Interferometric spatial coherence tomography: focusing fringe contrast to planes of interest using a quasi-monochromatic structured light source

Abstract

Interferograms of plane parallel optical flats are hard to interpret when acquired with coherent illumination because of the complex fringe pattern resulting from the superposition of three main contributions, namely from the reference surface and the front and back sample surfaces. We illuminate the sample by a field of high temporal and specially tailored partial spatial coherence. This limits the fringe contrast to sheets of adjustable position and thickness along the axis of the interferometer. We outline the technique and demonstrate its application together with phase shifting interferometry to extract the topography of front and back surfaces of transparent samples.