One needs to fit the reflectivity curves obtained in surface plasmon resonance experiments with theoretical models. A free software (for non commercial use) called Winspall exactly does that.
According to the developers, WINSPALL is a PC based software which computes the reflectivity of optical multilayer systems. It is based on the Fresnel equations and the matrix formalism. It can be used to analyze surface plasmon experiments. WINSPALL was developed in the Knoll group. WINSPALL is available for use without charge. It may not be reused for commercial purposes.
It is available for download here.
A tutorial to use this software is available here.
Many thanks for Prof. Barry Lavine for this information.