Coherence (physics)
Coherence in advanced physics is a phenomenon of electromagnetic waves.[1]
In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. In such a case the waves plot as identical: their peaks and troughs occur at the same time, and they have the same amplitude.
Coherence is an ideal property of waves. It produces stationary (i.e. temporally and spatially constant) interference.
The idea has several distinct concepts. These are limiting cases which never quite occur in reality. However, they allow an understanding of the physics of waves, and have become an important concept in quantum physics.
More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets.[2]
Coherence (physics) Media
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Two slits illuminated by one source show an interference pattern. The source is far to the left in the diagram, behind collimators that create a parallel beam. This combination ensures that a wave from the source strikes both slits at the same part of the wave cycle: the wave will have coherence.
Figure 1: The amplitude of a single frequency wave as a function of time t (red) and a copy of the same wave delayed by \tau (blue). The coherence time of the wave is infinite since it is perfectly correlated with itself for all delays \tau.:{{{1}}}
Figure 10: Waves of different frequencies interfere to form a localized pulse if they are coherent.
Figure 11: Spectrally incoherent light interferes to form continuous light with a randomly varying phase and amplitude
Figure 5: A plane wave with an infinite coherence length.
Figure 6: A wave with a varying profile (wavefront) and infinite coherence length.
Figure 7: A wave with a varying profile (wavefront) and finite coherence length.
References
- ↑ Hecht 1998. Optics 3rd ed, Addison Wesley Longman. pp. 554–574. ISBN 0-201-83887-7
- ↑ "Dr. SkySkull". "Optics basics: Coherence". Skulls in the Stars.