Optical Characteristics of an Holography Electron Microscope

Abstract

The growth in popularity of the technique of electron holography is primarily a result of the availability of a new generation of electron microscopes that operate with field emission electron sources of various types. While many important results were obtained by early workers in the field^224,311 utilizing standard thermionic emitters or pointed filaments to obtain a measure of increased brightness and coherence, the field emission source provided a large jump in capability for making interferograms with high contrast fringes, necessary for useful reconstructions of amplitude and phase components of an image. A significant number of TEM or STEM instruments, operating at 200–300 kV with either cold field emitters or field-assisted thermal emitters (Schottky emitters), are now extant. All of these instruments have the potential, with the installation of a simple biprism device, to make functional holograms that can provide information about a sample that is not available with any other technique.