Measurement of large aspherical mirrors using coordinate measurement machine during the grinding process

A new method has been developed to measure large aspherical mirrors accurately, quickly, and economically by using CMM (coordinate measurement machine). By using CMM to get the 3D coordinates of the actual points on the large aspherical mirrors and make bestfitting of actual surface and nominal surface, we can evaluate the surface of the large aspherical mirrors. It costs only 2 hours to measure an aspherical mirror with diameter larger than 1000mm. The results show good agreement with the results measured by Hartmann-Shack interferometer. Using this method, we can supervise the profile error to less than 5 μm PV during the grinding process. All the aspherical mirrors with dimensions within the range of the machine can be measured.