Improvements in optical metrology for high-performance variable-line-spacing x-ray gratings

Optical manufacturing technologies can only be as accurate, reliable, and efficient as the metrology techniques used to calibrate and guide the fabrication process and evaluate the results. The development of metrology capabilities has not kept pace with the need for increasingly high-resolution variable-line-spacing x-ray gratings for high-intensity coherent x-ray light sources. Thus, innovation in metrology is necessary for progress in grating manufacturing. We propose to develop a high-accuracy microstitching interferometry (MSI) system, based on commercially available interferometric microscopes, for direct measurement of surface topography over the entire clear aperture of a VLS grating. We plan to achieve higher accuracy and dynamic range than is currently available, without major modifications to the instrument itself, by leveraging calibration and data processing techniques under development by our collaboration: procedures for combining interferometric measurements to increase both image size and resolution, as well as test samples, measurement protocols, algorithms, and software to characterize and correct for the instrument response, reducing blurring, geometrical distortion, and other sources of systematic error. In Phase I we will develop test samples and data processing algorithms and use existing hardware for proof-of-principle tests. Based on the results of these tests, we will formulate the specifications required for a system suitable for MSI metrology with the most advanced VLS xray gratings. In Phase II, we will realize these specifications in a prototype MSI system based around an available interferometric microscope, and further develop our custom software. In Phase III, we will bring to market a complete VLS grating MSI system based on the developed and tested hardware, data acquisition and motion control system, and user-friendly data acquisition, processing, and analysis software. This will positively impact the US x-ray optics market, expanding the x-ray optical industry, and lead to a significant decrease of the cost of high-quality x-ray optics.