Interference of Three Electron Waves and Its Application to Direct Visualization of Electric Fields

We present a method for the interference of three electron waves and its application to direct visualization of pure-phase objects such as electromagnetic microfields. Using a transmission electron microscope equipped with a field-emission electron gun and two electron biprisms, an object wave and two reference waves at either side of the object wave are superposed to produce a new type of interference pattern. In this pattern, equal-phase lines of the object wave are directly displayed as intensity modulation of periodic interference fringes. An electric field around a latex particle, induced by electron-beam irradiation, has been observed. The electric charge of the particle is estimated, from an observed phase shift, to be 6.4 × 10−17C, which is equal to about 400 electrons. A change of the electric field around charged alumina particles at high temperatures has been observed dynamically.