Topography measurement by a reliable large-area curvature sensor
Optical topography measurement for aspheres and complex surfaces on the nanometer scale still leaves a gap, where available measurement systems have problems in achieving the demanded accuracy. Reasons for this are, among others, the extraordinary large dynamical range needed, the missing of absolute reference surfaces and the violation of the common path condition. A curvature-based topography measurement technique using a large-area sensor with high lateral resolution can fill this gap. The principles of such a sensor and a typical realisation are presented here. Although the primary aim is to measure the form of a surface with nanometer accuracy, e.g. photolithography lenses or mirrors, or reflection optics for synchrotron radiation, many other applications in different branches of industry, research and development will be possible, even with lower accuracy demands.