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Interferometry is the science and technique of superposing (interfering) two or more waves, which creates an output wave different from the input waves; this in turn can be used to explore the differences between the input waves. Because interference is a very general phenomenon with waves, interferometry can be applied to a wide variety of fields, including astronomy, fiber optics, optical metrology, oceanography and various studies of quantum mechanics. Interferometry can be applied to both one-dimensional waves such as time varying signals, or to mutli-dimensional waves such as coherent images produced by laser illumination. Image File history File links Information_icon. ...
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Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
A wave is a disturbance that propagates through space or spacetime, often transferring energy. ...
A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ...
Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length by total internal reflection. ...
Metrology (from Greek metron (measure), and -logy) is the science of measurement. ...
Thermohaline circulation Oceanography (from Ocean + Greek γÏάφειν = write), also called oceanology or marine science, is the branch of physical geography that studies the Earths oceans and seas. ...
Fig. ...
Interferometer
An interferometer works on the principle that two waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out, assuming both have the same amplitude. In the beginning, most interferometers used white light sources (e.g., Young's double slit experiment of 1805). Nowadays researchers often use monochromatic light sources like lasers, and even the wave character of matter can be exploited to build interferometers. One of the first examples of matter interferometers were electron interferometers, later followed by neutron interferometers. Around 1990 the first atom interferometers were demonstrated, later followed by interferometers deploying molecules. Currently it is not clear what the maximum particle size for interferometry might be. A wave is a disturbance that propagates through space or spacetime, often transferring energy. ...
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Double-slit diffraction and interference pattern The double-slit experiment consists of letting light diffract through two slits producing fringes or wave-like patterns on a screen. ...
1805 was a common year starting on Tuesday (see link for calendar). ...
A LASER (from the acronym of Light Amplification by Stimulated Emission of Radiation) is an optical source that emits photons in a coherent beam. ...
Overview Interferometry inherently depends on the wave nature of the object. ...
Interferometry inherently depends on the wave nature of the object. ...
An Atom interferometer is an interferometer based on exploiting the wave character of atoms. ...
In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure...
The highest-resolution astronomical images are produced using interferometers (at both optical and radio wavelengths). In order to perform interferometric imaging in optical astronomy at least three telescopes are required (more are preferred). One familiar use of the technique is in radio and optical interferometer telescopes. This article is in need of attention. ...
Types of Interferometers -
There are many other types of interferometers. They all work on the same basic principles, but the geometry is different for the different types. // Field and linear interferometers Fabry-Perot Michelson interferometer Mach-Zehnder interferometer Sagnac interferometer Double-slit interferometer Fourier-transform interferometer Astronomical interferometer / Michelson stellar interferometer Mireau interferometer (also known as a Mireau objective) (microscopy) Multi-beam interferometer (microscopy) Watson interferometer (microscopy) Linnik interferometer (microscopy) Diffraction-grating interferometer (white light) Gires-Tournois...
Michelson Interferometer -
 A Michelson interferometer. A very common example of an interferometer is the Michelson (or Michelson-Morley) type. Here the basic building blocks are a monochromatic source (emitting light or matter waves), a detector, two mirrors and one semitransparent mirror (often called beam splitter). These are put together as shown in the figure. A Michelson interferometer for use on an optical table. ...
interferometer diagram; for wiki by me File links The following pages link to this file: Speed of light Interferometry Categories: GFDL images ...
interferometer diagram; for wiki by me File links The following pages link to this file: Speed of light Interferometry Categories: GFDL images ...
A Michelson interferometer for use on an optical table. ...
A mirror, reflecting a vase. ...
There are two paths from the (light) source to the detector. One reflects off the semi-transparent mirror, goes to the top mirror and then reflects back, goes through the semi-transparent mirror, to the detector. The other first goes through the semi-transparent mirror, to the mirror on the right, reflects back to the semi-transparent mirror, then reflects from the semi-transparent mirror into the detector. A beam splitter is an optical device, that splits a beam of light in two. ...
Spheres reflecting the floor and each other. ...
If these two paths differ by a whole number (including 0) of wavelengths, there is constructive interference and a strong signal at the detector. If they differ by a whole number and a half wavelengths (e.g., 0.5, 1.5, 2.5 ...) there is destructive interference and a weak signal. This might appear at first sight to violate conservation of energy. However energy is conserved, because there is a re-distribution of energy at the detector in which the energy at the destructive sites are re-distributed to the constructive sites. The effect of the interference is to alter the share of the reflected light which heads for the detector and the remainder which heads back in the direction of the source. The wavelength is the distance between repeating units of a wave pattern. ...
