Curved detectors for future X-ray astrophysics missions

TL;DR

This paper discusses the development and testing of curved CCD detectors designed for future X-ray astrophysics missions, aiming to match the curved focal surfaces of lightweight, high-resolution optics to improve performance and simplify design.

Contribution

It introduces a novel curved CCD technology, detailing the curving process, surface accuracy, and baseline X-ray performance, advancing detector design for curved focal surfaces.

Findings

Surface non-conformance <5 μm RMS achieved

Curved CCDs maintain low noise and high charge-transfer efficiency

Baseline planar CCDs show excellent spectroscopic performance

Abstract

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 intial results on curving bare silicon samples and monitor devices and characterizing the surface geometric accuracy. The tests meet our accuracy requirement of <5 $\mu$m 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.