Post-sample aperture for low background diffraction experiments at X-ray free-electron lasers

The success of diffraction experiments from weakly scattering samples strongly depends on achieving an optimal signal-to-noise ratio. This is particularly important in single-particle imaging experiments where diffraction signals are typically very weak and the experiments are often accompanied by significant background scattering. A simple way to tremendously reduce background scattering by placing an aperture downstream of the sample has been developed and its application in a single-particle X-ray imaging experiment at FLASH is demonstrated. Using the concept of a post-sample aperture it was possible to reduce the background scattering levels by two orders of magnitude.Diffraction experiments with weakly scattering samples often suffer from a low signal-to-noise ratio due to unwanted background scatter. Improving the signal-to-noise ratio for single-particle imaging experiments is particularly important as the diffraction signal is very weak. Here, a simple way to minimize the background scattering by placing an aperture downstream of the sample is demonstrated.