Geometry of rays passing through a dioptre

The second section introduced the fundamental definitions of geometrical optics through caustics, using examples of reflective systems. Thus, image formation in geometrical optics highlighted the importance of caustics. The notion of object and image points now means that caustics and, more generally, the amplitude of the electric field are no longer an issue. This third section is therefore devoted solely to dioptric systems without the use of caustics, and is thus restricted to the directional approach.

In this section, the geometry of light rays is described by studying their orientation, which is closely linked to the properties of the materials in which they propagate. Homogeneous and isotropic materials, with a constant index n, are...