The radiometric theory of spatial coherence is presented with special attention to the validity of the approximations on which it is based. A new definition of the transverse coherence area is introduced and shown to be in general agreement with earlier definitions. In free-space propagation the product of the transverse coherence area and the intensity is shown to be constant along rectilinear rays, and, for radiation from uniform Lambert sources, a well-known paraxial formula for the transverse coherence area is extended to the extraparaxial domain. A decrease of the spatial coherence in free-space propagation takes place in regions with an increase of the intensity. For imaging systems this occurs in a finite part of image space whenever a real image of a diffusely radiating, extended object is formed at a finite distance.
© 2000 Optical Society of America
(030.1640) Coherence and statistical optics : Coherence
(030.5630) Coherence and statistical optics : Radiometry
(110.4980) Imaging systems : Partial coherence in imaging
(350.5500) Other areas of optics : Propagation
Hans M. Pedersen and Jakob J. Stamnes, "Radiometric theory of spatial coherence in free-space propagation," J. Opt. Soc. Am. A 17, 1413-1420 (2000)