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Instrument: FTIR SPECTROMETER : Fourier Transform Infrared Spectrometer
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FTIR SPECTROMETER - Fourier Transform Infrared Spectrometer

Traditional (dispersive) infrared techniques experience
difficulties due to the '1 wavenumber at a time' nature of data
acquisition. This leads to either a poor signal to noise ratio
in a spectrum or a very long time needed to obtain a high
quality spectrum. Both these situations cause problems with
kinetic work. The first gives inherent large errors, the second
prohibits in-situ work. These problems can be overcome using
Fourier transform infrared spectroscopy (FT-IR) that is based on
the interferometer originally designed by Michelson and a
mathematical procedure developed by Fourier that converts
response from the 'time' to the 'frequency' domain.

In the Michelson interferometer a parallel, polychromatic beam
of radiation from a source (A) is directed to a beam splitter
(B), made from an infrared transparent material, such as
KBr. The beam splitter reflects approximately half of the light
to a mirror, known as the fixed mirror (C), which in turn
reflects the light back to the beam splitter. The rest of the
light passes through to a mirror, moving continuously, at a
known velocity, back and forth along the direction of the
incoming light and this is known as the moving mirror (D). Upon
reflection from the moving mirror, radiation is then directed
back to the beam splitter. At the beam splitter some of the
light that has been reflected from the fixed mirror combines
with light reflected from the moving mirror and is directed
towards the sample. After passing through the sample (E) the
radiation is focused onto the detector (F). The detectors are
sufficiently fast to cope with time domain signal changes from
the modulatio n in the interferometer.

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