Subaperture stitching interferometry with reduced reference errors for ultrasmooth surfaces

摘要

Low-roughness ultrasmooth surfaces are under increasing demand in short-wavelength optical systems. Substitching interferometry has been used to measure the profiles of surfaces used in X-ray beam. To validate the stitching accuracy of our optical profiler, a comparison of stitching surfaces using a 10X objective and those directly measured using a 2.5X objective is performed with a resolution of 1 μm. By studying the multiple measurements and defocussing errors, the reference surface error is measured in various regions of a standard flat surface with random positions and rotation angles. In the final experiment, 25 subapertures measured using a 10X objective with reduced reference surface error are stitched to a 2.54 X 1.90 mm area. The comparison is between the stitching and the same area measured directly using the 2.5X objective, and the results show that a root-mean-square accuracy of ＜0.2 nm can be achieved.