Again. When you like to laser- **_cut**_ (not picture engrave) you'd like to have a constant energy per mm. The number of stepper pulses for the extruder is then directly proportional to the way and adjustable by the amount of extruded material. Routing the extruder step pulses to a MOSFET driven output (like the extruder heater) can be done via the pin-file. Using the stepper-drivers output will give you a AC - is rubbish.