Measurement errors induced by retardance deviation in a rotatable retarder fixed polarizer Stokes polarimeter

The retardance of an achromatic retarder may vary in the working frequency range and therefore deviate from its nominal value. In a rotatable retarder and fixed polarizer (RRFP) Stokes polarimeter, the retardance deviation of the retarder will result in significant measurement errors of the Stokes vector. The relationship between the retardance error and the measurement errors is theoretically derived in a RRFP Stokes polarimeter. Theoretical results show that the resultant measurement errors of the Stokes vector are determined by the retardance of the retarder, the retardance error and the Stokes vector under test, but are independent of the angular orientations of the retarder and the intensity measurements. Such measurement errors can not be reduced by choosing a set of optimum angular orientations or increasing the measurement number. To suppress such measurement errors in a complete RRFP Stokes polarimeter, the retarder with retardance from 110-deg to 135-deg is recommended. Simulation results in two measurement scenarios confirm the validity of the theoretical findings.