Coherence properties of nonstationary light wave fields

A spectral approach to the theory of partial coherence of nonstationary light [M. Bertolotti et al., Pure Appl. Opt. 6, 153 (1997)] is applied to the study of spatial coherence properties of nonstationary wave fields on propagation in free space. Three types of nonstationary light sources are considered-a point source, a spatially incoherent source, and a uniformly coherent source, the last being perfectly coherent in both space-time and space-frequency domains. An example of the diffraction pattern from a slit with nonstationary partially coherent illumination is used to illustrate the general discussion. (C) 1998 Optical Society of America.