The effect of surface roughness on fringe visibility in optical interferometry

Abstract

A review of theoretical results expressing the fringe visibility as a function of the r.m.s. surface roughness of the test piece for several types of interferometer is presented. Michelson, Fresnel mirror, shearing, holographic, and dual wavelength holographic interferometers are considered. The results for each of these arrangements are compared in terms of a common variable, that is the effective wavelength or contour separation. Results compare well in most cases considered. The preliminary calibration of the visibility of contour fringes observed in a dual index holographic interferometer with respect to the surface roughness of the object is also described. This experiment demonstrates that, following a more extensive calibration, surface roughness over a very wide range can be measured using the latter technique. The authors' main interest in these techniques is related to the simultaneous measurement of wear and surface roughness. A demonstration example of this type of measurement is also shown.