Interference Width in Off-axis Hologram
- Practical Electron Microscopy and Database -
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As shown in Figure 2557, in off-axis electron holography, the two parts of the electron beam originate equivalently from two sources, S1 and S2, induced by the biprism, as in the standard Young’s experiment.

schematic diagram of off-axis electron holography in transmission electron microscope

Figure 2557. Schematic diagram of off-axis electron holography in TEMs.

The interference width in the hologram, W, can be given by [1],

           interference width in the hologram ----------------------- [2557a]

where,
           α -- The deflection angle of the ray due to the action of the biprism,
           a -- The distance of the back focal plane of the objective lens to the biprism,
           R -- The radius of the biprism wire.

On the other hand, the width can also be given by, [2]

           interference width in the hologram ----------------------- [2557b]
where,
           UF -- The biprism voltage,
           f -- The focal length,
           γ0UF -- The deflection angle at the biprism filament. [3]

Practically, the width W of the hologram is limited by the coherent current of the electron beam and by the strength of excitation of the subsequent intermediate lens. [2]

 

 

 

 

 

[1] Missiroli, G.F., Pozzi, G., Valdre, U., 1981. Electron interferometry and interference electron microscopy. J. Phys. E 14, 649–671.
[2] Michael Lehmann, and Hannes Lichte, Tutorial on Off-Axis Electron Holography, Microsc. Microanal. 8, 447–466, 2002.
[3] Lichte, H. (1991). Electron image plane off-axis holography of atomic structures. Adv Optical Electron Microsc 12, 25–91.

 

 

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