Fresnel fringes

"Fresnel fringes" are produced in the following manner. A spherical wave scattered from the edge of a specimen interferes with the incident wave. Then, interference fringes are produced whose period becomes narrow with the distance from the edge of the specimen. The fringes produced at the specimen side cannot be seen practically. The fringe produced just outside the specimen appears bright at an underfocus condition of the objective lens, forming clear edge contrast. On the other hand, at an overfocus condition, a black fringe appears which makes the edge of the specimen image unclear. Thus, it is better to take a low-magnification image at an underfocus condition because the edge of the image is clearly seen at the underfocus. In the broad sense, the Fresnel fringe means the interference fringe produced in the region where Fresnel diffraction is applied.


TEM image of molybdenum oxide mounted on a carbon grid taken at an accelerating voltage of 80 kV.Fresnel fringes appear on the edge of the molybdenum oxide and carbon grid.
Since the image is taken at an underfocus condition, the Fresnel fringes produced just outside the specimen are observed bright.

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