The advantage of defining the spectrum in wavenumbers is that they are directly related to energy levels. A wavenumber represents the number of full waves of a particular wavelength per cm of length (typically in vacuum, where the index of refraction n=1). This leads us to the definition of the unit of spectral measurement: the wavenumber (cm -1), denoted as n. Each individual spectral component contributes a single sinusoid with a frequency inversely proportional to its wavelength to this signal. The X-axis of the interferogram represents the optical path difference. Thus, as we move away from the centerburst, the interferogram becomes a complex oscillatory signal with decreasing amplitude. Therefore, their contributions are all at maximum and a very strong signal is produced by the system’s detector.Īs the optical path difference, OPD, is increased, different wavelengths produce peak readings at different positions, and for a broadband signal, they never again reach their peaks at the same time. Its origin lies in the fact that all wavelengths are in-phase at the ZPD. The centerburst, the big spike in the center of Figure 4 is a telltale signature of a broadband source. Figure 3 shows the beam path of a two wavelength source Figure 4 is the interferogram of a broadband light source. It is usually significantly more complex than a single sinusoid, which would be expected if only a single wavelength of light was present. Interferogram is the name of the signal format acquired by an FT-IR spectrometer.
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