Pulsed versus continuous-wave (CW) laser cleaning — how they differ and why there is no simple answer

RC-Laser Team · 2 November 2026

Pulsed and continuous-wave (CW) lasers in cleaning: peak power, pulse duration, heat input and when each mode makes sense according to technical sources.

Two ways of delivering energy

A pulsed laser concentrates energy in short pulses, while a continuous-wave (CW) laser shines without breaks. Fraunhofer ILT states that laser cleaning uses pulsed or continuous radiation, and it does not compare the modes ^[11]. A review paper notes that the thermal-stress mechanism relies on very short pulses, and thermal ablation requires comparing the ablation thresholds of the layer and the substrate ^[6]. Cleaning most often uses nano- or microsecond pulses; pico- and femtosecond pulses reduce thermal effects and the risk of damaging the substrate ^[7].

Peak power, pulse duration and average power

Average power says how much energy the laser delivers over time, peak power how high the power is during a single pulse. Peak power is roughly pulse energy divided by pulse duration, so a laser with modest average power can have many times higher power within the pulse. A manufacturer describes an example laser with 750 W average power, 30 ns pulse duration, up to 80 mJ pulse energy and 3 MW peak power ^[13]; in one study a pulsed laser with 200 W average power was described as having high peak power, while the CW laser had 2000 W ^[1].

Heat input: pulsed does not mean “cold”

Short pulses limit heat conduction into the material: the author of a text on stone cleaning describes each nanosecond pulse as a very brief release of heat ^[9], and a study on bone shows that shorter pulses markedly reduce heat accumulation, while a sub-nanosecond 1064 nm laser generated significant heat and could cause cracking and charring ^[8]. That does not mean a pulse never heats. A pulsed laser with high average power heated stainless steel to about 350–675 °C with a longer processing time, producing an oxide layer and chromium depletion ^[10]; Polish authors write that despite the pulses, micro-melting of the surface is hard to avoid ^[12]. In a study on carbon steel, pulsed cleaning caused craters through thermal shock, while continuous cleaning caused heat accumulation and, with high heat input, growth of some grains ^[1]. In another study microhardness rose from 102 to 150 HV after direct continuous irradiation ^[3].

Thin and thick layers

The author of a doctoral thesis claims that pulsed lasers remove only tens of micrometres of rust, which is a limitation for building structures, while a high-power CW laser removes thicker layers and suits large structures ^[2]. This is the statement of a single work, without its own comparison of the two modes. Authors affiliated with a laser manufacturer, in a test of paint removal from aluminium and carbon steel, point to pulsed for precision cleaning, for example moulds, and CW for large steel structures and pipes ^[5]; the test covered two materials and two paint thicknesses. In another manufacturer’s example, short pulses remove layers on the order of single micrometres, such as paint, oil and oxides ^[13].

Why there is no simple answer to “which is better”

Results depend on the task. In the manufacturer’s test the CW laser melted the substrate even after the paint was removed, darkened the surface and raised roughness to about 1.5 times the initial value, while the pulsed laser left similar or lower roughness ^[5]. On a glass-fibre composite it was the other way round: with a double coating the pulsed mode left paint residue and easily damaged the primer, resin and fibre, while CW removed both layers and gave a clean surface ^[4]. In a study of oxide on Q235B steel the combination of both modes gave the best result: the pulse melted and vaporised the oxide and CW removed the residue ^[1]. None of the studies cited compares the modes at the same peak power on rust or stone. For stone we found no studies of CW lasers; the works on stone cited here describe pulsed lasers.

What this means for choosing a method for a given part

A cautious conclusion follows from the works cited: operating mode is one of several variables, alongside average power, pulse duration, scanning speed and the type of substrate and layer. So we do not claim that either mode is always safer or better. The choice of method for a specific part is decided by a test on a sample. We give an initial estimate from a photo, and the final price after viewing the item on site.

The studies cited concern specific materials and settings, and three sources come from authors affiliated with laser manufacturers. This text does not describe RC-Laser equipment.

Sources

1. Zhang et al. (2025), integrated pulsed-continuous laser cleaning of Q235B steel, Materials 18(6), 1247
2. Q. Wang (2023), doctoral thesis on continuous-wave laser treatment of corroded steel structures, Kyushu University
3. Cui et al. (2024), continuous-wave laser ablation of rust layers, Applied Sciences 14(12), 5052
4. Li et al. (2023), pulsed and continuous-wave laser paint removal on glass fibre-reinforced polymer composites, Infrared and Laser Engineering 52(2) (abstract)
5. Song et al. (2021), “Laser cleaning with continuous-wave vs. pulsed fiber lasers”, Laser Focus World (authors from a laser manufacturer)
6. Zhou et al. (2023), “The Fundamental Mechanisms of Laser Cleaning Technology and Its Typical Applications in Industry”, Processes 11, 1445
7. J. Brand (2026), “Introduction to laser cleaning in cultural heritage”, Analytical Methods (RSC), AMCTB 121
8. Rahman et al. (2023), ultra-short pulse laser cleaning of bone, Heritage 6
9. M. Cooper, “Recent Developments in Laser Cleaning”, Building Conservation Directory (text from the late 1990s)
10. Yoo et al. (2025), effect of high-power laser cleaning on 304L stainless steel, Micromachines 16(12), 1366
11. Fraunhofer ILT, “Cleaning”
12. T. Burakowski, W. Napadłek (2010), “Mikroobróbka laserowa – możliwości zastosowań w przemyśle”, Prace Instytutu Elektrotechniki 245 (in Polish)
13. Weiler, Cook, Evangelista, “Fast Short-Pulse Lasers Enhance Surface Cleaning”, Photonics.com (authors from Trumpf, a laser manufacturer)

Sources as of 2 November 2026.