Determination of optical constants for AXAF mirrors from 0.05 to 1.0 keV through reflectance measurements
We discuss calibration of the Advanced X-ray Astrophysics Facility (AXAF) high resolution mirror assembly (HRMA) through the use of surrogate coating process witness flats. Reflectance measurements of representative witness flats have been made at the Advanced Light Source (ALS) Synchrotron Facility over an energy range of 60 - 940 eV. We discuss the procedures used for these measurements and some preliminary results of our studies. The initial results show, for some energy regions, a reduction in reflectance expected from a pure iridium coating layer. The observed decrease in mirror reflectance is believed to be the combined result of the presence of an organic thin film on the mirror surfaces, plus the effects of carbon on the ALS beamline optics. It appears that the tested mirror surfaces have a maximum level of molecular contamination amounting to an effective carbon thickness of from 5 - 10 angstroms. The source of this contamination is not identified, although this amount is not surprising.