The X-ray detection system used to calibrate the Advanced X-ray Astrophysics Facility (AXAF) mirrors will include gas flow and sealed proportional counters. To meet the ultimate 1% goal of the calibration project, the transmission and uniformity of the windows must be well known for the soft X-ray wavelengths involved. Various window materials for use with proportional counters are examined for transmission at X-ray wavelengths in the range of 0.1 to 59 keV. These include the usual window materials (polypropylene and beryllium), as well as materials only recently employed for detector applications (polyimide and diamond). The transmission uniformity of beryllium at 1.49 keV is examined with a microchannel plate detector, producing a "shadowgraph" of the window material illuminated with soft X-rays. This technique allows us to investigate nonuniformities on a spatial scale of about .2 mm.

We are developing a system to calibrate reflectances of witness coupons to the AXAF flight mirrors at the National Synchrotron Light Source over the 0.05-12 keV energy range. These witness coupons will be coated in the same process as the AXAF mirror elements. One of the key issues is the accurate determination of mirror efficiencies across the absorption edges of the mirror coating elements. We present a series of refleetance measurements with 2 eV resolution of a nickel-coated flat mirror in the region of the Ni L-II (870 eV) and L-III (8f3 eV) absorption edges. Scans of reflectance versus grazing angle at fixed energies in this region show distinct interference fringes at grazing angles larger than the critical angle which are extinguished as the photon energy is increased beyond the low point of the L-III edge, indicating total absorption of the evanescent wave within the Ni film. At 51 arc minutes grazing angle, measured reflectance decreases smoothly by 35% and then recovers in an 8 eV band at the L-I1I edge. We have also measured reflectances in the M absorption edge region for gold, platinum, and iridium coated mirrors. We derive optical parameters n and k specific to the film for comparison to the existing data tables.

We discuss the development ofbeamline U3A at NSLS for AXAF telescope witness mirror reflectivity calibrations in the 1 -2 keV energy range. The beamline was originally constructed as a white light beamline and has been upgraded with the addition of a monochromator to meet the needs ofthe AXAF calibration program. The beamline consists of an upstream horizontally focussing gold coated elliptical mirror, a differential pumping section, a sample/filter chamber, a monochromator and a downstream filter set. The mirror is set at a 2 degree incident angle for a nominal high energy cutoff at 2 keV. The monochromator is a separated element, scanning, double ciystal/ multilayer design having low to moderate energy resolution. A fixed exit beam is maintained through the 7-70 degree Bragg angle range by longitudinal translation ofthe second scanning ciystal. Tracking is achieved by computer control ofthe scan motors with lookup table positioning ofthe crystal rotaiy tables. All motors are in vacuum and there are no motional feedthroughs. Several different multilayer or crystal pairs are co-mounted on the monochromator crystal holders and can be exchanged in situ. Currently installed are a W/Si multilayer pair (N60, 2d=75A), beiyl (2d=15.96A), and Na-3 alumina (2d=22.53A) allowing energy coverage from 180 eV to 2000 eV. Measurements th Na-f alumina and beryl show that beam impurity less than 0. 1% can be achieved in the 1-2 keV energy range. Measured resolving powers are E/i1E60 for W/Si, 500 -800 for alumina and 1500 to 3000 for beiyl. Initial results suggest that signal to noise and beam purity are adequate in the 1-2 keV region to achieve the 1% calibration accuracy required by AXAF. This allows overlap oflr MV edge data taken on x-ray beamline X8A and with low energy data taken on ALS beamline 6.3.2.

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