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Article by:Ouma George,Awel Eshetu and Bassein Natalia


h1. * Spatial and Temporal coherence*

Spatial coherence is a concept of wave disturbance describing  the correlation between periodic transmitted  energy (wave signals)  from one point to another,it can also be said that it is a mutual interdependence or connection of variable wave quantities of two different points in a given instant of time,the coherence  is presented as a function of distance and mapped as correlation against an absolute distance between points in question.

While spatial coherence is concerned with the phase correlation of waves in different  observation points, *{_}temporal coherence{_}* entails  the phase correlation of waves at a given point in space at two different instances of time,it is the measure of the average correlation between the value of a wave and itself delayed by a certain period of time depicting  the characteristics of how well a wave can create an interference with itself.The delay on which the correlation effect is emphatically low is denoted by the degree of _T{_}c (coherence time)[\[3\]|http://en.wikipedia.org/wiki/Coherence_(physics)], a state at which there is a significant  shift in amplitude.

{color:#000000}{*}Michelson--Morley experiment{*}{color}


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{color:#000000}Showing Temporal Coherence {color}


{widget:url=http://www.youtube.com/watch?v=F_95i81jjOA}


{color:#000000}When one of the mirrors is moved away gradually, the time for the beam to travel increases and the infringes become dull and finally are lost{color}


{color:#000000}{*}Young's interference experiment{*}{color}


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\---\-{color:#000000}Showing spatial coherence {color}


{widget:url=http://www.youtube.com/watch?v=sm_U7899EXQ}


{color:#000000}If the space between the two slits is increased, the coherence dies gradually and finally the infringes disappear{color}

*Ø References*
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1. Interference and coherence definitions \[Online source\]
Url:[http://en.wikipedia.org/wiki/Coherence_%28physics%29]














{anchor:2}2.Interference and Coherence applet \[Online source\]
Url:[http://serc.carleton.edu/NAGTWorkshops/deepearth/activities/40826.html]
















3.Temporal and spatial coherence definitions \[Online source\]
Url:[http://en.wikipedia.org/wiki/Coherence_%28physics%29]

4. Interference description \[Online source\]

Url:[http://www.physicsclassroom.com/class/waves/u10l3c.cfm]