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An axicon is a type of lens with one surface that has a conical shape and another that has a flat, or plano, surface. They may be convex, with a protruding cone or concave — a negative axicon. These lenses are also known as rotationally symmetrical prisms due to their properties and the effects on light that passes through them. The body of the lens may be cylindrical in shape or it may be a true cone. Axicons have a number of interesting properties that have led to them being used in several fields of science and industry, including optometry, physics research, and astronomy.
Lasers are important tools in science and industry, and axicon lenses have found a niche in the research and development of laser-based devices and applications. An axicon lens has the ability to transform a laser beam that passes through it perpendicular to and at the center of the flat side, resulting in a perfect cone of laser light, the angle of which is determined by the angle of the cone of the conic side of the lens. When projected onto a flat surface, the light will be seen as a ring. Moving the viewing surface closer to the lens will reduce the size of the ring, and moving it further away will cause the size of the ring to increase.
In medicine, axicons are sometimes used in laser corneal surgery. In this instance, two axicons are used. One is a normal axicon, and the other is a negative axicon. The two axicons are used in conjunction with one another to allow for a laser to be focused in a ring shape that makes it possible for the surgeon to shape the cornea in order to improve vision in some patients.
Physicists have developed a method using axicon lenses and mirrors to create a device that can produce a stream of individual atoms. This device and the atom streams it produces allow them to capture individual atoms for study, broadening understanding of atomic particles and particle physics. An extremely precise axicon mirror lens with a tiny hole is used for this type of device. Axicon lenses can even be used to test materials for structural defects. Ultrasonic waves are aimed at an axicon, which distributes them in such a way that they can be used to detect minor flaws in industrial parts and components by the way they pass through the object or material being tested.