+Light may consist of two or more components of well defined polarisation states; as a result, the total beam cannot be described with a single well defined Jones vector. Ellipsometers are designed to establish a well defined polarisation state of light incident on the sample; however non-uniform films or backside reflection from a substrate may cause the reflected beam to be partially polarised. As a result, the Jone's formalism is not sufficient for characterisation of these samples, and the more general Stokes formalise (with 4 component vectors) must be employed \cite{woolam2000} \cite{oates2011}.
+
+\begin{table}[H]
+ \centering
+ \begin{tabular}{lll}
+ \includegraphics[scale=0.75]{figures/ellipsometer/circular_polarisation} &
+ \includegraphics[scale=0.75]{figures/ellipsometer/elliptical_polarisation} &
+ \includegraphics[scale=0.75]{figures/ellipsometer/linear_polarisation} \\
+ \end{tabular}
+
+ \captionof{figure}{From left to right, circular, elliptical and linearly polaristed light, viewed down the axis of beam propagation}
+\end{table}