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:
“Art and ideology often interact on each other; but the plain fact is that both spring from a common source. Both draw on human experience to explain mankind to itself; both attempt, in very different ways, to assemble coherence from seemingly unrelated phenomena; both stand guard for us against chaos.”
—Kenneth Tynan (1927–1980)
“What though the traveler tell us of the ruins of Egypt, are we so sick or idle that we must sacrifice our America and today to some man’s ill-remembered and indolent story? Carnac and Luxor are but names, or if their skeletons remain, still more desert sand and at length a wave of the Mediterranean Sea are needed to wash away the filth that attaches to their grandeur. Carnac! Carnac! here is Carnac for me. I behold the columns of a larger
and purer temple.”
—Henry David Thoreau (1817–1862)