Collimator & Focus Lens
Collimating and focusing lenses in fused silica and ZnSe, with focal lengths from 63.5 mm to 254 mm. Each lens is edge-marked with its focal length and coating, so a replacement can still be identified after it is fitted.
Two lenses, two different jobs
Inside a fiber cutting head the beam is handled twice before it cuts anything. The collimating lens takes the diverging beam coming out of the delivery fiber and makes it parallel. The focusing lens then converges that parallel beam down to a spot at the workpiece. They look similar, they are bought in pairs, and they fail differently.
A collimator that has drifted or been replaced with the wrong focal length changes the beam diameter that reaches the focus lens, and therefore the spot that reaches the plate. The machine will still cut; the kerf will just be wider than the parameters expect, and the operator will spend a week chasing the gas settings.
What focal length actually changes
We supply focus lenses from 63.5 mm to 254 mm. D30 with FL100 and FL125 are the two we keep in stock for common fiber heads; anything else in the range is ordered against the head model. The short end of that range gives a small spot and a narrow depth of focus: less heat into the part, cleaner thin-sheet edges, but almost no tolerance for a plate that is not flat. The long end gives a bigger spot and a much deeper usable focus: it rides through thicker material and is far more forgiving on real-world sheet, at the cost of kerf width and a little cut speed.
The practical rule is that focal length should follow thickness, and that changing it is a parameter decision, not a repair. If you are moving a machine from 1 mm to 6 mm work, the lens is part of the change; if you are troubleshooting a cut that used to be good, the lens is a suspect, not a tuning knob.
Identifying the optic you are replacing
Our lenses are edge-marked with focal length and coating, which matters more than it sounds: once a lens is in the head, the only reliable identification is what was engraved on its edge. That is why we keep the marking on the part rather than on the box.
| What identifies a lens | Why it matters | What to send us |
|---|---|---|
| Focal length | Sets spot size and depth of focus; a mismatch shows up as a kerf that will not close | Edge marking, or the parameter set the machine was running |
| Diameter and thickness | Determines whether it seats in the cartridge at the correct height | Measure the old lens, or photograph it on a rule |
| Coating | 1064 nm AR for fiber; 10.6 µm for CO2. Wrong coating means absorption and heat | Machine type and laser source |
| Material | Fused silica for fiber, ZnSe for CO2; not interchangeable | Machine type |
| Head family | Cartridge and retaining geometry are family-specific | Head model |
Symptoms that point at the focus lens rather than the nozzle
| Symptom | What it suggests | First check |
|---|---|---|
| A burn spot or dark dot at the centre of the lens | Spatter or a failed protective window let energy reach the coating | Replace the window as well, or the new lens will fail the same way |
| Halo or rainbow ring around the beam area | Coating degradation; the lens is scattering instead of transmitting | Inspect under oblique light; compare cut quality on a test sheet |
| Power reading drops with no change in parameters | Absorption in the optic stack | Check window first, then the lens |
| Focus position drifts during a shift | Thermal lensing from a partly absorbing optic, or a loose cartridge | Check seating and the coolant path around the lens |
| Cut is clean but the kerf is wider than the parameter table | Collimator has been changed to a different focal length | Read the edge marking on the collimator |
Handling, storage and the mistakes that cost the most
- Never touch a coated surface, and never clean a lens that only has dust on it without first blowing the dust off.
- Store lenses in their case, not loose in a drawer with nozzles.
- Fit the coated face in the direction the original was fitted; reversing a lens is a common cause of a sudden power loss.
- Replace the protective window whenever a lens is replaced after a burn; a failed window is usually the reason the lens died.
Supply
We supply fused silica collimating and focusing lenses for fiber heads and ZnSe optics for CO2 systems, in wholesale quantities and under OEM packaging. Send the edge marking, the head model, or simply the machine make and model plus the thickness range you run, and we will confirm focal length, diameter and coating before shipping.