Wave refraction at an interface: Snell's law versus Chapman's law.

Energy streamlines provide insights into mechanisms of wave propagation and scattering and are often utilized to visualize wave fields. In contrast to rays, which are essentially an asymptotic, short-wave concept, energy streamlines adequately represent arbitrary wave fields. However, the usefulness of energy streamlines in studies of wave fields is limited by the fact that, unlike rays, no general laws governing energy streamline refraction are known. Here, a simple refraction law is derived for energy streamlines of acoustic and linearly polarized electromagnetic waves. It is shown that analysis of energy streamlines provides a helpful supplementary perspective on wave transmission through interfaces.