• Dry cleaning mechanism: Thermal ablation is the primary mechanism. When laser energy acts on the oxide film, the surface absorbs a large amount of energy, changing the ablation mechanism based on energy intensity and forming various surface morphologies. At low energy, the oxide film is partially removed with minimal remelted areas; at moderate energy, the oxide film is completely removed with negligible damage; at high energy, although the oxide film is removed, significant substrate damage occurs, forming ridge-like surface structures.
• Wet cleaning mechanism: At low energy densities, the main mechanism is laser-induced shock waves; at high energy densities, thermal ablation and phase explosion dominate. During cleaning, rapid cooling and heating of the titanium alloy form martensitic titanium alloy. When the energy density reaches a specific value, the surface transforms into a nanostructured protruded surface, which is of great significance for the subsequent application of titanium alloy materials.

High-Speed Rail: Paint on Aluminum Alloy Car Bodies

• Thin paint (thickness ≤ 40μm): Laser light sources with wavelengths of low paint absorption rate achieve better results through thermal vibration.
• Thick paint: Laser light sources with wavelengths of high paint absorption rate are required, using ablation mechanism for removal.
• Red paint stripping: The primary stripping mechanism for red paint is vibration. During cleaning, laser energy penetrates the substrate, and thermal stress generated by substrate temperature rise causes paint to peel off. The entire paint layer can be removed, leaving a loose network-like morphology of residual paint on the aluminum alloy surface.
• Blue paint removal: Under the same laser energy input, blue paint reaches a higher temperature than red paint but induces lower substrate thermal stress. When the paint temperature reaches the boiling point, it is removed through evaporation, accompanied by coupled mechanisms such as delamination, combustion, and plasma shock.

Marine Ships: Rust on High-Strength Steel Hull Surfaces

• Dry cleaning for rust removal: The main removal mechanism during dry cleaning of rust on high-strength steel hulls is vaporization of the oxide film upon energy absorption. The downward reaction force generated during vaporization of surface oxides helps remove thicker oxide films.
• Liquid film-assisted laser rust removal: The primary mechanism is phase explosion of liquid droplets upon energy absorption, generating impact forces to remove rust layers. The explosive boiling of the liquid film enhances the phase explosion mechanism’s effect on rust removal, enabling better removal of surface oxide films but struggling with deeply embedded oxides. Different rust layer removal mechanisms affect the flow of surface molten metal: lateral thrust from phase explosion promotes molten layer flow for a flatter surface, while oxide vapor from vaporization hinders liquid metal from filling pits.

Marine Environment: Marine Microorganisms on Aluminum Alloy Surfaces

• Laser parameters and cleaning effects: Lasers with narrow pulse width and high peak power achieve excellent cleaning results for marine microorganisms on aluminum alloy surfaces.
• Microorganism removal mechanism: The laser removal mechanisms for the extracellular polymeric substance (EPS) layer and barnacle substrates are ablation vaporization and shock wave stripping, respectively. Single chains of microbial macromolecules break during multiphoton absorption, decomposing into a large number of atoms. Under the combined action of plasma shock and ablation mechanisms, marine microorganisms are effectively removed.
• For organic substances such as paint and marine microorganisms: At low laser energy densities, photochemical effects break chemical bonds, resulting in deterioration, discoloration, or loss of activity. As energy density increases, phenomena such as ablation, vaporization, combustion flames, and plasma shock occur. For inorganic substances such as oxide films and rust: No changes occur at low energy densities; ablation and vaporization appear as energy increases.

• Cultural Heritage Laser Cleaning

  Pulsed lasers play a crucial role in cultural heritage preservation, meeting the requirements of non-destructive and high-precision cleaning for cultural relics such as stone artifacts, paper artifacts, and metal artifacts.