The X-ray quantum calorimeter sounding rocket experiment: Improvements for the next flight

We have developed a new calorimeter array to increase our collecting area by a factor of four. The 6 × 6 pixel device has a total area of 144 mm ², making it one of the largest X-ray microcalorimeter arrays yet constructed. A relatively thin high-z absorber consisting of a 0.7 μm HgTe layer supported on 15 μm high-purity silicon provides good efficiency up to photon energies of 1.5 keV. The heat capacity of this composite is low enough to obtain an energy resolution of μ6 eV FWHM on the 2 mm × 2 mm pixels when operated at a base temperature of 50 mK. The infrared blocking filters have also been improved. Room temperature radiation must be attenuated by about 9 orders of magnitude between 2 μm and 2 cm to avoid having photon shot noise dominate the detectornoise. Accomplishing this while maintaining a high transmission for very soft X-rays that can penetrate only a few μg cm ^-2 is a problem common to all soft X-ray calorimeters that observe external targets. We are constructing monolithic silicon two-layer support meshes with a 350 μm pitch front layer on a 5 mm pitch backing layer. These are 98% open and have >95% effective transmission over a 60° field of view, while providing robust support for 38 mm diameter filters consisting of 20 nm of aluminum on 50 nm of polyimide. Five of these filters in series provide the necessary infrared attenuation. Integral deicing heaters are ion implanted in the fine mesh to remove contamination when necessary.