Abstract

Sommargren¹ devised a method for measuring the roughness of optically plane surfaces. Interferometric techniques for optical alignment² of the sample in the Sommargren profilometer were presented by us earlier. However, this profilometer is not suitable for measuring the roughness of curved surfaces. Our present paper describes a heterodyne profilometer for measuring the roughness of cylindrical surfaces. It is based on a Twyman-Green heterodyne profilometer and uses a polarizing cube as the beam splitter and Zeeman split laser as the light source. Two collinear, orthogonal linearly polarized beams with a frequency difference of 1.5 MHz are separated by a polarizing cube at right angles to each other. A light beam of one frequency is focused on the cylindrical surface under test, while a beam of another frequency is focused on a reference-plane mirror. The reflected beams interfere at the detector to produce a beat-frequency signal. For measuring roughness, the cylindrical surface is displaced in small steps precisely parallel to its axis, and the phase of the beat frequency signal is measured as a function of displacement. Variation of the phase with the displacement provides the surface profile.

© 1990 Optical Society of America