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
The interferometer setup shown to the right was used in the famous Michelson-Morley experiment that provided evidence for special relativity. In Michelson's day, the interference pattern was obtained by using a gas discharge lamp, a filter, and a thin slot or pinhole. In one version of the Michelson-Morley experiment, they even ran the interferometer off starlight. Starlight is temporally incoherent light, but since for small instruments it can be considered as a point source of light it is spatially coherent and will produce an interference pattern. The Michelson interferometer finds use not only in these experiments but also for other purposes, e.g., in astronomical interferometers (see astronomical section below) and gravitational wave detectors. The Michelson-Morley experiment, one of the most important and famous experiments in the history of physics, was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University, and is considered by some to be the first strong evidence against the theory of...
The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest...
Albert Abraham Michelson. ...
Edward Morley (1887). ...
Coherence is the property of wave-like states that enables them to exhibit interference. ...
Look up point source in Wiktionary, the free dictionary. ...
A Michelson interferometer for use on an optical table. ...
Diagram showing a possible layout for an astronomical interferometer, with the mirrors laid out in a parabolic arrangement (similar to the shape of a conventional telescope mirror). ...
It has been suggested that Optical interferometry be merged into this article or section. ...
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Mach-Zehnder interferometer
 A Mach--Zehnder interferometer. -
Main article: Mach-Zehnder interferometer Interferometers are perhaps even more widely used in integrated optical circuits, in the form of a Mach-Zehnder interferometer, in which light interferes between two branches of a waveguide that are (typically) externally modulated to vary their relative phase. This interferometer's configuration consists of two beam splitters and two completely reflective mirrors. The source beam is split and the two resulting waves travel down separate paths. A slight tilt of one of the beam splitters will result in a path difference and a change in the interference pattern. The Mach-Zehnder interferometer can be very difficult to align, however this sensitivity adds to its diverse number of applications.[1] The Mach-Zehnder interferometer can be the basis of a wide variety of devices, from RF modulators to sensors to optical switches. Image File history File links Download high resolution version (1085x852, 33 KB) Summary A Mach--Zehnder interferometer. ...
Image File history File links Download high resolution version (1085x852, 33 KB) Summary A Mach--Zehnder interferometer. ...
The Mach-Zehnder interferometer is used to determine the phase shift caused by a small sample which is to be placed into one of the two beams D and U, respectively, from a coherent light source. ...
An integrated optical circuit is one or more circuits composed of solid-state optical components on a semiconductor or dielectric substrate. ...
The Mach-Zehnder interferometer is used to determine the phase shift caused by a small sample which is to be placed into one of the two beams D and U, respectively, from a coherent light source. ...
Look up waveguide in Wiktionary, the free dictionary. ...
In telecommunications, modulation is the process of varying a periodic waveform, i. ...
The Mach-Zehnder interferometer is used to determine the phase shift caused by a small sample which is to be placed into one of the two beams D and U, respectively, from a coherent light source. ...
The Mach-Zehnder interferometer is used to determine the phase shift caused by a small sample which is to be placed into one of the two beams D and U, respectively, from a coherent light source. ...
An RF modulator (for radio frequency modulator) is a small device that takes an input signal and outputs radio frequency-modulated signals. ...
In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits (IOCs) to be selectively switched from one circuit to another. ...
Sagnac interferometer -
A Sagnac Interferometer is an interferometry configuration in which a beam of light is split and the two beams are made to follow a trajectory in opposite directions. To act as a ring the trajectory must enclose an area. On return to the point of entry the light is allowed to exit the apparatus in such a way that an interference pattern is obtained. Image File history File links Schematic representation of a Sagnac interferometer This image is an illustration for the Sagnac effect article. ...
Image File history File links Schematic representation of a Sagnac interferometer This image is an illustration for the Sagnac effect article. ...
The Sagnac effect manifests itself in an experimental setup called ring interferometry. ...
