Reflective coating of 834 Å for imaging O + ions

Imaging upflowing O + ions of ionospheric origin and plasmaspheric O + can be achieved through solar resonance scattering at 834 A. Unfortunately, several strong background emissions, including the ones at 1025 and 1216 A due to geocoronal hydrogen atoms, pose serious problems. Most common optical coatings have higher reflectivity at 1025 and 1216 A than at 834 A. After examining a number of options, e have designed a multiple-layer coating that selectively reflects 834-A radiation and suppresses 1025- and 1216-A radiation. The structure of the coating material consists of a very thin (50 to 150 A) metal (nickel) layer on top of a semitransparent dielectric material (magnesium fluoride) over an aluminum substrate. Three such coatings were produced at NASA Goddard Space Flight Center using an existing coating facility that is not optimized for thin coatings. In spite of such fabrication difficulties, we have obtained encouraging results.