Fourier Transform InfraRed Spectrometer

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Fourier Transform InfraRed Spectrometer

• Katerina Nikolaeva

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Fourier Transform Optical System Diagram
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Interference of Two Beams of Light
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Sampling of an Actual Interferogram
He/Ne laser optical ruler ? 632 nm
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Interference is a Superpositioning of Waves
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Fourier Transform
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Fourier Transform
Intensity of the light observed by the detector
(1)
R energy reflected by the beam
splitter (from the fixed mirror), T
energy transmitted by the beam splitter (from the
moving mirror), S(?) energy from the
light source, s wavenumber, cm-1,
? wavelength, nm, ? optical
path difference between reflected and transmitted
beams, cm
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Fourier Transform
If polychromatic light is emitted instead of
monochromatic light, I(X) is given by the
integration of the previous equation with respect
to wave number
(2)
Equation (2) demonstrates that I(X) ia s Fourier
cosine transform of spectrum B(s) Thus an inverse
Fourier cosine transform of I(X) recovers the
original spectrum B(s)
(3)
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Process up to Obtaining a Spectrum
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Spectroscope
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Liquid Solid Samples
The liquid samples are measured using assembly
cell made of rectangular CaF2 windows and 1 mm
Teflon spacer
The solid samples are measured using a clip-on
cell
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FTIR advantages

• Higher sensitivity measurement
• Higher speed measurement
• Higher wavenumber accuracy
• Highly accurate spectrum subtraction