22 August 2009 CTE characterization of ZERODUR® for the ELT century
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Proceedings Volume 7425, Optical Materials and Structures Technologies IV; 742504 (2009); doi: 10.1117/12.823937
Event: SPIE Optical Engineering + Applications, 2009, San Diego, California, United States
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.
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Ralf Jedamzik, Thorsten Döhring, Thoralf Johansson, Peter Hartmann, Thomas Westerhoff, "CTE characterization of ZERODUR® for the ELT century", Proc. SPIE 7425, Optical Materials and Structures Technologies IV, 742504 (22 August 2009); doi: 10.1117/12.823937; http://dx.doi.org/10.1117/12.823937
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KEYWORDS
Mirrors

Temperature metrology

Statistical modeling

Zerodur

Large telescopes

Telescopes

Modeling

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