Editing Zone plate (section)

{{Short description|Device used to focus light using diffraction}}
[[Image:Zone plate.svg|right|thumb|210px|Binary zone plate: The areas of each ring, both light and dark, are equal.]]
[[Image:Zonenplatte Cosinus.png|right|thumb|210px|Sinusoidal zone plate: This type has a single focal point.]]

A '''zone plate''' is a device used to [[Focus (optics)|focus]] light or other things exhibiting wave character.<ref name="wmm">G. W. Webb, I. V. Minin and O. V. Minin,  “Variable Reference Phase in Diffractive Antennas”,  ''IEEE Antennas and Propagation Magazine'', vol. 53, no. 2, April. 2011, pp. 77-94.</ref>  Unlike [[lens (optics)|lenses]] or [[curved mirror]]s, zone plates use [[diffraction]] instead of [[refraction]] or [[Specular reflection|reflection]].  Based on analysis by French physicist [[Augustin-Jean Fresnel]], they are sometimes called '''Fresnel zone plates''' in his honor. The zone plate's focusing ability is an extension of the [[Arago spot]] phenomenon caused by diffraction from an opaque disc.<ref>{{ Citation | last = Wood | first = Robert Williams | author-link = Robert Williams Wood | date = 1911 | title = Physical Optics | publisher = The MacMillan Company | place = New York | pages = 37–39 | url = https://books.google.com/books?id=xxtLAAAAYAAJ&q=wood+physical+optics+%22zone+plate%22&pg=PA39 }}</ref>

A zone plate consists of a set of concentric rings, known as [[Fresnel zone]]s, which alternate between being [[opacity (optics)|opaque]] and [[transparency (optics)|transparent]]. Light hitting the zone plate will diffract around the opaque zones. The zones can be spaced so that the diffracted light constructively [[interference (wave propagation)|interferes]] at the desired focus, creating an [[Real image|image]] there.