On the left half of the photo you can see the top of an ordinary tripod in the foreground. Laying on top of it is one of those small laser pointers you can buy for $10 or so. All you can see from this angle is the brass cap on the back. This one runs on 3 hearing-aid batteries; these don't last long and are expensive, so I replaced them with a single 9V battery, which is in the white cardboard holder. A rubber band holds everything together, and keeps the 'on' button pressed. The laser is pointed at the white sheet on the blackboard in the distance. Unfortunately you can't see the red dot in this photograph.

On the right you can see my hand holding the propane torch. You can just see the blue of the flame, heating the air along the path of the laser beam.

The laser spot on the board jiggles as the beam is deflected this way and that as it passes through pockets of hot and cold (thin and thicker, faster and slower) air.