Nanometer profile measurement of large aspheric optical surface by scanning deflectometry with rotatable devices

Large aspheric optical mirrors and lens are wildly used in high-tech industry such as huge telescopes and synchrotron radiation facilities. The measurement uncertainty of the surfaces is needed to be under several tens of nanometers. Current methods such as interferometry method are not available for measuring aspheric surface with departure over hundreds of wavelength. In this paper, we proposed a new method called improved 3D deflectometry method. Rotatable optical devices are applied to enlarge the measuring range of autocollimator with highly accuracy but small measuring range. Data processing methods are also proposed to improve the measurement uncertainty. Experimental setup is designed based on proposed method. Spherical concave mirror with curvature radius of 5000 mm is measured successfully. The repeatability (mean standard deviation) of 10 times measurement is less than 10 nanometers.