Free-Space Propagation of the Generalized Radiance Defined in Terms of the Coherent-Mode Representation of Cross-Spectral Density Function

The equation for free-space propagation of the generalized radiance defined formerly by the authors in terms of the coherent-mode representation of the cross-spectral density function is derived within the accuracy of the paraxial approximation. It is shown that, in the short-wavelength limit, this generalized radiance obeys in a good approximation the fundamental radiative transfer law of classical radiometry.