Light-Scattering Spectroscopy

Abstract

So far the propagation of light was assumed to be straight or, at most, straight with a discontinuous change in the direction of propagation at a flat boundary between two media with different indices of refraction. Straight propagation of light holds only as long as the medium is homogeneous. If this is not the case and if the inhomogeneities are, in particular, of the size of the light wavelength scattering into arbitrary or well defined directions occurs. For purely geometrical or local inhomogenities with no time dependence the scattering is elastic which means without a change of the light energy. Depending on the size and nature of the optical inhomogeneity the processes are called Tyndall scattering, Mie scattering, or Rayleigh scattering. For time-dependent inhomogeneities the scattering process is inelastic and for inhomogeneities periodic in time sidebands to the excitation line occur. This is the case for the various forms of Brillouin scattering and Raman scattering. Such scattering experiments give valuable information on the electronic and vibrational states of the material.