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Simulation and validation of a prototype swing arm profilometer for measuring extremely large telescope mirror-segments

Manufacture of large aspheric optics is subject to the risk of producing the “perfectly wrong surface” (as exemplified by Hubble Space Telescope). For primary segments of segmented telescope (e.g. the 39m European Extremely Large Telescope) this is amplified by the possibility – indeed likelihood - of drift in the full-aperture optical system over several years of optical manufacture. Does segment #1 match segment #931 in conformance to the same parent asphere? If not, the telescope will fail to deliver the specified image-quality and miss some aspect of its science goals. Therefore, a second test, independent of interferometry, is mandatory. This paper explores the relevance of the swing-arm profilometer in this regard, and shows that it is an attractive candidate