Development of a spectropolarimeter for space use

Abstract

This thesis deals with the analytical design of a static spectropolarimeter for space use, based on birefringent media. It is about an instrument able to provide access to all four Stokes parameters of the detected light, at different wavelengths. In the first part of the thesis, the most important concepts and methods of polarimetry and of their applications in astrophysics are presented. Further, the proposed instrument is described, and the modulation function is derived, using the Mueller calculus. Because the material of the spectropolarimeter is Magnesium Fluoride (MgF2), an important attention was offered to the variation of the birefringence with wavelength. Two models for the description of the chromaticity of MgF2 were proposed and compared. Then the uncertainty calculus corresponding to this type of instrument was developed. Adjacently, considering the presence of noise, an extraction algorithm for the Stokes parameters was build and the behavior of the instrument in the presence of noise was tested. In the last part of the research, the off-axis case was also studied. After a detailed mathematical determination of the ray tracing with the help of Huygens constructions, several scenarios for the off-axis incidence were analyzed and the main limitations of the system were discovered.