A zone plate is a device used to focus light or other things exhibiting wave character. Unlike lenses or curved mirrors however, zone plates use diffraction instead of refraction or reflection. Based on analysis by 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.
A zone plate consists of a set of radially symmetric rings, known as Fresnel zones, which alternate between opaque and transparent. Light hitting the zone plate will diffract around the opaque zones. The zones can be spaced so that the diffracted light constructively interferes at the desired focus, creating an image there.
Read more about Zone Plate: Design and Manufacture
Famous quotes containing the words zone and/or plate:
“Light is meaningful only in relation to darkness, and truth presupposes error. It is these mingled opposites which people our life, which make it pungent, intoxicating. We only exist in terms of this conflict, in the zone where black and white clash.”
—Louis Aragon (1897–1982)
“Our press is certainly bankrupt in the “thrill of awe”Motherwise reverence: reverence for nickel plate and brummagem. Let us sincerely hope that this fact will remain a fact forever; for to my mind a discriminating irreverence is the creator and protector of human liberty.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)