Journal of Synchrotron Radiation, 01 September 2019, Vol.26(5), pp.1621-1630
Modern photon‐counting pixel detectors have enabled a revolution in applications at synchrotron light sources and beyond in the last decade. One of the limitations of the current detectors is their reduced counting linearity or even paralysis at high counting rates, due to dead‐time which results in photon pile‐up. Existing dead‐time and pile‐up models fail to reproduce the complexity of dead‐time effects on photon‐counting, resulting in empirical calibrations for particular detectors at best, imprecise linearization methods, or no linearization. This problem will increase in the future as many synchrotron light sources plan significant brilliance upgrades and free‐electron lasers plan moving to a quasi‐continuous operation mode. Presented here are the first models that use the actual behavior of the analog pre‐amplifiers in spectroscopic photon‐counting pixel detectors with constant current discharge ( the Medipix and CPix families of detectors) to deduce more accurate analytical models and optimal linearization methods. In particular, for detectors with at least two counters per pixel, the need for calibration, or previous knowledge of the detector and beam parameters (dead‐time, integration time, large sets of synchrotron filling patterns), is completely eliminated. This is summarized in several models of increasing complexity and accuracy. Finally, a general empirical approach is presented, applicable to any particular cases where the analytical approach is not sufficiently precise. The first analytical dead‐time models have been developed that offer a realistic description of dead‐time effects on the photon‐counting rates of modern pixel detectors with constant current discharge ( the Medipix and CPix families of detectors), using realistic models for the analog preamplifier circuits in pixels. Measurements with existing detectors with at least two thresholds and corresponding counters can now be linearized without calibration or knowledge of the detector and beam parameters (dead‐time behavior, integration time, fill pattern), enabling linear counting rates of 10 photons per pixel per second with minimal increase in noise.
Photon‐Counting ; Hybrid Pixel Detectors ; Detector Dead‐Time ; Photon Pile‐Up ; High Photon Flux ; Linearization
Permalink to record