While solving a problem that involved both the concepts, I stumbled upon the following fact, but I cannot somehow visualize the idea. Could anyone please give me some intuition as to why the above stated fact holds?

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    $\begingroup$ Er ... you can get partial interference for incident sources which have difference in polarization that is neither $0$ now $\pi/2$. $\endgroup$ Apr 9, 2016 at 23:54

1 Answer 1


Interference of electric field is basically addition of vectors. Two vectors sum up to a zero vector if, and only if, they are anti-collinear and they are of the same magnitude.

The condition of (anti)collinearity is achieved only in special cases. One of these are linearly polarized waves of the same polarization. (They moreover have to propagate under a similar angle for the interference fringes to have a good contrast, otherwise the vectors are not collinear anymore.)

If the field vectors are not collinear, like in waves of different polarisation, they can never subtract to zero.

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    $\begingroup$ This is all correct, but not being able to get compete cancellation doesn't mean that you don't have interference: it means that you have a limited range of interference contrast dropping to zero contrast when the source have perpendicular polarization. $\endgroup$ Apr 9, 2016 at 23:55
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    $\begingroup$ @dmckee You are right. But I felt the original question implies that one wants to get a high interference visibility and adapted my response to it. $\endgroup$
    – dominecf
    Apr 10, 2016 at 11:08

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