In physics, coherence length is the propagation distance from a coherent source to a point where a wave (e.g. an electromagnetic wave) maintains a specified degree of coherence. Within this distance, the wave in question is most similar to a perfect sinusoidal wave. The significance is that wave interference will be strong within a coherence length of the source, but not beyond it. This concept is also commonly used in telecommunication engineering.
This article focuses on the coherence of classical electromagnetic fields. In quantum mechanics, there is a mathematically analogous concept of the quantum coherence length of a wave function.
Famous quotes containing the words coherence and/or length:
“When the coherence of the parts of a stone, or even that composition of parts which renders it extended; when these familiar objects, I say, are so inexplicable, and contain circumstances so repugnant and contradictory; with what assurance can we decide concerning the origin of worlds, or trace their history from eternity to eternity?”
—David Hume (1711–1776)
“What journeyings on foot and on horseback through the wilderness, to preach the gospel to these minks and muskrats! who first, no doubt, listened with their red ears out of a natural hospitality and courtesy, and afterward from curiosity or even interest, till at length there “were praying Indians,” and, as the General Court wrote to Cromwell, the “work is brought to this perfection that some of the Indians themselves can pray and prophesy in a comfortable manner.””
—Henry David Thoreau (1817–1862)