co·her·ence   (kō-hîr'əns, -hěr'-)    n.   The quality or state of cohering, especially a logical, orderly, and aesthetically consistent relationship of parts. Physics The property of being coherent, as of waves.

Coherence

Co*her"ence\, Coherency \Co*her"en*cy\, n. [L. cohaerentia: cf. F. coh['e]rence.]

1. A sticking or cleaving together; union of parts of the same body; cohesion.

2. Connection or dependence, proceeding from the subordination of the parts of a thing to one principle or purpose, as in the parts of a discourse, or of a system of philosophy; consecutiveness.

Coherence of discourse, and a direct tendency of all the parts of it to the argument in hand, are most eminently to be found in him. --Locke.

coherence   (kō-hîr'əns, -hěr'-)  Pronunciation Key  A property holding for two or more waves or fields when each individual wave or field is in phase with every other one. Lasers, for example, emit almost perfectly coherent light; all the photons emitted by a laser have the same frequency and are in phase. Since quantum states can be described by a wave equation, coherence can hold for quantum states in general, though only among bosons. Coherence is generally possible in physical systems that may undergo superposition. Maintaining coherence of light is important in fiber optic communications. See also Bose-Einstein condensate.

coherence

a fixed relationship between the phase of waves in a beam of radiation of a single frequency. Two beams of light are coherent when the phase difference between their waves is constant; they are noncoherent if there is a random or changing phase relationship. Stable interference patterns are formed only by radiation emitted by coherent sources, ordinarily produced by splitting a single beam into two or more beams. A laser, unlike an incandescent source, produces a beam in which all the components bear a fixed relationship to each other

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