It is shown that the transmission of light through a thin dielectric film under conditions of frustrated total reflection can be used to measure the refractive index and thickness of the film. The refractive index and thickness have been measured for each of several magnesium fluoride films. The thickness was checked in each case by multiple beam interference and the refractive index compared with the results obtained by other authors for similar films. It appears that many present concepts on which the theory of the optical properties of thermally evaporated films is based are inadequate for the problems involved.
© 1958 Optical Society of America
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