title: Far-zone approximation for partially coherent sources.
abstract: A general condition is derived for the distance beyond which the far-zone approximation can be used in studying propagation of light from a partially coherent source. The distance steadily increases as a function of the coherence radius across the source, reaching the usual value in the coherent limit.
authors.affiliation: Dipartimento di Fisica, Università Roma Tre, Via della Vasca Navale 84, Rome 100146, Italy. gori@uniroma3.it
authors.forename: Franco
authors.initials: F
authors.lastname: Gori