Laser Cleaning Heads: Optics and Selection
A laser cleaning head delivers, steers and focuses the source beam onto the workpiece. Choose it as a matched source–scanner–lens assembly: wavelength, pulse regime, aperture, working distance and usable field all matter. The widest scan or highest wattage label alone cannot tell you whether the system will remove the contamination while preserving the required surface.
Oceanplayer Laser product photograph: the handheld head and delivery cable are separate from the main machine. Internal optical arrangements vary by model.What is inside a laser cleaning head?
A common two-axis fiber-laser cleaning head receives the beam, conditions it with collimating optics, steers it with galvanometer mirrors and focuses it through a scan lens. A galvanometer rotates a mirror through a controlled angle; it allows rapid spot motion without moving the whole head over the same short path.
Check the scope of the quoted assembly. A scan head may mean only the scanner and drives. A handheld cleaning gun normally includes a grip, trigger and associated controls. A complete cleaning head may also include optics, a protective window, purge connections, cooling or sensors. These features are not present in every design.
The laser source generates the beam. The head determines how that beam reaches the part. For example, SCANLAB’s collimation-module documentation shows fiber coupling and collimation as an assembly connected to the scanner; they need not be one inseparable housing.
Follow the beam from the source to the surface
Each stage has a different job. A weak cleaning result can come from optical loss, incorrect focus or beam motion as well as from the laser source itself.
- Fiber interface and collimator. The connector receives the delivered beam; collimation sets its diameter and divergence at the scanner. The interface and optical acceptance must suit the source.
- Scanning mirrors and drives. Mirror motion draws the trajectory. Aperture, tuning, acceleration, position feedback and laser timing affect the path that is actually delivered.
- Scan lens. The lens focuses the steered beam onto the intended work plane. Design wavelength, entrance beam and scanner geometry belong with the lens specification.
- Protective window. A replaceable barrier limits contamination of higher-value optics. It must also transmit the beam with suitably low absorption; ordinary clear glass is not an equivalent part.
- Supporting services. Where fitted, purge protects the window, cooling manages heat and distance sensing measures position. Extraction captures process emissions. These functions solve different problems.
Scanner designs also differ in feedback and thermal management. SCANLAB’s intelliSCAN documentation distinguishes analog position detectors from digital encoders and lists cooling variants. Avoid assuming that every head uses the same feedback device or can sustain the same duty.
How do the lens and scan field affect the result?
Changing the lens and changing the programmed scan width are different actions. A longer focal length can produce a larger field and a larger focused spot for the same input beam. Drawing a wider pattern with the existing optics does not automatically enlarge the spot; it changes the path and coverage, while edge performance still needs checking.
F-theta describes scan mapping
An F-theta lens aims to place the focus on a flat work plane with position approximately proportional to the optical scan angle: y ≈ fθ, with θ in radians. Real field curvature, distortion and spot variation remain specification items.
Use the optical beam angle in this relationship. The mechanical rotation of a single steering mirror produces twice that change in reflected-beam angle; controller conventions must be identified.
Telecentric describes beam incidence
An image-space telecentric scan lens keeps the chief ray—the center direction of the focused beam—close to perpendicular to the work plane across the field. An F-theta lens can also be telecentric: these are not mutually exclusive categories.
Consider it when angle consistency matters on small features or near field edges. It does not make a curved part flat or keep every height in focus. Request the specified telecentricity error.
Sill Optics’ scan-lens guide explains these properties and shows why changing mirror spacing or lens position can alter field size, spot diameter and telecentricity. A lens that screws into the housing is not necessarily an optical substitute.
| Quantity | What it describes | What to confirm on your assembly |
|---|---|---|
| Focal length | An optical property used in focus and scan mapping. | Exact lens model, wavelength and compatible entrance beam. |
| Working distance | The distance to the working plane from a specified physical reference. | The drawing’s datum; it is not automatically the focal length or nozzle-to-part distance. |
| Spot diameter | The beam size at a stated plane and under a stated convention. | Center and edge values, beam quality M², input diameter and focus condition. |
| Usable scan field | The area over which the process meets its required result. | Removal and substrate condition across that area, rather than geometric reach alone. |
Scroll the table sideways on small screens.
A catalog example: the lens changes the available field
IPG lists a 260 mm lens with a 112 × 112 mm field and a 500 mm lens with a 250 × 250 mm field for its D20 scanner’s multimode configurations. These are manufacturer catalog pairings, not cleaning-rate measurements, and the focal-length numbers are not working-distance values.
