Exact description of free electromagnetic wave fields in terms of rays.

A set of representations are proposed for vector electromagnetic waves in free space (or homogeneous media) of any state of coherence. These representations take the form of a radiance, i.e., the weight of a ray. The intensity, energy density or Poynting vector at any point correspond simply to the sum of the weights of all the rays through that point. This formalism is valid even for fields with components traveling in all directions, but without evanescent components.