Fizeau Interferometer–Fringe Sharpening

A vector representation of the formation of fringe profiles in a Fizeau (wedge) interferometer shows that, under certain conditions, off-axis illumination may lead to fringe sharpening. The incident angle is such that the beam is first reflected toward the apex of the wedge and, following a certain controllable number of reflections, is reflected away from the apex. A typical example is shown.