Spatial coherence of light passing through successive apertures

Abstract

The spatial coherence of light passing through a periodic sequence of lenses separated by apertures with uniform transmittances is studied in connection with the mode theory. The initial light launched into the periodic structure is assumed to be incoherent under quasi-monochromatic approximation. The propagation law of the mutual intensity passing through the structure is formulated by means of prolate spheroidal wavefunctions that are the normal modes of the periodic structure under consideration. Various features of spatial coherence and intensity distribution by the process of light propagation through the structure are investigated. As a result, the growth in spatial coherence and the convergence in intensity are observed and, furthermore, it has become obvious that this behaviour depends strongly on the width of the apertures employed in the periodic structure. In particular, the variation in spatial coherence is examined physically with relation to the eigenvalues of the integral equation for determining the normal modes of the periodic structure. Emphasis is placed through the whole analysis on the feature of spatial coherence rather than that of intensity distribution.