ABSTRACT
Finite size of the spectral bandwidth of a light source requires more powerful theory to process the optical phenomena accompanying such sources. The coherence theory, which is basically a statistical theory that describes the properties of the radiation field in terms of the correlation between the vibrations at different points in the field, offers the possibility to describe such phenomena. The waves originating from different points of a finite-size light source or even from the same point of a thermal source, exhibit random amplitude and phase fluctuations. If such wave fields illuminate, two points in space or the same point at different instants of time exhibit only partial correlation.
