We report progress in using nanoimprint lithography to fabricate high fidelity blazed diffraction gratings. Anisotropically etched silicon gratings with 200 nm period and 7.5°blaze angle were successfully replicated onto 100 mm diameter wafers with subnanometer roughness and excellent profile conformity. Out-of-plane distortion induced by residual stress from polymer films was also analyzed and found to be extremely low. The replicated blazed gratings were tested and demonstrated high x-ray diffraction efficiencies. This process was developed for fabricating blazed diffraction gratings for the NASA Constellation-X x-ray telescope.

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The Reflection Grating Spectrometer (RGS) on Constellation-X will require thousands of large gratings with very exacting tolerances. Two types of grating geometries have been proposed. In-plane gratings have low ruling densities (∼ 500 l/mm) and very tight flatness and assembly tolerances. Off-plane gratings require much higher ruling densities (∼ 5000 l/mm), but have somewhat relaxed flatness and assembly tolerances and offer the potential of higher resolution and efficiency. The trade-offs between these designs are complex and are currently being studied. To help address critical issues of manufacturability we are developing a number of novel technologies for shaping, assembling, and patterning large-area reflection gratings that are amenable to low-cost manufacturing. In particular, we report results of improved methods for patterning the sawtooth grating lines that are required for efficient blazing, including the use of anisotropic etching of specially-cut silicon wafers to pattern atomically smooth grating facets. We also report on the results of using nanoimprint lithography as a potential means for replicating sawtooth grating masters. Our Nanoruler scanning beam interference lithography tool allows us to pattern large area gratings up to 300 mm in diameter. We also report on developments in grating assembly technology utilizing lithographically patterned and micromachined silicon metrology structures ("microcombs") that have achieved submicron assembly repeatability.

Reflection gratings offer high dispersion and thus the potential for high spectral resolution in the soft x-ray band. The requirements of high efficiency and maximum collecting area at minimum mass lead to the desire for densely stacked and exquisitely flat thin-foil grating substrates. In the past we have successfully addressed the problems of thin substrate figure metrology and blazed grating profile fabrication. Our recently developed low-stress thin-foil metrology truss with 50 nm figure repeatability removed a metrology bottleneck and allows us to make progress in the shaping of thin-foil substrates. We present results on the figuring of 100 mm-diameter silicon wafers via magnetorheological finishing to a flatness below 100 nm peak-to-valley, allowing for sub-arcsecond reflection optics.

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