Complex observation in electron microscopy: V. Phase retrieval for strong objects with foucault knife-edge scanning

Abstract

Conventional phase retrieval in transmission microscopy is applicable only to weak objects that perturb the incidence with a phase that is π/2 or smaller. We propose a novel phase retrieval technique applicable to strong objects. The innovation core is the scanning of a knife-edge, which is conventionally fixed to recover phase information. The synchronous operation between the scanning of the knife-edge and the image accumulation enables a novel spatial filter, which draws phase retardations by objects in the form of their first derivative. Combining the left- and right-scanning of the knife-edge can completely expel image components that are non-linear to the wavefront functions. Theoretical formulation of knife-edge scanning filters and corresponding numerical simulations specific to an electron microscope are proposed. © 2004 The Physical Society of Japan.