Do you have a home-made, high-powered laser that you fear demonstrating because you might hurt someone? Here's the solution: fit it to a pen-holder/plotter derived from Evil Mad Scientist Labs's Watercolorbot.
It is a quite simple build made out of wood, some plastic from an old cutting board, a few screws and a 9g servo. The servo is controlled by an Arduino, when the signal that would normally turn the laser diode on is high the servo is set to an angle that pushes the pen against the paper. The design was inspired by the brush holder on the WaterColorBot by Evil Mad Scientist. In their design the pen is lifted up by the servo rather then being pushed down like I did it. I don't know what is best but it works both ways.
(via Evil Mad Scientist Labs)