Huygens’ Elementary Waves, Caustics, and their Relevance for the Understanding of Physics

The idea of propagating and permanently interfering wavelets, which was introduced by Huygens to describe the origin of light rays, proved to be one of the most fruitful concepts in physics. Local wavelets characterized by their amplitude and phase allow the calculation of complex proceedings not only in optics (eikonal) and mechanics (the action principle and the Hamilton-Jacobi-equations), but also in quantum mechanics (WKB-method) and in quantum field theory (path integrals, Yang-Mills concept). Thus they are one of the few pillars which support our conception of the creation of the world. To understand the connection of these different sections of physics, we join experiments on optical caustics with simplified theoretical descriptions in the short wavelength limit, where light behaves like a particle. We discuss the problem of wound optical wave fronts and show that torsion is a major hindrance for their propagation. The basis of the experiments is a polarizing interferometer with a calcite lens.