XF Range, CO2 Laser Focusing Lens
The XF series of lenses consist of two or three ZnSe lens elements. The design is such that
diffraction-limited performance is achieved in addition to an extended working distance which is 1.5
times the focal length. The lens elements are made from laser grade ZnSe, polished to a high standard
of surface smoothness and coated with ultra-low absorption anti-reflection coatings. XF series
lenses are mounted in a rugged aluminium mount with a black-anodised finish. The mounting thread
is 1.5″ dia. x 12TPI UNF 2A. The input clear aperture of all models is 25.4mm.
Four types are made as standard. The effective focal lengths are 1″, 1.5″, 2.5″, 5.0″. Note that the
clear working distance is longer than the focal length. Mounting details and working distances are
detailed in Figure 20.21 and Table 20.22.
The benefits of eliminating lens aberrations are explained in Technical Section 20.0.
The XF series of lenses provides the user with an extended working distance in addition to aberrationfree
performance. This can have beneficial effects in certain systems.
At short focal lengths the lens-to-workpiece distance extension allows greater freedom for the
inclusion of special nozzles and protective windows. At longer focal lengths, such as those suitable
for welding or the cutting of metals, the extended working distance leads to reduced back-spatter
(where the user has made efforts to reduce these effects by means of gas cross-flow etc).
A comparison between ULO Optics multi-element methods of eliminating aberrations and
competitive methods, is detailed in Technical Clarification Document 15. It is worth noting that the XF series
has extended working distance relative to other aberration-free lenses of the same focal length; this should
not be confused with the comparison between aberration-free lenses and meniscus lenses, where the
aberration-free lens may have a longer focal length and yet achieve the same spot size.
Rework of damaged lenses
In all cases the optical surface nearest the workpiece is flat, enabling easy re-furbishment to remove
backspattered material or damage caused by cleaning after prolonged use.
XF series lenses are designed for use with the XGNA series of nozzles