On 01/08/2018 11:26 PM, bitrex wrote:
On 11/17/2017 01:30 AM, Phil Allison wrote:
Jeff Layman wrote:

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** By all accounts, bouncing a IR laser off a widow is not practical.
The beam has to be precisely aligned *square on* to the window and
the resulting sound quality is abysmal.


I don't understand that. Why "square on"?


** The IR laser and its receiver have to be in the same location,
maybe hundreds of yards away rom the target window, so alignment is
near impossible.

Google the idea.



....Â*Â* Phil


It's one of those ideas that sounds both plausible and really clever
except for the small detail that it doesn't work. Like extracting audio
from ancient times off the decorative grooves cut into clay pots while
spun on a wheel

There are a lot of ways to skin that particular cat, and normal
incidence isn't required. Oblique incidence and a remote quad-cell
photodiode in another nearby building is perfectly doable. The transmit
laser would have a fast 2D scanner, and a separate data link would allow
closing a feedback loop to keep the reflected beam centred on the quad
cell. What the sound quality would be like, I don't know.

A fast, fine raster scan would allow lock acquisition in a few seconds.

Adaptive optics is used for much harder jobs than that, every day.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com