J-tech will not give it up.
There are several Laser grbl firmwares out there. Unfortunately they are all based on grbl 0.9g and earlier. That early and they have an "arc" bug that messes with BenCutLaser. T2Laser is ok with most of them, but J-tech is the best of the Laser versions. The new grbl 1.0/1.1 release has Laser Mode in it and it appears to work well. It just isn't out yet.https://github.com/nickw89509/LaserInk
It is open sourced;https://github.com/gnea/grbl/tree/dev
It has several different frequencies you can change to in cpu_map.h and default is .98KHz that is close to what J-tech is using for their PWM.
It is aimed at the Uno but will work with a change (16 to 14) of the block buffers on a Nano.
below in attachments;
grblUpload.ino.11bdevbuf14.hex already has the buffers changed no homing
grblUpload.ino.11bhoming.hex has buffers changed and homing for a single pin (D9) ready to be enabled.
You change $32=1 to enable "Laser Mode". $22=1 enables the homing.
These are Beta firmware!!!!
I hope this helps