Automatic Characterization of Sub-nm Surface Height Errors of Aspherical Mirrors by 2D Data Reconstruction

C53-07b-271229Optical manufacturing is a multi-billion-dollar industry that is an indispensable part of modern technology and science. The performance of any optical manufacturing process directly depends on the ability of its integrated optical surface metrology method to provide trustworthy feedback. High-accuracy metrology is vitally essential in manufacturing ultra-high-quality free-form mirrors designed to manipulate X-ray light with nanometer-scale wavelengths. Due to the shorter wavelength, requirements for the surface figure and finish of X-ray mirrors are three orders of magnitude more stringent than for visible-light optics. Correspondingly, the metrology integrated into X-ray mirror manufacturing must ensure the accuracy of optical surface fabrication on the sub-nanometer level. Improvements are needed not only for the classical plane, spherical, and sagittal cylindrical X-ray mirrors but, even more urgently, for free-form aspherical X-ray mirrors with moderately and strongly curved shapes, such as paraboloids, ellipsoids, hyperbolas, diaboloids, etc. The availability of such mirrors on the market will directly advance the fundamental and applied research performed at the DOE X-ray light facilities. As an adage say, if you can't measure it, you cannot make it. Any image/data is as good as how well the metrology tool is calibrated and performing. Metrology data serves as the feedback function for the manufacturing process. Our technology is based on thorough characterization of the metrology tool for both the resolution limit and lens distortion using the specially designed test artifact and data processing software. Once the performance limitation is quantitatively characterized, data processing is applied to correct the images, as if the images were taken under an idealized system. These data will be stitched together with high accuracy to characterize the full meter-scale aspherical x-ray mirrors. This would substantially improve the existing stitching interferometry with limited accuracy. Metrology is used in virtually every industry where the manufacturers need to measure the surface roughness for quality assurance (e.g., mirrors, car parts, and foods). The world's top companies highly value our results, requesting the test samples and software immediately after they become commercially available. The solution will improve reliability, exclude the "human factor," and simplify and expedite the calibration.