Interferential detection of small gaseous molecules and atmospheric pollution control

Fourier Transform Spectrosetry can be remarkably simplified in the case ofthe detection of siall gaseous aolecules by taking advantage of the periodicity ofthe absorption spectrua. The instruient includes an interferometric device adjustedto a fixed optical path difference used as a signature of the molecule. High sensi-tivity and remarkable discrisination power are obtained.1. BASIC PRINCIPLESmall aolecules have absorption bands coaposed of alaost equidistant lines;the absorption spectrum has then a periodic character. If So(a) is the continuous