"Douglas Taylor" writes:

"Sam Goldwasser" wrote in message
...
"Douglas Taylor" writes:

Is it possible to build your own FTIR?

I don't mean from scratch, I mean is it possible to build one out of
'parts'.

Sure, why not?

I ask because I just bought the electronics and beamsplitter/moving
mirror
assembly from a Nicolet Spectrometer. The moving mirror is a 'porch
swing'
type so I don't need air for an air bearing, the KBr beamsplitter looks
in
excellent shape. It would be neat to get this working in a stand-alone
mode.

You may be better off ignoring the electronics except maybe the detector
front-end and doing your own unless documentation is available.

I have given this some thought.... The electronic functions that are needed
a

1. Amp to drive the mirror motor - sort of a saw tooth drive signal
(audio freq bandwidth)
2. Laser signal phase lock loop - if the mirror moves at a constant
speed the laser interference signal will be a sine wave in the audio
spectrum, I think you couple this to the mirror drive to keep the mirror
speed constant.

So these together form a constant reference frequency drive.

3. A/D trigger signal - you use the laser reference zero crossings to
trigger the A/D

Is that a high enough sampling rate? I guess if it's IR, then the fringe
signal for the unknown spectrum will be a lower frequency but you still
need to obey Mr. Nyquist.

4. Start & End of scan - you need to know where the mirror is, either at
the start of the scan or end and either direct the mirror drive circuit to
tell the mirror motor to go forward or backward.
5. Digital interface - connect the A/D to a computer, monitor other
signals.

Sounds like a lot of basic electrical circuit stuff, nothing exotic. Maybe
it is possible to build.

I still need an laser and detector (working on it), but the real question
is can I operate the electronics independently?

You mean a laser for the reference?

Yes, an ordinary HeNe laser is what is used. The beamsplitter I have
has a small circular area in the middle which is where the laser reference
beam is directed. I comes out the other side of the interferometer into a
small detector.

So it sounds like you have an interesting project if you're in it for
the challenge. Even if you don't do the full FTIR, you could build a
nice accurate wavemeter with what you have.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
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