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Proceedings Paper

The use of diffractive imitator optics as calibration artefacts
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Paper Abstract

The testing of highly aspheric optics often requires complex test arrangements: these test systems can be multi-element and will have both fabrication and alignment errors present in the test wavefront. It may not be feasible to calibrate such systems with conventional optical shop practice. The use of diffractive imitator optics, with carefully controlled fabrication uncertainties, can be used to characterise these systems. We describe the use of reflective imitator CGH optics as calibration artefacts in the calibration of an optical test system used to test ELT primary mirror segments. The optical test system is designed to have two operational modes: one to measure a spherical reference optic; and one to measure the primary mirror segment. The use of diffractive imitators in this test system is designed to provide traceability between these two operational configurations, to quantify residual alignment aberrations, and to quantify fabrication errors in the test system. We outline the design of the optical test system, the design of three imitator CGH artefacts required to provide traceability between the two optical test modes, and our calibration approach. We demonstrate the calibration performance achieved with this approach. Without the use of these imitator artefacts, the absolute accuracy of the optical test is estimated to be 149 nm RMS wavefront, of which 47 nm RMS is attributed to midspatial wavefront errors and 141 nm RMS is attributed to alignment and prescription errors. The repeatability of this calibration has been established as better than 3 nm wavefront standard deviation, with an absolute accuracy of 19 nm RMS wavefront.

Paper Details

Date Published: 27 August 2015
PDF: 12 pages
Proc. SPIE 9575, Optical Manufacturing and Testing XI, 957516 (27 August 2015); doi: 10.1117/12.2189809
Show Author Affiliations
Paul C. T. Rees, Glyndŵr Univ. (United Kingdom)
John B. Mitchell, Glyndŵr Univ. (United Kingdom)
Andy Volkov, Glyndŵr Univ. (United Kingdom)
Jean-Michel Asfour, Dioptic GmbH (Germany)
Frank Weidner, Dioptic GmbH (Germany)
Alexander G. Poleshchuk, Institute of Automation and Electrometry (Russian Federation)
Ruslan K. Nasyrov, Institute of Automation and Electrometry (Russian Federation)

Published in SPIE Proceedings Vol. 9575:
Optical Manufacturing and Testing XI
Oliver W. Fähnle; Ray Williamson; Dae Wook Kim, Editor(s)

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