ZnSe Axicon

ZnSe Axicon Components

Axicon components
Axicon components have one conical surface, and are used to produce a ring focus. Most commonly,
axicon components have a second, flat, surface and are used in combination with a focusing lens (see
fig. 7.001). Umicore Laser Optics axicons are made from lasergrade ZnSe using a manufacturing process
suited to the axicon angle and the accuracy required. For accurate, small-angle axicons the manufacturing
process involves diamond-machining. Axicon components are usually made-to-order only.
Sizes and specifications
Standard available diameters are: 28.0mm, 38.0mm, 50.0mm. Axicon angles may be fabricated
within the range 1 arcminute up to 10 degrees. Typical manufacturing tolerances are listed below:
Diameter : +0/-0.1mm
Thickness : ± 0.2mm
ETV (Θ < 1°) : <0.02mm
ETV (Θ > 1°) : <0.05mm
Axicon function
See figure 7.001.
The position of the focus is determined by the focal length of the auxilliary focusing lens ‘L’. The
axicon component ‘A’ provides the angular displacement of the rays which form the ring focus. By
changing the distance ‘D’ of the axicon from the focal plane, the ring diameter may be varied within
reasonable limits.
The ring diameter may be calculated as follows.
Where È is the axicon angle (expressed in radians), and the refractive index of the axicon material
is ‘n’ then the ring diameter ‘d’ is:
d = 2(n-1)ΘD …. for small angles Θ
The width of the ring focus is twice the spot size that would be produced by lens L, given the properties of
the incident beam(1).Axicon diagram

ZnSe axicons are provided with low
absorption AR/AR coatings. These
products may be used at multi-kilowatt
laser power levels.
Related products and applications
Complete axicon assemblies, with builtin
‘zoom’ function(2), are described in
technical data section 25.
Typical applications include drilling of
user-controlled holes in paper, plastics
and similar materials. Very low-angle
axicons have been used to provide a
‘flat-topped’ intensity distribution at the focus,
allowing controlled part-penetration of artwork materials.

Axicon data

(1) See technical data section 20.0 for calculation of focused spot sizes.
(2) ‘Zoom’ variation of ring diameter, by control of ‘D’.
(3) Negative-surface ZnSe axicon components are not available. Axicon components with a
second spherical surface are discontinued.
(4) The detailed interaction of low-angle axicons and laser beams is a complex topic. Calculation
of actual intensity distributions in and around the focal plane requires many hours of computer
time. If in doubt about an application/specification requiring low-angle axicons, please
contact ULO Optics for assistance.