Mueller-matrix polarimeter using analysis of the nonlinear voltage-retardance relationship for liquid-crystal...

A method for using liquid-crystal variable retarders (LCVRs) with continually varying voltage to measure the complete Mueller matrix of a general sample is presented. The LCVRs are usually employed with fixed retardance values due to the nonlinear voltage-retardance behavior that they show. For the measurement method presented here, the nonlinear voltage-retardance relationship is first measured, and then a linear fit of the known retardance terms to the detected signal is performed. For a gap of air, the measurement error in the Mueller-matrix polarimeter is estimated at 1%-10%, depending on the Mueller-matrix element. Also, we present experimental results for a Glan-Thompson prism polarizer as a test sample, and we use the measured Mueller parameters as functions of the orientation of the optical axes of the polarizer as an indication of the quality of the polarimeter. In addition, results are compared to a typical step-voltage method to measure the Mueller matrix. Both methods give good results.