I know that a change of controller and/or firmware isn’t the answer you are looking for… but I agree with Mike about Grbl’s “laser mode” ($32=1). I’m unclear as to what Marlin’s laser capabiities are today but here is a post where I compared Marlin and Grbl with the same grayscale image… and which shows the stop/start action while raster engraving of Marlin – and lack thereof with Grbl – that I’ve seen.
I have a few V1 forum posts showing a few ceramic tile engravings as well. – David