Regular papers

Early days of coherence theory and the first Rochester conference on coherence

Institute of Optics, University of Rochester, Wilmot Building 275 Hutchison Road, Rochester, NY 14627-0186, USA

^* ewlupus@pas.rochester.edu

Received: 17 September 2010

Abstract

The terms coherence and correlations seem to have entered the optics vocabulary about the beginning of the twentieth century, many years after Maxwell discovered that light was an electromagnetic phenomenon. Prior to that time there were only a few investigations, which have a bearing on this subject. The first one was made by a distinguished French optical scientist E. Verdet who around 1865 asked a question which is equivalent to the following: if sunlight illuminates directly two pinholes in an opaque screen, how close must the pinholes be, so that the light which emerges from them can form interference fringes on superposition? He estimated the distance to be about 1/50 millimeter. In modern language this small distance is the diameter of the area of coherence formed by sunlight on the surface of the earth.