BUYER’S GUIDE
Why Wattage Isn't the Whole Story
When comparing pulsed laser cleaning systems, wattage is often the first number buyers notice.
200W. 300W. 500W.
But two pulsed laser cleaners with the same rated wattage can be very different systems.
One specification that helps explain the difference is pulse energy, typically expressed in millijoules (mJ).
Understanding what mJ means—and what it doesn’t mean—can help buyers avoid choosing a laser based on wattage alone.
WHAT DOES mJ MEAN?
mJ stands for millijoule, or one-thousandth of a joule. It is a unit of energy.
A pulsed laser produces a rapid sequence of individual laser pulses rather than delivering energy continuously.
Pulse energy describes the energy contained in an individual pulse.
On a laser specification sheet, the listed mJ value typically represents the maximum pulse energy available. The actual pulse energy during operation depends on the laser configuration and operating settings.
That is different from average laser power, which is normally expressed in watts (W).
HOW DO WATTS, mJ AND FREQUENCY RELATE?
For a regularly repeating pulse train, the basic relationship can be expressed as:
Average Power = Pulse Energy × Pulse Repetition Rate
But those numbers cannot simply be mixed and matched from the maximum values on a specification sheet.
A laser operates within a defined range. Its maximum pulse energy and full rated average power are not necessarily available simultaneously at every repetition rate.
At a given average power, increasing the number of pulses per second generally means less energy is available in each pulse.
This is one reason wattage and mJ need to be evaluated together rather than as independent measures of performance.
SAME WATTAGE DOES NOT MEAN SAME LASER
Consider two laser sources that are both rated at 500W.
That does not mean they deliver energy in the same way.
Published manufacturer specifications show 500W pulsed laser-source configurations with maximum pulse energies ranging from 1.5 mJ to 50 mJ, along with differences in beam quality.
Likewise, 300W laser-source families can be available with multiple pulse-energy and beam-characteristic configurations.
The rated wattage may be the same while other characteristics of the laser source are substantially different.
And the laser source is only part of the complete machine.
Real-world cleaning results also depend on the cleaning head, optics, scanner, machine controls, process settings and the application itself.
IS HIGHER mJ BETTER?
Not necessarily.
Higher pulse energy is not a universal measure of laser-cleaning quality or suitability.
Pulse energy interacts with several groups of variables:
LASER CHARACTERISTICS
Pulse width
Repetition frequency
Beam quality
Beam profile
OPTICS, DELIVERY & SCANNING
Spot size
Scan field
Lens and optical configuration
Scan speed
Pulse overlap
APPLICATION
Material or substrate
Contaminant or coating
Surface condition
Required finish
Throughput requirements
Changing one variable can change how the overall process behaves.
That is why statements such as “higher mJ is always better” or “a specific mJ is always best for a certain material” should be treated cautiously.
WHY DOES PULSE WIDTH MATTER?
Pulse width is commonly expressed in nanoseconds (ns).
It describes how long an individual laser pulse lasts.
The same amount of pulse energy delivered over a shorter period produces higher peak power. This is one reason pulse energy and pulse width need to be considered together.
Pulse duration can influence how the laser interacts with the contaminant and underlying material, so mJ alone does not describe the complete pulse.
WHY DO SPOT SIZE AND OPTICS MATTER?
What also matters is how concentrated the pulse energy is when it reaches the surface.
The same pulse energy spread across a larger spot is less concentrated than when it is delivered over a smaller area.
That is why pulse energy must be considered alongside spot size, beam characteristics, lens configuration and the rest of the optical system.
WHAT DOES kHz MEAN?
Pulse repetition rate is commonly expressed in kilohertz (kHz).
It describes how frequently the laser produces pulses.
Frequency interacts with pulse energy, average power, scan speed and pulse overlap.
It is another operating variable that needs to be considered as part of the complete process.
THE COMPLETE LASER CONFIGURATION MATTERS
Pulse energy is important, but it is only one part of the system.
When evaluating a pulsed laser cleaner, LSI Industrial may consider factors such as:
Rated average laser power
Maximum pulse energy
Pulse-width range
Frequency range
Laser-source configuration
Beam quality and beam profile
Cleaning head
Lens and focal configuration
Scan capability
Cooling method
Material being cleaned
Contaminant or coating
Required finish
Throughput requirements
The objective is not to select the machine with the largest number.
The objective is to identify a configuration appropriate for the work being performed.
WHY TWO 300W MACHINES CAN PERFORM DIFFERENTLY
Imagine two pulsed laser cleaners advertised as 300W.
At first glance, they may appear equivalent.
But one system may use a different pulse-energy configuration, beam quality, beam profile, pulse-width range, cleaning head or optical setup than the other.
Those differences can affect how energy reaches the work surface and can produce different results on a particular application.
This is one reason comparing laser cleaners by wattage and price alone can be misleading.
WHAT SHOULD A BUYER LOOK FOR?
Start with the application—not the specification sheet.
Useful questions include:
What material are you cleaning?
What needs to be removed?
How thick or difficult is the contamination or coating?
How sensitive is the underlying surface?
What finish needs to remain after cleaning?
Does the cleaned surface need to meet a particular condition for a subsequent process such as coating or welding?
How large is the work area?
How quickly does the work need to be completed?
Will the equipment be used in a shop or in the field?
Once those requirements are understood, the technical configuration can be evaluated around the application.
THE LSI INDUSTRIAL APPROACH
LSI Industrial does not recommend pulsed laser cleaning equipment based on wattage alone.
We evaluate the application first, then identify the laser configuration that should be considered for the required cleaning process.
Depending on the application, that evaluation may include wattage, pulse energy, pulse width, frequency, beam characteristics, optics, cleaning head and other system variables.
For specialized applications, representative testing or additional technical validation may be recommended before final configuration.
THE BOTTOM LINE
Watts tell you a laser source's rated maximum average power.
A specification sheet's mJ rating tells you the maximum energy available in an individual pulse.
Neither number, by itself, tells you which laser cleaner is right for your application.
The better question isn't:
“What wattage or mJ should I buy?”
It's:
“What laser configuration is appropriate for what I need to remove, from this material, at the finish and production rate I require?”
LET'S REVIEW YOUR APPLICATION
Not sure which pulsed laser configuration fits your cleaning process?
Email photos of the part or surface to sales@lsiindustrial.com, tell us what you're trying to remove, and briefly describe your current process. You can also start through our Contact page.
LSIIndustrial.com
sales@lsiindustrial.com
Ontario, California