There is an opaque screen with two narrow slits in it in the z = 0 plane (shown in cross section in the x-z plane — the slits come out of the paper in the y direction) a small distance \(s...There is an opaque screen with two narrow slits in it in the z = 0 plane (shown in cross section in the x-z plane — the slits come out of the paper in the y direction) a small distance s apart. The important thing is to produce illumination at the opaque screen in which the frequency is in a narrow range and the phase of the light reaching the two slits is correlated.