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
In the Sagnac configuration, the position of the interference fringes is dependent on angular velocity of the setup. This dependence is caused by the rotation effectively shortening the path distance of one beams, while lengthening the other. A Sagnac interferometer has been used by Albert Michelson and Henry Gale to determine the angular velocity of the Earth. It can be used in navigation as a ring laser gyroscope, which is commonly found on fighter planes[2]. Angular velocity describes the speed of rotation. ...
Albert Abraham Michelson. ...
Henry Gordon Gale (September 12, 1874 - November 16, 1942) was an American astrophysicist and author. ...
Fabry-Perot interferometer
 A Fabry-Pérot interferometer or etalon -
Main article: Fabry-Perot interferometer A Fabry-Pérot interferometer or etalon is typically made of a transparent plate with two reflecting surfaces, or two parallel highly-reflecting mirrors. (Technically the former is an etalon and the latter is an interferometer, but the terminology is often used inconsistently.) Its transmission spectrum as a function of wavelength exhibits peaks of large transmission corresponding to resonances of the etalon. It is named after Charles Fabry and Alfred Pérot. Image File history File links Diagram of an etalon; File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
Image File history File links Diagram of an etalon; File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
A Fabry-Perot etalon. ...
Spheres reflecting the floor and each other. ...
Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ...
The visible spectrum is the portion of the optical spectrum (light or electromagnetic spectrum) that is visible to the human eye. ...
The wavelength is the distance between repeating units of a wave pattern. ...
Charles Fabry Maurice Paul Auguste Charles Fabry (June 11, 1867 / Marseille, France – December 11, 1945 / Paris, France) was a French physicist. ...
Alfred Perot Jean-Baptiste Alfred Pérot (November 3, 1863 / Metz, France – November 28, 1925 / Paris, France) was a French physicist. ...
Fabry-Pérot interferometers are widely used in telecommunications, lasers and spectroscopy for controlling and measuring the wavelength of light. Recent advances in fabrication technique allow the creation of very precise tunable Fabry-Pérot interferometers. Fabry-Pérot interferometers also form the most common type of optical cavity used in laser construction.
Types of Interferometry
Coherent interferometry Coherent interferometry uses a coherent light source (for example, a helium-neon laser), and can make interference with large difference between the interferometer path length delays. The interference is capable of very accurate (nanometer) measurement by recovering the phase.
One of the most popular methods of interferometric phase recovery is phase-shifting by piezoelectric transducer (PZT) phase-stepping. By stepping the path length by a number of known phases (minimum of three) it is possible to recover the phase of the interference signal, with 2π = λ / 2. Quartz: When a force is applied to the tetrahedon a displacement of the cation charge towards the center of the anion charges occurs Over the past 50 years piezoelectric sensors have proven to be a versatile tool for the measurement of various processes. ...
Coherent interferometry suffers from a 2π ambiguity problem: that is, if between any two measurements the interferometric phase jumps by more than 2π the phase measurement is incorrect. However by combining interferometry results obtained using multiple wavelengths of illumination, such as in digital multi-wavelength holography, the ambiguity interval can be extended to indefinitely large dynamic ranges of measurement.
The applications of coherent interferometry are wide ranging: Nanometer surface profiling, Microfluidics, Mechanical stress/strain, Velocimetry, and high-definition metrology of large parts and assemblies in manufacturing. Microfluidics deals with the behavior, precise control and manipulation of microliter and nanoliter volumes of fluids. ...
High-definition metrology refers to measurment of dimensional or other attributes of a surface or an object in which measurements are made densely across the observable extent of that surface or object, so that the measured attribute of the surface or object can be portrayed (displayed) with high-definition. ...
Inertial navigation In inertial navigation, ring laser gyroscopes are used that can detect rotation through optical interferometry of laser beams travelling around a circumference in opposite directions (Sagnac interferometer). The effect is amplified by using optic fibres wound around thousands of times. An inertial navigation system measures the position and altitude of a vehicle by measuring the accelerations and rotations applied to the systems inertial frame. ...
A ring laser gyroscope uses interference of laser light within a bulk optic ring to detect changes in orientation and spin. ...
The Sagnac effect manifests itself in an experimental setup called ring interferometry. ...
Speckle Interferometry -
In optical systems, a speckle pattern is a field-intensity pattern produced by the mutual interference of partially coherent beams that are subject to minute temporal and spatial fluctuations. This speckling effect is most commonly observed in the fields of fiber optics and astronomical speckle imaging. In optical systems, a speckle pattern is a field-intensity pattern produced by the mutual interference of partially coherent beams that are subject to minute temporal and spatial fluctuations. ...
