K3PGP has a nice website which I’ve seen before since he and I share some common interests: astronomy and lasers, notably. He’s got an interesting page on his K3PGP Experimenters Corner that detail his experiments with laser communications. Basically, he created a beacon transmitter which transmits 30 second long pulses of particular frequencies spaced 0.5hz apart. This modulates an IR diode, which flashes up to the night sky. Five miles away, he targets the region with a PIN diode laser reciever, which is fronted by a 12 inch Fresnel lens. Incredibly enough, he can easily receive characters sent this way. It’s very slow speed (two chars per second), but it’s a neat trick.