19 June 2002 Simultaneous distance, slope, curvature, and shape measurement with a multipurpose interferometer
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The use of interferometers is usually divided into two areas, single-dimensional length measurement where the distance along an optical axis is measured and interferometric surface or wavefront measurement where the laterally varying phase distribution of a largely extended wavefront is the property of interest. In this presentation a combination of the two types of use will be presented. One of the applications which requires simultaneous measurement of distance, slope and curvature is high-accuracy form measurement of aspheres and free form surfaces by the Large Area Curvature Scanning (LACS) method. For a high-accuracy LACS set-up it is most important to measure (and control) the absolute distance between the interferometer and the surface under test, as well as the slope of the wavefront. In the present set-up, a commercial general purpose interferometer is used. The simultaneous measurement of distance, slope, curvature and shape with this instrument is presented. Special emphasis is laid on the specific fringe evaluation method. It uses a model of the real interferogram image and the superimposed disturbing effects. A suitable global optimization method allows the desired quantities to be determined rapidly and reliably. For the future use of LACS, a new, specifically designed multi-purpose interferometer is introduced which can be used in LACS systems with nanometer form measurement accuracy.
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Ingolf Weingaertner, Ingolf Weingaertner, Michael Schulz, Michael Schulz, Clemens Elster, Clemens Elster, Joachim Gerhardt, Joachim Gerhardt, Axel Lucas, Axel Lucas, } "Simultaneous distance, slope, curvature, and shape measurement with a multipurpose interferometer", Proc. SPIE 4778, Interferometry XI: Applications, (19 June 2002); doi: 10.1117/12.473554; https://doi.org/10.1117/12.473554

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