There's a room with one laser beam and four mirrors.
The pentagram is not
a perfect star (as in the achievement artwork), so don't try to make one.
Rotate the mirrors by using your tractor beam on the red orb nearest it. There are also three mirrors below the water line, and you will need to use these (and also for the solution to escape the room).
You will want the lower-right mirror to remain flat. With the lower-left mirror, angle the beam onto the second-from-right mirror below the water. That will bounce the beam up to the top-right mirror. Using that one, angle the beam onto the left-most mirror below the water, which bounces the beam onto the lower-right mirror.
This completes your pentagram, but
you must go down and admire your complete work for the achievement to pop.
Bonus: solution for escaping the room:
This video from "aka Scratch" demonstrates this achievement.