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Proceedings Paper

Subaperture stitching interferometry for testing mild aspheres
Author(s): Paul Murphy; Jon Fleig; Greg Forbes; Dragisha Miladinovic; Gary DeVries; Stephen O'Donohue
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Paper Abstract

Interferometric tests of aspheres have traditionally relied on so-called "null correctors". These usually require significant time and expense to design and fabricate, and are specific to a particular asphere prescription. What's more, they are tedious to align and calibrate. Aspheres can also be tested without null correction (using a spherical wavefront), but such capability is extremely limited. A typical interferometer can acquire only a few micrometers of fourth-order aspheric departure due to high-density interference fringes. Furthermore, standard software packages do not compensate for the impact upon a non-null measurement of (i) the part's aspheric shape or (ii) the interferometer's optical aberrations. While fringe density and asphere compensation severely limit the practical utility of a non-null asphere measurement, subaperture stitching can directly address these issues. In 2004, QED Technologies introduced the Subaperture Stitching Interferometer (SSI(R)) to automatically stitch spherical surfaces (including hemispheres). The system also boosts accuracy with in-line calibration of systematic errors. We have recently added aspheric capability, extending non-null aspheric test capability by an order of magnitude or more. As demonstrated in the past on annular zones of nearly nulled data, subaperture stitching can extend the testable aspheric departure. We present a more generally applicable and robust method of stitching non-null aspheric phase measurements. By exploiting novel compensation schemes and in-line system error calibration, our subaperture stitching system can provide significantly better accuracy and increased testable aspheric departure over an unstitched non-null test. Examples of stitched non-null tests are analyzed in this paper, and cross-tested against corresponding null tests.

Paper Details

Date Published: 14 August 2006
PDF: 10 pages
Proc. SPIE 6293, Interferometry XIII: Applications, 62930J (14 August 2006); doi: 10.1117/12.680473
Show Author Affiliations
Paul Murphy, QED Technologies (United States)
Jon Fleig, QED Technologies (United States)
Greg Forbes, QED Technologies (United States)
Dragisha Miladinovic, QED Technologies (United States)
Gary DeVries, QED Technologies (United States)
Stephen O'Donohue, QED Technologies (United States)


Published in SPIE Proceedings Vol. 6293:
Interferometry XIII: Applications
Erik L. Novak; Wolfgang Osten; Christophe Gorecki, Editor(s)

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