I’m not sure that this will make a difference: As far as I understand it, the IR lasers are already pulsed.
My experiments with PCB engraving resulted in burnt underlayer mainly for epoxy based boards. With hardpaper/phenolic paper I had some success. My experiments are currently parked, but I think I will give this a last try at some point, using raster engraving rather than vector engraving. My problem mainly was that with vector engraving it was difficult to get a consistent and uniform power distribution.