Thermal stress test of the depth-graded platinum/carbon reflectors

The ASTRO-H hard x-ray telescope (HXT) is designed to reflect hard x-rays with energies up to 80 keV. It will make use of thin-foil, multinested conical optics with depth-graded platinum/carbon (Pt/C) multilayers. We report on thermal stress tests of the HXT reflectors. The reflectors were fabricated on a heat-formed aluminum substrate of thickness gauged at 200  μm of the alloy 5052. This was followed by an epoxy replication on Pt/C-sputtered smooth Pyrex cylindrical mandrels to acquire the x-ray reflective surface. For the thermal tests, the reflectors were maintained at three different temperatures: −5, 50, and 60°C, respectively, for a week. We found that the surface of the reflectors were significantly changed at temperatures of 60°C or higher. The change appears as wrinkles with a typical scale length of a few tens of microns. No changes on the surface were observed from the −5 and 50°C samples. There was also no change in the x-ray reflectivity for these two temperatures.