Qualification of the X-ray spectral performance of the DEPFET pixels of the DSSC imager

The first DEPFET module (128 x 512 pixels) of the DSSC pixel detector, designed for user experiments at the European X-ray Free Electron Laser, has been fully instrumented and an experimental campaign has been carried out with X-ray lines to qualify the main performance figures and to collect calibration data. X-ray spectra fitting has been optimized with consideration to the main sources of systematic errors to achieve gain calibration within 1% accuracy, which is a key issue for its successful operation at XFEL. The most important result is the equivalent noise charge of 16 el rms on average. This shows the potential of the DEPFET-based pixel to reach single-photon imaging down to the lowest photon energy (0.25 keV) at 4.5 MHz frame frequency that can be extrapolated at camera level with high confidence.