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M.P. Kowalski (NRL), T.W. Barbee, Jr. (LLNL), K.F. Heidemann (Carl Zeiss), H. Gursky, J.C. Rife (NRL), W.R. Hunter (SFA), G.G. Fritz, R.G. Cruddace (NRL)
In the extreme ultraviolet, high spectral resolution and sensitivity are required for measuring linewidths and Doppler shifts and for resolving the many weak lines, absorption edges and other features that may appear in the spectra of astrophysical sources. For over a decade we have been pursuing the goal of achieving high effective area at normal-incidence by using ultra-smooth holographic ion-etched gratings that have been coated with high-reflectance multilayers. The four flight gratings for the J-PEX sounding rocket spectrometer have been fabricated using the holographic ion-etching technique. The gratings are spherical (4000 mm radius of curvature), large (160 mm x 90 mm), and have a laminar groove profile of high density (3600 grooves/mm). They have been coated with a high-reflectance multilayer of Mo/Si. We present the results of grating surface measurements, made using an atomic force microscope. The average roughness of the first grating is about 3 Å rms after coating. We also present efficiency calibration maps, made over the wavelength range 225-245 Å using synchrotron radiation. At an angle of incidence of 5º and a wavelength of 234 Å, the average efficiency of the first grating in the first inside order is 10.4 ± 0.5 the derived groove efficiency is 34.8 ± 1.6 exceed all previously published results for a high density grating.
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