I took picture of my oscilloscope reading. I hooked my scope up to the:
(yellow) signal wire from the hexagon motor
(blue) signal from the TEMT6000 phototransistor
Unfortunately I am not a whiz at tuning in the scope. I also have no way of running this motor at low speed. The lines are shaky for reasons - who knows why. And in case anyone else wants to do this same thing - I just found out that, when I run the mirror, the laser beam is so much easier to line up with my jig since it would be in a line, instead of trying to push that mirror around delicately without touching the perfectly polished mirror surface.
Anyway. I can see there are 7 signals for every 1 signal of the motor pulse. Yes, there are 7 sides of the mirror, makes this a HEPTAGON polygon mirror, not a hexagon. I have the clock signal into the motor driver 6k pulse TONE() out from Arduino.
I have no way of slowing down this motor to spin, so it either goes faster than I can see or I spin with my hands. The motor out tachometer pulse appears to be very low voltage so I need to make a transistor or opto coupler circuit if I want to use an interrupt signal to match the timing pulse of the actual motor. I am only running at 12 volts. I believe this module expects to get 24 volts - it could go faster - but I want accuracy now, not speed.