How to optimize parameters to improve laser cleaning effect

1、 Key parameters and their effects of laser cleaning

In the laser cleaning process, the cleaning effect mainly depends on multiple key laser parameters, including wavelength, pulse duration, energy density, spot size, and beam quality. By selecting and optimizing these parameters reasonably, not only can efficient removal of pollutants be achieved, but also the thermal impact and damage risk to the substrate can be effectively reduced, thereby improving the overall cleaning quality and stability.

wavelength
Laser wavelength is a fundamental physical property of the laser beam, and different materials absorb different wavelengths significantly differently. Metals generally absorb shorter wavelengths (such as 1064 nm fiber lasers) better, making them suitable for laser rust removal and pre-weld oxide removal. Organic materials and polymers, on the other hand, are more suited to UV or visible wavelengths due to their higher absorption and reduced thermal impact. The removal of coatings and paints is also closely related to wavelength selection. For applications requiring high selectivity, 532 nm or 355 nm lasers can be considered. Choosing the right wavelength can significantly improve the efficiency and stability of laser surface treatments.

Pulse duration
Pulse duration refers to the duration of a single laser pulse. Shorter pulses increase peak power and minimize thermal diffusion, effectively removing contaminants while minimizing thermal damage to the substrate. Nanosecond and microsecond pulses are suitable for most industrial cleaning applications, such as large-area rust removal and coating removal. Picosecond and femtosecond pulses, however, are more suitable for cleaning high-precision and sensitive materials due to their minimal thermal impact, but they come at the expense of higher equipment costs.

Energy density
Energy density, the distribution of laser energy per unit area, is one of the most critical process parameters in the cleaning process. If the energy density is too low, the contamination layer cannot be effectively removed; if it is too high, the substrate may melt or burn. It is usually necessary to find an optimal range close to the material’s ablation threshold to ensure cleaning efficiency while avoiding side effects. When removing rust or coatings with lasers, experimentally determining the appropriate energy density is a key step in ensuring process stability.

Spot size and beam quality
The spot size determines the coverage efficiency and precision of cleaning. Small spots are suitable for precise cleaning of fine areas, while large spots are more suitable for rapid cleaning of large areas. Furthermore, the better the beam quality and the more uniform the focus, the more stable and consistent the cleaning. In practical applications, it is also necessary to properly control the scanning speed and pulse overlap ratio to avoid streaks or missed scans and achieve uniform cleaning results.

In summary, wavelength determines material absorption efficiency, pulse duration affects thermal effects and precision, and energy density determines whether cleaning can be both efficient and safe. Spot size and beam quality balance efficiency and consistency. When applying laser cleaning technology, companies should comprehensively adjust these key parameters based on different materials and process requirements to achieve optimal cleaning results and production efficiency.

2. Parameter optimization for different materials and applications

Different materials have distinct physical and chemical properties. Therefore, laser cleaning parameters must be selected and optimized based on these characteristics. Indiscriminately applying the same laser parameters can lead to inefficient cleaning and even irreversible damage to the substrate. Below, we explore parameter optimization strategies for three application categories: metals, organic materials, and paints and coatings.

Metal materials
Metal surface cleaning is one of the most widely used applications of laser cleaning, typically including laser rust removal, pre-weld oxide scale removal, and surface pretreatment.

Wavelength: Most metals absorb near-infrared wavelengths well, with 1064 nm fiber lasers becoming the near-standard choice. They not only guarantee high absorption rates but also offer stable and reliable industrial performance.

Pulse Duration: Short laser pulses (nanoseconds or microseconds) are recommended. This provides concentrated and precise energy, effectively removing oxides and rust while avoiding excessive heat transfer to the metal substrate, reducing the risk of surface melting and deformation.

Energy Density: Energy density should be controlled within a medium-to-high range to ensure rapid removal of rust or oxides while preserving the surface quality of the metal substrate.

Application Example: In laser rust removal of steel structures, 1064 nm nanosecond pulses with a medium-to-high energy density achieve uniform, controllable cleaning while maintaining efficiency.

organic materials
Organic materials (e.g., plastics, rubbers, composites) are generally more sensitive to heat and therefore require finer parameter control during cleaning.

Wavelength: Organic materials absorb UV wavelengths very well, so 355 nm UV lasers are often preferred. Compared to infrared wavelengths, UV laser energy is more readily absorbed by contaminants, reducing thermal diffusion and preserving the integrity of the material structure.

Pulse Duration: Ultrashort pulses (picosecond or even femtosecond) are recommended. Their extremely high peak power enables “cold peeling,” significantly reducing side effects such as carbonization and ablation, making them ideal for sensitive polymer materials.

Energy Density: Low to moderate levels are recommended. Excessive energy density can easily cause carbonization or surface blackening, damaging the appearance and performance of organic materials.

Application Example: When laser cleaning aerospace composite surfaces, UV picosecond lasers are used. They can remove oil and adhesive residue at low energy densities while maintaining the material’s mechanical properties.

Paints and coatings
Lasers also excel in removing paint and coatings and are widely used in industries such as shipping, rail transportation, automotive manufacturing, and aerospace.

Wavelength: Common choices are 1064 nm fiber lasers or 532 nm green lasers. The former offers high efficiency and is suitable for large-area coating removal; the latter performs better when higher selectivity is required, especially when the substrate is sensitive to infrared light.

Pulse Duration: Short pulses more effectively concentrate energy on the coating, promoting rapid removal without thermally damaging the underlying metal or composite material.

Energy Density: A medium range is typically selected to ensure rapid coating degradation while avoiding etching or melting the substrate, ensuring the integrity of the cleaned surface.

Application Example: In ship hull maintenance, using a 1064 nm laser to remove paint from large areas significantly improves work efficiency and reduces secondary contamination while maintaining the steel surface quality.

Different materials exhibit fundamental differences in their absorption and tolerance to lasers, so laser cleaning applications should be tailored to the specific material. Metals are suited to 1064 nm fiber lasers combined with short pulses and medium-to-high energy density for efficient rust and oxide layer removal. Organic materials require UV lasers combined with ultrashort pulses and low energy density to minimize thermal damage and carbonization. Paints and coatings can choose between 1064 nm and 532 nm, combining short pulses with medium energy density for both high efficiency and substrate protection. Appropriate parameter optimization not only improves cleaning efficiency and surface quality but also extends equipment life and reduces operating costs. This is key to enterprises’ application of pulsed laser cleaning and laser surface treatment technologies.