High accuracy and precision measurement method of the extinction coefficient and retardance of non-perfect linear polarizers

Abstract

Linear polarizers, even high quality ones, may present non-negligible extinction transmission and retardance. The value of the extinction transmission measured using the Malus law is unreliable in most of the cases. Both parameters can be determined using Mueller–Stokes polarimetry but the results are even less trustworthy. In this work we propose a new method for measuring the extinction coefficient and retardance of a polarizer with high accuracy and precision. It requires the use of an auxiliary polarizer and a waveplate, along with circularly polarized and linearly polarized light sources. This method has increased accuracy than previous methods based on Malus law or Mueller–Stokes polarimetry, and is insensitive to background noise fluctuations, increasing precision. We have numerically tested the reliability of the method when several experimental errors are introduced, showing that it is robust to them. Also, the method has been experimentally implemented to characterize commercial polarizers, and a synthetic linear polarizer with a controllable retardance produced by a liquid crystal. We show that our experimental method is more precise than Malus method and Mueller–Stokes polarimetry. The uncertainty in the extinction coefficient is reduced up to 7 times compared with Malus law and two orders of magnitude respect to Mueller–Stokes polarimetry methods. The uncertainty in the extinction ratio decreases up to two orders of magnitude respect to Malus law method and 7 times respect to Mueller–Stokes polarimetry. The uncertainty in the retardance is reduced up to 2 orders of magnitude respect to Mueller–Stokes polarimetry.