High-accuracy metrology is vitally important in manufacturing and optimally using ultra-high-quality free-form mirrors designed, for example, for space X-ray telescopes to manipulate X-ray light with nanometer-scale wavelengths. Due to the shorter wavelength, requirements on the surface figure (shape) and finish (roughness) of X-ray mirrors are many orders of magnitude more stringent than for visible-light optics. The metrology integrated into X-ray mirror manufacturing must ensure the accuracy of optical surface fabrication on the sub-nanometer level over a large area (on the scale of a meter and even more) strongly aspherical optical elements with the sagittal ROC on the order of a meter and less, whereas the tangential ROC can reach a few hundred meters. The absence of the required metrology is the major limitation of modern technology used for the fabrication of X-ray mirrors. As an adage says, "If you can't measure it, you can't make it." Binary Pseudo Random Array test artifacts and accompanying data processing software offer unparalleled advantages to quantitatively characterize the instrument transfer function (ITF) of the metrology tools and enable data reconstruction to reveal the "true" surface. Previously, BPRA Based methodology has been validated with planar wavefront. In this Project, BPRA-based test artifacts & data processing methodology is adapted for the Cylindrical Wavefront Interferometry for inspection and calibration for mid-long range spatial frequencies. In Phase II, we will develop BPRA test artifacts with adjustable Radius of Curvature, and Computer Generate Holograms combined with BPRA for thorough calibration, and then data reconstruction based on the measured calibration data. The final product will be the BPRA test artifact with user-friendly and GI-controlled software. Anticipated
Benefits: This product improves the integrated metrology process. The ability to assess the high accuracy and high-efficacy metrology is key to further improvement of the optical fabrication and lowering the cost of the X-ray optics. Both precision optics manufacturers and metrology tool makers are strongly interested in this technology. They all agree on the importance of metrology to further improve the product quality in optics and provide better metrology tools (including interferometers) to the customers.
