Current activities towards traceable form measurements of aspheres with a tiltedwave interferometer

Aspheres enable high-quality optical systems with less lenses while maintaining or even improving imaging quality. A reason for this is that they have more degrees of freedom compared to spherical surfaces. Therefore, imaging errors can easily be compensated for. This is why such complex lenses are becoming increasingly popular. However, their potential can only be utilised if the production quality is high, which is currently still limited by form measuring metrology. At the Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany, a traceable reference measurement setup based on tilted-wave interferometry is currently under development. Tilted-wave interferometry is a promising but challenging measurement technique. Since the measurement principle combines special interferometric measurements with model-based evaluation principles, it is a prime example of modern optical metrology: No measurement result is possible without comprehensive modelling of the entire system. Traceable measurement results with sufficiently low uncertainty are a major challenge. This contribution presents current activities at PTB to tackle this task.