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Two sources of waves are [[coherent]] if they [[emit waves ]] [[wave]]s with a constant [[Phase Difference|phase difference]].

*'''Coherent ''' sources produce waves [[wave]]s that are in sync, having a constant [[phase ]] relationship. Necessary *'''Coherence is necessary for producing clear [[Interference Pattern|interference patterns]]. *'''Coherent waves ''' [[Visible Light|visible light]] are typically [[monochromatic ]] and have the same [[frequency]]. Essential *'''Coherence''' is essential in applications like lasers[[laser]]s, holography, and [[interferometry]]. *'''Coherence ''' can be temporal (constant phase difference over time) or spatial (constant phase difference  across space). *The degree of '''coherence ''' affects the visibility and contrast of [[Interference Fringe|interference fringes]]. *Achieving '''coherence ''' often involves stabilizing the [[frequency ]] and [[phase ]] of the [[wave ]] sources. 

Laser light is coherent and can produce clear interference and diffraction patterns. *In a [[Double Slit Experiment|double-slit experiment]], '''coherent ''' light sources create distinct and stable [[Interference Fringe|interference fringes]].