High-resolution X-ray gratings enable state-of-the-art spectrometer
X-ray-optics technology has progressed such that future astrophysics X-ray observatories will have orders-of magnitude better performance than existing observatories such as NASA's Chandra X-ray Observatory. High-resolution soft X-ray spectroscopy offers particularly useful observations that can provide information about the evolution of large-scale structure in the universe, conditions near black holes, stellar atmospheres, and more.
Spectrometers employing novel critical-angle transmission (CAT) X-ray gratings promise spectral resolving power, R, as high as 5000—at least 5-10 times that of present instruments. In 2016, an SMD-sponsored team produced and successfully demonstrated this new technology. A high-resolvingpower, soft X-ray objective grating spectrometer for deployment in space requires a lightweight focusing optic with very good angular resolution and gratings that can disperse X-rays to the largest possible angles with high efficiency and minimal aberrations. Realizing the challenging CAT grating design required almost a decade of development and breakthroughs in advanced nanofabrication technology including patterning, etch and atomic level deposition. Demonstrating this capability in the lab was challenging, however, and required a combination of unique state-of-the art nanofabrication processes and test hardware such as a long X-ray beamline and a spectrally narrow source.
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Electron micrograph of cross-section through a CAT grating showing the atomically smooth nano mirrors (left), and a tested 32 mm-wide CAT grating coated with platinum using atomic layer deposition (right). Credit: R. Heilmann, MIT, and A. Bruccoleri, Izentis, LLC
Recent large-area CAT grating next to a U.S. quarter coin. Credit: R. Heilmann, MIT, and A. Bruccoleri, Izentis, LLC