Each FTIR spectrometer is composed by three basic optical elements: (a) An IR source, (b) an interferometer, comprised by a beam splitter and two mirrors (one fixed and one moving) and (c) a detector. The working principle of an FTIR spectrometer is briefly described in Fig. 1. The beam produced by the IR source passes through an aperture. Then it is optically filtered before entering into the interferometer, which constitutes the “heart” of the spectrometer. The operation of the interferometer is described in detail in the next sections. The motion of the interferometer’s moving mirror modulates the light beam, which when exits the interferometer is led to the sample. The light that was transmitted thought (or reflected by) the sample is finally focused on the detector, which measures its intensity, i.e. its power.