MEASURING SPECTRAL TRANSMITTANCE AND REFLECTANCE WITH A MICHELSON $INTERFEROMETER^{\ast}$
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Date
1964
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Ohio State University
Abstract
The use of a Michelson interferometer to measure the amplitude and phase of the radiation transmitted by, or reflected from, a plane slab of material placed in one arm of the interferometer is described. This technique has been used in the infrared by $Bell^{1}$ and by Chamberlin, Gibbs and $Gebbie^{2}$ for the determination of the index of refraction of materials. The method may be extended to reflection measurements. The introduction of an optical element into one arm of a Michelson interferometer will change the interferogram from I(x), where x is the optical path difference between the beams traversing the two arms of the interferometer, to $I^{\prime}(x)$. The fourier transform of I(x) is the spectral power density $P_({\nu})$ of the radiation passing through the instrument (modified, of course, by the spectral sensitivity of the instrument). The fourier transform of $I^{\prime}(x)$ is $T_({\nu})P_({\nu})$. $T_({\nu})$ is the spectral transmittance, both the amplitude and the phase, of the slab in the one arm of the interferometer. $T_({\nu})$ may be derived from the interferograms I(x) and $I^{\prime}(x)$. The square of the real part of this complex amplitude transmittance is the power transmittance. Measured data on the transmittance of a sheet of Mylar are used to illustrate the method. The influence of the chaneled spectra in the phase function is shown and the spectral course of the index of refraction of Mylar is obtained. Results obtained by comparing the reflection of an aluminized mirror with the reflection of KBr in an uncollimated Michelson $interferometer^{3}$ are used to show how the method may be applied to reflectance measurements. The spectral course of the complex reflectance including the absolute value of the phase through the reststrahlen region are obtained.
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$^{\ast}$ This investigation was carried out under a contract between The Air Force Cambridge Research Laboratories and The Ohio State University Research Foundation. $^{1}$ Bell, Sympsoium on Molecular Structure and Spectroscopy Columbus, Ohio, June 15, 1962. $^{2}$ Chamberlin, Gibbs, and Gebbie, Nature 198, 874 (1963). $^{3}$ Steel, J. Opt. Soc. Am. 54, 151 (1964).
Author Institution: Laboratory of Molecular Spectroscopy and Infrared Studies, Department of Physics, The Ohio State University
Author Institution: Laboratory of Molecular Spectroscopy and Infrared Studies, Department of Physics, The Ohio State University