This amazing demo shows how you can transmit sound over a laser beam. The transmitter modulates power to a laser pointer with audio from a headphone jack. The receiver is just an earphone and a solar cell; no power source. I assembled both in minutes, and it was strange (in a good way) to hear music whenever I held the cell in the beam. As seen in MAKE Volume 16, the Spy Tech issue!
Laser Voice Transmitter and Receiver