Coherence filters and some of their uses

It has been predicted theoretically and verified experimentally that the spectrum of light radi- ated by a partially coherent source may change on propagation, even in free space. The change depends not only on the spectrum of the source but also on its spatial coherence properties [1]. Such correlation-induced spectral changes have become the subject of great interest in the last few years and have led to a new branch of optics, which is sometimes referred to as spatial- coherence spectroscopy.