|MadSci Network: Physics|
Dear Stewart, Yes, you are correct. This does work as a means of detecting audio vibrations from distant objects, such as windows. The optics train for such a sensitive device requires the use of a technique known as interferometry. This aids in the elimination of background noise. An advanced version of this type laser microphone is describe at this URL... => http://www.williamson-labs.com/laser-mic.htm So, who originally came up with the idea of a microphone which would modulate light with sound? On June 3, 1880, Alexander Graham Bell transmitted the first wireless telephone message on his newly-invented "photophone" over 213 meters (~700 feet) using sunlight. The device allowed for the transmission of sound on a beam of light. Bell's photophone worked by projecting voice through an instrument toward a mirror. Vibrations in the voice caused similar vibrations in the mirror. Bell directed sunlight into the mirror, which captured and projected the mirror's vibrations. The vibrations were transformed back into sound at the receiving end of the projection. However, until the development of modern fiber optics, technology for the secure transport of light inhibited use of Bell's invention. For details of Bell's patent, read this URL... => http://histv2.free.fr/bell/bell5.htm If you're more curious, you can easily make your own laser microphone and receiver to tranmsit voice or music. Check out this URL... => http://www.scitoys.com/scitoys/scitoys/light/light.html Good Luck! ---* Dr. Ken Beck
Try the links in the MadSci Library for more information on Physics.