Axicon Lenses

custom axicon lenses, conical lens, bessel beam lens An axicon has a unique lens design where one surface is conically shaped and the other is plano. When the collimated light exits through the conical surface it produces a focus line which projects as a ring. This ring exhibits a very close estimation of a Bessel beam dependent on the positioning.

This nearly non-diffractive ring has a constant width, however the diameter increases as the distance between the axicon and image plane increases. The diameter of this ring is directly influenced by the refractive index of the material, the alpha angle (α) and then distance from the apex to the image plane.

Knight Optical can supply axicon lenses to our customer’s specifications. Typical materials used are UV fused silica and Schott BK7, however alternatives are available including zinc selenide for NIR and IR applications. Below are our typical manufacturing capabilities, but these can vary dependent on the material, so please enquire for further information:

	Diameter (mm)	Alpha angle (α)	Form Error (lambda)	Scratch/dig
Axicon lens	3 to 300mm+	0.5° to 40°	< 0.25	< 60/40

Knight Optical are pleased to offer our extensive custom optic service thanks to our many years experience in the industry. For more information on our custom axicon lenses or to enquire about any of our optical components, please contact our technical sales team.

Capabilities

Capabilities – Axicon Lenses

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Additional Information

Axicon lenses can come in positive or negative design, dependent on whether the conical surface is convex or concave respectively.
They are also known as rotationally symmetric prisms due to their effect on the light that enters them.
The cone (or apex) angle is 180°-2α.
Combining an axicon lens with a spherical lens can produce an annular focus beam.

Coatings

Knight Optical can also apply an optical coating to your axicon lens to enhance their transmission or reduce the surface reflections.

Antireflective (AR) coatings, including broadband coatings, are commonly applied to optimise the performance over certain wavebands.

Quality Assurance

A critical parameter on an axicon lens is the apex angle which Knight Optical can verify on our Starrett AV300.
Surface form error is measured on our Zygo Verifire XPZ.
Transmission, reflection and optical density measurements are conducted on our Agilent Cary 7000 Spectrophotometer which can perform spectral scans at multiple angles of incidence and different polarisations.
All optics are 100% visually inspected before packaging, our staff are trained to ISO 10110 and MIL-0-13830A, and can check down to 10/5 scratch/dig which is especially critical in laser applications.

Typical Applications

Ophthalmic applications including laser eye surgery, where both a positive and negative axicon lens are used, to shape the cornea.
Optical coherence tomography (OCT) whereby using an axicon lens can produce a high lateral resolution over longer focus depths.
Astronomy applications such as telescopes where replacing a typical spherical lens with an axicon lens allows for deeper depth of focus.
Other applications include atom trapping and laser research.

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