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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. ==Applications== One application of axicons is in telescopes, where the usual spherical objective is replaced by an axicon.〔 Such a telescope can be simultaneously in focus for targets at distances from less than a meter to infinity, without making any adjustments. It can be used to simultaneously view two or more small sources placed along the line of sight. Axicons can be used in laser eye surgery. Their ability to focus a laser beam into a ring is useful in surgery for smoothing and ablating corneal tissue. Using a combination of positive and negative axicons, the diameter of the ring of light can be adjusted to obtain the best performance.〔(【引用サイトリンク】url=http://www.edmundoptics.com/technical-resources-center/optics/an-in-depth-look-at-axicons/ )〕 Axicons are also used in optical trapping.〔 The ring of light creates attractive and repulsive forces which can trap and hold microparticles and cells in the center of the ring. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Axicon」の詳細全文を読む スポンサード リンク
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