or magnetic moment. The optical anisotropy of a particle is calculated from the dielectric anisotropy using the anomalous diffraction light-scattering approximation. Evaluation of the integral expressions shows that the theory is qualitatively in accord with experimental measurements of birefringence and dichroism in dispersions of particles of size commensurate with the optical wavelength.