GPZ25 Zoom Lens Assembly

The GPZ25 zoom lens is designed for CO2 laser beams of up to 2000W power, depending upon input
beam diameter. It has a clear input diameter of 25mm; a zoom focal length range of 50mm to 127mm, and
a fixed focal plane. The low beam compression ratio used in model GPZ25 gives this general purpose lens
its high power-handling capability. The 2.54:1 range of focal length results in a 6.5:1 range of energy density
and depth-of-focus for a given input beam. During the zoom action, which is manually controlled by the
laser operator, the system will not require any change of gas nozzle and will not generally need a change of
z-axis setting. Model GPZ25 has a mechanical fitting exactly equivalent to standard 1.1″ diameter mounted
lenses, such as the 11ZLF and 11TF types.
Technical Specifications
Dimensions : see figure 24.531.
Zoom range : 47.7mm to 129.1mm.
Engraved range : 50.0mm to 127.0mm.
Beam compression ratio: 1.15 to 1.
Input fitting : 1.5″ x 12TPI UNF 2A.
Output fitting : 1.875″ x 20TPI UNF.
Input aperture : 25.0mm diameter.
Max gas pressure : 200psi., safety factor > x2.
Centration : < 2 arc min (see section 24.00).
Cooling : Air, or indirect water cooling via WMA (see section 20.3).
Construction : 4 ZnSe lens elements in black-anodised aluminium housing, plus
ZnSe protection window.

GPZ lens assembly
Associated Equipment
The GPZ25 zoom lens is a direct fit to models FF25 (section 63.1) and CFF25 (section 63.2) manual focus
units, either directly or via the WMA water-cooling mount accessory.
The 1.5″ x 12TPI mounting thread is identical to that of the standard M11 cell used for 11MZLF, 11HGP and
11TF lenses (sections 8.10, 20.1), and so this zoom lens may be retro-fitted to equipment designed for those
lens types.
At the output of the lens the thread fitting is designed to accept either of two gas nozzles:
Model GNA50 for up to 90psi (section 20.6) or,
Model SNA50 for up to 200psi (section 9.10).
(NB: GNA nozzles have an external control ring for speedy setting of nozzle stand-off. See applications notes
Applications notes
Zoom lenses may be used to determine the ideal cutting or processing parameters for a range of materials and
material thicknesses. A change of material or material thickness may need a change of assist gas type or
pressure. If so, the nozzle stand-off may also require minor adjustment for best results.
In applications where assist gas is used, the gas flow conditions will almost always need modifying to suit the
changes in optical setting if the requirement is optimum process speed.
Special features
The zoom action of model GPZ25 requires that two of the lens elements move axially. These moving
elements are specially centred within their mounting cells to accuracies of a few seconds of arc. As a result,
the beam-wander during the zoom action is minimized. With a correctly aligned input beam, lateral focus
shift will be less than 0.05mm.
The low beam compression ratio of this lens leads to larger output optics. These lenses are protected from
backspatter by a plane ZnSe output window, 38mm diameter and 3mm thick.