Differences Between Pulsed Laser Cleaning Machines and Continuous Laser Cleaning Machines

Introduction

Briefly introduce the development and applications of laser cleaning technology.

State the purpose of this article: to compare the main differences between pulsed laser cleaning machines and continuous laser cleaning machines.

I. Core Fundamentals of Laser Cleaning Technology

Laser cleaning utilizes the interaction between laser and the surface of a material to remove contaminants (such as oxide layers, grease, coatings, rust, etc.) through physical or chemical effects. Its core principle is based on the precise control of laser energy and the selective interaction with surface materials. Due to different energy output modes, continuous and pulsed lasers exhibit significantly different cleaning mechanisms.

II. Basic Principle of Continuous Laser Cleaning Machines

1. Energy Output Characteristics

Continuous Laser (CW Laser): Emits a stable and continuous beam with evenly distributed energy over time. It features relatively high average power (typically ranging from several hundred watts to several kilowatts), but lower peak power.

Typical wavelengths: CO₂ laser (10.6μm), fiber continuous laser (1.06μm), etc. The wavelength affects the absorption efficiency of materials.

2. Cleaning Mechanism

Mainly thermal effects:

Continuous laser irradiation heats the surface layer gradually. As the contaminants (e.g., oxide scales, grease) absorb the energy, their temperature rises, leading to:

• Thermal expansion and delamination: Due to differing thermal expansion coefficients between the contaminant and the substrate, continuous heating builds up interface stress, ultimately causing cracking and detachment of the contaminant.

• Vaporization / decomposition: Organic contaminants (like paint, resin) can vaporize or decompose into gases under high temperature. Metallic oxides may melt or reduce and peel off.

Auxiliary mechanisms:
In some applications, continuous laser heating generates micro-airflows or molten droplets that help flush contaminants off the surface, enhancing cleaning efficiency.

3. Key Parameters and Effects

• Power density: Determines the heating rate. Must stay below the damage threshold of the substrate to avoid thermal damage.

• Scanning speed: Affects heat accumulation. Too slow causes overheating of the substrate; too fast results in incomplete cleaning.

III. Basic Principle of Pulsed Laser Cleaning

1. Energy Output Characteristics

Pulsed Laser: Emits energy in short pulses (ranging from nanoseconds to picoseconds). Each pulse has high energy, with peak power reaching megawatts, though average power remains lower (from tens to hundreds of watts).

Typical wavelengths: Nd:YAG lasers (1064nm, 532nm), fiber pulsed lasers, excimer lasers (UV spectrum), etc. Shorter wavelengths are better suited for precision cleaning.

2. Cleaning Mechanism

Multiple physical effects in synergy:

• Photothermal effect: The pulsed laser delivers energy in a short burst, rapidly heating the contaminant to vaporization threshold, generating recoil pressure that detaches it.

• Photomechanical effect (shockwave): Rapid expansion of contaminants from high-energy pulses creates shockwaves, “cracking” them off the substrate—especially effective for brittle oxide layers.

• Photochemical effect (UV pulses): Ultraviolet lasers break chemical bonds in organic contaminants, decomposing them into volatile small molecules. The substrate experiences minimal thermal impact.

Non-thermal damage characteristic:
With ultrashort pulse durations (nanoseconds), energy is confined to the contaminant layer. The substrate doesn’t conduct heat quickly enough, resulting in an extremely small Heat-Affected Zone (HAZ), ideal for cleaning precision components.

3. Key Parameters and Effects

• Pulse energy and frequency: Pulse energy determines cleaning strength, while frequency affects the number of pulses per second. Must be adjusted according to contaminant thickness.

• Pulse width: Shorter pulses yield higher peak power and stronger photomechanical effect, suitable for thin-layer precision cleaning. Longer pulses (microseconds) resemble thermal effects of continuous lasers.

IV. Principle Comparison: Continuous vs. Pulsed Laser Cleaning

5. Core Differences Between the Two Technologies

6. Application Extension: Combining Principles with Use Cases

Continuous Laser Cleaning:
Typically used in heavy industrial scenarios such as rust removal on steel surfaces, paint stripping in automotive manufacturing, and large-area contaminant removal. It utilizes continuous thermal effects to quickly process extensive areas with high cost-efficiency.

Pulsed Laser Cleaning:
Indispensable in precision-demanding fields like microelectronics (removing contaminants from chip surfaces), aerospace (coating removal from turbine blades), and cultural heritage conservation (cleaning rust from bronze artifacts). Its non-thermal damage and high-precision features make it ideal for delicate applications.

7. Conclusion

The core difference between continuous and pulsed laser cleaning lies in their energy output modes:
The former focuses on "continuous heating", making it suitable for large-scale, rough cleaning tasks;
The latter is characterized by "instantaneous high-energy impact", enabling precise and non-destructive cleaning.

Understanding the underlying mechanisms of both technologies helps in selecting the most appropriate laser cleaning solution based on real-world needs — such as material type, level of contamination, and precision requirements.