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From: John Rabson <john.rabson@numeo.fr>
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Date: Sun, 9 Oct 2011 10:16:13 +0200
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To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Laser link...
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Scott,

Did you have any trouble with temperature-sensitivity of the optical =
filter?   When doing experiments at 633 nm (He-Ne red) I had to use a =
narrow band filter to keep that part of the ambient light out of the =
photomultiplier, even though the lab was lit with a mixture of blue and =
green fluorescent tubes to minimise the amount of red.

The first attempt did not work at all.  The photomultiplier was cooled =
with dry ice* and the optical filter pass band shifted too much.  I had =
to isolate the PMT and the filter with some optical fibre to keep the =
filter at room temperature.

73
John F5VLF
* a bit below the temperature you get in winter I think

On 8 Oct 2011, at 23:14CEST, Scott Tilley wrote:

> Hi Stefan
>=20
> I've created a wide-band audio link before using a laser.  In fact, I =
used it to bounce the audio I wanted to send off of a passive reflector. =
 Wideband and excellent fidelity is possible, just ensure the object you =
are bouncing off is very stable otherwise you'll get microphonics =
(useful if you want to hear what's going on somewhere else :-)........  =
I strongly recommend the use of a very narrow band interference type =
filter for the laser wavelength you are using, mount this over the PIN =
diode detector...  This way the system is usable day or night without =
noticeable degradation due to sunlight.
>=20
> 73 Scott