8 March 2013 DMD-based scanning of steep wavefronts for optical testing of freeform optics
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Abstract
Optical, full field testing of aspheres and especially freeform optics still remains a challenging task. Till now, various measurement setups for wavefront characterisation have been presented for functional testing. These are primarily based on microlens arrays in front of a photosensitive semiconductor in combination with an analysis logic. Compared to other sensor types for optical testing the Shack-Hartmann sensor (SHS) features a high flexibility with regard to wavefront deformations. For SHS the measurement range is limited due to the measurement principle that all measurement points are detected simultaneously by an imaging device and the signals must be separable - thus the dynamic range is defined by the number of micro-lenses and the resolution of the imaging sensor. Here, we present an approach for wavefront measurements which increases the dynamic range and the lateral resolution simultaneously. The concept is based on a selection and thereby encoding of single sub-apertures of the wavefront under test and to measure the wavefronts slope consecutively in a scanning procedure. In contrast to the LCD based approaches, here the selection of the sub-apertures and thus the scanning procedure is performed by a digital micro-mirror array (DMD). The use of a DMD allows high lateral resolution as well as a very fast scanning ability. The measurement concept and performance of this method will be demonstrated for different freeformed specimens like progressive eye glasses. Furthermore, approaches for calibration of the measurement system will be characterised comprehensively and the optical design of the detector will be discussed in detail.
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S. Stuerwald, R. Schmitt, "DMD-based scanning of steep wavefronts for optical testing of freeform optics", Proc. SPIE 8618, Emerging Digital Micromirror Device Based Systems and Applications V, 86180L (8 March 2013); doi: 10.1117/12.2004845; https://doi.org/10.1117/12.2004845
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