Spatial coherence and Young-Michelson interferometry

The intensity distribution at the exit of a Young-Michelson interferometer is analysed in Fourier domain. it shows that two numbers are necessary for describing properly the variation of the visibility of the interferogram fr inges. One of them is the complex degree of spatial coherence, which descri bes the correlation between the contributions from the Young's slits. The s econd number describes the correlation between the Young's interferograms r eflected by the mirrors of the Michelson interferometer, that is, the corre lation of optical fields that contain another correlation term.