Experimental investigation of critical points in optical coherence function

By using an unconventional holography, referred to as coherence holography, developed recently, we will explore the whole phase field in an optical coherence function and present the direct experimental investigation to the coherence critical points, including coherence phase saddles, coherence phase extrema and coherence phase singularities. We have observed the local phase structures around the coherence critical points, and studied the relationship between the saddles and the extrema in the optical coherence function. Some topological rules associated with the coherence critical points, such as topological sign rule governing the coherence vortices and topological index conservation during the reaction of the coherence vortices, are also investigated by experiments. © 2010 SPIE.