Picosecond or femtosecond is a question about the material, and often about cost
Femtosecond pulses give the cleanest result. Picosecond sources are cheaper and more robust, and for many metals the difference in outcome is small.
Both picosecond and femtosecond sources are described as ultrafast, and both remove material with far less thermal damage than nanosecond pulses. Choosing between them is a genuine engineering decision rather than a matter of buying the shortest pulse available.
What pulse duration governs
The relevant comparison is pulse duration against the time for energy to transfer from electrons to the lattice, which in metals is of the order of a picosecond.
A femtosecond pulse deposits its energy and is over before that transfer occurs, so material is removed essentially before it can heat conventionally. A picosecond pulse overlaps the transfer, so some thermal diffusion occurs during the pulse.
In practice that means femtosecond produces less melt, less recast and sharper feature edges. The size of the difference depends heavily on the material.
Where the difference is large
Dielectrics and transparent materials. Glass, sapphire and polymers. Non-linear absorption depends strongly on intensity, and femtosecond pulses reach the required intensity far more readily. Picosecond processing of glass is possible but with a narrower window and more cracking.
Very fine features. Where feature size approaches the heat diffusion length during a picosecond pulse.
Thin films on sensitive substrates. Where any thermal load reaches the underlying layer.
Where it is small
Metals at moderate feature sizes. For many metal ablation applications, picosecond results are close enough to femtosecond that the difference does not appear in the finished part.
Processes with subsequent finishing. Where a light polish or etch removes the small difference anyway.
The commercial dimension
Picosecond sources are generally less expensive, offer higher average power for the money, and have simpler architectures — no pulse compressor to maintain, less sensitivity to alignment. In production, robustness has value.
How to decide
The reliable method is to process the actual material at both durations and inspect the result against the actual requirement. Suppliers and application labs will run these trials.
What does not work is choosing femtosecond because it is technically superior, when the application is metal ablation with a subsequent finishing step. That buys pulse duration the process cannot use and costs money and reliability that it can.
This article was produced by the LasersNews AI desk and reviewed by our editors.
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