First results from a next-generation off-plane X-ray diffraction grating

Abstract

Future NASA X-ray spectroscopy missions will require high throughput, high resolution grating spectrometers. Off-plane reflection gratings are capable of meeting the performance requirements needed to realize the scientific goals of these missions. We have identified a novel grating fabrication method that utilizes common lithographic and microfabrication techniques to produce the high fidelity groove profile necessary to achieve this performance. Application of this process has produced an initial pre-master that exhibits a radial (variable line spacing along the groove dimension), high density (>6000 grooves/mm), laminar profile. This pre-master has been tested for diffraction efficiency at the BESSY II synchrotron light facility and diffracts up to 55% of incident light into usable spectral orders. Furthermore, tests of spectral resolving power show that these gratings are capable of obtaining resolutions well above 1300 ($\lambda/\Delta\lambda$) with limitations due to the test apparatus, not the gratings. Obtaining these results has provided confidence that this fabrication process is capable of producing off-plane reflection gratings for the next generation of X-ray observatories.Comment: 17 pages, 10 figures, Submitted to Experimetal Astronom

Performance testing of an off-plane reflection grating and silicon pore optic spectrograph at PANTER

“…The spectrograph HEW includes contributions from the telescope figure, telescope alignment, and grating contributions in the form of grating alignment, grating figure, and groove induced aberrations. While we expect grating groove induced aberrations to be small (∼0.5 arc seconds) based on previous measurements, 4 we cannot currently deconvolve these individual contributions. In future tests, a mask would be utilized to stop down the azimuthal extent of the SPO in order to characterize the contributions of the SPO as a function of radius and allow for deconvolution of the telescope and grating contributions.…”

“…The relative order efficiencies for these gratings are presented in Ref. 4, demonstrating the large difference in efficiency among the AE1st, AE2nd, and AE3rd orders at the Mg-K energy. Although we observed some small flux from the −2nd and −3rd orders, due to time limitations of the test campaign, we obtained high statistic observations of only the −1st-order Mg-K line, whose LSF we use to characterize the spectrograph performance.…”

“…The grating substrates are 100 × 100 × 0.7 mm 3 Si wafers with a central grooved area of 25 × 32 mm 2 , where the long dimension is in the optical axis. The grooves are radially ruled such that the spacing between adjacent grooves decreases toward the focus to match the convergence of the telescope, described in detail by McEntaffer et al 4 Fig . 1 Block diagram of the test chamber silicon pore optics (SPO) and grating integration.…”

“…The gratings used in this test were developed at the University of Iowa and are detailed in Ref. 4. This test was the first time that off-plane diffraction gratings were aligned with an SPO and two off-plane gratings were aligned to one another in situ to produce an overlapped spectrum.…”

Fabrication of large-area and low mass critical-angle x-ray transmission gratings

“…For example we can use Technology Development Module optics from Zhang et al 32 in the Marshall Space Flight Center Stray Light Test Facility as an imaging system. 33 However, demonstrating R = 3000 at this facility has only recently become possible using very high diffraction orders and many hours of integration time for a single diffraction peak. It is far from trivial to find or construct a facility that has better capabilities today.…”