Re: High speed photodiode amp

On Sat, 13 Jan 2007 18:07:43 GMT, Sven Wilhelmsson
<sven@xxxxxxxxxxxxx> wrote:

On Sat, 13 Jan 2007 08:10:33 -0800, John Larkin wrote:

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


Yes, a rotating mirror seems reasonable to me.
If the CO2 laser can be controlled and pulsed repeatedly, and if the
pulses can be synchronized to the mirror with a controllable skew, then a
cheap pyroelectric detector , maybe even a thermocouple, could be used
to scan the pulse profile in a way similar to a sampling oscilloscope.

Sven W
http://home.swipnet.se/swi


Right, if things are synchronizable. The first sampling "oscilloscope"
was a mechanical-contact sampler driving a galvo pen recorder, used to
plot AC generator waveforms. 1890's, I think.

John

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