Arbitrarily short coherence length in wave fields within finite lossless source regions.

We show that it is possible to construct stochastic source distributions that generate wave fields with any desired spatial coherence properties inside a prescribed finite region, regardless of the refractive-index distribution therein. In particular, we demonstrate that there is no universal sinc-function form for the field correlations produced by statistically homogeneous and isotropic source distributions within large lossless regions, contrary to what is suggested by previous work. The results also disprove the commonly held belief that in lossless source regions the coherence length of the light is bounded below by the blackbody coherence length-that is, by approximately half the wavelength of the field.