Imagine a beam of light diverging from a source and being incident on a detector. Now imagine a similar set up but with one main difference. The difference is that on its journey to the detector the beam passes through a second beam such that in the overlap region the two beams interfere. Having passed through the overlap region the beam is then incident on the detector. My question is, if everything else apart from the prescence of the second beam is kept the same are there any differences in what can be detected? As far as I know at present all similar detectors would record the same results. Having passed through the overlap region the beam would emerge with the same properties as it would have if there was no overlap region. Is that correct? I will be very grateful if anyone can confirm or clarify. Thank you.