Re: High speed photodiode amp

On Sat, 13 Jan 2007 09:22:20 +0100, Rene Tschaggelar <none@xxxxxxxx>
wrote:

John Larkin wrote:

On Sat, 13 Jan 2007 00:45:48 +0100, Rene Tschaggelar <none@xxxxxxxx>
wrote:

Robert,
contrary to what others tell, you'll have aproblem.
The speed is not high speed, rather low speed, at
least what we're usually used to. No, your problem
is the source. CO2 at 10um requires a sensor that
is sensitive in that range. Silicon isn't. Germanium
isn't. A thermopile is, but has nowwhere the
required bandwidth. Possibly a LN2 cooled CdHg
something.

Rene

10 microns? That's practically RF!


Indeed. I've see an antenna array with recifiers,
a nice photolitho job. The recifier being a quantum
dot between 2 crossed Lambda-half. At liquid helium
I believe. That device would be able to be as fast
as Robert wishes, but the support equipment tends to
the unwieldy.

Rene

OK, if photodiodes are out, how about this:

Use a rotating mirror, maybe a surplus supermarket scanner assembly or
an official laser-deflection galvo. Maybe his system has galvos
already. Or a mirror on a Dremel. Sweep the laser spot across a
surface, maybe just a *** of black paper, and image that with a
thermal imager. Microsecond resolution looks perfectly feasible, sort
of a streak camera thing. Things need not be synchronized... just wait
for the occasional random hit.

My FLIR imager will snapshot roughly a 200x200 pixel image and tell
you the temperature of every pixel. If you lay your hand on your desk
for a few seconds, it will image the thermal handprint for a minute or
so. It would easily image the laser light itself, or the latent
thermal pattern left behind.

Maybe one of those novelty "mood sensor" temp-sensitive lcd strips
would work too.

Maybe you could sweep it across a piece of paper and note the burn
pattern. Probably not very linear.

What else would image a heat pattern? A row of 100 thermocouples? A
frosty beer bottle?

John

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