Environmental Engineering Reference
In-Depth Information
Motor drive
Piston
Movable mirror
Light source
Fix mirror
Beam splitter
Sample cell
Detector
(interferogram data)
Readout
(wavenumber spectrum)
Computer
(Fourier transform)
Figure 8.17
Schematic diagram of a Fourier transform infrared (FTIR) spectrometer
Michelson interferometer
: This includes a beam splitter (germanium film
on a KBr plate support), one fixed mirror, and one movable mirror. The
beam splitter is semitransparent, allowing the generation of two beams,
one of which falls on a fixed mirror and the other on the mobile mirror.
The two beams travel through the sample before hitting the detector. The
moving mirror oscillates in time between two extreme positions. The
transmitted signal, which varies with time, is recorded as an
interferogram
.
Detector: It is similar to dispersive spectrometer, but employs pyroelectric
bolometer as detector, and has fast response time required by the fast scan.
Deuterated triglycine sulfate (DTGS) is an example of pyroelectric material.
8.3.2 Dispersive Infrared Instruments (DIR)
The optical designs for the dispersive IR instruments do not differ greatly from
the double-beam UV-VIS spectrophotometers except that the sample and refer-
ence compartments are always located between the infrared sources and the
monochromator
in infrared instruments. Major components of
the dispersive
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