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Linear contrast transfer theory can be applied to weakly scattering objects, for instance thin amorphous TEM specimen, which leads only to a small phase shift on the diffracted electron wave. The diffractogram intensity is the power spectrum of the recorded image and can be given in the simple coherent form,
D(g) ≈ |O(g)|2 sin2[χ(g)] -------------------------------- [4186]
where,
g -- Object frequency vector
χ -- Wave aberration function
sin2[χ(g)] -- Oscillating patterns of circular, elliptic, or hyperbolic shape (Thon rings [1])
|O(g)|2 -- Scattering power of thin amorphous objects
|O(g)|2 decreases slowly towards higher spatial frequencies and is azimuthally isotropic.
[1] F.Thon and Z. Naturforsch, 21a (1966) 476.
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