All About Pulse Width
Pulse width, also called pulse duration, is the length of time an individual laser pulse lasts and is often expressed in nanoseconds for laser-marking systems. Adjustable pulse duration is a key control on many MOPA fiber laser sources, but many other lasers provide a fixed pulse duration or operate as continuous-wave sources without discrete pulses.
What changes physically
For the same pulse energy and a comparable pulse shape, a shorter pulse delivers that energy over less time and therefore produces higher peak power. For the same pulse energy and a comparable pulse shape, a longer pulse has lower peak power, but its longer duration gives heat more time to transfer into the surrounding material. Actual laser sources may change pulse energy, pulse shape, or available average power as pulse duration and pulse frequency change, so real output may not follow the ideal comparison exactly.
Material interaction
Shorter pulses with sufficient peak intensity may favor rapid surface removal while limiting the time available for heat to spread into the surrounding material. Longer pulses may provide more time for heat transfer and can therefore favor melting, oxidation, annealing, or a broader heat-affected area. Which material response dominates depends on the laser wavelength, pulse energy, pulse frequency, scanning speed, focus accuracy, focused spot size, surface condition, and material.
Examples
In a controlled test, shorter pulse durations may help produce clean coating removal or fine ablation when limiting heat transfer into the surrounding material is important. When developing MOPA Laser color settings for stainless steel, test a broad range of pulse durations. Some colors may be easier to reproduce with lower power and longer pulses, while others may respond better to higher power and shorter pulses. Use controlled test matrices to examine how pulse duration interacts with power, pulse frequency, and scanning speed when searching for repeatable color. Intentional focus offsets slightly above or below the material surface can also change the focused spot size and energy distribution, leading to entirely different results from the same combinations of other laser parameters, so record and test focus distance as part of the process.
Interactions
Pulse duration cannot be interpreted in isolation from the other laser parameters. Pulse frequency controls how often pulses are emitted, scanning speed affects their spacing along the workpiece, and commanded power helps determine the energy available to the process. Selecting a different pulse duration may also change the laser source's permitted pulse-frequency range, maximum pulse energy, or achievable average power. Consult the manual for the exact laser source model to find the permitted pulse-frequency range for each pulse duration and the frequency below which available average power begins to decrease, sometimes described as a power-down cutoff or base frequency. Review manufacturer charts showing pulse shape, pulse energy, peak power, and average power across different pulse durations and pulse frequencies, because they may reveal operating limits that are not apparent from the software controls alone.
Read What Is Power Down Cutoff Frequency? for the physical reason this threshold exists and how to interpret it.
Testing
Use a controlled, documented test matrix that remains within the laser source manufacturer's permitted ranges for every pulse duration and pulse frequency tested. Allow each test sample to cool, then inspect it under consistent lighting and magnification. Record whether the result shows material removal, melting, oxidation, annealing, surface-texture change, or only an apparent color change.