ZERODUR: progress in CTE characterization

Abstract

In 2010, SCHOTT introduced a method for the modeling of the thermal expansion behavior of ZERODUR ® under arbitrary temperature profiles for an optimized production of material for the upcoming Extremely Large Telescope (ELT) projects. In 2012 a new product was introduced based on this method called ZERODUR ® TAILORED. ZERODUR ® TAILORED provides an evolution in the specification of the absolute Coefficient of Thermal Expansion (CTE) value by including the individual customer requirements in this process. This paper presents examples showing the benefit of an application oriented approach in the design of specifications using ZERODUR ® . Additionally it will be shown how the modeling approach has advanced during the last years to improve the prediction accuracy on long time scales. ZERODUR ® is known not only for its lowest CTE but also for its excellent CTE homogeneity as shown in the past for disc shaped blanks typical for telescope mirror substrates. Additionally this paper presents recent results of CTE homogeneity measurements in the single digit ppb/K range for a rectangular cast plate proving that the excellent CTE homogeneity is independent of the production format.