 Binary zone plate: The areas of each ring, both light and dark, are equal.
 Sinusoidal zone plate: This type has a single focal point. A zone plate is a device used to focus light. Unlike lenses however, zone plates use diffraction instead of refraction. Created 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. Image File history File links This is a lossless scalable vector image. ...
Image File history File links This is a lossless scalable vector image. ...
Image File history File links Download high resolution version (1000x1000, 296 KB) Description: Frenels zone plate with sinusoidal transparency. ...
Image File history File links Download high resolution version (1000x1000, 296 KB) Description: Frenels zone plate with sinusoidal transparency. ...
An image that is partially in focus, but mostly out of focus in varying degrees. ...
A lens. ...
The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ...
The straw seems to be broken, due to refraction of light as it emerges into the air. ...
Augustin Fresnel Augustin-Jean Fresnel (pronounced [] in AmE (or fray-NELL), [] in French) (May 10, 1788 – July 14, 1827), was a French physicist who contributed significantly to the establishment of the theory of wave optics. ...
In optics, an Arago spot is a bright point which appears at the center of the shadow of a circular object in light from a point source. ...
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. Zone plates produce equivalent diffraction patterns no matter whether the central disk is opaque or transparent, as long as the zones alternate in opacity. Symmetry is a characteristic of geometrical shapes, equations and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ...
In optics and radio communications, a Fresnel zone (pronounced as FRA-nel Zone), named for physicist Augustin-Jean Fresnel, is one of a (theoretically infinite) number of a concentric ellipsoids of revolution which define volumes in the radiation pattern of a (usually) circular aperture. ...
A substance or object that is opaque is neither transparent nor translucent. ...
Transparent glass ball In optics, transparency is the property of allowing light to pass. ...
The intensity pattern formed on a screen by diffraction from a square aperture Diffraction refers to various phenomena associated with wave propagation, such as the bending, spreading and interference of waves passing by an object or aperture that disrupts the wave. ...
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
Design and manufacture To get constructive interference at the focus, the zones should switch from opaque to transparent at radii where  where n is an integer, λ is the wavelength of the light the zone plate is meant to focus and f is the distance from the center of the zone plate to the focus. When the zone plate is small compared to the focal length, this can be approximated as The integers are commonly denoted by the above symbol. ...
The wavelength is the distance between repeating units of a wave pattern. ...
 . For plates with many zones, you can calculate the distance to the focus if you only know the radius of the outermost zone, r N, and its width, Δ rN:  In order to get complete constructive interference at the focus, the amplitude of the diffracted light waves from each zone in the zone plate must be the same. This means that for an evenly illuminated zone plate, the area of each zone is equal. Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation, that is, magnitude of the maximum disturbance in the medium during one wave cycle. ...
Because the area of each zone is equal, the width of the zones must decrease farther from the center. The maximum possible resolution of a zone plate depends on the smallest zone width, Angular resolution describes the resolving power of any optical device such as a telescope, a microscope, a camera, or an eye. ...
 Because of this, the smallest size object you can image, Δl, is limited by how small you can reliably make your zones.
Zone plates are frequently manufactured using lithography. As lithography technology improves and the size of features that can be manufactured decreases, the possible resolution of zone plates manufactured with this technique can improve. Photolithography is a process used in semiconductor device fabrication to transfer a pattern from a photomask (also called reticle) to the surface of a substrate. ...
Unlike a standard lens, a zone plate produces subsidiary intensity maxima along the axis of the plate at odd fractions (f/3, f/5, f/7, etc.), though these are less intense than the principal focus.
If the zone plate can be constructed such that the opacity varies in a gradual, sinusoidal manner, the resulting diffraction causes only a single focal point to be formed. This type of zone plate pattern is the equivalent of a transmission hologram of a converging lens. Holography (from the Greek, Όλος-holos whole + γÏαφή-graphe writing) is the science of producing holograms; it is an advanced form of photography that allows an image to be recorded in three dimensions. ...
Applications
Physics There are many wavelengths of light outside of the visible area of the electromagnetic spectrum where traditional lens materials like glass are not transparent, and so lenses are more difficult to manufacture. Likewise, there are many wavelengths for which there are no materials with a refractive index significantly larger than one. X-rays, for example, are not refracted by glass or other materials, and so require a different technique for focusing. Zone plates eliminate the need for finding transparent, refractive, easy-to-manufacture materials for every region of the spectrum. The same zone plate will focus light of many wavelengths to different foci, which means they can also be used to filter out unwanted wavelengths while focusing the light of interest. The wavelength is the distance between repeating units of a wave pattern. ...
Legend: γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves: EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High...
A lens. ...
Transparent glass ball In optics, transparency is the property of allowing light to pass. ...
The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ...
In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...
In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ...
Photography Zone plates are also used in photography in place of a lens or pinhole for a glowing, soft-focus image. One advantage over pinholes (aside from the unique, fuzzy look achieved with zone plates) is that the transparent area is larger than that of a comparable pinhole. The result is that the effective f-number of a zone plate is lower than for the corresponding pinhole and the exposure time can be decreased. Photography is the process of making pictures by means of capturing light on a light-sensitive medium, such as a sensor or film. ...
Photographic lens One of Canons most popular wide angle lenses - 17-40 f/4 L The zoom lens of the Canon Elph A photographic lens (or more correctly, objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images...
Principle of a pinhole camera. ...
A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ...
A photograph with an exposure time of 25 seconds A photograph of a night-time sky with an exposure time of 8 seconds. ...
Video Printed photographs of zone plates are often used in evaluating the performance of television cameras and color television encoders and decoders. The continuously varying patterns of dark and light represent the very worst-case condition for cross color artifacts, (also known as "strobing"), producing a striking pattern of flickering color interference on an otherwise black and white image. Electronically generated zone plate patterns are also available as DVD recordings.
See also Fresnel Lens displayed in the Musée national de la marine in Paris, France A Fresnel lens is a type of lens invented by Augustin-Jean Fresnel (pronounced fre-NELL in scientific and lighting applications, although often incorrectly pronounced FREZ-nell). ...
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