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Instrument: FOURIER TRANSFORM SPECTROMETERS
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Description
A Fourier transform spectrometer (abbreviated FTS) is a
Michelson interferometer with a movable mirror. By scanning the
movable mirror over some distance, an interference pattern is
produced that encodes the spectrum of the source (in fact, it
turns out to be its Fourier transform ). Fourier transform
spectrometers have a multiplex advantage over dispersive
spectral detection techniques for signal, but a multiplex
disadvantage for noise.

In its simplest form, a Fourier transform spectrometer consists
of two mirrors located at a right angle to each other and
oriented perpendicularly, with a beamsplitter placed at the
vertex of the right angle and oriented at a 45? angle relative
to the two mirrors. Radiation incident on the beamsplitter from
one of the two "ports" is then divided into two parts, each of
which propagates down one of the two arms and is reflected off
one of the mirrors. The two beams are then recombined and
transmitted out the other port. When the position of one mirror
is continuously varied along the axis of the corresponding arm,
an interference pattern is swept out as the two phase-shifted
beams interfere with each other.

Additional information available at
"http://scienceworld.wolfram.com/physics/FourierTransformSpectrometer.
html"

[Summary provided by Science World]