Determination of Mueller Matrix for Metal Substrates by Stokes Polarimetry

This article focuses on a polarization measurement method based on Mueller calculus for determining the polarization properties of metal substrates. As the Mueller matrix of a medium provides all its polarization-altering properties, the presented method enables to predict the effect of any optically absorbing media on the polarization state of light beam. For the measurement, a polarized beam of light is reflected off the substrate under study and the change in state of polarization is measured in terms of Stokes parameters. Simple formulae have been derived to deduce the values of matrix elements from the measured Stokes parameters. The presented method facilitates determination of the optical properties of any absorbing medium even though the optical constants are unidentified. It has been validated by the estimation of Mueller matrix elements of a few metal reflectors (Cu, Al and SS304) using Fresnel's equations and comparing the theoretical values with the experimentally determined values. It has been verified further by measuring the complex refractive index of a sample (brass: Cu-Zn alloy) using the principle angle method and comparing the results with that obtained by newly developed method. For the materials under study, the average absolute error in the measurement of matrix elements is found to be <; 0.01 and the standard deviation is <; 0.02. The main advantage of the method is that the polarization properties of any optically absorbing medium can be determined using a simple optical setup at any desired wavelength.