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Author: Subject: spectroscope
kyanite
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[*] posted on 17-7-2005 at 13:26


Wow, I'm dumber that I thought!:P

So we can skip all the bolometers and detector crap by using an IR camera...
Brilliant. That makes things so much more simpler!

cd spectroscope
Damn, this looks fun. Easy too. :D
I think I'm going to take a whack at it.
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[*] posted on 18-7-2005 at 13:52


I was told that most B/W cameras cover a portion of IR as well, thats why when its very dark you still see some shadows on the screen. I didnt check any specs to see how good it would be for this.
Also I think that some home video cameras have the night vision button that all it does (I think) converts IR to green so you can record and see in the dark.
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[*] posted on 21-7-2005 at 10:46


"Wow, I'm dumber that I thought! "

Does anyone remember a few posts back where I pointed out that the bit of the IR spectrum that normal cameras will see isn't the bit usually used for IR spectroscopy.
What about the bit where someone cited the IR spectra in their textbooks as a good place to start when looking for the range of IR you need (well done, BTW, and quite correct)?

[Edited on 21-7-2005 by unionised]
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[*] posted on 25-7-2005 at 06:19
Interferometer


UV and visible spectra provide very little information. The best method to identify chemicals is nuclear magnetic resonance (NMR) - not really feasible at home. IR is fairly useful, but It may be better to use another approach to recording IR spectra.

Most IR spectrometers use a Michelson interferometer. It does away with any need for frequency separation (no prism/grating).

So source of IR - glowing filament (light bulb)

Detector - some kind of solid state device should work nicely.

Beamsplitter - a plastic sheet can work

moving mirror - tricky part needs to be precise, its position is usually monitored by a laser.

Have fun!
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my nootloss
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[*] posted on 25-7-2005 at 09:28


I am sorry but what propose would the moving mirror serve? If a mirror is indeed needed then I think it would have to be a frontal mirror.

And why would we not need the UV and visible spectra? Why not just use frequency separation, and pick up as many wavelengths as we can? And I had thought that UV was all most the only thing some substances put out. And if IR works better with out frequency separation then we could just let it pick up the light before it gets separated
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[*] posted on 25-7-2005 at 13:53


Said inferometer uses two crossed beams (actually more than two, Google it) and an adjustable mirror to cause adjustable interference. Unless I'm thinking of the speed-of-light measuring apparatus. I seem to recall both with the same device though...

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[*] posted on 27-7-2005 at 07:07


Michelson did dabble in speed of light measurements. The interferometer was however used to disprove the existence of luminiferous aether.
The method has been sucessfully adapted to measure IR spectra. What happens is the IR beam is split into two. These two beams travel different distances, then are recombined. If one of the path lengths is varied (moving mirror) an interference pattern is generated at the detector. Now if a sample is placed in the beam some frequencies will be removed and a different interference pattern will be obtained. The missing frequencies can be found by fourier tranformation. Sounds improbable, but it works.
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[*] posted on 29-7-2005 at 08:35


Ok maybe that sounds a bit difficult. What about NQR (nuclear quadrupole resonance) I made a spectrometer with just one active component (a FET) and it worked. The computer interface was a little more difficult. Next I am going to try it through the sound card to bypass the interface which is a bit temperamental.
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