Future mega-pixel imaging x-ray detectors will require excellent spectral response at soft (E<1keV) x-ray energies while operating at fast frame-rates. We have characterized the sub-keV spectral resolution of two low-noise MIT Lincoln Laboratory CCDs in detail. These devices are identical in format but differ in gate structure and output stage design. We report measurements of the shape of the spectral redistribution function as a function of energy for each of these sensor types and compare our measurements with theoretical expectations. We also assess the implications of the observed response functions for scientific performance in deep x-ray imaging and high-resolution spectroscopy applications.
Future X-ray astrophysics missions will survey large areas of the sky with unparalleled sensitivity, enabled by lightweight, high-resolution optics. These optics inherently produce curved focal surfaces with radii as small as 2 m, requiring a large area detector system that closely conforms to the curved focal surface. We have embarked on a project using a curved charge-coupled device (CCD) detector technology developed at MIT Lincoln Laboratory to provide large-format, curved detectors for such missions, improving performance and simplifying design. We present the current status of this work, which aims to curve back-illuminated, large-format (5 cm x 4 cm) CCDs to 2.5-m radius and confirm X-ray performance. We detail the design of fixtures and the curving process, and present initial results on curving bare silicon samples and monitor devices and characterizing the surface geometric accuracy. The tests meet our accuracy requirement of <5 μm RMS surface non-conformance for samples of similar thickness to the functional detectors. We finally show X-ray performance measurements of planar CCDs that will serve as a baseline to evaluate the curved detectors. The detectors exhibit low noise, good charge-transfer efficiency, and excellent, uniform spectroscopic performance, including in the important soft X-ray band.
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