An Etymological Dictionary of Astronomy and Astrophysics
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Two or more wave sources are said to be coherent sources if the phase difference between a pair of points, one in each source, remains constant.

Coherent, adj., → coherence.

Light waves that have the same wavelength and possess a fixed phase relationship, as in a laser.

→ coherent; → light.

A branch of optics that uses coherent radiation to produce holographic three-dimensional images of objects.

→ coherent; → optics.

A scattering process in which the scattered radiation bears the same frequency and phase as the incident radiation.

→ coherent; → scattering.

One of two light beams derived from the same source in → interference experiments. It is impossible to obtain interference from two separate sources because their → wavefronts do not have a constant → phase difference. In → Young's experiment, → Fresnel's biprism, → Fresnel's mirrors, and → Lloyd's mirror the two sources always have a point-to-point correspondence of phase, since they are both derived from the same source.

→ coherent; → source.

The lack of a fixed phase relationship between two or more waves. → coherent.

Incoherent, from negation prefix → in- + → coherent; → wave.

Radiation having waves that are out of phase in space and/or time; radiation which is not → coherent.

→ non-; → coherent; → radiation.

The absorption of a photon and its re-emission at a different frequency (in the observer's frame of reference) by scattering atoms.

→ non-; → coherent scattering.