Make a simple laser communicator that converts a sound source into light that travels across a room, and back into sound with very little quality loss.
http://scitoys.com/scitoys/scitoys/light/light.html#laser_communicator
http://www.edn.com/article/CA243224.html
http://www.edn.com/archives/1998/071698/15di.htm
http://www.misty.com/people/don/laserdon.html
focus on nitrogen and dye lasers
http://technology.niagarac.on.ca/people/mcsele/lasers/
http://www.web-ee.com/Schematics/PIN%20Diode%20Amp/uv_sensitive_photodetector.htm
some simple laser effects
http://www.west.net/~science/laser.htm
can provide a full-duplex 115.2 kbit/sec data connection between the serial ports of two computers which are separated by a distance of many hundreds of metres
http://www.alphalink.com.au/~derekw/upntcvr.htm