Determination of the optical constants of thin films based on normal-incidence reflectance measurements

Complex-valued optical constants of thin films can be determined in various ways, such as polarization changes upon grazing reflection and simultaneous measurements of the reflectance (R) and the transmittance. In this work, we report that the reflectance-only measurement in normal incidence can also be used to evaluate optical constants when it is combined with two-step analysis methods, i.e., the Kramers-Kronig transformation of R to obtain the phase change upon the reflection and the numerical analysis of the Fresnel equation. By examining the influences of the uncertainty in R or in the phase on the final results, we show that the precise measurement of R over a broad spectral range is essential to guarantee the accuracy of the optical constants determined in this method.