Performance of a focal plane detector for soft X-ray imaging spectroscopy based on back-illuminated sCMOS

Spectroscopy focusing array (SFA) and polarimetry focusing array (PFA) are the two major payloads of the enhanced X-ray Timing and Polarimetry mission (eXTP). Nested Wolter-I X-ray mirror module is implemented in SFA and PFA to achieve a high effective area. When evaluating the properties of the mirror module, the alignment of the optical axis of the X-ray mirror module and a quasi-parallel X-ray beam is a prerequisite for ensuring accuracy of the results. To assist the alignment of the X-ray mirror module, an X-ray focal plane detector with one of the largest detection areas, is designed based on a back-illuminated scientific complementary metal–oxide–semiconductor transistor (sCMOS) sensor(GSENSE6060BSI; Gpixel Inc). Then the characteristics of readout noise, dark current, and split-pixel event properties of the detector are studied with the self-developed multi-target fluorescence X-ray source in a 100-m long X-ray test facility. The energy calibration is performed based on the single-pixel event, and the energy non-linearity of the detector is also observed. Finally, based on the optical model, the eXTP mirror module is simulated, and the alignment test of the Wolter-I X-ray mirror module designed for Einstein Probe/Follow-up X-ray Telescope via the “Burkert test” method is demonstrated.