STANDARD SPECTRA WITH THE IMPROVED FOURIER TRANSFORM SPECTROMETER OF OULU
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Date
1985
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Ohio State University
Abstract
The infrared standard spectra and about 2500 wavenumbers of lines between $500 cn^{-1}$ and $900 cm^{-1}$ have been produced with our modified Fourier transform spectrometer system. These spectra of $H_{2}O,\ N_{2}O,\ CO_{2}$ and OCS and the wavenumbers of lines will be presented in ``Handbook of Infrared Standards with Spectral Maps and Molecular Parameters” by G. Guclachvili and K. Narahari Rao. The spectra were the first true measurements with our new cube corner interferometer built at our laboratory. The maximum optical path difference of the interferometer is now $8 m$ providing a theoretical resolution of $0.0009 cm^{-1}$. In these measurements the spectral resolution was between $0.002 cm^{-1}$ and $0.003 cm^{-1}$. This is more than twice better than in our earlier measurements with the flat mirror interferometer. However, the signal to noise ratio is even better than before using the same source (Globar) and detector (Golay). This means, that the cube corner interferometer works in practice clearly better than older one. The absorption path length was 1 m. The pressures in the measurements were $H_{2}O$: 2 Torr, $N_{2}O: 0.5$ and 1.5 Torr, $CO_{2}: 0.06$ and 0.2 Torr and OCS: 0.5 Torr. Although the spectra were first ones with the new system the results were quite good. Especially the accuracy of the wavenumbers inside the spectral bands was high. In the best conditions it was $\pm 13 \cdot 10^{-6} cm^{-1} (\pm 0.39 MHz)$ defined as a standard deviation. It is limited only by the signal to noise ratio. The absolute accuracy is more difficult to calculate, because there may be several source of systematic errors: the precision of the reference $lines^{1}$, pressure shifts and phase errors. We have estimated it to be about $\pm 60 \cdot 10^{6} cm^{-1}(\pm 1.8 MHz)$.
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$^{1}$J.S. Wells, F. R. Petersen, A. G. Maki, and D. J. Sukle, Appl. Opt. 20, 1676 (1981).
Author Institution: Department of Physics, University of Oulu; Department of Physics, University of Oulo
Author Institution: Department of Physics, University of Oulu; Department of Physics, University of Oulo