Method for the non-contact rapid and accurate acquisition of the surface topology of objects

Abstract

The method allows contact-less, precise and rapid measurement of the macroscopic shape of objects. The method is based on the Michelson-interferometer with the object mirror being replaced by the object to be measured. A low coherent light source is used. As either the reference mirror or the object is moved, an intensity modulation can be observed on the observation screen. The height information can be derived from determining the maximum depth of modulation in association with the movement. The determination of the depth of modulation has required full sampling of the modulation at a high sampling rate, or quasistatic movements. Therefore common methods are rather slow. The envelope of the modulation is directly extracted by modulating the light source synchronously to the modulation of the interference patterns and by using a solid-state imaging array which shows low pass characteristics in terms of time. The method allows to move the object or the reference mirror significantly faster than in conventional short coherent interferometers at a far lower sampling rate. If a light source cannot be modulated, the flux of light hitting the target or the sensitivity of the photodetector can be modulated instead.

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