The influence of beam patterns in laser cleaning on the cleaning effect

1. Introduction

Laser cleaning is a non-contact surface treatment technology that utilizes high-energy laser beams to act on material surfaces, causing contaminants, deposits, or coatings to vaporize, delaminate, or undergo photochemical decomposition. Compared with traditional methods such as chemical cleaning and abrasive blasting, laser cleaning offers advantages such as environmental friendliness, controllability, and minimal substrate damage.

Among the various process parameters, the beam profile (or beam mode) is one of the key factors affecting the cleaning results. The beam mode determines the energy distribution within the laser spot, which directly influences contaminant removal mechanisms, cleaning efficiency, thermal effects, and substrate safety.

2. Common Beam Profiles in Laser Cleaning

Laser sources may output different modes or intensity distributions. In laser cleaning, the following beam characteristics are typically involved:

1. Gaussian Mode

The Gaussian mode exhibits a peak energy density at the spot center that gradually decays toward the edges, forming a bell-shaped energy distribution. This mode provides strong focusing capability and is particularly suitable for localized high-energy cleaning, where thin and highly absorbent contamination layers can be rapidly vaporized or gasified. However, the highly concentrated energy may induce localized overheating, requiring appropriate scanning strategies for control.

2. Top-Hat (Flat-Top) Mode

The top-hat mode features a uniform energy distribution within the spot area, with a sharp boundary transition. This mode is advantageous in large-area cleaning applications and scenarios involving thermally sensitive substrates—such as aerospace aluminum components, cultural stone surfaces, and heritage bronze artifacts—because its uniform energy input minimizes hotspots and micro-damage. It also performs well in pre-coating surface preparation and degreasing applications.

3. Ring Mode

The ring mode has low energy density in the center and higher energy density in the annular region, forming a “doughnut-shaped” pattern. This mode enhances thermal shock-based delamination and is suitable for harder or thicker contamination layers such as mill scale, rust layers, or certain coating systems. The low-energy center reduces the risk of deep substrate damage.

4. Structured Light

For high-precision or high-throughput scenarios, structured beams such as Bessel beams and multi-spot arrays may be employed to achieve extended depth of focus, higher coverage efficiency, or better compatibility with automated cleaning systems. These beams are often used in combination with high-speed galvanometer scanners to improve industrial productivity.

3. Mechanisms by Which Beam Mode Influences Cleaning Performance

Beam mode influences laser cleaning outcomes through the following mechanisms:

1. Determines the Contaminant Removal Mechanism

Laser cleaning may involve vaporization/gasification, micro-explosive delamination, photochemical decomposition, and thermal shock cracking.
Gaussian mode tends to drive rapid energy accumulation, promoting vaporization;
top-hat mode provides stable thermal fields conducive to micro-explosive or layered delamination;
ring mode generates circumferential thermal stress to initiate crack propagation at the contaminant–substrate interface.

2. Defines the Thermal Affected Zone (TAZ) on the Substrate

Different energy concentration characteristics alter the thermal load distribution:
Gaussian mode produces localized high-temperature regions;
top-hat mode delivers uniform heating over larger areas;
ring mode reduces central overheating through its low-energy core.
These distinctions are critical in aerospace parts, railway components, and heritage conservation applications.

3. Influences Cleaning Efficiency and Required Scan Passes

Top-hat modes generally achieve higher cleanliness in fewer passes;
Gaussian modes may require additional scanning due to weak edge energy;
ring modes may outperform in removing strongly adhering contamination layers.
Proper mode selection improves cleaning speed while reducing energy consumption and processing time.

4. Affects Cleaning Uniformity and Surface Consistency

In continuous large-area cleaning tasks, beam uniformity directly affects surface appearance.
Industries such as mold manufacturing, heritage restoration, and pre-coating treatments may encounter color shifts or surface roughness variation if localized over-cleaning occurs.
Top-hat beams mitigate such effects by promoting consistent treatment.

4. Beam Mode Selection Recommendations for Typical Applications

Based on industrial experience and experimental validation, different sectors exhibit mode preferences:

Rail Transit & Metallurgy
Removal of mill scale and thick rust layers → Ring mode is advantageous due to thermal cracking and delamination performance.

Heritage Conservation & Stone Cleaning
Thermally sensitive substrates → Top-hat mode minimizes micro-cracking and discoloration risks.

Mold Manufacturing & Die-Casting
Contaminants such as oils, release agents, and thin oxides → Gaussian or top-hat mode both applicable.

Aerospace Coating Preparation
High surface quality and uniformity requirements → Preference for top-hat mode.

5. Technology Development Trends

With the rapid industrialization of laser cleaning, beam mode control is evolving toward:

✔ Switchable Beam Modes
Allowing one machine to handle multiple cleaning scenarios, enhancing process flexibility.

✔ Digital Beam Shaping
DOE (diffractive optical elements) or SLM (spatial light modulators) enabling real-time beam modulation for improved uniformity.

✔ Intelligent Detection & Adaptive Control
AI-driven contamination recognition and automatic application of optimal beam profiles and process parameters.

✔ Multi-Spot Arrays for Industrial Throughput
Supporting robotic and automated production lines for improved coverage and efficiency.

6. Conclusion

Beam mode plays a crucial role in laser cleaning processes, influencing removal mechanisms, efficiency, thermal effects, and substrate safety. Proper mode selection significantly improves cleaning quality, reduces energy consumption, and expands applicability to advanced industrial domains.

With continued advances in beam shaping and intelligent control, beam mode engineering will become a key competitive factor in laser cleaning equipment, enabling higher efficiency, higher quality, and safer cleaning operations.