Lets say....a little bit after the double slits, we place another set of double slits (one pair of double slits for each of the "original" double slit) thus a total of 6 slits two slits in the first plane (say at y = 10) and four in the next plane/series (say at y = 10.02) the x-axis (and z-axis) would run the length (and breadth) of the detector How would the interference pattern look like? Would the pattern be such that, first you have you account for (and build the paths through) the first double slit and then use that to build a paths through the next four slits? and the pattern would be the interaction of the final four (coherent) wave functions? note: the concept of series and parallel are interchangeable, depending upon how one views it. in this case series is supposed to mean placing four slits right after the two slits.