A review of thermal effects and substrate damage control in laser cleaning

Laser cleaning has the advances of environmental friendliness, high quality and efficiency, no secondary damage, simple process, safety and reliability, easy to realize automation and low operation and maintenance costs. The application in manufacturing and remanufacturing fields such as aerospace, automobile manufacturing, shipbuilding, and electronics industry is becoming increasingly widespread. Laser cleaning exerts an integrated effect through photon pressure, thermal ablation, vibrational waves, and plasma bursts, facilitating high-quality and efficient surface cleaning of substrates. The thermal effects serve as the primary mechanism driving thermal ablation and plasma bursts, predominantly governing most cleaning scenarios. The laser's thermal effects are employed to eliminate surface contaminants, yet its residual influence may concurrently inflict damage on the substrate. How to avoid substrate damage is a challenge for the engineering of laser cleaning technology. This paper focuses on the thermal effects and minimizing damage in laser cleaning. The mechanism of contaminants removal by thermal effects and the influence of residual thermal radiation on the substrate surface are comprehensively explained. The thermal response characteristics of substrate surface are clarified for different pulse widths, scanning speeds and energy densities. Theoretical validation analysis was performed by means of simulation. The feasibility of using laser-induced breakdown spectroscopy and photoacoustic techniques for real-time monitoring of substrate damage is discussed. Studies have demonstrated that the application of diverse cleaning methods, the selection of appropriate laser parameters, and real-time monitoring of the cleaning state can achieve the dual objectives of efficient cleaning and maintaining the integrity of the substrate.