interferometer

interferometer

In astronomy, an instrument in which the electromagnetic radiation from a celestial object is collected along two or more different path lengths and then brought together to form an interference pattern.
When any electromagnetic wave is sampled it has amplitude (how strong the wave is) and phase (the point the wave pattern has reached between peaks and troughs). If two light beams from the same point source have travelled slightly different paths and are then brought together, an interference pattern is formed. Where the two sets of waves are in phase, the pattern is bright, and where they cancel it is dark.
Astronomical interferometers exploit this basic physical principle as a way of increasing resolving power. A star image, for example, is a disc and not a point source. With a pair of mirrors there will be a critical separation at which the interference pattern disappears because the bright fringes from one side of the disc coincide with dark fringes from the other side. The first successful astronomical application of this principle was the Michelson stellar interferometer. In basic radio interferometry, telescopes are used in pairs and the resulting interference patterns analysed by computer.
By using more than two elements (e.g. mirrors or antennas) in an interferometer, it is possible to produce high-resolution maps or images, a technique often known as aperture synthesis.
Interferometry has been an essential observational tool in radio astronomy for decades. More recently it has become feasible to extend the technique fully into the infrared and optical wavebands. A number of dedicated instruments for optical interferometry have been constructed, such as the Cambridge Optical Aperture Synthesis Telescope in the UK and the Navy Prototype Optical Interferometer in the USA. In addition, several projects for the construction of very large telescopes have been specifically designed so that optical interferometry can be carried out. These include the Keck Observatories, the Very Large Telescope and the Large Binocular Telescope.