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coherent light

(beam of light at a single frequency)

Coherent light is light consisting of coherent waves, i.e., matching in wavelength. The term is generally used for waves from a point source or for plane waves (basically, a beam of waves moving in the same direction, the waves in lock-step). In concept, coherent light could be from separated sources if the separate light beams have the same similarity (e.g., identical to that from a point source masked to produce separate beams). Lasers (the visible light analog of masers) produce a beam of such light, all the light the same wavelength, which is unchanging, and very nearly in plane waves, i.e., the beam is moving very close to parallel.

One 1995 astronomical observation has been interpreted as a natural laser, but masers are more common. Lasers are also used for adaptive optics, in detectors for gravitational wave, and some high energy electromagnetic radiation, and in carrying out particle physics experiments of cosmological significance.


(optics)
http://en.wikipedia.org/wiki/Coherence_(physics)

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