Development of balloon-borne hard X-ray telescopes using multilayer supermirror

We present new results in the development of high throughput hard X-ray telescopes with multilayer supermirror coatings. Basic technique to make the supermirror are at first developed in deposition of constant d spacing multilayers. The reflector of multilayer on the float glass achieves high reflectivity, limited by the surface roughness of substarate, while, we need more improvement in getting comparable reflectivity of multilayers on the replica foil. We put the mask just in front of sample, it reduce the non uniformity of the thickness less than 2 %. In order to maximize the effective area and field of view, we have optimized the supermirror parameters; d spacing, number of layer pairs, and thickness ratio of heavy and light element. Multiblock method is introduced to design the supermirror, and it gives high reflectivity of ∼ 30 % in the 25 - 40 kev band. A test supermirror sputtered on a glass sample exhibits reasonable reflectivities of about 20 - 30 %. We designed a telescope system with 45 cm diameter, 20 cm mirror length in two stage, and focal length of 8 m. The effective area of four such telescopes is 320 cm² for the X-rays between 25 and 40 keV. We plan the application of this type of telescopes to the balloon experiment named InFOC μ S to reveal hard X-ray images of clusters of galaxies or supernova remnants.