Processing pulses from TES microcalorimeter X-ray detectors

Microcalorimeter X-ray detectors employing a transition-edge sensor are capable of very high energy resolution, but achieving this in practice depends on an understanding of the readout process. The combination of thermal cooling and thermoelectric feedback present in most circumstances produces a pulse whose area and amplitude both vary nonlinearly with photon energy. The resolution is further affected by the presence of pileup pulses in the pulse or baseline that need to be detected and rejected down to an arbitrarily small level. We describe here a method that includes both the rejection of pileup pulses and the correction of the nonlinearities. We have implemented the process in a system that accepts pulses from multiple detectors and analyzes them in real time. An initial brief X-ray spectrum from a standard sample supplies sufficient data for pulse characterization and energy calibration. The system is then also enabled to combine pulses from multiple detectors into an energy-calibrated histogram in real time