A round robin comparison of freeform form measurements was carried out by the project partners and stakeholders of a European metrology research project. Altogether six measuring instruments were considered: five different (pointwise and areal) optical devices and one tactile device. Three optical freeform surfaces were used for the comparison measurements, where two specimens were measured by five instruments and one specimen by four instruments. In this paper, the evaluation methods and results of this round robin are presented for the three freeform surfaces made from a temperature-stable material, Super Invar ^®. The freeforms had diameters of 40 mm, 50 mm and 100 mm and best-fit radii of 39.75 mm (convex), 40.9 mm (convex) and 423.5 mm (concave). For comparison, the bilateral pointwise differences between the available measurements were calculated. The root-mean-square values of these differences ranged from 15 nm to 110 nm...

The paper presents the effect of mechanical mounting of optical reference elements on their surface shape. Optical reference surfaces are key elements when traceable, highly accurate and precise optical surface measurements are required. In order to calibrate measuring instruments and compare the metrological capabilities of different metrology institutes, universities and other stakeholders, the reference artefacts were developed. Different measurement instruments require a different way of mounting and the reference artefacts are supposed to be useful for reliable and repeatable calibration of a great majority of the instruments worldwide. However, not only their shape was critical, but also the way of mounting was crucial. FEM analyses followed by experiments have revealed an unacceptable surface shape error in the order of hundreds of nanometres in the case of the commonly used screw mount, even for low applied torques. Other...

Die Mikrowellensynthese ist ein essentieller Bestandteil der Fontänenuhren. Mit ihr werden die für die Zustandspräparation und die Anregung des Uhrenübergangs benötigten Mikrowellensignale erzeugt. Unsicherheiten in diesem Teilsystem wirken sich direkt auf die Gesamtunsicherheit der Fontänenuhren aus. Durch Anpassungen im Synthesizer-Design wurden die Unsicherheitsbeiträge der Mikrowellensynthese auf ein vernachlässigbares Niveau reduziert und im Rahmen einer neuen Evaluation verifiziert.