Most small diode lasers have an input that is designed to take a PWM signal to turn
the laser on and also to control its power level. This input will take a logic level
signal and the main power input is left on continuously. Your breakout board most
likely has some outputs that are logic level that you can use to control the laser
in this way.
I don't know about configuring Vectric, but the most sensible way to configure
Mach4 is to use the spindle controls for the laser. M3 and M5 would turn the laser
on and off while the S word would control the PWM to set the power level.
The above will result in "exact stop" operation with the motion being planned
to come to a complete stop before the M3 or M5 turns the laser on or off.
Mach4 does have provision for some special M codes to turn a signal on or off
without stopping but you may not be able to use these because, first they
do not allow for PWM to control power level, and second, most controllers
do not yet support these codes. This is true for the PMDX SmartBOBs.