Question
Sat May 07, 2011 By: Ankit Bhardwaj

What are coherent light sources ?

Expert Reply
Sat May 07, 2011
Two sources of light are said to be coherent if the waves emitted from them have the same frequency and are 'phase-linked'; that is, they have a zero or constant phase difference.
 
When interfering, two waves can add together to create a larger wave (constructive interference) or subtract from each other to create a smaller wave (destructive interference), depending on their relative phase. Two waves are said to be coherent if they have a constant relative phase. The degree of coherence is measured by the interference visibility a measure of how perfectly the waves can cancel due to destructive interference.
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