Abstract

A heterodyne profilometer,¹ similar to that of Sommargren, has been assembled. A test surface (plane or spherical) is mounted on a rotating table for roughness measurement. To avoid errors due to tilt of the test surface, the normal of the plane surface must be set parallel to its axis of rotation, and for a spherical surface, its center of curvature must lie on the optical axis of the setup. For proper alignment of the test surfaces, two interferometric techniques are devised. In one of the techniques, a laser Twyman-Green interferometer is built into the profilometer setup such that the test surface acts as one of the two mirrors of the interferometer. The tilt of the surface is detected by observing the symmetry of the fringe pattern with reference to the optical axis. In the other technique, an optical flat is placed perpendicular to the axis of rotation and Fizeau fringes are observed between the test surface and the optical flat. In both of the above optical arrangements, the fringe pattern should remain stationary and symmetrical for a well-aligned test surface.

© 1989 Optical Society of America