# Diffraction pattern from a controlled single-slit experiment

I'm returning to the old thought experiemnt of a controlled electron beam pointing at one or two slits. By controlled I mean that the electrons are released with sufficient time between firings that no two subsequent electrons should interact.

I found the this paper (https://iopscience.iop.org/article/10.1088/1367-2630/15/3/033018) where they perform exactly this experiment - but the results surprised me and I wondered if anyone could help me clarify.

When both slits are un-masked we see the good ol' inteference pattern - a big sinc for the single slit modulated by narrow fringes from the interaction. But in the edge cases, where only one slit is unmasked, I'm surprised that we still seem to see narrow fringes (maybe clearest in the penultimate couple of panels).

How are these occuring?

• I suspect that the "moveable mask" is imperfect. – garyp Apr 6 '20 at 13:05
• I’m wondering, why teaching not starts with single edges. Even behind a single edge fringes are visible. Furthermore the first experiments with electrons were made with a wire (wherefore two edges) and not with a slit. – HolgerFiedler Apr 7 '20 at 9:25

By looking at the paper we can see that they used a setup where the 'mask' appears after the double slit (by $$240\mu \text{m}$$). So, we would still expect interference effects. We can also see that there is a difference between when the right slit is covered vs when the left is covered, and that is that the interference effect is stronger on the opposite side (what you'd expect if the mask was post the double slit).