Editing Bloch's theorem (section)

=== Applicability ===
The most common example of Bloch's theorem is describing electrons in a crystal, especially in characterizing the crystal's electronic properties, such as electronic band structure. However, a Bloch-wave description applies more generally to any wave-like phenomenon in a periodic medium. For example, a periodic [[dielectric]] structure in [[electromagnetism]] leads to [[photonic crystal]]s, and a periodic acoustic medium leads to [[phononic crystal]]s. It is generally treated in the various forms of the [[dynamical theory of diffraction]].