MadSci Network: Physics

Subject: Can a laser be used as a long distance microphone?

Date: Thu Jul 29 01:04:03 2004
Posted by Stewart Alexander
Grade level: grad (science) School: North Carolina State University
City: Raleigh State/Province: NC Country: United States
Area of science: Physics
ID: 1091081043.Ph

I was thinking about this, and I am wondering if one focused a laser beam on a surface, say a pane of 
glass would it reveal the vibrations of the medium it hit?

The pane of glass or object would vibrate due to the pressure exerted on it, in terms of a voice, this 
transverse sound wave would impact the glass and make it minutely jiggle, right?

If the glass vibrates from the speech in a certain way, this could be picked up by a laser, if what I think 
is right. Then with a computer and considerable processing power one could de-noise this data and 
turn it back into speech.

If a laser can pick up the vibrations in the medium it hits and carry this information efficiently,  this 
would make for a very effective surveillance microphone. 

One could "hear" a person talking on a cellphone inside of  a car (if the windows were rolled up) from as 
far away as there was the ability to make a line of site hit of a laser to that car. 

Re: Can a laser be used as a long distance microphone?

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