Ultrahigh Precision CTE Measurements

Poor CTE homogeneity can impact the performance of a telescope in at least two ways. First, if the CTE and/or the homogeneity of the CTE of a mirror blank exceeds known design parameters, then the resulting mirror will simply be unusable. Knowing the CTE and/or the homogeneity of the CTE of a mirror blank can therefore be used as a screening tool such that CTE-poor blanks are not machined and polished into mirrors only to be discarded after discovering the finished mirror does not perform well over temperature. Secondly, since a mirror may be manufactured at one temperature, say 300K, and operated at or undergo temperature swings during operation. While corrective measures exist, they still are a function of the mirror substrate#39;s CTE homogeneity. This is why it is extremely important to discover these inconsistencies and defects early in the manufacturing process. In this proposal, we will outline our system to non-destructively test a 100mm sample of low CTE material, with the intention of scaling it up to much larger sample sizes to accommodate the need to test 4m diameter blanks prior to machining