We propose a scheme to extract the refractive index and the extinction coefficient of dielectrics. The extraction needs only a reflectance spectrum with reliable successive maxima of fringing oscillations measured from a dielectric film that is either freestanding or on metal. With the film thickness known in advance, we determine the refractive index spectrum from the fringing oscillation periods and then the extinction coefficient spectrum from the upper envelope. The method is demonstrated to work well for GaAs and Ge. (C) 2015 Optical Society of America
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