What is an axicon (and what they can do for us)

In 1954 axicons were defined by John McLeod as rotationally symmetrical optical devices able to produce a line image lying along the axis from a point source of light. Nowadays we understood a“line image“ as a focal distribution with axial dimension significantly higher than conventional lenses do. Consequently an axicon have no definite focal point but a focal segment distribution. A typical example is a lens with a weak conical surface on one face. Before Laser devices spread, they were used for very different technical and metrological purposes as, for instance, optical alignment. On the other hand, we can co…