In principle the complex refractive index n+ik and the thickness t of the most recently deposited material should be simultaneously determinable from the three independent quantities \r(p)\(2), \r(s)\(2) and r(p)r(s)* returned by polarimetric measurements. However, this goal has generally not been realized due to a lack of accuracy and signal-to-noise capabilities of present technology. By investigating the properties of the Jacobian matrix I show that the need for high accuracy is a direct consequence of the strong correlations among n, k, and t within the polarimetric parameters. Further, I show that this limitation can be circumvented by taking advantage of the spectral correlations between the refractive indices of the substrate and overlayer. As an example I determine n, k, and t independently for a 1.1 Angstrom thick layer of GaAs deposited on a GaAs/AlGaAs/GaAs pseudo-substrate from real-time data. (C) 2004 Elsevier B.V. All rights reserved.