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Proceedings Paper

CTE characterization of ZERODUR® for the ELT century
Author(s): Ralf Jedamzik; Thorsten Döhring; Thoralf Johansson; Peter Hartmann; Thomas Westerhoff
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Paper Abstract

This review paper summarizes the extensive investigations that have been performed at SCHOTT to achieve a deeper understanding of the CTE homogeneity of ZERODUR® within single blanks and the casted formats (boules). Especially for the upcoming Extremely Large Telescope (ELT) projects like E-ELT or TMT with at least several hundreds of mirror segments the reproducibility of the mean CTE, CTE homogeneity and axial gradient is very important while keeping the CTE quality assurance process economic at the same time. Statistics of CTE homogeneity measurements on a ZERODUR® boule suitable for an economical production of ELT mirror substrates using the improved dilatometer will be presented. It will be shown, that it is possible to achieve tight CTE specifications by utilisation of processes existing at SCHOTT, while at the same time guaranteeing a long term reproducibility. The CTE measurement is optimized for a temperature interval from 0°C to 50°C. We developed a model to extrapolate the CTE behaviour to specific temperature conditions at the telescope site.

Paper Details

Date Published: 21 August 2009
PDF: 11 pages
Proc. SPIE 7425, Optical Materials and Structures Technologies IV, 742504 (21 August 2009); doi: 10.1117/12.823937
Show Author Affiliations
Ralf Jedamzik, SCHOTT AG (Germany)
Thorsten Döhring, SCHOTT AG (Germany)
Thoralf Johansson, SCHOTT AG (Germany)
Peter Hartmann, SCHOTT AG (Germany)
Thomas Westerhoff, SCHOTT AG (Germany)

Published in SPIE Proceedings Vol. 7425:
Optical Materials and Structures Technologies IV
Joseph L. Robichaud; William A. Goodman, Editor(s)

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