Fourier Transform Spectroscopy

T he difficulties that always plague an experimental spectroscopist are those associated with resolving power, light-gathering ability, and wavelength and photometric accuracy. He sees a spectrum, such as that of atmospheric water vapor shown in Fig. 1, and deduces from it information about the atoms or molecules which gave rise to it. Such spectrograms can be taken at wavelengths from the far ultraviolet (about 10-6 cm), through the visible (a bout 10-4 cm) , to the infrared (101 cm). They are made by passing a beam of white light through a sample of material and dispersing the light with a prism. The dispersed light , the spectrum, is then analyzed by moving a narrow slit across it and recording what passes through the slit with a suitable detector and recording system. If the slit is made narrow in order to see fine detail , then little light energy reaches the detector and the result is low signal-to-noise in the recording and low accuracy in the measured quantities. Over the past ten years there have been advances in spectroscopy that have greatly alleviated these difficulties when others are accepted in