1 June 1990 Metal multilayer mirrors for EUV/ultrasoft x-ray wide-field telescopes
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Metal multilayer mirrors have been designed for the ALEXIS satellite, which is to carry six wide-field telescopes to perform an all-sky survey in three narrow EUV/ultrasoft x-ray wavelength bands. Comprised of alternating layers of molybdenum and silicon, the mirrors are optimized to provide maximum reflectivity at angles from 12.5 to 17.6° off normal incidence and at wavelengths of 133, 171, or 186 Å. Simultaneously, the mirrors use a "wavetrap" to suppress reflectivity at 304 Å, where the extremely strong geocoronal line of He II causes severe background problems. Low reflectivity at 304 Å is achieved by superposing two layer pairs that provide destructive interference with an effective 2d spacing of 152 Å. Calculations predict the 186 Å design will have a peak reflectivity at 186 A of 35% and a 304 Å reflectivity less than 10-5 compared to a peak reflectivity at 186 Å of 40% and 304 Å reflectivity of 3 x 10-3 without the wave- trap. In the laboratory the 304 Å reflectivity on a multilayer sample with a wavetrap has been measured to be as low as 10-4 . We present details of the calculations and laboratory measurements of the reflectivity performance obtained with prototype mirrors.
Barham W. Smith, Jeffrey J. Bloch, Diane C. Roussel-Dupre, "Metal multilayer mirrors for EUV/ultrasoft x-ray wide-field telescopes," Optical Engineering 29(6), (1 June 1990). https://doi.org/10.1117/12.55638 . Submission:

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