Fourier transform infrared spectrometry: A tool for modern agricultural research

Abstract

The concept of using a two-beam interferometer for the measurement of infrared spectra has taken almost a century to come to fruition. Michelson first devised the concept of the interferometer which now bears his name in 1887. However it was not until about sixty years later that Fellgett recognized the multiplex advantage attained for spectra measured using a Michelson interferometer, i.e., the fact that information from all wavelengths in the spectral region under investigation is sampled throughout the entire measurement. In the early 1950’s, Jacquinot proved that the light-grasp of an interferometer was greater than that of a monochromator operating at the same spectral resolution. The combination of the Fellgett (or multiplex) and Jacquinot (or optical throughput) advantages of an interferometer leads, in theory at least, to a sensitivity advantage for interferometrically measured spectra of between two and three orders of magnitude for data acquired in equal times. Only recently, however, has the performance which may be predicted on theoretical grounds started to be achieved in practice, and Fourier transform infrared (FT-IR) spectrometers based on Michelson (and other two-beam) interferometers is now the most popular technique for measuring high quality infrared spectra of samples of many different types.