Understanding the light path inside a fiber marking machine is not academic. Almost every practical question — how fast can it mark, how fine can the detail be, why does the mark change when the part is a little thicker — comes back to three components: the laser source, the galvo scanner and the f-theta lens.
The light path, step by step
- The fiber laser source generates the beam. Most industrial marking machines use a wavelength around 1064 nm — near-infrared — which metals absorb well. That is the main reason fiber marking is so widely used on metal parts.
- The collimator and beam expander shape the beam into a clean, parallel bundle of the right diameter.
- The galvo scanner — two small, very fast mirrors on precision motors — steers that beam by angle. Because the mirrors are light and the motors are fast, this is what makes laser marking so quick: the beam is positioned optically rather than by moving a heavy table.
- The f-theta lens takes those scanning angles and converts them into a linear position on a flat working field, keeping the focus on a flat plane across the whole area.
- The workpiece absorbs the energy, and the material responds by annealing, changing colour, foaming or vaporising — depending on how the energy is delivered.
What decides the mark
- Power density at the surface — power concentrated into a small spot, not total power, is what changes the material.
- Pulse energy and frequency — the balance between how much energy each pulse carries and how many pulses arrive per second.
- Marking speed and overlap — how closely consecutive pulses are spaced. This drives both appearance and cycle time.
- Focus position — the beam converges to its smallest point at the focal plane. Move the part away from it in either direction and the spot grows, the energy density drops, and the mark changes.
Why spot size and working field are the central trade-off
Focus a beam more tightly and the spot gets smaller: finer detail, higher energy density. But the lens that does this also gives a smaller working field, and the depth of focus — the distance over which the mark still looks good — becomes shallower. A taller or less flat part becomes harder to mark evenly.
Go the other way, with a longer focal length, and you get a larger field and a more forgiving focus, at the cost of a larger spot and coarser detail. Choosing a machine, or a lens, is largely the job of picking the right point on that trade-off for your parts.
Where the limits come from
- Speed is limited by the galvo mirrors and the energy the material needs to respond.
- Detail is limited by spot size, which is limited by the lens and the beam quality.
- Evenness across the field is limited by how flat and how well corrected the field is.
None of these are mysteries while the light path is clear — and almost all of them are set long before the operator touches a parameter screen.
Have a specific part or material you are not sure about? Send us the details and we will tell you whether the process fits — or run a sample so you can see the result before you decide.