Wavy lines in my burns

[LsrSal (Sal)]

Strange texture while engraving

I’m new to Lightburn and still looking if it’s worth to buy a license after the trial ends. My laser is an Atomstack P9 M50, I’m doing a lot of engraving test with different materials with the builtin “Material Test” function. What I get as result is a strange pattern while engraving, not consistent between power and speed. I attach a picture because it’s difficult to explain. Line markings seems not affected, but everything is “Fill” result with this distorted texture, on the box with speed…