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
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