The Pendellösung effect or phenomenon is seen in diffraction in which there is a

beating Beat, beats or beating may refer to: Common uses * Patrol, or beat, a group of personnel assigned to monitor a specific area ** Beat (police), the territory that a police officer patrols ** Gay beat, an area frequented by gay men * Battery ...

in the intensity of electromagnetic waves travelling within a crystal lattice. It was predicted by P. P. Ewald in 1916 and first observed in electron diffraction of

magnesium oxide Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions ...

in 1942. At the exit surface of a

photonic crystal A photonic crystal is an optical nanostructure in which the refractive index changes periodically. This affects the propagation of light in the same way that the structure of natural crystals gives rise to X-ray diffraction and that the atomic ...

(PhC), the intensity of the diffracted wave can be periodically modulated, showing a maximum in the "positive" (forward diffracted) or in the "negative" (diffracted) direction, depending on the crystal slab thickness. The Pendellösung effect in

s can be understood as a beating phenomenon due to the phase modulation between coexisting plane wave components, propagating in the same direction. This thickness dependence is a direct result of the so-called Pendellösung phenomenon, consisting of the periodic exchange inside the crystal of the energy between direct and diffracted beams. The Pendellösung interference effect was predicted by dynamical diffraction and also by its fellow theories developed for visible light.

References

Condensed matter physics Metamaterials Photonics {{CMP-stub