I am playing with a laser cutting/engraving machine. There is a small wedge with the machine, with 3 widths, each width having a text on it :

• cutting 7mm wood (close to the surface)
• cutting 5mm wood
• engraving and cutting 3mm wood (far from the surface)

It allows you to set the height of the laser. I try to understand what would be the best setting to engrave rock. I understand that to etch on wood, you want a large laser to burn it instead of vaporizing it. There are even toturials on defocussing the laser to get better blacks (larger laser, more burning, less vaporizing). Random example : https://www.youtube.com/watch?v=Xcg1y2cQl-o

Now, I want to engrave rock. I don't want a larger laser. I want the hotter tinniest spot on the surface of the rock. I start to get great results on black rock (1000mm/s, 10W, 3 passes).

To get the more focused spot, should I go with the setting close to the surface "cutting 7mm wood" or with the seeing far from the surface "engraving and cutting 3mm wood" ?

Has any of you tried to engrave rock ? Do you have tips ?