I want to ask a question about double slit interference and the pattern that it produces on a screen (for example in Young's Experiment with a laser beam). I understand the reason that you see a series of light and dark spots - constructive and deconstructive interference due to different path differences. However, I do not understand why the central maximum is a lot brighter than all the subsidiary maxima. The intensity is higher in the centre, but why? Surely if complete constructive interference is occuring in all of these spots then the combined amplitudes will be the same and hence the brightness/intensity will also be the same? Is it to do with the number of rays that converge at each point? or the angle at which they hit?
Many thanks in advance!