I’m working through the archive and working out how best to share ideas… lets try this:
Set up as below, the rotating mirror should be mounted such that it can be easily spun. A small electrical motor is ideal. The mirror on the turning fork should be a very light one eg Mylar. When set up and running the laser beam will trace a waveform on the screen.
A really nice way to show the vibrations of a fork correspond to the classic wave drawings.