Various technologies for the testing of asphere and freeform optics and their calibration

Metrology is a prerequisite for all advanced fabrication methods.For precision optical systems, optical surfaces require form accuracies down to nanometer level -accross areas with lateral dimensions measuring centimeters to decimeters, or even larger for astronomical instrumentation.This poses a challenge specifically for aspheric and freeform surfaces that scientists have tackled ever since the fabrication technologies allow the production of these, from an optics designer point of view, superior surfaces.In this work, we discuss several state of the art metrology approaches with a focus on calibration.Specifically, we restrict ourselves to interferometric areal methods that have the potential to acquire a dense 2D surface deviation map within a short data acquisition time of less than a minute.