A new method and a novel facility for ultra-precise 2D topography measurement of large optical surfaces

We present a novel deflectometric method for the ultra-precise 2D topography measurement of large optical surfaces. The approach is a 2D extension of the established Extended Shear Angle Difference (ESAD) technique, which has previously been limited to the 1D form measurement of plane or slightly curved surfaces. We report in detail on the new 2D ESAD scanning facility capable of measuring large (up to 600 mm in diameter) optical surfaces and present first measurement results. Information on the mathematical algorithms involved in the data acquisition and analysis are given and the mathematics used in the reconstruction of 2D topography maps from a set of angle difference data are described. The intricacies of 2D angle measurement with a modified autocollimator and calibration issues are discussed.