Fundamentals · 6 min read
Pulsed vs. continuous-wave: the difference that decides your job
Two machines both described as 'laser cleaners' behave completely differently on your material. How to tell which one a contractor is bringing, and when it matters.
Every laser cleaning company describes their process as gentle, precise and non-destructive. Some of them are running equipment that is none of those things on your material. The distinction is not marketing — it is a hardware difference, and you can ask about it directly.
Continuous-wave: a constant beam
A CW laser emits without interruption. Typically 1,000 to 3,000 watts, aimed at moving quickly across large areas of robust material.
The consequence is sustained heat input. Energy keeps arriving while heat conducts down into the substrate, so surface temperature climbs and keeps climbing. On structural steel or a pipeline exterior that is entirely fine and genuinely the efficient choice. On aluminium it risks distortion and annealing. On wood it scorches before the coating clears. On stone it can cause thermal shock and colour change.
Pulsed: bursts with gaps
A pulsed fiber laser fires in nanosecond bursts separated by dead time. Peak power during the pulse is very high; average power stays low.
That structure changes the physics. Energy is delivered faster than thermal diffusion can carry it into the substrate, and the gaps let accumulated heat dissipate before the next pulse arrives. Removal happens at the coating; the material underneath stays cool. Aircraft aluminium comes off under 120°C — unannealed, undistorted.
The trade is speed. Pulsed systems are slower per square foot and cost more. On a big plain surface with nothing to protect, that is a real disadvantage and an honest contractor will say so.
Which to insist on
| Structural steel, tanks, pipeline exterior | CW is faster and cheaper | Either works |
|---|---|---|
| Aircraft aluminium and thin panels | CW risks distortion and annealing | Pulsed |
| Wood, timber, log walls | CW scorches before the coating clears | Pulsed, always |
| Stone, brick, adobe | CW risks thermal shock and colour change | Pulsed |
| Patinated bronze and fine art | CW cannot discriminate finely enough | Pulsed, always |
| Moulds, tooling, fine detail | CW is too blunt | Pulsed |
The four parameters, and why they exist
On a pulsed system, four things are tuned independently. Together they set the energy density — the fluence, in joules per square centimetre — landing on the surface, and fluence is what determines whether you remove a coating or damage a substrate.
- Power — how much energy is available.
- Pulse frequency — how many bursts per second. Counter-intuitively, lowering frequency at constant power raises the energy in each individual pulse.
- Pulse duration — how long each burst lasts. Shorter concentrates energy in time and reduces heat transfer into the substrate.
- Scan speed — how fast the spot moves, which sets how many pulses land on any given point.
The correct approach on unfamiliar material is to start conservative and raise fluence progressively — and the safest first move is usually reducing frequency rather than increasing power, because it raises energy per pulse without adding average heat. Watching for the warning signs while you do it: surface waviness, colour change in the substrate, any sign the base material is being reached.
Three questions worth asking any contractor
- Is your system pulsed or continuous-wave, and at what wattage? If they cannot answer immediately, that is your answer.
- How do you establish parameters for a material you have not worked before? You want to hear about test patches and progressive fluence, not "we have a preset."
- Show me a job where the settings were wrong. Anyone experienced has one. Anyone who claims otherwise has either not done much or is not being straight with you.