Optically interferometric roughness measurements for spherical surfaces by processing two microscopic interferograms

This paper discusses a method to carry out optical interferometric measurements for the surface roughness of spheres in a biomedical application to an artificial joint, using two beams of a Michelson interferometric microscope with digital image processing and a computational system. There will be two kinds of microscopic interferograms formed from the interference between the measurement beams reflected from the artificial joint surface and the reference beams from the reference surface. One interferogram has equal circular interference fringes and another has localized arc interference fringes. To process these two interferograms by using a digital image processing system, the edges of each of the interference fringes which are modulated by the micro-structure of the artificial joint surface can be extracted. The paper proposes an algorithm for the calculation of the standard reference mean circles and mean curves from each of the fringe edges by using the least square fitting method and to obtain the profile departures from the reference mean circles and mean curves and the surface roughness parameters.