Equivalence theorem of light waves on scattering from media with different types

The equivalence theorem of light waves on scattering from two media with different types, i.e. the continuous medium and the particulate medium, is discussed. It is shown that the normalized spectral density or the spectral degree of coherence of the scattered field may demonstrate identical distribution when certain conditions between these two media are satisfied. As an example, the scattering of light waves from a Gaussian-centered quasi-homogeneous medium and from a collection of particles with Gaussian-centered quasi-homogeneous distribution is investigated, and the condition for identical normalized spectral density and the condition for identical spectral degree of coherence of the scattered field are obtained.