Caustic (optics)

As a caustic (from gr καυστός, kaustos, "burned", about lat causticus, " burning " ) is referred to in the technical optics a room, are bundled in the rays of light. An important characteristic is the unilateral increase in the concentration of light and its sharp boundary. Compared to the concentration of light is being phased out. With caustic can also be meant only the sharp bounding surface.

Converging lenses and concave mirrors to focus parallel light entering only ideally in focus. As a result of aberrations of the light is collected in a finite extensive caustic.

Species

A distinction is made between Catacaustic and Diakaustik. It also occasionally distinguish between caustic first and second kind, depending on whether the beam parallel or divergent ( as in a not infinitely distant point light source) incident.

Catacaustic

The deflection of the beam is done by specular reflection, ie on a curved reflecting surface. A typical example is the " coffee cup Catacaustic ": when light falls obliquely in a cup with shiny inside, one can observe a heart-shaped light concentration at the bottom of the cup or in a muddy cup of content. The sharp interface is described mathematically in special cases by a cardioid or Nephroide.

Diakaustik

The deflection of the beam is done by refraction. A typical example of a Diakaustik is the light collection with a lens.

On a sunny day you may well observe a sufficiently bright flat ground, the pattern produced by light waves under shallow water.

Rainbow

In rainbow every drop of water concentrates the light by refraction at the entrance and by reflection at the back in a caustic. The concentration of light at the interfaces is perceived as a bright arc in the sky. By the exiting light entry and the additional color separation of the light results in several light sheets in different colors.

Importance in laser beams

The beam propagation (see also in beam quality ) of a laser beam before and especially after the focus (for example, for material processing by laser ) is described by the beam caustic.

The beam parameter product is the product of the radius of the beam waist and the half -propagation or divergence angle and describes a hyperboloid of revolution ( or parts thereof) similar to beam caustic. The beam parameter product does not change with a focus, that is, you get a small focus diameter only at the expense of a larger divergence or convergence angle or a large numerical aperture.

Importance in computer graphics

In 3D computer graphics caustics have long been the most difficult to be simulated appearance, as they are concentrated and can be simulated well only by means of the light sources from operating procedures. Method for calculating the global illumination must also simulate caustics, what about the 1995 developed photon mapping algorithm for the first time generally and efficiently managed. In the light path notation caustics are the paths of type LS DE, ie at least a specular and a subsequent diffuse reflection.