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TEM Basics

 
Diffraction at an aperture
    D
 

Diffraction at an aperture (leading to Airy rings) limits the resolution of many optical systems.

Use the simulation to show that the size of the central disc of illumination varies inversely with the size of the aperture (W).

where

(q is the angular deflection of the beam at the aperture.)

16% of the intensity (electrons in the TEM) falls outside the central disc. Adjust the brightness in the simulation to see how low the intensity of the rings is compared to that of the central disc. The Rayleigh criterion for resolution indicates how close together two points can be brought together before they can no longer be distinguished as separate.

If you are feeling ambitious, calculate how much of the intensity lies in the second Airy ring and beyond (i.e. not the central spot or the first ring).

 
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