As laser pointers became available to physics teachers, we took to puffing clouds of chalk dust, fog-in-a-can, or other particulate scattering agents into our classrooms to demonstrate the the magic of light amplification by the stimulated emission of radiation.
One year, I initiated a school-wide fire alarm during such a demonstration. The previous summer, the custodians had been tasked with cranking up smoke detector sensitivity to 11, unbeknownst to me.
Another thing we began doing was to shine our laser beams into water-filled fish tanks. The beams were again more visible when a scattering agent was deployed. Some used milk, some likes Pine-Sol. I used contact lens cleaning solution before settling on Mop-N-Glo.
But fish tanks were heavy, and the gallons and gallons of water made them downright unwieldy. It was a teacher-only demonstration activity.
As nice as it is for students to remember Physics as the class where the teacher did cool things, I wanted them to remember it was the class where they did cool things.