[sdiy] OT: Laser Microphones?

[Andy Main]

The quick answer is yes, the easiest way (as others have said) is to
make an interferometer. A simple Extrinsic Fabry-Perot could be made and
you could look at the phase of the returned signal.  Dual frequency
interrogation provides a larger dynamic range with greater accuracy
(I've read papers with up to 5 wavelength interrogation).  It would be
an ambitious DIY project, and you will undoubtedly pick up unwanted
vibration, especially from flexible membranes.  I've seen quite a few
papers on this topic though.

Andy.

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Glen
Sent: 01 September 2003 06:23
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] OT: Laser Microphones?

Does anyone know of any internet links regarding laser-based
microphones,
other than those designed for surveillance? It just seems to me that
someone would have tried to make a microphone that used a laser, and use
it
for "normal" high fidelity recording purposes. Unfortunately, all the
information I can find is related to bouncing a laser off someone's
window,
to listen to conversations on the other side of the window.

Couldn't the beam be bounced off a reflective membrane mounted very
close
to the laser, and then analyze the reflected beam, to record sounds in
the
same room as the laser? I'm wondering what advantages there might be to
laser pickup of the membrane's vibrations, compared to magnetic
(dynamic),
or electrostatic (condenser) pickup of the membrane's vibrations. 

It shouldn't be as prone to pickup of stray magnetic fields as a dynamic
mic, and therefore should work well around CRT's and other magnetic
devices. I think it might also offer the potential to have less
background
hiss than a typical condenser, and have a potentially large dynamic
range.

Does anyone know of any attempts to create such a microphone?

later,
Glen