What is "axicon"

n. A specialized lens with a conical surface.

An axicon is a specialized type of lens which has a conical surface. An axicon images a point source into a line along the optic axis, or transforms a laser beam into a ring. It can be used to turn a Gaussian beam into an approximation to a Bessel beam, with greatly reduced diffraction. Axicons were first proposed in 1954 by John McLeod.

Axicons are used in atomic traps and for generating plasma in linear accelerators. They are used in eye surgery in cases where a ring-shaped spot is useful.

Axicon is usually characterized by the ratio of the diameter of the ring to the distance from the lens tip to image plane d/l.