A bigger field can reduce repositioning. Whether it increases accepted area per hour also depends on spot size, required passes, turn time and the surface result.
Input beam size matters too. A larger collimated beam can support a tighter focus when the optics and aperture allow it; clipping can defeat that advantage. Edmund Optics discusses beam diameter and focus tolerance. For an ideal center-field estimate with explicit beam assumptions, use the F-theta lens and spot-size calculator.
Which numbers describe the energy at the surface?
Keep three widths separate: the focused spot diameter, the programmed spot-center travel, and the effective cleaned width that actually passes inspection. A 100 mm drawn line is not a 100 mm optical spot.
For a steady, equal-energy pulse train, average pulse energy is Ep = Pavg / frep. Use power at the measurement plane you mean, and distinguish laser repetition rate from the scanner’s pattern frequency. Burst operation or changing pulse modes needs the source’s actual pulse-energy data.
Fluence is pulse energy per area and can vary across the spot. For a circular Gaussian spatial profile with 1/e² radius w, the on-axis peak is:
The factor of two matters: total pulse energy divided by πw² is not the Gaussian peak. RP Photonics’ “Fluence” article by Dr. Rüdiger Paschotta states this convention. Continuous-wave (CW) exposure instead needs a duration or dwell history; there is no pulse energy to insert.
Calculated example: double the spot diameter
Assume 100 W average power at the workpiece, 20 kHz equal-energy pulses and an ideal circular Gaussian spot. Each pulse carries 5 mJ. These are illustrative inputs, not cleaning settings or a damage threshold.
| Quantity | Smaller spot | Larger spot |
|---|---|---|
| 1/e² diameter | 0.40 mm | 0.80 mm |
| Radius in centimeters | 0.020 cm | 0.040 cm |
| Gaussian peak fluence | 7.96 J/cm² | 1.99 J/cm² |
Scroll sideways on mobile.
Doubling diameter increases the reference area fourfold, so peak fluence falls to one quarter. Widening the drawn line without changing the spot does not produce this same optical change.
Fluence alone cannot predict removal or substrate damage. Pulse duration, spatial profile, pulse spacing, repeated exposure, absorption and heat accumulation remain part of the process. A calculation is useful for comparing defined conditions; a sample establishes whether those conditions meet the surface requirement.
Why do scan patterns leave stripes or hot spots?
Coverage depends on motion in more than one direction. Describe pulse spacing along the trajectory, pitch between scan lines, and movement of the entire head or workpiece. A single “overlap” percentage does not identify all three.
On a straight segment with constant spot speed u, pulse-center spacing is p = u / frep. At 2,000 mm/s and 20,000 pulses/s, p is 0.10 mm. Against a stated 0.40 mm diameter, the geometric linear overlap is 1 − p/d = 75%. This is a calculated one-dimensional ratio; it is not a cleaning recommendation or a measure of total deposited energy.
Likewise, line-to-line overlap can be described as 1 − s/w only when the line pitch s and the chosen effective track width w are defined. If spacing exceeds width, tracks have a gap rather than overlap. Gaussian tails and a material’s removal threshold make the effective cleaned width different from the nominal beam diameter.
Spirals and crossing patterns provide other trajectories, but their names do not specify speed, phase, spacing or dwell. At reversals, reduced velocity can concentrate repeated exposure unless timing compensates. Review the trajectory and compare straight sections with turning zones before changing power. Select spacing from the measured track and the required surface result, not a universal overlap percentage.
What must match before you fit a cleaning head?
A useful specification identifies the complete source, delivery fiber, head, lens, window and controller. Average watts alone cannot establish optical compatibility: pulse energy, duration, peak intensity and thermal loading impose different demands.
| Interface | Information to document | Why it changes the decision |
|---|---|---|
| Source and optics | Source model, wavelength, CW or pulsed mode, average power, pulse-energy and duration range; coating and damage-limit basis. | A CW thermal rating does not establish tolerance to short pulses, or vice versa. |
| Fiber and entrance beam | Connector, beam diameter and divergence, applicable fiber-core and numerical-aperture (NA) data, clear aperture and back-reflection restrictions. | Mechanical fit does not establish safe optical coupling or freedom from clipping. |
| Lens and field | Lens model, scanner spacing, field correction, spot definition, working-distance datum and approved protective window. | Changing one part can change focus, field and returned reflections. |
| Scanner and controller | Supported paths, practical speed/frequency limits, laser timing, external motion, fault response and safety interfaces. | Maximum width and maximum speed may not be available together for the chosen pattern. |
| Duty and service | Cooling, ambient limits, sustained-load evidence, consumables, calibration and replacement procedure. | A short demonstration does not establish shift-long stability. |
Scroll sideways on mobile to read the complete comparison.
