Advantages of a logarithmic sampling scheme for XPCS experiments at the European XFEL using the AGIPD detector

The European XFEL, currently under construction, will produce a coherent X-ray pulse every 220 ns in pulse trains of up to 2700 pulses. In conjunction with the fast 2D area detectors currently under development, it will be possible to perform X-ray Photon Correlation Spectroscopy experiments on sub-microsecond timescales with non-ergodic systems. The Adaptive Gain Integrating Pixel Detector (AGIPD) will be able to record approximately 350 images of every pulse train. This study investigates the influence of the sampling scheme (linear/logarithmic) on the data quality for the AGIPD and possible second generation modifications for XPCS experiments. It is observed that employing the logarithmic sampling significantly reduces the error of the determined relaxation times above approximately 10 mu s due to the larger accessible time base (approximately factor 9 larger compared to the linear scheme). No significant difference between the errors of smaller determined relaxation times was observed, although the linear scheme produced data of higher fidelity (larger signal to noise ratio). In conclusion the use of a logarithmic sampling scheme is advantageous for the type of experiment investigated in this study.