Axicon Lens

28 Jul 2022

Axicon Lens Introduction

An axicon lens is a special lens with one plano (flat) surface and one conical surface. Also known as a rotationally symmetric prism, an axicon lens creates a focal line along the optical axis using interference, and can convert a laser beam into a ring shaped beam of light. Axicons are typically defined by their apex angles.

At Shanghai Optics we produce high-precision axicon lenses for medical, scientific and industrial applications. From eye surgery to optical tweezers to laser drilling, from optical coherence tomography to particle physics, these prisms play a very important role in a wide range of optical systems.

Understanding Axicon Lenses

To convert a collimated beam of light into a ring, one places the axicon lens with the flat side facing the collimated beam. Light enters at a perpendicular angle, in the center of this flat side, then travels along the axions optical axis and and leaves the lens as a cone of light. When projected onto a planar surface this light can be seen to be a ring. The closer the surface, the smaller the diameter of the ring.

While a Gaussian beam would deteriorate over distance, the beam profile produced by an axicon begins by nearly propagating the properties of a Bessel beam which maintains a stable intensity distribution as it propagates. In fact, it generates a very good approximation within its depth of focus, which can be calculated from the radius of the beam entering the axicon, the index of refraction of the axicon, and the angle α.  If the angle of refraction is small, this can be approximated by radius/ (index of refraction-1) α.

Beyond the depth of focus, an axicon lens produces a uniform ring-shaped beam.

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