Laser Cleaning: Mechanism, Features & Applications

01 Background

In industrial and other fields, traditional cleaning methods such as chemical cleaning and mechanical grinding have long been dominant. However, chemical cleaning produces a large amount of chemical waste liquid, leading to environmental pollution and potential corrosion risks to precision components. Mechanical grinding can remove surface contaminants but often damages the substrate, is ineffective for complex structures, and generates dust harmful to operators’ health, while failing to meet high-precision cleaning demands.

With the rapid development of advanced industries such as aerospace, rail transportation, and marine engineering, the cleaning requirements for components have become increasingly stringent. Large and complex structures—such as aircraft engine inlets, high-speed train bodies, and ship hatches—require high cleaning precision, efficiency, and surface integrity. Traditional methods can no longer meet these requirements.

At the same time, with growing global environmental awareness, the manufacturing industry faces increasing pressure to reduce pollution and resource consumption. Laser cleaning, as a green technology, provides an eco-friendly alternative with no chemical waste, low energy consumption, and non-contact operation. It offers a sustainable solution for industrial cleaning challenges and is seeing rising demand across multiple fields.

02 Mechanism of Laser Cleaning

Laser cleaning utilizes a high-energy-density laser beam to interact with surface materials, causing contaminants, coatings, or oxides to detach or decompose from the substrate.

The process involves multiple physical mechanisms, including thermal ablation, stress vibration, thermal expansion, evaporation, phase explosion, vapor pressure, and plasma impact. Together, these effects enable efficient cleaning while preserving the integrity of the base material.

Depending on the cleaning medium, laser cleaning can be classified into:

• Dry laser cleaning

• Wet laser cleaning

• Laser shockwave cleaning

Dry Laser Cleaning

This is the most widely used method. The laser beam irradiates the surface directly, generating thermal expansion that overcomes van der Waals forces to remove contaminants.

Key parameters influencing cleaning include:

• Laser intensity: Low energy density favors evaporation and phase explosion; higher density enhances ablation and shockwave effects. Excessive intensity may generate plasma and damage the substrate.

• Wavelength: Determines energy coupling; short wavelengths favor photochemical ablation, while longer wavelengths promote photothermal ablation.

• Pulse width: Long pulses emphasize thermal ablation but reduce selectivity; short and ultrafast pulses generate high temperatures and shockwaves for precise, minimal-damage cleaning.

• Incidence angle: Oblique incidence often improves efficiency compared to perpendicular irradiation.

Wet Laser Cleaning

A thin liquid film is applied to the surface prior to irradiation. Laser heating rapidly vaporizes the liquid, producing strong shockwaves that remove contaminants.

Laser Shockwave Cleaning

• Dry laser shockwave cleaning: Plasma generated by focused laser beams creates impact forces to remove particles, though blind spots may occur. Adjusting the incidence angle or using dual-beam configurations improves efficiency.

• Hybrid laser shockwave cleaning: Includes vapor-phase, underwater, and wet shockwave cleaning, leveraging fluid interactions for enhanced removal.

03 Aerospace Applications – Oxide Removal from Titanium Alloy Inlets

Nanosecond pulsed lasers are effective for removing oxide films from titanium alloy inlets, minimizing heat damage and preventing re-oxidation.

• Dry cleaning: Ablation dominates. At low energy, partial oxide removal occurs; at optimal energy, complete removal with minimal substrate damage is achieved; excessive energy causes surface ridges and structural damage.

• Wet cleaning: At lower energy, shockwave effects dominate; at higher energy, ablation and phase explosion occur. Rapid heating and cooling produce martensitic titanium alloys, and nano-structured surfaces can enhance material performance.

04 Rail Transportation – Paint Removal from Aluminum Alloy Train Bodies

Laser cleaning provides tailored solutions for coatings of varying thickness and color:

• Thin coatings (≤40 μm): Removal is more efficient with lower-absorption wavelengths via vibrational mechanisms.

• Thick coatings: Best removed with higher-absorption wavelengths through ablation.

• Red paint: Removed mainly through vibration-induced thermal stress.

• Blue paint: Absorbs more heat under the same energy, removed via evaporation, layer cracking, combustion, and plasma shock.

05 Marine Applications – Rust Removal from High-Strength Steel

• Dry cleaning: Rust oxides absorb laser energy, vaporize, and generate recoil forces that help remove thick oxide layers.

• Wet cleaning with liquid film: Liquid absorbs energy, undergoes explosive boiling, and produces shockwaves to detach rust. Phase explosion creates lateral forces, flattening the surface, while vaporized oxides may hinder molten metal flow.

06 Marine Biofouling Removal – Aluminum Alloy Surfaces

High peak power, narrow pulse lasers are highly effective in removing marine organisms.

• Mechanism: Extracellular polymeric substances (EPS) and barnacle substrates are removed through ablation, vaporization, and shockwave stripping. Multiphoton absorption breaks molecular chains, producing ions and plasma that enhance cleaning.

Organic matter (e.g., coatings, biofilms) undergoes chemical bond breaking and discoloration at low energy, while higher energy causes ablation, vaporization, plasma shocks, and flame.
Inorganic contaminants (e.g., oxides, rust) show little effect at low energy but undergo ablation and vaporization at higher densities.

07 Cultural Heritage Conservation

Pulsed lasers are widely used in the preservation of cultural artifacts, offering non-destructive and precise cleaning for stone, paper, metal, and other materials.

Examples include:

• Stone artifacts: Roman marble sculptures, urns, and temple reliefs.

• Paintings: Renaissance and 19th-century oil paintings.

• Metal artifacts: Bronze statues, silver weapons, 19th-century military ornaments.

• Other heritage items: Gilded wooden frames, African reed mats, and ancient Egyptian glassware.

Laser cleaning allows for selective removal of dirt and deposits while preserving delicate surfaces, making it an indispensable tool in heritage conservation.