With increasingly stringent environmental protection regulations and growing public awareness of environmental protection and safety in my country, laser cleaning is considered the most environmentally friendly, reliable, and effective solution due to its non-contact nature, minimal thermal effect, lack of consumables, and applicability to various materials.

However, will using such a high-energy laser beam for cleaning damage the substrate?

To answer this question, we must begin with the essence of laser cleaning. The following will introduce the principle of pulsed laser cleaning, which is widely used in laser cleaning.

1. The duration of a single pulse of a high-energy laser beam is extremely short, absorbed only by contaminants on the substrate surface.

The duration of a single pulse is only nanoseconds (1 ns = 1 × 10⁻⁹ s).

A human blink takes approximately 0.2 seconds; the blink of an eye is 200 million times longer than the duration of a single laser pulse.

2. The absorption of high energy causes a rapidly expanding plasma (highly ionized unstable gas) to form around the contaminants, generating a shock wave. This shock wave fragments and removes the contaminants.

Laser cleaning does not rely solely on instantaneous thermal action; it involves multiple mechanisms, including vaporization, phase explosion, and vibration.

3. This plasma is only generated when the laser energy density exceeds a certain initial cleaning threshold, at which point contaminants begin to be removed. However, when the laser energy density exceeds another damage threshold, the substrate is damaged. Therefore, by adjusting the laser parameters to ensure the energy density of the laser pulse remains strictly between the cleaning and damage thresholds, effective cleaning can be achieved while preventing damage to the substrate.

On the other hand, from a materials science perspective, taking steel, the most widely used material for laser cleaning, as an example, changes in the microstructure of steel require reaching a corresponding phase transformation temperature. To achieve a surface hardening effect, conventional carbon steel needs to be heated to above 860℃ and held at that temperature for a certain time. For martensitic structures, a tempering effect requires holding at around 200℃ for a certain time. In practice, laser cleaning is completed instantaneously; this characteristic allows laser cleaning to effectively prevent changes in the mechanical properties or hardness of metallic materials.

Table 1 Chemical Elements of EH36 Carbon Steel
Elements: C, Mn, Si, S, P, Fe
Content: ≤0.18, 0.9-1.60, ≤0.50, ≤0.035, Balance

Figure 1 Comparison of Metallographic Structure of EH36 Carbon Steel Before and After Laser Cleaning

For example, after cleaning EH36 carbon steel with the Xiangming Laser HST-1000 cleaning machine, no change was observed in its cross-sectional structure. Therefore, by reasonably controlling the process window and utilizing its ultra-high frequency and ultra-short action time, non-destructive processing can be achieved without affecting the surface morphology or cross-sectional metallographic structure of the cleaned object, thus preserving its original characteristics.

Combined with the special scanning trajectory and energy dynamic matching control module independently developed by Xiangming Laser, truly non-destructive cleaning can be achieved.