A photon is just a small packet of light energy, so a photon cannon is anything that shoots a lot of light out at the same time. In order to have destructive power, a beam of light needs to be concentrated. By using a lens, you can make your photon canon bright enough to be at least annoying and possibly dangerous to the eyes, so don’t aim the photon cannon at people; only use the cannon to signal people on the moon or for some other harmless purpose.
1. Gather a bunch of extremely bright lights together. Spotlights would be good for this purpose, but a bunch of flashlights will do in a pinch. Put them in a circle on the ground, facing straight up. Attach them together to keep them in alignment.
2. Wire the power switches of all the lights together so that you can turn them on at the same time. If you are using spotlights, simply leave them in the on position and turn the circuit on from a heavy duty power strip.
3. Cover your light source with a fresnel lens with a long focal length. You can either use a single lens over the top of all your lights, or one lens for each light (see Resources below). The focal length determines at what distance the beam will focus, so make it adequate for your uses. (The moon is over 200,000 miles away.)
4. Mount a reflector above the array. Attach a large mirror to a movable mount.
5. Adjust the mirror to reflect the light at the correct angle. Then stand back and turn on the switch.