Circular Functions/Aperture Function 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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A point object produces a spherical wavefront with a uniform amplitude distribution. After passing through a system, the wavefront is cut by the circular edge of the aperture, and the distribution A(x,y) is given by a circular function defined by,

         Circular Functions in EMs ---------------- [3746a]

where,

          ρ is the radius of the aperture.

If the system is an objective aperture in EMs, the circular function (sometimes called aperture function) is given by

         Circular Functions in EMs ---------------- [3746b]

where,

          α -- The semi angle subtended by the objective aperture.

For practical HRTEM imaging, a sufficiently large objective aperture is normally used such that no loss of imaging information originates from the aperture and the effect of circular function, A(k), can be ignored.

 

 

 

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