Temporal Coherence/Incoherence in EMs
- Practical Electron Microscopy and Database -
- An Online Book -

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This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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The temporal coherence is the degree to which the wave can be approximated as monochromatic.

In EMs (especially in TEMs), the temporal coherency effects comes from the small instabilities in the accelerating voltage and electron gun emission over time, which will give the illumination a small energy spread, and from variations in the lens currents, which induces focus variation with time. Because the electrons with different energy are focused at different planes, the total effect of the temporal coherency variations is to create a defocus spread Δ (usually in the order of a few nm) due to the chromatic aberration. Therefore, the temporal coherence affects the overall envelope function.

FEG-TEMs with field-emission electron sources [1 - 2] offering much better spatial and temporal coherence than those offered by CTEMs with LaB6 and W (tungsten) electron guns. Therefore, FEG-TEMs have allowed images to contain much higher spatial frequencies [3 - 4].

 

 

[1] M.T. Otten, W.M.J. Coene, Ultramicroscopy 48 (1–2) (1993) 77–91.
[2] T. Honda, T. Tomita, T. Kaneyama, Y. Ishida, Ultramicroscopy 54 (2–4) (1994) 132–144.
[3] W. Coene, G. Janssen, M. Op de Beeck, D. van Dyck, Phys. Rev. Lett. 69 (1992) 3743–3747.
[4] M. Op de Beeck, D. van Dyck, W. Coene, Ultramicroscopy 64 (1–4) (1996) 167–183.

 

 

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