Abstract

It was shown in a recent publication¹ that, in general, the normalized spectrum of light changes on propagation through free space. For light generated by sources of a certain class, which includes the usual thermal sources, the normalized spectrum was, however, found to be invariant on propagation provided that the degree of coherence of the source satisfies a certain scaling law. In this paper the analysis is extended to light from quasi-homogeneous, primary, planar sources. An analogous scaling law is derived. It is also shown that with sources of this type, a single relation exists between the spectrum of the primary source distribution and the spectrum of the light in the source plane. The results are illustrated by black-body sources.

© 1986 Optical Society of America