Kavli Affiliate: Ralf K. Heilmann
| First 5 Authors: Ralf K. Heilmann, Alexander R. Bruccoleri, Jungki Song, Matthew T. Cook, James A. Gregory
| Summary:
High-resolution ($R = lambda /Delta lambda > 2000$) x-ray absorption and
emission line spectroscopy in the soft x-ray band is a crucial diagnostic for
the exploration of the properties of ubiquitous warm and hot plasmas and their
dynamics in the cosmic web, galaxy clusters, galaxy halos, intragalactic space,
and star atmospheres. Soft x-ray grating spectroscopy with $R > 10{,}000$ has
been demonstrated with critical-angle transmission (CAT) gratings. CAT gratings
combine the relaxed alignment and temperature tolerances and low mass of
transmission gratings with high diffraction efficiency blazed in high orders.
They are an enabling technology for the proposed Arcus grating explorer and
were selected for the Lynx design reference mission grating spectrometer
instrument. Both Arcus and Lynx require the manufacture of hundreds to perhaps
$approx 2000$ large-area CAT gratings. We are developing new patterning and
fabrication process sequences that are conducive to large-format volume
processing on state-of-the-art 200 mm wafer tools. Recent x-ray tests on 200
nm-period gratings patterned using e-beam-written masks and 4x projection
lithography in conjunction with silicon pore focusing optics demonstrated $R
approx 10^4$ at 1.49 keV. Extending the grating depth from 4 $mu$m to 6
$mu$m is predicted to lead to significant improvements in diffraction
efficiency and is part of our current efforts using a combination of deep
reactive-ion etching and wet etching in KOH solution. We describe our recent
progress in grating fabrication and report our latest diffraction efficiency
and modeling results.
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