Let geometry and handling narrow the options
For a handheld job, compare head mass together with cable drag, grip, reach and access to the surface. For a fixed or robotic job, compare mounting datums, cable routing, external motion and service clearance. On varying heights, check whether controlled repositioning or a qualified dynamic-focus system is needed.
For angle-sensitive features, investigate telecentricity. For a broad surface, compare usable field and accepted area per cycle. These are reasons to test a configuration; none automatically selects a pulsed or CW source without the material and removal requirement.
Protect the window, then diagnose changes in performance
The protective window limits contamination of the optics behind it. Deposits can absorb the beam and create local heating; damage may develop before the loss is obvious from the cleaning result. LASER COMPONENTS describes the debris shield’s role and the importance of low-absorption optics.
Purge and extraction have different jobs
An approved purge or air knife discourages deposition near the window. Local exhaust captures the plume at the work area. Purge does not remove the need to control airborne contamination.
Keep the capture point effective through the full motion path, and select filtration for the actual removed material and generated emissions. Laserax’s extraction guidance explains source capture and monitoring of filtration performance. Use the head supplier’s specified gas quality, flow and pressure; no generic air setting fits every design.
Inspect with emission safely disabled and the equipment secured as its procedure requires. Follow the exact window part number and permitted inspection, cleaning or replacement method. Do not fire with the window removed.
Inspect first; clean only when permitted
LASER COMPONENTS’ optics-handling guide warns that wiping larger particles can scratch optics and that eyeglass wipes may leave harmful additives. Its advice also differs by coating. Do not turn one solvent or wiping method into a universal instruction for an assembled cleaning head.
Use the inspection interval and condition limits in the machine manual. Record window condition, operating hours, application, extraction status and the reason for replacement. Repeated failures call for a review of deposition, installation and optical load. The laser-lens cleaning and damage guide covers cleaning-versus-replacement decisions in more detail.
| Symptom | Compare first | Next investigation |
|---|---|---|
| Weaker cleaning everywhere | Known reference sample, recipe, standoff and safely inspected window. | If the change persists, check source status and escalate optical-output or alignment checks to qualified service. |
| Center passes; edges fail | Same surface at center and edge with controlled height. | Field calibration, edge spot/focus, incidence and local scan speed. A smaller pattern is a diagnostic comparison, not proof of repair. |
| Bands or hot turnarounds | Pulse spacing, line pitch, head advance and turning zones. | Trajectory timing, speed changes and overlap definitions; separate motion effects from material variation. |
| A new window fails quickly | Correct part, installation, purge, extraction and deposit location. | Recurring plume exposure, handling contamination or excessive optical load. Stop using suspect optics. |
Scroll sideways on small screens. Do not open sealed optics or bypass protective functions to investigate a symptom.
How should you qualify a head on your parts?
Test the configuration over the conditions it will encounter. The decision is whether it delivers the required surface consistently at a useful production rate, with manageable service needs.
- Define the endpoint. Identify the substrate and contaminant, required removal, permissible material loss or roughness, and the downstream coating, bonding or other functional requirement.
- Map field and height. Compare center, edges and corners of the intended field at nominal and expected height offsets. Keep surface condition and inspection method comparable.
- Include real duty. Check results after warm-up and through a representative run. Include handling, robot moves, multiple passes, inspection and interruptions when reporting accepted area per hour.
- Keep the configuration traceable. Record source/head/lens/window identifiers, focus reference, pulse and scan settings, motion, purge, extraction and measured outcomes. Retain a baseline for later drift checks.
Can I change only the lens to get a wider cleaning field?
Only within a combination approved for that source and scanner. Confirm beam diameter, lens position, coatings, back reflections, focus datum and the required correction file. Recheck the spot and surface result across the new field. A matching mounting thread alone is insufficient.
Will a distance sensor keep a curved part in focus?
It can support standoff control if its accuracy, response, surface response and optical datum are suitable. A sensor reading at one point does not show that an entire wide field on a curved part is in focus. The system also needs motion or focusing hardware and control that can act on the measurement.
Send Oceanplayer Laser the material and contaminant, part drawing or photos, required finish, work area and production duty. If you already have a laser, include its exact source model and current head/lens details so the discussion starts with the actual interfaces.