Although, in electron microscopy, an object is usually observed by using the intensity of an electron beam transmitted through it, the phase distribution of the electron beam also provides different information about the object. It has been difficult, however, to obtain the phase information because of the low coherence of an electron beam. Recent development of a coherent field emission electron beam and related techniques, such as electron holography, has provided a way to observe microscopic objects and fields by precisely measuring the phase information of an electron beam. It has, for example, become possible to observe the dynamics of individual vortices in superconducting thin films
