Interferometry
The Interférométrie is a method of measurement which exploits the Interférence S intervening between several Onde S coherent between them.
Examples of applications
Interferometry is used in Astronomie as well with Télescope S optics as with Radiotélescope S. Its advantage is to allow a resolution equivalent to that of a mirror (or radio telescope) of diameter equivalent to the difference between the combined instruments. The contrast of the fringes then makes it possible to obtain information on the size of the object observed or the angular Séparation between two objects observed (for example, a system star - Planet). This method was initially developed by the French Antoine Labeyrie in the years 1970.
One usually uses interferometers seeks some in many fields of physics. For example, of the interferometers of Michelson allowed to carry out the Expérience of interferometry of Michelson and Morley which showed that the Speed of light is Isotrope and independent of the reference frame, and who could invalidate the assumption of the ether. Attempts to detect the gravitational waves (as the project VIRGO) also use it.
The measurements taken with interferometers often depend on the Wavelength. One thus makes use of it in Spectrométrie to determine the luminous Specter of various sources of light.
Interferometry is also used to estimate the quality of optics. Indeed in certain applications, optics used should not have " défauts" (i.e.: no stripes, bumps,…), indeed, thanks to the figure of interference obtained one can detect the defects of glass for thus correcting them.
Interferometers are used in the scientific formation in the field of the Optique.
Interferometry is also used in the field of underwater acoustics: there exist SONARs by interferometry.
Some interferometers
Interferometers with division of the wave front
One speaks about interferometer with division of the wave front when the waves interfering between them come from various points of the wave.The simplest way of carrying out interferences is to use Fentes of Young which are simply two slits side-by-side. They make it possible to divide the beam of light into two, to then make them interfere (an example of image obtained is given opposite).
A optical Réseau consists of a series of slits. It is thus, to some extent, a generalization of the slits of Young, because the beam of light is divided into many parts which interfere between them. It is seldom considered however that it constitutes with him only an interferometer, but one can make use of it in apparatuses such as the Goniomètre.
Interferometers with division of amplitude
One speaks about interferometer with division of amplitude when the waves interfering between them come from division in several beams of the amplitude of the wave on all its surface. These interferometers are often of better quality, and are thus used in measurements of optics of precision.The principle of a Interféromètre of Michelson is to divide the beam of incidental light into two, then to dephase a beam compared to the other, and finally to make them interfere: they are interferences with two waves.
The Interféromètre of Mach-Zehnder and the interferometer of Sagnac function on the same principle that the precedent, but their design is different.
A Interféromètre of Fabry-Pérot consists of two parallel blades between which the light carries out return tickets, and the weak fractions which come out from it with each return ticket interfere between them: they are interferences with multiple waves.
The Prisme of Wollaston can be used to carry out an interferometry.
Interferometers in the world
Radio operator interferometers
-
the radiohéliographe of Nançay (Expensive, France), dedicated to the observation of the solar Crown, in waves radiometric (CNRS, Osbervatoire of Paris/Meudon and ENS)
- the Interferometer of the plate of Bore-hole (the Alps, France), observing in millimetre-length waves,
- VLA in the USA, close to Socorro
- ATCA in Australia
- Allen Telescopes Array (ATA), Lassen Volcanic National Park, E. - U.
Interferometers with gravitational waves
Optical interferometers
- See the article: optical Interferometer at long base
Interferometry in teledetection
The interferometry term, in active teledetection (imagery starting from a Radar), indicates the technique or the methods using at least two images complexes* of a Radar to synthesis of opening (RSO) (SAR or Synthetic Aperture Radar in English), in order to obtain extra informations on the objects present in only one image RSO, by exploiting the contained information in the phase of signal RSO. This technique finds applications direct in geophysics thanks to its capacity to detect displacements of a centimetric nature.* a rough image radar is known as complex, when it has an amplitude and a phase
See too
Related articles
- Interference
- Slits of Young
- Interferometer of Michelson
- Interferometer of millimetre-length Fabry-Pérot
- Observation
External bonds
-
a video explanatory on the phenomenon of interference
- a video explanatory on the principle of the interferometers video
- explanatory on the interferometers with division of the wave front
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