Design of a static spectropolarimeter

An innovative model of a static spectropolarimeter able to cover the entire Stokes vector and suitable for the study of massive stars was advanced a few years ago by William Sparks. The model, employing a birefringent modulator formed by two anti-parallel wedges stoked together by an intermediary part of the same material has the advantage of being extremely compact, avoiding any movements or turning components. By its architecture, the device can induce a complete modulation on a vertical direction of any incoming polarized light, ensuring the determination of the Stokes vector through a single measurement. Because the modulation is also wavelength dependent, spectral information can be derived. Into this presentation the first results related to the behaviour of this model in the presence and absence of noise are introduced. Thus, in the ideal conditions of the absence of noise, the existence of a unique solution, as incoming state of polarization, was proved. Then, in a noisy environment, it was shown that the determination of the Stokes parameters is accompanied by an error which depends closely to the level of noise and to the orientation of the analyzer. The error affecting the extraction of the Stokes parameters was investigated with regard to the orientation of the analyzer, providing a way to choose the best configuration of the instrument. Lastly, the impact of the tilted rays inside the instrument was also considered.