Abstract

A hologram, first described and named by Gabor (1949), permits a medium such as photographic film, which responds only to intensity, to store the complete amplitude and phase information which characterizes an electron wavefront. The hologram is formed by allowing some fraction of a coherent electron wave which has interacted with a specimen to interact again with original incident wave so as to generate an interference pattern. If the hologram is then itself illuminated by a coherent light source and optical system which mimic the original electron-optical system then a pair of images -one real and the other virtual -can be reconstructed and viewed. Because the hologram contains both the amplitude and the phase data of the wavefront, errors and distortions in either component due to aberrations in the objective lens can be corrected by optical manipulates before the image is reconstructed. With the advent of commercial field emission transmission electron microscopes capable of generating both high resolution images and highly coherent electron beams, these holographic techniques are now available as practical tools to improve TEM performance as well as to create new modes of images (Tonomura 1987).

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