Direct observation of electrostatic microfields by four-electron-wave interference using two electron biprisms

A new method has been developed for directly visualizing electromagnetic microfields in real time by the interference of four-electron waves obtained using a transmission electron microscope equipped with a field-emission gun and two electron biprisms. When one object wave and three reference waves interfere, equal-phase lines of the object wave are displayed as the intensity modulation of the interference fringes, in the manner same as in the three-electron-wave interference. The advantage of the four-electron-wave interference is that equal-phase lines are observed without precisely adjusting the angle between the two biprisms or rigorously controlling the fringe spacings of the two biprisms.