Fourier Transform Infra Red Spectrometers:

In compare to the dispersive IR spectrometers, while the signal from the sample is dispersed and the response at every wavelength (or wave number) is measured individually, a FT instruments collect the response at all the wavelengths concurrently. In these multiplex instruments the monochromator is replaced through an interferometer and the response of the sample to the overall range of IR radiation is suitably modulated and collected within the time domain. These are then decoded using the Fourier transformation. Thus it is named the Fourier transform infra red spectrometer (FT-IR).

The primary instrument design for an FT-IR instrument is quite easy. A schematic diagram displaying different elements is given in Figure. The IR radiation from the source is first directed into an interferometer from whereas it is passed by the sample compartment and then it reaches to the detector.

Figure: A Schematic diagram showing different components and the optic path of a FT-IR spectrometer