Development of imaging x-ray telescopes at Tongji University

The imaging x-ray telescope (IXT) was first developed at the Institute of Precision Optical Engineering of Tongji University in 2007. Since then, we have made great progress on the development of mirror fabrication, coatings, and optic assembly. In this paper, we intend to provide an overview of the progress. Currently, we can routinely produce cylindrical mirror substrates with angular resolution of 30″ to 60″. To improve the effective area, coatings using C, Ni, and Pt layers were designed and achieved a high reflectivity at 0.5 to 10 keV. During the optic assembly, an in-situ measurement system and a three-dimensional ray-tracing program have been developed, thus guiding the assembly process in real time. Several prototypes have been fabricated, and one of them with 21 mirror layers was calibrated at the MPE PANTER x-ray test facility in Germany. The IXT prototype, with a focal length of 2052.5 mm, is characterized by a measured half-power diameter of 111″ and effective area of 39  cm2 at 1.49 keV.