coherence

"Coherence" is used to indicate the degree of the capability of interference of the electrons emitted from an electron gun. The spatial coherence length of the electrons exiting from the electron source, i.e., the interference distance along the direction perpendicular to the traveling direction of the electrons is determined by the source size and the wavelength of the electrons. A highly coherent electron source is essential for electron holography, where the electron waves are directly brought into interference. Such an electron source or a small-sized source is also required for taking a high-contrast crystal structure image formed. The temporal coherence length, i.e., the interference distance along the traveling direction of the electrons is determined by the monochromaticity and wavelength of the electrons exiting from the source. The temporal coherence has not become a matter of discussion yet in the case of TEM.

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