I. Working Principle of Laser Cleaning Technology
Laser cleaning technology refers to a process that uses high-energy laser beams to irradiate the surface of a workpiece, causing contaminants, rust, or coatings to evaporate or peel off instantly, thereby achieving cleanliness. The core lies in selective absorption of materials and instantaneous conversion of energy.
Precise Energy Delivery: A laser generates coherent light with high brightness, good directionality, and a specific wavelength, which irradiates the contaminant surface.
Selective Absorption: Different materials have significantly different absorption rates for specific laser wavelengths. By selecting a wavelength that is "easily absorbed by contaminants but hardly absorbed by the substrate," the laser energy is mainly absorbed by the contaminants, leaving the base material virtually undamaged. When a high-energy-density laser beam strikes the surface to be cleaned, it rapidly heats the target area, causing the temperature to rise sharply above the boiling point, thereby achieving evaporation or peeling of contaminants.
Instantaneous Conversion and Removal: The energy absorbed by contaminants is converted into thermal energy within an extremely short time (typically nanoseconds, picoseconds, or even femtoseconds), causing a sharp temperature rise. Contaminants are removed through several mechanisms: decomposition/evaporation (when temperature exceeds the decomposition/vaporization point, contaminants turn into vapor); thermal-expansion-induced fracture and ejection (extremely high heating rates create significant temperature gradients and thermal stress within the contaminant layer, causing violent expansion and fragmentation); interfacial peeling (thermal expansion coefficient differences between contaminants and substrate generate interfacial stress, causing the contaminant layer to peel off as fragments). High-energy beams absorbed by rust layers, paint layers, etc., can also form rapidly expanding plasma and generate shock waves that break contaminants into fragments.
Compared with traditional cleaning methods, laser cleaning features include:
It is a "dry" cleaning process that requires no cleaning fluids or chemical solutions, with cleanliness far exceeding chemical cleaning;
It works on a wide range of contaminants and substrate materials;
By adjusting laser process parameters, contaminants can be effectively removed without damaging the substrate surface;
It can be easily automated;
Equipment can be used long-term with low operating costs;
It is a "green" cleaning process—the waste is solid powder, small in volume, easy to store, and essentially non-polluting.
II. Applications of Laser Cleaning Across Industries
Laser cleaning technology is a rapidly developing new cleaning technology that has applications in railways, aerospace, marine, automotive, molds, nuclear power, machinery, electric power, cultural heritage, and more. Typical applications include:
Mold Cleaning: In tire manufacturing, molds must be thoroughly cleaned at regular intervals. Laser cleaning enables "in-situ cleaning" without removing molds from equipment—saving time and labor, avoiding mold damage, and producing no pollution.
Weapon Equipment Cleaning: Laser cleaning efficiently removes rust and contaminants from equipment surfaces, and by setting different parameters, can form a dense oxide protective film on metal surfaces, enhancing surface strength and corrosion resistance. Heavy weapons stored in humid environments often develop mold on optical components and electrical connectors; laser cleaning effectively removes mold.
Aircraft Paint Removal: When fighter jets require repainting, laser cleaning can completely remove old paint layers without damaging the metal surface. Chemical immersion/wiping, the traditional method in aviation, generates large amounts of chemical waste and poses health risks; laser cleaning enables high-quality paint removal from aircraft skins with easy automation.
Cultural Heritage Conservation: The "Palace Museum Hospital" in Beijing has used laser cleaning technology to restore and preserve its collections. Sculptures at Amiens Cathedral in France and Cologne Cathedral in Germany have regained their splendor through laser cleaning. The Parthenon sculptures and the Caryatids of the Erechtheion at the Athens Acropolis have also been restored via laser cleaning. In 2012, the Louvre exhibited Leonardo da Vinci's The Virgin and Child with Saint Anne after laser cleaning.
Electronics Industry Cleaning: In chip manufacturing, laser cleaning can precisely remove dust particles as small as 0.1 micrometers (one-hundredth the thickness of a human hair), significantly improving chip yield rates—and it is indispensable in complex structures like 3D chip packaging.
Nuclear Power Plant Pipeline Cleaning: Laser cleaning can achieve remote operation through fiber optics, making it suitable for cleaning hazardous locations such as nuclear facilities.
Rail Transit: Currently, pre-welding cleaning of steel rails relies on grinding wheels, which causes substrate damage and consumes large amounts of consumables. Laser cleaning provides a green cleaning solution for high-speed railway track laying.
III. Technical Challenges and Outlook
Despite its significant advantages, laser cleaning faces challenges:
Material Adaptability: Different materials respond differently to laser cleaning. Laser cleaning technology that is mature for stone in Europe can cause yellowing when applied to Chinese white marble (Han Baiyu). In September 2020, under the guidance of the Ministry of Science and Technology, the "China-Greece Belt and Road Joint Laboratory for Cultural Heritage Conservation Technology" was officially approved, jointly established by the Palace Museum and the Foundation for Research and Technology-Hellas (IESL). The teams are addressing this technical difficulty by adjusting multi-wavelength combinations and using ultrashort-pulse (picosecond laser) technology to reduce thermal effects and avoid substrate damage.
Standardization Gap: The lack of standards is a key obstacle to promotion—different cultural relics require customized parameters. In 2021, the first national standard for laser cleaning was initiated in Wuhan, led by organizations including AVIC Integrated Technology Institute.
In terms of technology integration, in the Pompeii project in Italy, laser cleaning was combined with hyperspectral imaging to build a full-cycle "diagnosis-restoration-monitoring" management system, providing a model for technological synergy. As technology becomes more intelligent and collaboration globalizes, laser cleaning will continue to drive sustainable development.
