Interference of three electron waves by two biprisms and its application to direct visualization of electromagnetic fields in small regions

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 observed phase shift, to be 6.4×10−17 C, which is equal to about 400 electrons. A change of the electric field around charged alumina particles at high temperatures has been observed dynamically. Magnetic flux lines emerging from a barium ferrite particle are also visualized.