Axicons

Axicon lenses or conical lenses are rotationally symmetric optical elements that have one plane and one conical surface. An interesting feature of an axicon lens is that it can be used to turn a Gaussian beam into a close estimation of a Bessel beam with greatly reduced diffraction, although a true Bessel beam would need an infinite energy to create. Two key properties for these lenses to memorize are that they image a point source into a line along the optic axis and can convert a circular laser beam into a hollow ring. Axicons are used in optical coherence tomography, laser drilling, optical trapping as well as in ophthalmic surgeries requiring ring shaped laser output.