Sunday 31 March 2019

waves - Relating Temporal Coherence and Intensity of Interference Pattern


In trying to understand the phenomenon of coherence a bit deeper, I have come to face the following question.


Suppose one uses an interferometer (Micheloson-Morley, Mach-Zehnder, etc) to measure the temporal coherence of a wave. As the wave works its way through the device, it gets split into two parts such that one part travels a slightly longer path and becomes temporally delayed. Then, the two parts are superposed onto each other and the picture is sent to the detector.


It is here where my question comes in. Looking at the detector, how does one determine whether the signal is highly coherent or whether it is not?


I understand that if the signal is monochromatic or very close to being one, then the interference pattern would remain constant in amplitude and retain periodicity. On the other hand, if the signal's spectrum is composed of multiple frequencies, then the interference patters would "live and breathe" in space.


How do we relate this intensity to the amount of coherence?




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