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Abstract

Structure determination is one of the most important application areas of 4th generation light sources. This method in particular can fully exploit the coherent and pulsed nature of the X-ray radiation delivered by X-ray free-electron lasers (XFEL) as the European XFEL. The focus of scientific interest in this area is understanding the physical, biological, and chemical properties of samples on the nanometer scale. The properties of the Xrays provided by the FEL enable Coherent X-ray Diffraction Imaging (CXDI), an experimental technique where a sample is irradiated with coherent X-rays and a far-field diffraction pattern is registered with an imaging detector. By the nature of the underlying physics, the spatial resolution, at which the sample can be probed with the CXDI technique, is only limited by the wavelength of the X-ray radiation and the exposure time if a detector can record the diffraction pattern to very large solid angles. The resolution that can be achieved under real experimental conditions, on the other hand, depends strongly on additional parameters. Amongst others, the Shannon pixel size, linked to the detector resolution, the coherent dose that can be deposited in the sample without changing its structure, and the signal-to-noise of the detected scattered radiation at high q, or equivalent to that at high scattering angles 2Q, have a strong influence on the resolution. The signal-to-noise ratio at high q defines the “effective” maximum solid angle in a specific experiment setup up to which a detector can efficiently detect a signal and in consequence determines the achievable resolution.

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