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Proceedings Paper

Rigorous efficiency calculations for blazed gratings working in in- and off-plane mountings in the 5-50-Å wavelengths range
Author(s): Leonid I. Goray
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Paper Abstract

Both classical (in-plane) and conical (off-plane) grating configurations can be used in the spectrometer being developed for the Spectroscopy X-ray Telescope (SXT), which is assigned for the Constellation-X mission. Rigorous absolute efficiency calculations of gold-coated diffraction gratings with ideal triangular, trapezoidal, and polygonal profiles have been carried out for both possible spectrometer mountings by the PCGrate-SX program based on a modified integral method, with due account of random roughness. Optimum grating parameters and spectrometer configuration providing maximum theoretical efficiency were determined. Rigorous calculations performed with optimization showed that blazed grating absolute efficiency for the in-plane configuration similar to that employed in the XMM-Newton X-ray telescope cannot exceed 0.2-0.3 at the maxima in the minus first diffraction order within the relevant range of grazing angles, frequencies, and blaze angles. By contrast, using a grazing off-plane mounting permits one to compute gratings with a few times higher theoretical absolute efficiency in first diffraction orders, both at the maxima and on the average, for much higher grating frequencies and blazing angles. Unlike the classical mount, conical diffraction gives rise to noticeable polarization effects and Rayleigh anomalies in TM polarization. In view of the possibility of fabricating almost ideal triangular grooves by anisotropic etching of smooth graze-cut (111) silicon wafers by interference lithography and of compensating aberrations by properly modifying the frequency and/or grating groove curvature, the off-plane grating configuration may turn out preferable, particularly if a high spectral resolving power can be reached. A comparison with efficiency calculations and measurements is presented.

Paper Details

Date Published: 29 January 2004
PDF: 11 pages
Proc. SPIE 5168, Optics for EUV, X-Ray, and Gamma-Ray Astronomy, (29 January 2004); doi: 10.1117/12.505679
Show Author Affiliations
Leonid I. Goray, International Intellectual Group, Inc. (United States)


Published in SPIE Proceedings Vol. 5168:
Optics for EUV, X-Ray, and Gamma-Ray Astronomy
Oberto Citterio; Stephen L. O'Dell, Editor(s)

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