Partially coherent optical fields

Abstract

In the first part of this paper the concept of partial coherence is explained and previous research on partially coherent optical fields are reviewed. A generalized Huygens' principle, applicable to such fields is then formulated, which expresses the intensity I( P) at a typical point P in the field, in the form of an integral taken twice independently over an arbritrary surface. In order to determined I( P) it is necessary to know: (1) the intensity at every point of the surface and (2) a certain correlation factor (called the coherence factor) for all pairs of points on the surface. Next it is shown that apart from a single geometrical phase factor depending on the positions of the points, the coherence factor is essentially the Fourier transform of the intensity function of the source. The results accord particularly well with claims made by Michelson many years ago (and not hitherto related to systematic opitcal theory) that it is possible in principle to determine the insensity across stellar sources from the measurements of interference fringes in a suitable inteferometer.