Flat-Top vs Gaussian Beam for Pulsed Laser Cleaning Machines: How to Choose the Right Beam？

In pulsed laser cleaning systems, the energy distribution of the laser spot is a critical factor that is often underestimated in real-world equipment selection.

In practice, even when laser power, pulse width, and repetition frequency are identical, the cleaning results can differ dramatically solely due to differences in beam profile.

At present, the two most common beam types used in pulsed laser cleaning applications are:

• Gaussian Beam
• Flat-Top Beam (Top-Hat Beam)

This article systematically analyzes their essential differences from four engineering perspectives:
physical characteristics, cleaning mechanisms, practical cleaning results, and application-based selection logic.

1. Understanding Gaussian and Flat-Top Beams from an Engineering Perspective

Fundamental Characteristics of Gaussian Beams

A Gaussian beam exhibits a highly non-uniform energy distribution characterized by:

• Maximum energy density at the center
• Rapid decay of energy toward the edges
• A sharp, peak-shaped spot profile

👉 From an engineering perspective, Gaussian beams are defined by high peak energy density.

Fundamental Characteristics of Flat-Top Beams

A flat-top beam features a much more uniform energy distribution:

• Nearly constant energy density across the entire spot
• No pronounced central energy peak
• Smooth energy transition at the edges

👉 From an engineering perspective, flat-top beams emphasize energy uniformity and process controllability.

2. Differences in Cleaning Mechanisms During Pulsed Laser Cleaning

The core principle of pulsed laser cleaning is:

To trigger removal of the contamination layer within an extremely short time window, while minimizing thermal impact on the substrate.

Cleaning Mechanism of Gaussian Beams

• Extremely high instantaneous energy at the spot center
• Strong localized interaction with contaminants
• Easily triggers:
  • Intense photomechanical stripping
  • Localized instantaneous vaporization

Although cleaning efficiency can be very high, there are inherent risks:

⚠️ Potential drawbacks include:

• Micro-melting at the center
• Surface microstructural coarsening
• Local substrate damage
• Non-uniform cleaning, especially at spot edges

Cleaning Mechanism of Flat-Top Beams

• Uniform energy delivery across the entire spot
• Contaminants respond simultaneously over the cleaning area
• The stripping process is more stable and controllable

✅ Key advantages include:

• High cleaning uniformity
• Lower thermal influence on the base material
• Excellent process repeatability and consistency

3. Practical Differences in Cleaning Results (Engineering Observations)

Typical Results After Gaussian Beam Cleaning

• Deeper cleaning in the central region
• Possible residual contamination near the edges
• Under microscopic inspection:
  • Noticeable surface roughness variation
  • Higher risk of micro-damage

👉 Best described as point-impact-driven cleaning.

Typical Results After Flat-Top Beam Cleaning

• Clearly defined and uniform cleaning boundaries
• Consistent appearance across the entire treated area
• Under microscopic inspection:
  • Uniform surface texture
  • Minimal substrate damage

👉 Best described as area-controlled stripping.

4. Application-Based Selection Recommendations

Applications Better Suited for Gaussian Beams

Gaussian beams are not “inferior”; they are task-specific tools and perform well in scenarios such as:

• Heavy or stubborn rust layers
• Thick coatings or thick oxide layers
• Cast parts and heavy industrial components
• Applications with low surface integrity requirements

👉 The primary objective in these cases is maximum cleaning efficiency.

Applications Better Suited for Flat-Top Beams

Flat-top beams represent the mainstream trend in high-end pulsed laser cleaning:

• Precision mold cleaning
• Pre-welding surface preparation
• Aluminum oxide layer removal in lithium battery manufacturing
• Stainless steel and aluminum alloy surface treatment
• Cultural relic conservation and wood restoration

👉 The priority here is process consistency, surface safety, and a wide processing window.

5. Relationship Between Single-Mode / Multi-Mode and Gaussian / Flat-Top Beams

A common misunderstanding in engineering practice is:

Single-mode ≠ Gaussian, and multi-mode ≠ flat-top (although they are strongly correlated)

General engineering observations include:

• Single-mode laser sources:
  • Naturally produce Gaussian-like beams
  • Offer excellent beam quality
  • Deliver highly concentrated energy
• Multi-mode laser sources combined with beam-shaping optics:
  • Are more suitable for generating flat-top beams
  • Perform better in large-area, uniform industrial cleaning

👉 The final beam profile is primarily determined by the optical beam-shaping system, not the laser source alone.

6. Conclusions for Equipment Selection

In pulsed laser cleaning applications:

• Gaussian Beam = High impact, high efficiency, higher risk
• Flat-Top Beam = High uniformity, high controllability, high stability

From an industry development perspective:

Pulsed laser cleaning is evolving from
“Can it clean?”
to
“Can it clean consistently, safely, and reproducibly?”

As a result, for medium- to high-end industrial applications,
flat-top beam technology is increasingly becoming the preferred choice.

Direct Comparison: Flat-Top vs Gaussian Beam