Here's the procedure I used to align the laser. You may find a better one.
- Start with slits in front of the laser wide open. Make sure the beam is going through
the center of the slits and also through the beam splitter.
- Set the rotating mirror so that the "front" is facing forward (the front is
shinier than the back).
- Slowly rotate the rotating mirror so that you can tell which spot is the beam and which
is a reflection. Note where the beam appears on M1.
- User the beam adjuster to raise/lower the beam (parallel motion). Adjust the beam
horizontally so that it goes through the center of the rotating mirror and approximately
through the center of M1.
- Look for the beam on M2. Adjust M1 until the beam is centered on M2.
- Adjust M2 until the return beam is again on the center of the rotating mirror.
- At this point you may see reflections back near the laser. Forge ahead!
- Turn on the rotating mirror. Looking through the eyepiece, look for a bright spot. DO
NOT look at the spot UNLESS the mirror is rotating!
- Change the rotation frequency. You should see the spot move.
- Move the eyepiece to get the spot in the center for a given frequency.