evolved Laser Interferometer Space Antenna (eLISA)
A space project, initially → LISA, consisting of a configuration of three satellites, aimed to detect low frequency → gravitational waves that cannot be measured by ground-based detectors. The detection range will be from about 0.1 milliHz to 1 Hz. One "mother" and two "daughter" spacecrafts will be brought into an orbit around the Sun, which is similar to the Earth's orbit. The satellites will fly in a near-equilateral triangle formation, with a constant distance of one million km between, following the Earth along its orbit at a distance of around 50 million km. The mother spacecrafts carries two and each of the daughter spacecraft carry one free-flying → test masses that will be kept as far as possible free of external disturbances. The mutual distances of the test masses from satellite to satellite will be measured by means of high-precision, → Michelson-like laser → interferometry. In this way, the extremely small distance variations between the test masses of two satellites can be detected which are caused by the passages of a gravitational waves. The required measurement accuracy of the distances amounts to typically 1/100 of the diameter of a hydrogen atom (10-12 m) at a distance of two million km.
Fr.: interféromètre Fabry-Pérot
A type of interferometer wherein the beam of light undergoes multiple reflections between two closely spaced partially silvered surfaces. Part of the light is transmitted each time the light reaches the second surface, resulting in multiple offset beams which can interfere with each other. The large number of interfering rays produces an interferometer with extremely high resolution, somewhat like the multiple slits of a diffraction grating increase its resolution.
The design was conceived by French physicists Charles Fabry (1867-1945) and Alfred Pérot (1863-1925) in the late nineteenth century; → interferometer.
Fr.: interféromètre hétérodyne
An → interferometer using a technique that involves introducing a small → frequency shift between the optical frequencies of the two interfering light beams. This results in an intensity modulation at the → beat frequency of the two beams for any given point of the → interference pattern. A convenient way of introducing such a frequency shift is by means of an acousto-optic modulator.
1) Physics: A device that divides a beam of light into a number of
beams and re-unites them to produce → interference.
→ Fabry-Perot interferometer;
→ Michelson interferometer.
Fr.: interféromètre laser
An optical instrument using laser → beams to form → interference pattern. There are two types of laser interferometers: → homodyne and → heterodyne. A homodyne interferometer, like → Michelson interferometer, uses a single-frequency laser source. A → heterodyne interferometer uses a laser source with two close frequencies.
Laser Interferometer Gravitational-Wave Observatory (LIGO)
nepâhešgâh-e mowjhâ-ye gerâneši bâ andarzaneš-sanji-ye leyzeri
Fr.: Observatoire d'ondes gravitationnelles par interférométrie laser
A facility dedicated to the detection and measurement of cosmic → gravitational waves. It consists of two widely separated installations, or detectors, within the United States, operated in unison as a single observatory. One installation is located in Hanford (Washington) and the other in Livingston (Louisiana), 3,000 km apart. Funded by the National Science Foundation (NSF), LIGO was designed and constructed by a team of scientists from the California Institute of Technology, the Massachusetts Institute of Technology, and by industrial contractors. Construction of the facilities was completed in 1999. Initial operation of the detectors began in 2001. Each LIGO detector beams laser light down arms 4 km long, which are arranged in the shape of an "L." If a gravitational wave passes through the detector system, the distance traveled by the laser beam changes by a minuscule amount -- less than one-thousandth of the size of an atomic nucleus (10-18 m). Still, LIGO should be able to pick this difference up. LIGO directly detected gravitational waves for the first time from a binary → black hole merger (GW150914) on September 14, 2015 (Abbott et al., 2016, Phys. Rev. Lett. 116, 061102). The Nobel Prize in physics 2017 was awarded to three physicists (Rainer Weiss, Barry C. Barish, and Kip S. Thorne) for decisive contributions to the LIGO detector and the observation of gravitational waves. LIGO had a prominent role in the detection of → GW170817, the first event with an → electromagnetic counterpart.
Laser Interferometer Space Antenna (LISA)
ânten-e fezâyi-e andarzanešsanj-e leyzeri
Fr.: Observatoire d'ondes gravitationnelles par interférométrie laser
A collaborative project between → NASA and → ESA to develop and operate a space-based gravitational wave detector sensitive at frequencies between 0.03 mHz and 0.1 Hz. LISA detects gravitational-wave induced strains in → space-time by measuring changes of the separation between fiducial masses in three spacecraft 5 million km apart. Ultimately, NASA and ESA decided in 2011 not to proceed with the mission. LISA was not the highest ranked mission in the 2010 Decadal Survey and funding constraints prevented NASA from proceeding with multiple large missions (http://lisa.nasa.gov). → LISA pathfinder.
Fr.: Interféromètre de Michelson
An apparatus that produces interference fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are brought back together, an interference pattern results. It is used to measure very precise lengths, such as the wavelength of light, and for high-resolution spectroscopy.
Andarzanešsanj, → interferometer.
Fr.: interféromètre radio
An → interferometer designed for radio frequencies.
Fr.: interféromètre Virgo
A → Michelson interferometer using → laser beams designed to detect → gravitational waves. It consists of two 3-km-long arms, which house the various machinery required to form a → laser interferometer. The gravitational waves searched for have frequencies between 10 Hz and 10 kHz. Virgo has been designed and built by a collaboration between the French Centre National de la Recherche Scientifique (CNRS) and the Italian Istituto Nazionale di Fisica Nucleare (INFN). It is now operated and improved in Cascina, a small town near Pisa on the site of the European Gravitational Observatory (EGO), by an international collaboration of scientists from France, Italy, the Netherlands, Poland, and Hungary. The initial Virgo detector observed the sky between 2007 and 2011 together with the two interferometers of the → Laser Interferometer Gravitational-Wave Observatory (LIGO), located in the United States. Virgo underwent a major upgrade after a long shutdown period. The "Advanced Virgo" overhaul lasted 5-year and costed 23 million Euros. The upgraded observatory was inaugurated on 20 February 2017 and, notably, detected the → GW170817 event.
VLT Interferometer (VLTI)
Fr.: interféromètre VLTI
An interferometer using a combination of the four 8.2 m VLT telescopes with the assistance of one or more of the the four 1.8 m Auxiliary Telescopes in order to achieve a very high spatial resolution. The system works in the visible and near- and mid-infrared wavelengths.