Here is my 'all-tube variable speed dekatron spinner'. It uses a Russian INS-1 neon bulb as the active element in the relax oscillator. Shining a blue-violet laser pointer at the neon bulb, causes it to strike at lower voltage. Its due to the photoelectric effect (discovered by Einstein). The switching frequency goes up, and stalls the dekatron. So the spinning stops, when the light hits it. Note, this will not work with red laser pointers. Blue photons have more energy than red ones. I don't have a green laser pointer, so I don't know how it will effect it.