A concentrated boundary of light formed by the intersection of reflected or refracted rays in an optical system with spherical aberration. Instead of converging to a single sharp focal point, the rays bunch up along a curved surface, creating a distinct, high-intensity pattern often seen at the waist of a highly aberrated beam.
You can see the caustic forming on the burn paper just past the focal plane of that cheap singlet.
In high-power laser systems, accidentally focusing a beam into a caustic on an optical component can easily exceed its damage threshold.
Also heard as
- caustic curve
- caustic surface
Related terms
Spherical aberration
An optical defect where light rays passing through the edge of a lens focus at a different point than central rays.
Beam waist
The narrowest point of a focused or propagating laser beam, where its wavefront is flat.
Caustic curve
A two-dimensional cross-section of the envelope formed by reflected or refracted rays.