This was a fun project and, while really simple, could be expanded into something really cool.
I mounted a green laser pen and pointed it to a circular mirror. That mirror was mounted to a small computer fan and slightly bent so that when the light is reflected it comes back in a circular motion. Add some fog to that and you are all set.
For the laser pen, I got one that I could wire to a wall wart. I originally had it planned to be outside so I didn’t want to worry about changing batteries.
The mirrors I got at a hobby store. I think it was only a dollar or two.
It takes some trial and error as far as distance and angle of the mirror but in the end it worked.