Development of a high spatial resolution detector for at-wavelength metrology of x-ray optics

Abstract

Recent advancements in the field of x-ray astronomy have relied significantly on innovations in grazing-incidence x-ray optics technology, especially for the hard x-ray range for energies above 10 keV. The behavior of these x-ray telescopes for current and planned astrophysical and solar imaging missions needs to be well understood, and fully characterizing the optics includes measurements of the point spread function and effective area for flight optics as a function of energy and off-axis position as well as understanding the scattering and reflectivity properties of substrate coatings. This requires unique detectors with large areas, very high spatial resolution, high sensitivity, photon counting capability and energy discrimination. We report on the development of a detector that is well suited to meet these requirements. The key piece of the instrument is a high spatial-resolution, electron-multiplying charge-coupled device. The detector is back-thinned and optically bonded via a fiberoptic taper to a purpose-fabricated high resolution, high brightness CsI:Tl scintillator with a microcolumnar structure. A prototype version of this camera was used to calibrate the x-ray focusing optics for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission successfully operating in space since its launch in June 2012. Here we present our recent work on the design of the EMCCD detector and scintillators, fabrication, assembly and testing of the full detector system as well as our software development efforts for single photon detection and energy discrimination. Also included are first results from our recent measurement campaign at the x-ray stray light calibration facility of NASA's Marshall Space Flight Center.