Speckle imaging (also known as video astronomy) describes a range of high-resolution astronomical imaging techniques based either on the shift-and-add (image stacking) method or on speckle interferometry methods. ...
Holography A special application of optical interferometry using coherent light is holography, a technique for photographically recording and re-displaying three-dimensional scenes. The technique also lends itself to monitoring small deformations in single wavelength implementations as well as dimesional metrology of large parts and assemblies and larger surface defect detection when used in multi-wavelength implementations.. 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. ...
Low-coherence interferometry Low-coherence interferometry utilizes a light source with low temporal coherence such as white light (for example, LED/SLD, halogen lamp) or high specification femtosecond lasers. Interference will only be achieved when the path length delays of the interferometer are matched within the coherence time of the light source (note: using a femtosecond source is somewhat more intricate).
The chief benefit of low-coherence interferometry is that it does not suffer from the 2π ambiguity of coherent interferometry, and is therefore suited to profiling steps and rough surfaces. The axial resolution of the system is determined by the coherence length of the light source and is typically in the micrometer range.
Optical coherence tomography is a medical imaging technique based in low-coherence interferometry, where subsurface light reflections are resolved to give tomographic visualization. Recent advances have striven to combine the nanometer phase retrieval with the ranging cabability of low-coherence interferometry. Optical coherence tomography (OCT) is an interferometric, non-invasive optical tomographic imaging technique offering millimeter penetration (approximately 2--3 mm in tissue) with sub-micrometre axial and lateral resolution. ...
Geodetic standard baseline measurements A famous use of white light interferometry is the precise measurement of geodetic standard baselines as invented by Yrjö Väisälä. Here, the light path is split in two, and one leg is "folded" between a mirror pair 1 m apart. The other leg bounces once off a mirror 6 m away. Only if the second path is precisely 6 times the first, will fringes be seen. Yrjö Väisälä (IPA: ) (September 6, 1891 - July 21, 1971) was a Finnish astronomer and physicist. ...
Starting from a standard quartz gauge of 1 m length, it is possible to measure distances up to 864 m by repeated multiplication. Baselines thus established are used to calibrate geodetic distance measurement equipment on, leading to a metrologically traceable scale for geodetic networks measured by these instruments. Quartz is one of the most common minerals in the Earths continental crust. ...
It has been suggested that geodetic system be merged into this article or section. ...
Metrology (from Greek metron (measure), and -logy) is the science of measurement. ...
A geodetic network is a network of triangles which are measured exactly by techniques of terrestrial surveying or by satellite geodesy. ...
More modern geodetic applications of laser interferometry are in calibrating the divisions on levelling staffs, and in monitoring the free fall of a reflective prism within a ballistic or absolute gravimeter, allowing determination of gravity, i.e., the acceleration of free fall, directly from the physical definition at a few parts in a billion accuracy. In construction, level (as an adjective) is to horizontal what plumb is to vertical. ...
Free fall in its strictest sense is the condition of acceleration which is due only to gravity. ...
Astronomical Interferometry In astronomy (such as with the Keck telescopes), interferometry is used to combine signals from two or more telescopes to obtain measurements with higher resolution than could be obtained with either telescopes individually. This technique is the basis for astronomical interferometer arrays, which can make measurements of very small astronomical objects if the telescopes are spread out over a wide area. If a large number of telescopes are used a picture can be produced which has resolution similar to a single telescope with the diameter of the combined spread of telescopes. These include radio telescope arrays and more recently astronomical optical interferometer arrays such as COAST, NPOI and IOTA, resulting in the highest resolution optical images ever achieved in astronomy. The VLT Interferometer is expected to produce its first images using aperture synthesis soon, followed by other interferometers such as the CHARA array and the Magdalena Ridge Observatory Interferometer which may consist of up to 10 optical telescopes. If outrigger telescopes are built at the Keck Interferometer, it will also become capable of interferometric imaging. Diagram showing a possible layout for an astronomical interferometer, with the mirrors laid out in a parabolic arrangement (similar to the shape of a conventional telescope mirror). ...
A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ...
The W. M. Keck Observatory is home to the two largest optical/near-infrared telescopes at the 4,145 meter (13,600 ft) summit of Mauna Kea in Hawaii. ...
50 cm refracting telescope at Nice Observatory. ...
