Hi,
Simply fit a limit switch at the position you need the stepper to start at.
Then when your code starts in setup.
Check to see if limit is activated.
If not execute a homing function to bring the stepper home.
It would not be a good idea on power up using your laser, as you have no idea where it is pointed.
If the limit switch will not give you the position accuracy you need, then use the limit switch to pull the stepper to a safe position that you know you can power up the laser, then do the mirror alignment method.
Tom... 