We report iridium optical constants fitted from synchrotrxi reflectance data. Specifically, we have used the NKFIT algththin of Di Windt' to derive ö(E) and f(E) frmi 2-12 keV reflectance calibrations of AXAF witness mirrors. The model is applied at each energy separately, to fit four to nine data points fran reflectance-versus-energy scans at selected grazing angles. The stability of the model in the presence c( gaussian noise has been tested extensively. We report the results af several bias studies, involving the generation and analysis c artificial daui Bias studies have been used to determine the optimal grazing angles to be scanned in the various X-ray energy ranges to ccndithm the optical constants. They have also been used to investigate the effects of mthvidual errant data points on the resulting fits and derived optical constants. The results will aid in eliminating systematic errors in the derived optical constants. We also present results af our investigation of the Debye-Wall& and Nevot-Croce3 roughness crrection algorithms as applied to ir measurements. The Nevot-Croce method gives a much better representation atthe data, however its rigrous justification in this experiment is lacking, and the roughness parameter derived is not constant with energy. A more self-consistent model for roughness correction is sought.
Preparations have been underway to construct and test a facility for grazing incidence reflectance calibrations of flat mirrors at the National Synchrotron Light Source. The purpose is to conduct calibrations on witness flats to the coating process of the flight mirrors for NASA’s Advanced X-ray Astrophysics Facility (AXAF). The x-ray energy range required is 50 eV–12 keV. Three monochromatic beamlines (X8C, X8A, U3A) will provide energy tunability over this entire range. The goal is to calibrate the AXAF flight mirrors with uncertainties approaching 1%. A portable end station with a precision-positioning reflectometer has been developed for this work. We have resolved the vacuum cleanliness requirements to preserve the coating integrity of the flats with the strict grazing-angle certainty requirements placed on the rotational control system of the reflectometer. A precision positioning table permits alignment of the system to the synchrotron beam to within 10 arcsec; the reflectometer’s rotational control system can then produce grazing angle accuracy to within less than 2 arcsec, provided that the electron orbit is stable. At 10–12 keV, this degree of angular accuracy is necessary to achieve the calibration accuracy required for AXAF. However the most important energy regions for the synchrotron calibration are in the 2000–3200 eV range, where the M-edge absorption features of the coating element, iridium, appear, and the 300–700 eV range of the Ir N edges. The detail versus energy exhibited in these features cannot be traced adequately without a tunable energy source, which necessitates a synchrotron for this work. We present the mechanical designs, motion control systems, detection and measurement capabilities, and selected procedures for our measurements, as well as reflectance data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.