Repetition frequency is one of the most critical parameters in pulsed laser cleaning machines， yet it is often overlooked or misunderstood.
While many users focus on laser power or single pulse energy, repetition frequency directly influences cleaning speed, surface quality, energy distribution, and thermal behavior. Understanding this parameter is essential for correct process setup and stable, repeatable cleaning results.
This article explains what repetition frequency is, how it affects pulsed laser cleaning behavior, and how to select an appropriate frequency range for different applications.
What is Repetition Frequency？
Repetition frequency, also known as pulse repetition rate, refers to the number of laser pulses emitted per second.
It is typically expressed in:
- Hz (hertz)
- kHz (kilohertz)
For example:
- 20 kHz means 20,000 pulses per second
- 100 kHz means 100,000 pulses per second
In simple terms, repetition frequency defines how often the laser fires pulses.
A Simple Way to Understand Repetition Frequency
If a single laser pulse is considered one energy “strike,” then:
- Single pulse energy represents the strength of one strike
- Repetition frequency represents how fast those strikes occur
In other words, repetition frequency determines how many times the surface is hit per second.
Engineering Significance in Pulsed Laser Cleaning
In pulsed laser cleaning, repetition frequency directly affects:
- Cleaning speed
- Surface smoothness
- Single pulse energy
- Risk of thermal accumulation
Repetition frequency is not inherently better when higher or lower. Its effect depends on how it interacts with other laser and process parameters.
Relationship Between Repetition Frequency and Single Pulse Energy
At a fixed average laser power, repetition frequency has a direct impact on single pulse energy.
Single Pulse Energy ≈ Average Power ÷ Repetition Frequency
This means:
- Higher repetition frequency results in lower single pulse energy
- Lower repetition frequency results in higher single pulse energy
For example, on the same 200 W pulsed laser system:
- At 20 kHz, single pulse energy is high
- At 50 kHz, single pulse energy is moderate
- At 100 kHz, single pulse energy is low
This relationship explains many real-world differences in cleaning performance.
Cleaning Behavior at Different Frequency Ranges
Low Repetition Frequency (10–30 kHz)
At low repetition frequencies, single pulse energy is relatively high and pulse impact is strong.
This setting is effective for aggressive removal tasks but may leave more visible cleaning traces. Thermal accumulation is generally low due to longer intervals between pulses.
Typical applications include heavy rust, thick oxide layers, and thick coating removal.
Medium Repetition Frequency (40–80 kHz)
Medium repetition frequency provides a balanced combination of energy and speed.
Cleaning is more uniform, process stability is higher, and surface quality is generally good. This range is widely used in industrial applications.
Typical applications include general industrial rust removal, pre-weld surface cleaning, and mold maintenance.
High Repetition Frequency (Above 100 kHz)
At high repetition frequencies, single pulse energy is lower, but pulse density is high.
The cleaning action becomes gentler and more uniform, resembling a controlled brushing effect. However, improper settings may increase the risk of thermal accumulation.
Typical applications include thin oxide layers, precision cleaning of aluminum and stainless steel, and low-damage surface treatment.
Matching Repetition Frequency with Scanning Parameters
Repetition frequency must be properly matched with scanning speed, spot size, and pulse overlap ratio.
If repetition frequency is too high while scanning speed is too slow, heat may accumulate on the surface.
If repetition frequency is too low while scanning speed is too fast, incomplete cleaning may occur.
Repetition frequency should always be treated as a system-level parameter rather than an isolated setting.
Common Misconceptions
Common incorrect assumptions include:
- Higher repetition frequency always produces better cleaning results
- Lower repetition frequency is always safer
The correct understanding is:
- Repetition frequency defines cleaning rhythm
- Single pulse energy defines removal capability
- Pulse width defines how gently energy is delivered
These parameters must work together for optimal performance.
Recommended Frequency Ranges by Cleaning Objective
| Cleaning Objective | Recommended Frequency |
|---|---|
| Heavy rust / thick coatings | 10–30 kHz |
| General industrial cleaning | 40–80 kHz |
| Precision / low-damage cleaning | 80–150 kHz |
These ranges are based on practical engineering experience rather than theoretical limits.
Engineering Summary
In pulsed laser cleaning:
- Repetition frequency controls the cleaning rhythm
- Single pulse energy determines whether contamination can be removed
- Pulse width influences how gently the energy interacts with the surface
Correct repetition frequency selection is essential for achieving stable, repeatable, and low-damage cleaning results.
