The thickness and the complex refractive index of a moderately thin absorbing film on a transparent substrate of known optical properties can be determined by measuring the values of reflectance of the sample from opposite sides, and the transmittance. The technique and its use in measuring properties of films of RbI in the uv are described. Errors are reduced by averaging the values of thickness obtained at several wavelengths and by iterating the computations.
G. BALDINI and L. RIGALDI, "Ultraviolet Optical Constants of Thin Films Determined by Reflectance Measurements," J. Opt. Soc. Am. 60, 495-498 (1970)