Profilometry using an optical stylus with interferometric readout

Abstract

Summary form only given. In this paper, we describe the development of a simple and combined measurement system to measure the surface profile of work-pieces with large steps. In order to achieve high lateral resolution we believe that it is best to adopt a laser dynamic focusing mechanism in the measurement system. Fortunately, a simple and low cost device, the optical pickup head used in the CD-ROM, can be used to detect the focus position on the tested surface. To achieve both high accuracy and a large measurement range, the Michelson distance interferometer must be utilized. Another necessary device is a stage driven by a motor or translator through a feedback controller. The optical head and the retroreflector of the interferometer are put together on the stage. The dynamic focusing is carried out through the closed-loop system that consists of the optical head, the tested surface and the translator. The work presented utilizes a commercially available CD optical head, a stage driven by the piezoelectric translator (PZT) and a Renishaw interferometer. The PZT follows the profile of the tested surface and keeps the objective lens of the optical head a constant distance from it. A retroreflector of the interferometer is attached to the stage, so that the movement of the PZT, and hence the surface profile, can be measured by the interferometer with high accuracy.