The role of coherence in the study of speckle patterns is considered. It is shown that the type of coherence used in such analysis has an important difference from the "classical" coherence concepts. The analogy between speckle and thermal radiation is explored. The second-order coherence properties of speckle are summarized. Finally, some aspects of speckle that do not arise in classical coherence theory are discussed.
Joseph W. Goodman,
"Role Of Coherence Concepts In The Study Of Speckle", Proc. SPIE 0194, Applications of Optical Coherence, (25 October 1979); doi: 10.1117/12.957910; https://doi.org/10.1117/12.957910