Fine lines and moiree patterns with 2.5D engraving

Hello everyone,

I engraved a brass coin today with my fiber laser. I used the 3D Sliced function with 80% power, 500mm/s speed and 847dpi resolution at 256 layers.

After carefully cleaning the coin with a dremel and bristle discs, I noticed that there are fine lines and moiree patterns. What tricks can I use to prevent such patterns from appearing? Should I use a higher resolution or defocus the laser slightly? I suspect these are artifacts of the individual lasered lines and the crosshatching.

I use a 30W fiber laser from Cloudray with a 110x110 theta lens. The calibration actually looks good so far.

Thank you for any help!

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