Deflectometric profilometers provide the metrology for the accurate measurement of optical surfaces which are not easily accessible to classical interferometers, e.g., due to the dynamics of their topography, their size, or the need of independence from calibrated reference surfaces of matched topography. Applications include the measurement of optics used in synchrotron beamlines and the definition of flatness standards. One application of deflectometric scanning is the Extended Shear Angle Difference (ESAD) method, which has been developed to provide highly accurate measurements of the slope and topography of near-plane and slightly curved optical surfaces. ESAD combines deflectometric and shearing techniques in a unique way to enable error minimization and traceability. A facility achieving sub-run repeatability, reproducibility, and uncertainty of topography measurement was built at the Physikalisch-Technische Bundesanstalt (PTB). ESAD utilizes the straight propagation of light as well as traceable measurands to provide a flatness standard with highest accuracy which is to serve as the starting point of the traceability chain in flatness measurement. It will be reported on the ESAD device and on measurement results. Measurement comparisons involving ESAD deflectometry and an independent deflectometric scanning system will be presented. Information on the adjustment of the pentaprism, the specimen under test, and the axes of the autocollimator will be given. It will be reported on the reduction of the systematic errors in the angle difference measurement down to the milliarcsec (few nrad) level.
Advances in X-Ray/EUV Optics, Components, and Applications