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M. P. Kowalski, R. G. Cruddace, J. C. Rife (NRL), T. W. Barbee, Jr. (LLNL), W. R. Hunter (SFA, Inc.), K. F. Heidemann, H. Kierey (Carl Zeiss)
In the EUV spectra of astrophysical sources, high spectral resolution and sensitivity are required goals for measuring line widths and Doppler shifts and for resolving the many weak lines, absorption edges and other features that may appear. We have been pursuing these goals by depositing high-reflectance multilayers on ultra-smooth holographic ion-etched gratings of high groove density. At near-normal incidence we have achieved grating groove efficiencies of 34% in the first order using laminar gratings, near the theoretical limit of 40.5%. For blazed gratings, the theoretical limit in a chosen order is 100% but the highest measured values are only ~25%. Accurate control of the groove profile is the key factor, and this becomes difficult when the groove density is high and the blaze angle is only a few degrees. Such configurations are typical of high-resolution EUV spectrometers, such as with the successful J-PEX sounding rocket experiment or with the proposed APEX satellite instrument. However, a new technique has been developed at Carl Zeiss where a grating of relatively high blaze angle is overcoated with a liquid polymer, which is then hardened. The resulting grating has a reduced blaze angle, accurate profile, and reduced roughness. We present the results of efficiency measurements on blazed test gratings that were overcoated with a liquid polymer, cured, and then coated further with state-of-the-art multilayers. Record values were achieved in both measured efficiency and grating groove efficiency.
This work is supported by the Office of Naval Research and NRL under Work Unit AMCORS (76-3641), and by NASA Space Astrophysics and Research Analysis under NDPR W-19,881.
The author(s) of this abstract have provided an email address for comments about the abstract: michael.kowalski@nrl.navy.mil
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.