Diagram showing a possible layout for an astronomical interferometer, with the mirrors laid out in a parabolic arrangement (similar to the shape of a conventional telescope mirror). ...
Angular resolution describes the resolving power of any optical device such as a telescope, a microscope, a camera, or an eye. ...
50 cm refracting telescope at Nice Observatory. ...
The 64 metre radio telescope at Parkes Observatory The Very Large Array, an interferometric array formed from many smaller telescopes, like many larger radio telescopes. ...
This article is in need of attention. ...
COAST. the Cambridge Optical Aperture Synthesis Telescope, is a multi-element optical interferometer with baselines of up to 100 metres, designed to observe stars with angular resolution as high as one thousandth of one arcsecond (much higher resolution than can be obtained with individual telescopes such as the Hubble Space...
The Navy Prototype Optical Interferometer (NPOI) is an interferometer operated by the US Naval Observatory, the Naval Research Laboratory and The Lowell Observatory. ...
The Infrared Optical Telescope Array (IOTA) began with an agreement in 1988 among five Institutions, the Smithsonian Astrophysical Observatory, Harvard University, the University of Massachusetts, the University of Wyoming, and MIT/Lincoln Laboratory, to build a two-telescope stellar interferometer for the purpose of making fundamental astrophysical observations, and also...
One of the four telescopes that make up the VLT, named Kueyen. ...
Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. ...
The CHARA Array is an astronomical optical interferometer operated by The Center for High Angular Resolution Astronomy (CHARA) at Georgia State University. ...
The Magdalena Ridge Observatory Interferometer will be an optical array composed of ten telescopes, each approximately 1. ...
This article needs to be wikified. ...
Astronomical interferometers come in two types -- direct detection and heterodyne. These differ only in the way that the signal is transmitted. Aperture synthesis can be used to computationally simulate a large telescope aperture from either type of interferometer. Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. ...
Astronomical direct-detection interferometry
 A simple two-element optical interferometer.
 A single large telescope with an aperture mask over it (labelled Mask), only allowing light through two small holes. One of the first astronomical interferometers was built on the Mount Wilson Observatory's reflector telescope in order to measure the diameters of stars. This method was extended to measurements using separated telescopes by Johnson, Betz and Towns (1974) in the infrared and by Labeyrie (1975) in the visible. The red giant star Betelgeuse was among the first to have its diameter determined in this way. In the late 1970's improvements in computer processing allowed for the first "fringe-tracking" interferometer, which operates fast enough to follow the blurring effects of astronomical seeing, leading to the Mk I, II and III series of interferometers. Similar techniques have now been applied at other astronomical telescope arrays, including the Keck Interferometer and the Palomar Testbed Interferometer. Download high resolution version (382x759, 13 KB)A two-element optical interferometer which is optically identical to this telescope with an aperture mask Picture from my project. ...
Download high resolution version (382x759, 13 KB)A two-element optical interferometer which is optically identical to this telescope with an aperture mask Picture from my project. ...
Download high resolution version (306x637, 9 KB) A telescope with a mask covering it allowing light through two holes. ...
Download high resolution version (306x637, 9 KB) A telescope with a mask covering it allowing light through two holes. ...
a) shows a simple experiment using an aperture mask in a re-imaged aperture plane. ...
Diagram showing a possible layout for an astronomical interferometer, with the mirrors laid out in a parabolic arrangement (similar to the shape of a conventional telescope mirror). ...
The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California. ...
Betelgeuse (Alpha (α) Orionis) (also written Betelguese and Betelgeux) is a semiregular variable star located 427 light-years away [1]. It is the second brightest star in the constellation Orion, and the ninth brightest star in the night sky. ...
Schematic diagram illustrating how optical wavefronts from a distant star may be perturbed by a turbulent layer in the atmosphere. ...
This article needs to be wikified. ...
The Palomar Testbed Interferometer is a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. ...
Techniques from Very Long Baseline Interferometry (VLBI), in which a large aperture is synthesized computationally, were implemented at optical and infrared wavelengths in the 1980s by the Cavendish Astrophysics Group. This providing the first very high resolution images of nearby stars. In 1995 this technique was demonstrated on an array of separate optical telescopes as a Michelson Interferometer for the first time, allowing a further improvement in resolution, and allowing even higher resolution imaging of stellar surfaces. The same technique has now been applied at a number of other astronomical telescope arrays, including the Navy Prototype Optical Interferometer and the IOTA array and soon the VLTI, CHARA and MRO Interferometers. This article needs cleanup. ...
Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. ...
The Cavendish Astrophysics Group (formerly the Radio Astronomy Group) is based at the Cavendish Laboratory at Cambridge University. ...
COAST, the Cambridge Optical Aperture Synthesis Telescope, is a multi-element optical interferometer with baselines of up to 100 metres, designed to observe stars with angular resolution as high as one thousandth of one arcsecond (much higher resolution than can be obtained with individual telescopes such as the Hubble Space...
The Navy Prototype Optical Interferometer (NPOI) is an interferometer operated by the US Naval Observatory, the Naval Research Laboratory and The Lowell Observatory. ...
The Infrared Optical Telescope Array (IOTA) began with an agreement in 1988 among five Institutions, the Smithsonian Astrophysical Observatory, Harvard University, the University of Massachusetts, the University of Wyoming, and MIT/Lincoln Laboratory, to build a two-telescope stellar interferometer for the purpose of making fundamental astrophysical observations, and also...
The four telescopes of the European Southern Observatory Paranal site. ...
The CHARA Array is an astronomical optical interferometer operated by The Center for High Angular Resolution Astronomy (CHARA) at Georgia State University. ...
The Magdalena Ridge Observatory Interferometer will be an optical array composed of ten telescopes, each approximately 1. ...
Projects are now beginning that will use interferometers to search for extrasolar planets, either by astrometric measurements of the reciprocal motion of the star (as used by the Palomar Testbed Interferometer and the VLTI) or through the use of nulling (as will be used by the Keck Interferometer and Darwin). Infrared Image of a possible extrasolar planet (lower left) in the Constellation Taurus, taken by the Hubble Space Telescope. ...
The Palomar Testbed Interferometer is a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. ...
The four telescopes of the European Southern Observatory Paranal site. ...
This article needs to be wikified. ...
Darwin is a proposed European Space Agency (ESA) mission designed to directly detect Earth-like planets orbiting nearby stars, and search for evidence of life on these planets. ...
A detailed description of the development of astronomical optical interferometry can be found here. Impressive results were obtained in the 1990s, with the Mark III measuring diameters of 100 stars and many accurate stellar positions, COAST and NPOI producing many very high resolution images, and ISI measuring stars in the mid-infrared for the first time. Additional results include direct measurements of the sizes of and distances to Cepheid variable stars, and young stellar objects. COAST. the Cambridge Optical Aperture Synthesis Telescope, is a multi-element optical interferometer with baselines of up to 100 metres, designed to observe stars with angular resolution as high as one thousandth of one arcsecond (much higher resolution than can be obtained with individual telescopes such as the Hubble Space...
The Navy Prototype Optical Interferometer (NPOI) is an interferometer operated by the US Naval Observatory, the Naval Research Laboratory and The Lowell Observatory. ...
The Infrared Spatial Interferometer (ISI) is an astronomical interferometer array of three 65 inch (1. ...
A Cepheid variable is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute stellar luminosity. ...
Interferometers are mostly seen by astronomers as very specialized instruments, capable of a very limited range of observations. It is often said that an interferometer achieves the effect of a telescope the size of the distance between the apertures; this is only true in the limited sense of angular resolution. The combined effects of limited aperture area and atmospheric turbulence generally limit interferometers to observations of comparatively bright stars and active galactic nuclei. However, they have proven useful for making very high precision measurements of simple stellar parameters such as size and position (astrometry) and for imaging the nearest giant stars. Angular resolution describes the resolving power of any optical device such as a telescope, a microscope, a camera, or an eye. ...
An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ...
This article does not cite its references or sources. ...
Giant star is a star that has stopped fusing hydrogen in its core. ...
For details of individual instruments, see the list of astronomical interferometers at visible and infrared wavelengths. This article or section does not cite its references or sources. ...
