Interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have a greater amplitude or a lower amplitude if the two waves are in phase or out of phase, respectively. Coherent sources of light If the phase difference the waves from two sou sources reaching any point in space does not change with time rather it remains constant then these sources of light are known as 'coherent sources of light'. This property of the waves is known as coherence . A wave which appears to be a pure sine wave for an infinitely large period of time or in an infinitely extended space is said to be a perfectly coherent wave. Thus there are two different criteria of coherence. (i) Temporal coherence and (ii) Spatial coherence. (i) Temporal Coherence Definition: Temporal coherence refers to the correlation between the phase of a wave at a given instant of time. It is a me...
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