Method for determining the optical constants of a thin film on a transparent substrate

A method has been proposed for exact calculation of the optical parameters n and k of a thin film on a transparent substrate by simultaneously solving the equations for two of the envelopes of the transmission and reflection spectra. The singularity of the solution and the convergency area are proved, and the influence of the inaccuracies in drawing the envelopes upon the errors made during the calculation of n and k is also investigated. The method is most accurate for the envelopes of the transmission minima and the reflection maxima in the region of strong and medium absorption. The accuracy of other methods which use data from the transmission or reflection envelopes has also been investigated. The present method describes correctly the change of n in the region of medium and strong absorption for an amorphous film with composition Ge₂₈As₁₂S₆₀.