Validation of the virtual experiment of the tilted-wave interferometer

Tilted-wave interferometry (TWI) is a promising but challenging measurement technique for the form measurement of aspheres. At the Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany, a traceable reference measurement setup for the form measurement of aspheres based on tilted-wave interferometry is currently under development. Since the measurement principle combines special interferometric measurements with model-based evaluation principles, virtual experiments (VEs) play a crucial role in this application and, to ensure high-quality form measurements, the VE of the TWI must be validated. Within the European ViDiT project, the VE of the TWI is validated by measurement of a calibrated reference surface. The results are assessed using uncertainty evaluation methods developed within the project, which account for the use of the VE. In this contribution, the validation method is demonstrated, and the validation results are presented. To this end, a calibrated spherical section is used for the validation of TWI measurements. The traceable reference measurements of the spherical section consist of independent measurements of the absolute radius and of the sphericity, i.e. its deviation from an ideal spherical surface. These reference measurements are subsequently used to validate the VE of the TWI.