ABSTRACT
The production of a ring of light has applications in laser material processing and machining, particle manipulation (optical tweezers), and corneal surgery. It is well known that axicons (conical lenses) can produce light ring patterns. An axicon combined with a focusing lens produces a ring pattern at the focal plane of the lens. A combination of a positive (convex) and negative (concave) axicon pair can be used to achieve a variable (zoom) ring diameter. Negative axicons are expensive and more difficult to obtain. Fortunately, a zoom system can be achieved by using two positive axicons. Axicons were introduced by McLeod1 as early as 1954 as an optical element. The ring forming properties of axicons are discussed in detail in the excellent papers by Belanger and Rioux2 and Rioux et al.3 They present a zoom system using two axicons, one positive and one negative. The axicon depth of focus is treated by Lit and Tremblay.4 Shi et al.5 use an axicon structured lens to obtain a large depth of focus. This is related to the subject of nondiffracting beams. Axicons are used to generate Bessel-like beams.6 Zeng et al.7-9 treat the application of axicons to optical trepanning in considerable detail. Goncharov et al.10 give a design for an axicon system that produces a line focus.
