It is demonstrated that the interference oscillations in the intensity of light reflected from a substrate during deposition of a semitransparent film allows one to determine the optical constants of the film by graphical techniques. The method assumes that the optical constants of the substrate are known, and that the optical constants of the film are not a function of film thickness. This technique is applicable in any wavelength region, although surface irregularities, which are more important at short wavelengths, will generally lead to an overestimate of k. A discussion of probable errors is presented. Because the method is dependent on multiple reflections through the deposited film it is useful only for small k, or, more precisely, 2πk/n < 1.
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