# Paint Removal with Pulsed Laser: Theory Simulation and Mechanism Analysis
## 1 Introduction  
The continuous development of laser technology has enabled its widespread application in the communication, medical, and manufacturing fields. Laser paint removal, which is an efficient paint layer treatment method, is a new application. Compared to the traditional physical and chemical paint removal methods, laser paint removal has several advantages: (1) non-contact cleaning with small impact on the substrate; (2) less environmental pollution, and easy disposal of the resultant waste; (3) high cleaning efficiency with low costs; and (4) good controllability. This technology can be used to remove paint off the surface of buildings, bridges, aircraft, vehicles, and various mechanical equipment. Although it has been widely studied, its physical mechanism is complicated, proving to be a challenge for researchers.  
Laser paint removal involves a series of complex processes, such as melting, evaporation, and combustion. [PERSON] [1] summarized and classified the laser cleaning mechanism into six kinds of action mechanisms: ablation, rapid heating and cooling caused by vibration waves, selective vaporization, light pressure, gasification pressure, and plasma burst. Research by [PERSON] [2] andZhou [3] portrayed the laser process as an ablation effect. [PERSON] [4] and [PERSON] [5] highlighted the application of a thermoelastic vibration model in laser cleaning. [PERSON] [6] investigated the influence of thermal stress during the laser paint removal process and found that paint absorbed laser energy, formed a large temperature gradient, and was finally removed by thermal stress. A study by [PERSON] et al. [7] showed that ablation and thermo-mechanical actions were the main mechanisms used for the absorption medium and transparent medium, respectively. [PERSON] et al. [8] studied laser paint removal behavior using a high-power continuous CO\({}_{2}\) laser. They found that the paint removal mechanism was not an independent action, but one that included thermal stress, laser soft ablation, and plasma effects. Several factors--such as the physical and chemical properties of the attachment, physical parameters of the substrate materials and the laser beam, and the cleaning environment--determine which mechanism is dominant.  
All of these findings provide important references to study laser paint removal. We found that the use of functional groups and elemental valence changes to study this technology was relatively low.  
The experiment performed in this paper aimed at investigating the laser mechanism of paint removal. A finite element model of mobile pulse laser cleaning was established by using COMSOL Multiphysics software. The calculation of temperature fields during laser cleaning was used to aid the analysis. A cleaning experiment was also carried out. Furthermore, to determine the decomposition process, the chemical and physical characteristics of the surface cleaned by the laser were analyzed by XPS. By analyzing changes in the functional groups and chemical valence of C, O, N, Al, and Ti on the surface of the sample before and after cleaning, as well as SEM images of the cleaning surface and the collected particles, the laser paint removal mechanism was comprehensively studied; a high repetition frequency fiber laser was used for the study.