Beam Steered Lasers
Key Takeaways
- Mirrors move, not the laser or the part — that is what makes high-speed marking possible.
- Two galvanometers, one per axis, provide beam motion within the marking field.
- A flat-field lens focuses the beam to achieve high power density across the whole field.
- Scan speed, field of view and beam quality are the three limits that bound what a scan head can do.
Beam Steered Lasers
A beam steered laser marking system moves the focused laser spot across a stationary part using fast, computer-controlled mirrors rather than moving the part or the laser itself. Two lightweight mirrors mounted on galvanometer motors deflect the beam in X and Y, and a flat-field lens keeps it focused across the whole marking area. The part sits still; only the beam moves.
This is the architecture behind essentially all modern industrial marking, and it is why laser marking became viable for high-speed production in the first place.
How the Optical Train Works
- Beam expander. Enlarges the raw beam so that the focusing lens can produce a smaller spot — a larger beam at the lens gives a tighter focus.
- X and Y galvanometer mirrors. Very low inertia mirrors driven by closed-loop galvo motors, capable of repositioning in fractions of a millisecond.
- F-theta lens. The critical component. An ordinary lens focuses onto a curved surface, which would put the mark out of focus away from centre. An f-theta lens is corrected so the focal plane is flat and so displacement is linearly proportional to scan angle, keeping geometry undistorted.
Field Size, Spot Size and the Trade-off
The f-theta lens focal length sets the marking field, and it cannot be chosen without consequence:
| F-theta focal length | Marking field | Focused spot | Best for |
|---|---|---|---|
| Short (e.g. 100 mm) | Small | Smallest | Fine codes, micro-marking, high resolution |
| Medium (e.g. 160–254 mm) | Moderate | Moderate | General production marking |
| Long (e.g. 330 mm+) | Large | Largest | Large parts, at reduced resolution and irradiance |
A larger field always costs resolution and power density. Because irradiance is power divided by spot area, a bigger spot spreads the same wattage more thinly — which on a marginally absorbing polymer can be the difference between a mark and no mark. Specifying an oversized field “for flexibility” is a common and costly mistake.
Three-Axis and Dynamic Focusing
A standard two-axis system marks on a flat plane. Adding a motorised focusing module before the galvos — a third axis — lets focal height be varied on the fly, so contoured, stepped and cylindrical plastic parts can be marked in focus throughout. For moulded components with significant draft or curvature this is often essential rather than optional.
Parameters the Operator Controls
- Marking speed — mirror traverse rate, which together with power and repetition rate sets energy delivered per unit length.
- Jump speed and delays — how fast the beam repositions between marked segments. Incorrect jump, mark and polygon delays cause the classic defects: burned corners, rounded starts and tails on vectors.
- Hatch pattern and line spacing — for filled areas, controlling both appearance and cumulative heat input.
- Focus offset — deliberate defocusing is sometimes used to widen the spot and soften the mark.
On plastics these timing parameters matter more than on metals, because polymers are far less tolerant of the localised heat accumulation that poor delay settings produce. Troubleshooting guidance is collected in troubleshooting common laser engraving problems on plastics.
Related Terms and Reading
- Plastics laser marking solutions
- Laser irradiance
- How to mark plastic with a laser
- Laser marking and machine vision codes for traceability
Applying this in production
The Sabreen Group provides independent engineering support for galvanometer marking system specification, field selection and parameter development. If you are specifying a process, qualifying a material or troubleshooting a production problem, our engineering services team can help. Contact us to discuss your application.
Frequently Asked Questions
What is a beam steered laser?
A laser system using dynamic optical components — galvanometer mirrors or MEMS scanners — to rapidly direct and control the beam position without moving the laser source or the workpiece. It is the standard architecture for industrial marking.
How does beam steering actually work?
Adjustable mirrors tilt or rotate to change the beam direction, with one galvanometer handling the X axis and one the Y axis to provide motion within the marking field. A flat-field lens assembly then focuses the light to achieve high power density at the surface.
Why is beam steering faster than moving the part?
Because mirrors have far less mass than a workpiece or a laser head. Rapid beam movement allows high processing rates in engraving, marking, cutting and additive manufacturing that mechanical motion systems cannot match.
What limits the performance of a scan head?
Scan speed and acceleration limits of the mirror or scanner movement cap processing speed. Field of view is set by the range of mirror angles and the optical setup. And maintaining beam focus across the whole field constrains achievable quality.
What is a flat-field lens for?
It focuses the laser to maintain high power density across the entire marking field, compensating for the fact that a steered beam would otherwise travel different distances to different points, defocusing toward the field edges.
