I use light burn for everything laser related.
I’ll create my svg file one Adobe illustrator (but you could use Inkscape).
Once I have my design, I save as svg. Then I import the svg into light burn. I’ve done a lot of testing with different powers and speeds to find what burns the best. I also test in scrap before burning my final designs.
When I switched to a more powerful laser, I had to start over on power and feed speed.
If you’re trying to convert a raster image (jpg) then I’d just use light burn. Test the different greyscale types to see which works.
There’s a lot of trial and error with lasers. Make a test design with a bunch of filled squares. Set each square to a different power 10, 20, 30 etc etc. All at the same speed and run the test.
If that doesn’t produce the darkness you want, then slow down or speed up the feed speed on all the squares and run it again.
Once you find a speed that you like, then you can use the different powers to get your greyscale. Save this light burn file and use it on future materials to get your powers faster.
One other thing on “fill” is the step over. I think light burn defaults to a (.1mm) step over. I usually change this to at least (.2mm).