Optimizing the signal-to-noise ratio for X-ray photon correlation spectroscopy

An analysis is presented of how to optimize the experimental beamline configuration for achieving the best possible signal-to-noise ratio (SNR) in X-ray photon correlation spectroscopy experiments using area detectors. It is shown that there exists an optimum detector distance; namely, the highest SNR is achieved by matching the angular pixel size with the angular source size. Binning several pixels together can increase the SNR by permitting to match the shape of a detector pixel to the shape of the source. It is also shown that collimating slits several times wider than the effective transverse coherence length are optimal; further, it is demonstrated that the energy dependence of the SNR is dictated by the energy dependence of detector efficiency and source brilliance. Ultimately the effects of focusing and low longitudinal coherence are discussed.