Dose requirements for resolving a given feature in an object by coherent x-ray diffraction imaging

We address the question of what dose is required to image an object by coherent x-ray diffraction imaging (CXDI) and to resolve a certain sub-unit or feature of that object. We show that a necessary condition for being able to resolve the detail is that the feature can be imaged by itself. The quality of the reconstruction of the feature is nearly independent of the surrounding, whether it is embedded in a larger object or not. This allows one to easily estimate the dose requirements for identifying atoms and clusters in larger objects. We illustrate the result by a numerical example and give an estimate for the dose required to resolve single atoms of different elemental species in CXDI experiments at free-electron laser and synchrotron radiation sources.