Artifact reduction in the CSPAD detectors used for LCLS experiments

Abstract

The existence of noise and column-wise artifacts in the CSPAD-140K detector and in a module of the CSPAD-2.3M large camera, respectively, is reported for the L730 and L867 experiments performed at the CXI Instrument at the Linac Coherent Light Source (LCLS), in low-flux and low signal-to-noise ratio regime. Possible remedies are discussed and an additional step in the preprocessing of data is introduced, which consists of performing a median subtraction along the columns of the detector modules. Thus, we reduce the overall variation in the photon count distribution, lowering the mean false-positive photon detection rate by about 4% (from 5.57 × 10-5 to 5.32 × 10-5photon counts pixel-1 frame-1 in L867, cxi86715) and 7% (from 1.70 × 10-3 to 1.58 × 10-3photon counts pixel-1 frame-1 in L730, cxi73013), and the standard deviation in false-positive photon count per shot by 15% and 35%, while not making our average photon detection threshold more stringent. Such improvements in detector noise reduction and artifact removal constitute a step forward in the development of flash X-ray imaging techniques for high-resolution, low-signal and in serial nano-crystallography experiments at X-ray free-electron laser facilities.An under-diagnosed detector artifact is reported and corrected for in a sparse photon-counting regime. Standard deviation in false-positive photon count is reduced by up to 35%, with improved or identical true positive rates.