I worked around numerous laser tables. We had what were basically ping-pong paddles with paint that glowed when hit by the laser. If the beam “got loose” they would wave the paddles around to find the beam and slowly track it backwards to the divergent point, usually a mirror bumped out of position.
One time they were taking photos of the beam operating in a dark room. The side light from a beam was too weak to register on the film so they had a bunch of us crouched around the table blowing cigarette smoke. Each person had one section of the beam we had to keep lit. It was about a 30 second exposure with me constantly puffing away. I don’t smoke and damn near threw up. I was dizzy for a long time.