3. Periodic masks (Talbot effect)

Periodization of pinholes can produce interesting effects in a configuration where FN < 1. Indeed, such a combination has the property of generating self-images that reproduce themselves periodically along the axis of propagation; this is the self-imaging effect or Talbot effect. Compared with coded masks, the Talbot effect makes it possible to project a pattern while mastering diffractive effects. It's a remarkable phenomenon, different from what can be obtained with refractive and reflective optics, and capable of producing lines or points of light without using the focusing principle. In the introduction to his article on this phenomenon, Patorski waxes lyrical about its scientific interest