I've been cutting some 3mm poplar plywood with my Mr Beam II.
While the cut lines are sharp and linear on the top of the plywood, they have a "pulsed" look on the bottom side of the plywood. As can be seen in the attached picture, every few millimeters there is a larger scorch mark visible. These scorch marks are very regular, which is why I don't think they are a result of natural variations in the wood fibres.
Interestingly, they also don't appear on all cut lines, sometimes the cut is a straight, sharp line without any larger scorch marks.
They don't seem to be a problem, but I'm interested how these spots come to be. Do other people also experience this kind of "pulsed" look?
Ok, so the pulsed look was from the reflection of the laser from the metal grid below the plywood.
I reduced the number of passes (which I had set a bit too high, as sporadically the laser would leave some material behind due to natural wood variations), and now this is reduced quite a lot.
Another solutions suggested to me was to lay a different material below the plywood. Should work too, but for now I'm fine with my adjusted plywood settings.
You're probably right.
Due to the regularlyness with which the scorch marks appeared I was strongly biased towards a software issue and I tried to disprove your theory by lasering some mdf. However, this phenomenon did not appear there. That definitely supports the theory that it's due to the material itself, and not the software.
I would assume this is the result of the middle layer of the plywood which normally has its fibers aligned in a 90° angle compared to the other layers. Thus simply a result of the different fiber intensity.