Inversion of normal-incidence (R,T) measurements to obtain n + ik for thin films

A new algorithm is described for numerical inversion of the equations Texp = T(n,k) and Rexp = R(n,k), where Texp and Rexp are measured normal-incidence transmission and reflection of a thin film on a thick substrate, and n + ik is the complex index of refraction of the thin film. The procedure simultaneously provides all pairs (n,k) consistent with the values of (T,R) measured at a specific wavelength and known film thickness. It requires no initial estimates for n and k.