Nanometer profile measurement of large aspheric optical surface with improved deflectometry method - Principle introduction and experimental verification

Deflectometry methods are widely used for flatness measurement of optical surfaces with subnanometre uncertainty. In the other hand, the limitation of measuring range of the autocollimator makes it unavailable for surfaces with large angle change. In this paper, a new method is proposed to enlarge the measuring range of the autocollimator so that surfaces with large slope change are measurable. The data processing methods are introduced and experimental setup is built. A concave mirror with large slope change is measured to verify the basic principle of proposed method. The experiment result proved that the measuring range of deflectometry method is enlarged with proposed method. The repeated experiments result shows that the repeatability of the measured profile is less than 15 nanometers.