Can a CW laser clean a surface?

Many so-called Chinese CW laser models are on the market, claiming to be a cheap cleaning solution. Yes, the CW laser is a very cheap laser, but it can not be compared with the pulsed laser. Laser cleaning is a surface balance equation between heating and cooling down. The contamination present on the surface must be quickly heated without heating the surface and damaging it. This sensitive balance is only possible with pulsed lasers that will shoot very short ( 100 nanoseconds long) heat-energy- bullets to the surface. In time, the bullet size can be regulated over the software and optical lenses. Although we shoot 100,000 bullets a second (100Khz) with a specific energy value (millijoule), the surface can cool down between the laser bullets. This prevents the surface from overheating and provokes melting on the surface. Every material consists of atoms and electrons circling around, if energy is added to a material, the electrons start to vibrate more. Returning to the normal state is called electron relaxation time, measured in nanoseconds. A pulsed laser can make the electron vibrate but leaves enough relaxation time to bring the electron back in normal relaxation mode. Therefore, you need a pulsed laser to obtain a cleaning result that can be repeated. A continuous wave laser or CW shoots a constant amount of energy to the surface, which you cannot control manually. The bandwidth of useability is 1 against 1000 for a pulsed laser. A CW laser is used for cutting, welding, hardening or cladding. Even in the cutting and welding process, research is developing towards pulsed systems to have more control on the surface. The heat impact is not wanted because it creates oxides in the melt pool. With a CW laser, you create an unwanted overheating effect on your surface; sandblasting will be needed to paint a quality reference surface. CW lasers are mainly a Chinese marketing joke to mislead customers at low prices. They are not on the same quality level as the Western companies about production processes and final customer quality.

In the future, we will see shorter pulse lengths be used for cleaning. Scientific lasers with femto and pico second pulses already exist but are expensive. With a femtosecond pulse duration, the energy transition to the surface is so short that heat impact does not affect the material.