Nanometer profile measurement of large aspheric optical surface by scanning deflectometry with rotation devices-development of three dimensional measuring facility and experiment

Large aspheric optical surfaces with high accuracy are widely used in huge telescopes and large X-ray facilities. Profile measurement methods with uncertainty less than one hundred nanometers are strongly required for those accurate surfaces. Scanning deflectometry methods have been used for flatness measurement with sub-nanometer uncertainty. However, the limited measuring range makes it unavailable for optical surface with large angle change. In this paper, we have proposed new methods for large aspheric optical surfaces with large angle change. Rotation devices are used for the enlargement of autocollimator measuring range and methods are proposed for the elimination of pitch error of linear scanning stage. Then a three dimensional measuring machine based on pitch angle pre-measurement method is developed for axial symmetric optical surface measurement. Pitch angle of linear stage is measured before the measurement of the sample surfaces and used for compensation to the angle data of sample surfaces. The repeatability of profile measurement result is less than 30 nanometres.