Noise limit on practical electron ptychography

Ptychography is a wavelength-limited phase retrieval method that promises to provide sub-0.5Å resolution in the electron microscope, even if the lens employed (which is required only to form an illumination spot) can itself only achieve rather modest resolution. The fidelity of a practical specimen reconstruction using ptychography hinges on various experimental factors, the major one of which is the source brightness. Achieving a high degree of coherence of an electron beam requires source demagnification which reduces the electron counts reaching the detector for a given exposure time. Specimen drift, damage and contamination also limits the practical exposure time. In this paper we investigate the effect of the counting statistics required for a good quality ptychographic reconstruction