A 2-D heterodyne polarimeter for the determination of parameters in twisted nematic liquid crystal cells

In this paper, an experimental method for measuring the 2-D cell parameter distribution of a twisted nematic liquid crystal is presented. Based on phase-sensitive imaging polarimeter with a common-path heterodyne configuration, this study adopts an integrating-bucket method to extract 2-D phase distribution on the detected heterodyne signal for the inverse calculation of the azimuth angle (entrance director angle), twist angle, and cell gap. The advantage of the heterodyne scheme introduces high sensitivity on phase detections, and the multiple parameters could be easily extracted through the genetic algorithm. The measurement range of the azimuth angle is from 0° to 180° without ambiguity. By using standard 8-bit gray-level charge-coupled device, the experimental results show that the 2-D standard deviation of 0.4°, 0.7°, and 0.032 μm in the measurement of azimuth angle, twist angle, and cell thickness have been obtained.