Coating of the HEFT telescope mirrors. Method and results

We report on the coating of depth graded W/Si multilayers on the thermally slumped glass substrates for the HEFT flight telescopes. The coatings consists of several hundred bilayers in an optimized graded power law design with stringent requirements on uniformity and interfacial roughness. We present the details of the planar magnetron sputtering facility including the optimization of power, Ar pressure and collimating geometry which allows us to coat the several thousand mirror segments required for each telescope module on a time schedule consistent with the current HEFT balloon project as well as future hard X-ray satellite projects. Results are presented on the uniformity, interfacial roughness, and reflectivity and scatter at hard X-ray energies.