Characterisation of Liquid Crystals for broadband optimal design of Mueller matrix ellipsometers

The optimal design over a broad spectral range of Liquid Crystal (LC) based Polarisation State Generators (PSG) and Polarisation State Analyzers (PSA), requires detailed knowledge of the spectral behaviour of the LCs. The full Mueller matrix measurement formalism based on the Eigenvalue Calibration Method, does in principle not require an exact modelling of the polarizing components, however, it is required that the condition number for both the PSG and the PSA is close to optimum over a wide spectral range. Two LC technologies are investigated here, Ferroelectric LC (FLC), and Liquid Crystal Variable Retarders (LCVR). In the case of a FLC based PSG, additional components, such as fixed retarders also need to be properly characterised in order for a proper broad spectral optimal design. These issues are here studied by characterizing the FLCs, the LCVRs and the fixed retarders with the help of a commercial visible Mueller matrix ellipsometer, and a polarizer-rotating sample-rotating analyzer near infra red set-up. The results are analyzed in the framework of the optimal condition number over a broad spectral range.