High speed photodiode amp

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 sheet 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

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

Robert, as soon as the electric power is turned off, the longest any power is available would be the upper state liftime, at zero radiation that is. The value of the upper state lifetime for CO2 is known, I'd have to look it up in some books that are not here at home.

Rene

Hmmm, IR photographic film?

Divert a small fraction of the laser pulse and fine focus it on a moving IR film, or move the spot with a rotating mirror.

Wasn't that an "oscillogram"? :-)

I've got this image of a spinning mirror inside a 1-lb coffee can that's painted black on the inside, with a little holder for a 4"x5" piece of sheet film; a little hole in the side that's normally covered with black tape, and, of course, your sync system.

Spin up the mirror, turn off the room lights, open the tape, and fire the laser.

Develop the film, and you should be able to measure the trace. :-)

Kind of an amalgamation of Michelson-Morley and Daguerre. ;-)

Cheers! Rich

Robert,

Normal fluorescence or phosphorescense results in emission at lower energy, thus wavelengths beyond 10 microns. Multiphoton fluorescence would produce emission at higher energy but requires very high peak powers (sub-nanosecond pulse duration) such that the first absorbed photon is still in the excited state when the second arrives.

Down the road from you at U of M Chemistry Electronics Shop,

Steve

I don't know if you ever got a useful answer to your query, but I just came across a product that is made for this purpose: