Abstract
Electromagnetic fields are not observable with conventional electron microscopy: The fields deflect an incident electron beam but no contrast is produced in the electron micrograph for the fields since all the electrons deflected at an object point are focused into a single image point through the electron lens. The information about the electomagnetic fields is included in the deflection distribution or the phase distribution of an electron beam, which is lost in electron micrographs. Electron interferometry has been carried out since 1950s using a transmission electron microscope equipped with an electron biprism to make ultra-fine measurements. The advent of a "coherent" field-emission electron beam has greatly expanded the range of applications and possibilities: Electric and magnetic fields are directly observed as equipotential lines and magnetic lines of force in an electron-holographic interference micrograph. Precision in phase measurement has increased to 2π/50 thanks to a phase amplification technique peculiar to holography.In magnetic field observation, contour fringes in an interference micrograph directly indicate projected magnetic lines of force in h/e flux units. An example of a magnetic field micrograph is shown in Fig. 1.
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