Astronomical heterodyne interferometry Radio wavelengths are much longer than optical wavelengths, and the observing stations in radio astronomical interferometers are correspondingly further apart. The very large distances do not always allow any usable transmission of radio waves received at the telescopes to some central interferometry point. For this reason many telescopes instead record the radio waves onto a storage medium. The recordings are then transferred to a central correlator station where the waves are interfered. Historically the recordings were analog and were made on magnetic tapes. This was quickly superseded by the current method of digitizing the radio waves, and then either storing the data onto computer hard disks for later shipping, or streaming the digital data directly over a telecommunications network e.g. over the Internet to the correlator station. Radio arrays with a very broad bandwidth, and also some older arrays, transmit the data in analogue form either electrically or through fibre-optics. A similar approach is also used at some submillimetre and infrared interferometers, such as the Infrared Spatial Interferometer. Some early radio interferometers operated as intensity interferometers, transmitting measurements of the signal intensity over electrical cables to a central correlator. A similar approach was used at optical wavelengths by the Narrabri Stellar Intensity Interferometer to make the first large-scale survey of stellar diameters in the 1970s. Submillimetre Astronomy is the branch of observational astronomy that is conducted at submillimetre wavelengths. ...
Image of two girls in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ...
The Infrared Spatial Interferometer (ISI) is an astronomical interferometer array of three 65 inch (1. ...
An intensity interferometer is the name given to devices that use the Hanbury-Brown and Twiss effect. ...
The Narrabri Stellar Intensity Interferometer was the first astronomical instrument to measure the diameters of a large number of stars at visible wavelengths. ...
At the correlator station, the actual interferometer is synthesized by processing the digital signals using correlator hardware or software. Common correlator types are the FX and XF correlators. The current trend is towards software correlators running on consumer PCs or similar commodity hardware. There also exist some radio astronomy amateur digital interferometers with correlator, such as the ALLBIN of the European Radio Astronomy Club.
As the usual radio astronomy interferometer is digital it does have a few shortcomings, some due to sampling and quantization effects, in addition to the obvious need for much more computing power, as compared to analog correlation. The output of both digital and analog correlator can be used to computationally synthesize the interferometer aperture in the same way as with direct detection interferometers (see above). Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. ...
References - John E. Baldwin and Chris A. Haniff. "The application of interferometry to optical astronomical imaging." Phil. Trans. A, 360, 969-986, 2001. (download PostScript file)
- J. E. Baldwin, "Ground-based interferometry — the past decade and the one to come" in Interferometry for Optical Astronomy II, volume 4838 of Proc. SPIE, page 1. 22-28 August 2002, Kona, Hawaii, SPIE Press, 2003. (download PostScript file)
- J. D. Monnier, Optical interferometry in astronomy, Reports on Progress in Physics, 66, 789-857, 2003 IoP. (download PDF file)
- P. Hariharan, Optical Interferometry, 2nd edition, Academic Press, San Diego, USA, 2003.
- Adolf F. Fercher, Wolfgang Drexler, Christoph K. Hitzenberger and Theo Lasser, "Optical coherence tomography — principles and applications," Reports on Progress in Physics vol. 66, no. 2, pp. 239-303, 2003. Available: iop.org.
- E. Hecht, Optics, 2nd Edition, Addison-Wesley Publishing Co., Reading, Mass, USA, 1987.
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Books - Basics of Interferometry, 2E by P. Hariharan Outstanding introduction to the world of optical interferometry with summaries at the beginning and end of each chapter, several appendices with essential information, and worked numerical problems / Practical details enrich understanding for readers new to this material / New chapters on white-light microscopy for medical imaging and interference with single photons(quantum optics)
See also This article or section does not cite its references or sources. ...
Diagram showing a possible layout for an astronomical interferometer, with the mirrors laid out in a parabolic arrangement (similar to the shape of a conventional telescope mirror). ...
Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. ...
William Herschel knew as early as 1779 (Herschel 1805) that stars appeared much larger in telescopes than they really were but he did not know why. ...
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...
Very Long Baseline Interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy, in which the data received at each antenna in the array is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. ...
Optical coherence tomography (OCT) is an interferometric, non-invasive optical tomographic imaging technique offering millimeter penetration (approximately 2--3 mm in tissue) with sub-micrometre axial and lateral resolution. ...
// Field and linear interferometers Fabry-Perot Michelson interferometer Mach-Zehnder interferometer Sagnac interferometer Double-slit interferometer Fourier-transform interferometer Astronomical interferometer / Michelson stellar interferometer Mireau interferometer (also known as a Mireau objective) (microscopy) Multi-beam interferometer (microscopy) Watson interferometer (microscopy) Linnik interferometer (microscopy) Diffraction-grating interferometer (white light) Gires-Tournois...
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