Propagation of a generalized radiance in paraxial optical systems.

It is demonstrated that the symmetric form of the generalized radiance remains invariant on propagation along rays through lossless paraxial optical systems described by their ABCD matrices. This result is derived directly on the basis of the cascaded Huygens-Fresnel integral, and it holds for all states of the field coherence. When combined with quasihomogeneous sources the result leads to a fully consistent wave theory of radiometry with partially coherent light.