Simple polarization measurement of a depolarizing retarder with diattenuation

Abstract

A method is proposed to measure the polarimetric parameters of a depolarizing retarder with diattenuation (DRD). The retardance is expressed as a tangent function that recovers its correct sign as opposed to the usual calculation of the retardance through a cosine function. The depolarizing parameters of a pure depolarizer, normally retrieved with the Lu-Chipman decomposition method, can be calculated directly, through the Fourier transform of three different measured irradiances. This method needs the measurement of one of the axes of the DRD. Assuming the retardance between zero and π, the proposed method can then distinguish if this axis is the fast or slow axis without any additional measurements, as is required in other characterization methods. As a result the correct Mueller matrix of the DRD is always recovered. Two examples are presented and validated using a dual rotating retarder polarimeter (DRR) calibrated with the eigenvalue calibration method (ECM).