Achromatization of waveplate for broadband polarimetric system

A broadband polarimetric system with enhanced performance is highly desired in many applications, such as remote sensing. To achromatize a waveplate by combining a stack of retardance plates made of same material with different azimuths, two merit functions are presented in this Letter. The first merit function based on the Jones theorem directly accounts for the equivalent retardance and azimuthal angles of the combined plates. The second one can search for the optimal equivalent azimuthal angles automatically by using the condition number κ2 based on 2-norm or the equally weighted variance EWV, two figures of merit for the full-Stokes polarimeters, as the objective function. Our study within the framework of the simplest full-Stokes polarimeter shows that, for the super-achromatic 131.8° waveplate consisting of seven quartz plates, the root-mean-square errors of the κ2 and EWV are about 0.49% and 0.07%, and the maximum deviations of the equivalent retardance and azimuthal angle are approximately 0.42° and 0.59°, respectively, over the waveband of 0.4-0.7 μm. For the super-achromatic quarter-wave plate comprising seven quartz plates, the maximum deviations of the equivalent retardance and azimuthal angle are only 0.18° and 0.7°, respectively.