31 August 2006 Influence of striae on the homogeneity of the linear thermal expansion coefficient of ZERODUR
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Proceedings Volume 6288, Current Developments in Lens Design and Optical Engineering VII; 62880M (2006); doi: 10.1117/12.674751
Event: SPIE Optics + Photonics, 2006, San Diego, California, United States
Abstract
The ZERODUR production, consisting of established processes used in the manufacturing of high homogeneous optical glasses, results in excellent blanks with low stress birefringence, striae content and outstanding homogeneity of the coefficient of thermal expansion. For future extremely large telescope projects like OWL (OverWhelmingly Large Telescope) or TMT (Thirty Meter Telescope), with at least several hundreds of mirror blanks, the material homogeneity within a single blank is extremely important. Previously, the stress birefringence of 2m class mirror blanks could be reduced to amounts far below our catalog values. Striae in ZERODUR, if present, are weak band-like density fluctuations within the material with only minimum influence on the properties of the material. This paper presents the results of dilatometric measurements on the influence of standard grade striae within ZERODUR on the homogeneity of the CTE. All CTE measurements have been carried out using our new dilatometer setup with improved reproducibility.
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Ralf Jedamzik, Peter Hartmann, "Influence of striae on the homogeneity of the linear thermal expansion coefficient of ZERODUR", Proc. SPIE 6288, Current Developments in Lens Design and Optical Engineering VII, 62880M (31 August 2006); doi: 10.1117/12.674751; http://dx.doi.org/10.1117/12.674751
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KEYWORDS
Birefringence

Zerodur

Mirrors

Temperature metrology

Inspection

Thirty Meter Telescope

Large telescopes

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