Laser cleaning technology is a new technology based on the interaction effect between laser and matter. It is unlike traditional mechanical cleaning, chemical cleaning, and ultrasonic cleaning methods, laser cleaning does not require any CFC type organic solvents that damage the ozone layer, is pollution-free, noiseless, and harmless to humans and the environment. It is a "green" cleaning technology.

Laser cleaning includes both physical and chemical processes, and in many cases, it is mainly physical processes accompanied by some chemical reactions. The main processes can be summarized into three categories, including gasification process, shock process, and oscillation process, respectively corresponding to wet laser cleaning technology, laser plasma shock wave technology, and dry laser cleaning technology.

Gasification process: When high-energy laser is irradiated on the surface of a material, the surface absorbs laser energy and converts it into internal energy, causing the surface temperature to rapidly rise above the material's vaporization temperature, thereby causing pollutants to detach from the material surface in the form of steam. When the absorption rate of surface pollutants to laser is significantly higher than that of substrate to laser, selective vaporization usually occurs. A typical application case is the cleaning of dirt on stone surfaces. As shown in the figure below, the pollutants on the surface of stone have a strong absorption of laser and are quickly vaporized

The typical process dominated by chemical reactions occurs when using ultraviolet laser to clean organic pollutants, known as laser ablation. UV laser has a shorter wavelength and higher photon energy, such as KrF excimer laser, which has a wavelength of 248nm and a photon energy of up to 5 eV, exceeding 40 times the photon energy of CO2 laser (0.12 eV). Such high photon energy is sufficient to break the molecular bonds of organic compounds, causing the C-C, C-H, C-O, etc. in organic pollutants to break after absorbing the photon energy of the laser, resulting in cracking and gasification. As a result, organic pollutants are removed from the surface.

Impact process: The impact process is a series of reactions that occur during the interaction between laser and material, resulting in the formation of shock waves on the surface of the material. Under the action of shock waves, surface pollutants undergo fragmentation, turning into dust or debris that detach from the surface. There are various mechanisms that cause shock waves, including plasma, steam, rapid thermal expansion and contraction, etc

Oscillation process: Under the action of short pulses, the process of material heating and cooling is extremely rapid. Due to the different thermal expansion coefficients of different materials, surface pollutants and the substrate will undergo high-frequency and varying degrees of thermal expansion and contraction under short pulse laser irradiation, causing oscillation and causing pollutants to peel off from the material surface. During this peeling process, material vaporization may not occur, nor may plasma be generated. Instead, the shear force formed at the interface between the pollutant and the substrate under the action of oscillation disrupts the bond between the pollutant and the substrate

The structure of the laser cleaning machine, which mainly consists of laser system, beam adjustment and transmission system, movable platform system, real time monitoring system, automatic control and operation system, as well as its working principle, was introduced.