This is a drawing explaining two-slit diffraction: Planar wavefronts with wavelength λ (straight, vertical blue lines in the left-hand side of the image) arrives from the left at a barrier (thick yellow line) which have two slits or holes in it, at a distance d from each other. On the right-hand side of the barrier, the circular wavefronts that "leak" through the slits interfere with one another. This causes the light to scatter so that in certain directions, called orders (gray arrows labeled m0, m1, and m2), the light "concentrates" in beams while little or no light is emitted in the directions in between these orders.
