Verification of the coating performance for the AXAF flight optics based on reflectivity measurements of coated witness samples
The iridium coating of the AXAF flight optics by Optical Coating Laboratories, Inc. (OCLI) has taken place over the past eight months. During the coating effort, it was necessary to verify the performance of the coatings continually as deposition parameters were changed to accommodate the different geometry of each optic. In addition, quick look reflectivity measurements have been completed for witness samples coated during each run. The minimum reflectivity to be met was 82 percent at 20 arcminutes grazing angle and 50 percent at 34 arcminutes grazing angle. THis can be compared with a theoretical reflectivity, based on the Henke coefficients, of 88 percent and 62 percent at 20 and 34 arcmin respectively. Previous measurements by P. Slane, et al., gave mean values of 84 percent at 20 arcmin and 51 percent at 34 arcmin grazing angle. Measurements reported here were carried out by the SAO reflectivity laboratory, which is part of the AXAF mission support team. The quick look results of both the qualification samples and the production samples are presented along with the test results from the scaleup and verification runs that were used to set the coating parameters.