Interferometers Fellgett advantage

The other principal advantage which applies to Fourier transform spectroscopy is the multiplex or "Fellgett" advantage 21,64) n yas P. Fellgett who first pointed out that there is an advantage when the data in all elements of a spectrum are obtained simultaneously instead of being measured for each element successively. In Fourier transform spectroscopy, the radiation in the Michelson interferometer is not separated into spectral elements. The interferogram contains... 

Unlike the Fellgett advantage, throughput is not dependent upon the wavelength or detector used in the instrument. For this reason interferometers enjoy the ability to record and detect spectra of weakly emitting or weakly absorbing samples in either the optical or infrared regions of the spectrum. This property has been heavily exploited in the field of FT-IR. 

The resolution of the light into its various frequency components is accomplished by (i) gratings or prisms in dispersive instruments, (ii) interferometers (such as the Michelson124 interferometer see below) in Fourier transform spectrometers (Fellgett s125 advantage), or (iii) for X rays, bent LiF crystal or graphite monochromators. 

A major improvement in the signal-to-noise ratio of NMR spectra was achieved in 1964 by the conception of Fourier tran orm (FT) spectroscopy. The basic principle — parallel data acquisition, leading to the multiplex advantage — was already applied by Michelson in 1891 in optical spectroscopy and explicitly formulated by Fellgett in 1951. However, the approach used in optics, spatial interferometry, is unsuited for NMR spectroscopy, since an interferometer with the necessary resolution would require a path length of at least 3 y. l(f m. — Richard R. Ernst [1]... 

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