Abstract
Interferometry is widely used in nanometer profile measurement of flat and spherical surface. However, it is difficult to measure aspheric surface using interferometers, because it is impossible to make a large reference surface with nanometer accuracy. Scanning defletometry based on ESAD (Extended Shear Angle Difference) is used to measure ultra-precise large near-flat and slight curved optical surface with the accuracy of sub-nanometer. However, it is not possible for it to measure aspheric surface because of the limitation of the measuring range of autocollimators. To make this method feasible to measure large aspheric optical surface, we proposed a new measuring method using autocollimator with rotatable optical devices fixed on linear motion stage. To eliminate the influence of the pitching error of the scanning stage, we made the rotatable optical devices have the same effect with a pentaprism. The simulation of the error analysis of the method is done. Primary experiments on measuring optical sphere mirrors with diameter of 50 mm are done to verify the influence of the stage moving errors. The rotatable optical devices that we designed are proved effective on eliminating the pitching error of the moving stage.
