where the molecules reveal their wave nature
After 1.5 m of free flight, the molecules reach the grating. At this position, they are delocalized over a region of 5 µm. This seems small, but it is large compared to the period of the grating.
The nanomechanical gratings we use are manufactured in the group of Ori Cheshnovsky at the University of Tel Aviv. By focusing a beam of fast gallium ions, gratings with a period of 100 nm can be written into thin membranes of different types, covering conductive and insulating substrates and thicknesses ranging between tens of nanometers down to a single layer of atoms.
The period of 100 nm is 50 times smaller than the 5 µm the molecules are delocalized at. As we cannot say through which of the 50 possible slits the molecule is going, we have to treat it as if it would traverse all of them.
After the molecules passed the gratings, they fly another 60 cm towards the detector.