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Proceedings Paper

Distance-dependent influences on angle metrology with autocollimators in deflectometry
Author(s): Ralf D. Geckeler; Andreas Just
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Paper Abstract

The application of electronic autocollimators to the deflectometric measurement of synchrotron optics in beamline metrology laboratories is steadily increasing. The main reason for this is the availability of commercial high-resolution autocollimators capable of providing highly stable angle metrology down to aperture sizes of a few millimeters, even for uncoated optical surfaces. The measuring beam of the autocollimator not only provides the straight propagation of light as a natural straightness standard, but also tracing back the angle measurement to primary standards via calibration enables one to measure surface shape without any recourse to material straightness artifacts. The Physikalisch-Technische Bundesanstalt (PTB) provides the traceability of angle measurements by autocollimators to the radian (rad) - the SI unit of the plane angle - by use of its WMT 220 angle comparator. The fundamental principle of this comparator is the subdivision of the circle, representing an error-free natural standard of 2π rad. It is realized by various self- and cross-calibration methods. Autocollimators are calibrated by direct comparison with this primary standard with standard uncertainties down to 0.003 arcsec (15 nrad). As the aperture sizes of autocollimators decrease, issues such as the transferability / applicability of the calibration to the measurement conditions in the deflectometric set-up become more and more significant. In this paper we are focusing on the investigation of the influence of the distance between the autocollimator and the surface under test on its angle response. Information on the optimized use and accurate calibration of autocollimators for deflectometric applications is provided.

Paper Details

Date Published: 3 September 2008
PDF: 12 pages
Proc. SPIE 7077, Advances in X-Ray/EUV Optics and Components III, 70770B (3 September 2008); doi: 10.1117/12.793742
Show Author Affiliations
Ralf D. Geckeler, Physikalisch-Technische Bundesanstalt (Germany)
Andreas Just, Physikalisch-Technische Bundesanstalt (Germany)


Published in SPIE Proceedings Vol. 7077:
Advances in X-Ray/EUV Optics and Components III
Ali M. Khounsary; Christian Morawe; Shunji Goto, Editor(s)

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