5. Multi-wave interference

When more than two waves from the same source are superimposed at the same point in space, they form a more complicated interference phenomenon, known as multi-wave interference. The amplitude of the resultant can also be estimated by trigonometric calculations or geometrical constructions. By way of example, we deal with the interference given by three Young-type slits between three waves of the same amplitude and whose phases are in arithmetical progression. We then present results for more complex phenomena, such as diffraction gratings with a very large number of lines, and bangs produced by reflecting blades or Fabry-Perot interferometers.