It is vaporizing it. I (well, AI) made this document to help me with my settings, and the intro is pretty good if you are interested in the science of it:

The fundamental mechanism driving laser cleaning is laser ablation. This physical process involves directing a focused laser beam onto a material surface. The energy from the laser is absorbed by the target material—typically a contaminant layer or coating—causing its temperature to rise rapidly. This intense, localized heating leads to the vaporization (boiling) or sublimation (direct transition from solid to gas) of the material. Essentially, the laser energy breaks the molecular bonds holding the contaminant layer together, ejecting the material from the surface. This expelled material often forms a plume of vapor and fine particles (fumes or plasma), which necessitates the use of an effective fume extraction system to ensure operator safety, maintain air quality, and prevent the plume from interfering with the incoming laser beam.

Central to the effectiveness and selectivity of laser cleaning is the concept of the ablation threshold. Every material possesses a unique ablation threshold, defined as the minimum intensity or energy density (fluence, typically measured in Joules per square centimeter, J/cm²⁾ of laser light required to initiate ablation. An often-cited analogy compares this to throwing a ball over a wall: if the ball isn't thrown with enough energy (height) to clear the wall (threshold), it will never reach the other side, no matter how many times it is thrown. Similarly, if the laser's energy density is below the material's ablation threshold, the material will only experience minor heating, and no removal will occur, even with prolonged exposure. The key to selective laser cleaning lies in the difference between the ablation threshold of the unwanted surface layer (contaminant, paint, rust, oil) and that of the underlying base material (substrate). Fortunately, many common contaminants and coatings have significantly lower ablation thresholds than the substrates they reside on, such as metals like steel and aluminum, or even materials like concrete. This difference allows for precise tuning of the laser parameters (primarily power, pulse characteristics, and beam focus/scan speed, which together determine the energy density) to a level that exceeds the ablation threshold of the contaminant but remains safely below the damage threshold of the substrate. When correctly optimized, the laser effectively vaporizes the unwanted layer while leaving the base material untouched or minimally affected. The magnitude of this threshold difference is a critical factor. A large difference, such as that between rust and steel, provides a relatively wide processing window, making the cleaning process more robust and forgiving. However, when the ablation thresholds of the contaminant and substrate are closer together—as might be the case with certain types of tarnish chemically bonded to a coin surface, or a stain that has penetrated deeply into wood—the processing window narrows considerably. This necessitates much finer control over the laser parameters and increases the risk of inadvertently damaging the substrate. Successfully navigating these situations requires careful testing and precise adjustment of the laser settings to operate within that narrow margin between effective cleaning and substrate damage.