Consider Young's double-slit experiment with slit width a and slit separation d, is it possible that it does not fulfill the Rayleigh Criterion i.e. the distance of the 1st order minimum from its central maximum due to one slit is smaller than the distance between the central maxima of each slit?

If so, how would the diffraction pattern differ from the normal ones usually found online i.e. the double-slit pattern enveloped by a single slit due to diffraction?


1 Answer 1


The Rayleigh criterion is based on the separation of two diffraction patterns.

In the usual examples the two sources are not coherent and so no interference pattern is seen.

In the case of the double slits there is an interference pattern but the diffraction patterns from each of the slits overlap almost completely and so there two slits are not resolved.

If the separation of the slits is increased then the diffraction patterns due to each of the slits can be resolved and where they overlap there will be an interference pattern as shown below:

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There is a related post What happens if separation between slits is greater than separation between slits and screen in YDSE experiment? which may be of interest?

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