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An Evaluation of the Practical Performance of a Digilab FTS-14 Fourier Transform Infrared Interferometer Working in the Region of 4000 to 400 cm−1

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Abstract:

The performance of a Digilab FTS-14 Fourier transform infrared interferometric spectrometer has been evaluated in terms of (1) sensitivity and signal/noise ratio (in comparison with a high quality infrared grating instrument), (2) the attainment of very high absolute signal/noise ratios by use of double-precision arithmetic, (3) photometric accuracy, (4) wavenumber accuracy, (5) resolution, (6a) water vapor cancellation and double-beam operation, (6b) ratioing facilities against stored reference spectra, (7) the measurement of very high optical densities, and (8) miscellaneous other operational considerations. It is shown that, compared with a diffraction grating spectrometer of good performance, over most of the spectral region the interferometer enables the attainment of more than an order of magnitude improvement in signal/noise ratio (S/N) for a given time of scan and resolution. This improvement in S/N was found to reach a maximum of about 40 times at 2000 cm−1 when the full wavenumber range (3600 cm−1) is measured with the highest resolution (0.5 cm−1). This corresponds to the measurement of 7200 spectral elements, n. The S/N improvement is proportional to n ½ and is correspondingly reduced for more limited ranges of spectral measurement or for more limited resolutions. The enhanced S/N can alternatively be traded for rapid scanning. The performance of the interferometer is shown to be very good in relation to the other operational parameters listed above. Substantial additional advantages–particularly in relation to automated operation, ratioing of related spectra, and flexibility in modes of plotting wavenumber or intensities–occur from the use of a dedicated minicomputer with, or as part of, a spectrometer.

Keywords: Fourier-transform; Infrared; Signal/noise ratio

Document Type: Research Article

DOI: http://dx.doi.org/10.1366/000370278774331783

Affiliations: School of Chemical Sciences, University of East Anglia, Norwich, NR4 7TJ, England

Publication date: January 1, 1978

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