Determination of Coherence Length from Directionality
In this contribution we shall present a method for obtaining the coherence conditions on a planar, quasi-monochromatic, possibly virtual, source from the angular distribution of its emission. The result is obtained by assuming a special functional dependence of the cross-spectral density function [cf. Eq. (2.13)]. As an example of current interest we will discuss the coherence properties of thermionic emission sources which are widely used in electron microscopy and whose coherence properties become of increasing importance for the image evaluation problem in electron microscopy.
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