Sampling in x-ray ptychography

Coherent diffractive imaging (CDI) is a means of overcoming the resolution and image contrast limitations of electron and x-ray lenses. The central tenet of the method is that the intensity of the diffraction pattern must be measured on a sufficiently fine pixel pitch, which is inversely related to the size of the illuminated region of the object. We show here that ptychography---a form of CDI that uses many diffraction patterns---is not subject to this constraint. Using a variant of the ePIE inversion algorithm, we demonstrate experimentally that the sampling requirement in ptychography is independent of illumination size.