The solar corona is a complex and dynamic region primarily controlled by the magnetic fields. Hence the routine measurement of these fields is crucial. Magnetic field information remains embedded in the polarization profiles of the spectral lines, which can be quantified through spectropolarimetry. Differential Hanle effect is a promising diagnostic tool to probe weak coronal magnetic fields and their vector properties. In a recent study we have found several combinations of spectral lines located in the wavelength range 100 to 1210 Å suitable for the above purpose whose critical Hanle field lies in the range of 0.01-200 Gauss. Since the background emission from the Sun’s underlying layers, such as the photosphere and the chromosphere, is almost negligible at these short wavelengths, the coronagraphic technique is not required to study the solar corona, thereby enabling both on-disk and off-limb measurements. Yet there is no EUV polarimeter built for solar observations. In this context we explored a few polarimeter concepts based on the configurations of two and three reflecting mirrors. The performances of these configurations are studied in terms of their throughput and polarizing power using Zemax software in the wavelength range 740-780 Å. They are also compared with different coating materials namely, BaF2, MgF2 and LiF. It is found that BaF2 has significantly higher throughput and polarizing power in the above stated wavelength range.
In a dual-frequency liquid crystal (DFLC), when the frequency of the applied voltage is more than a critical value (fc), the dielectric anisotropy of the material changes from positive to negative. This causes the director to switch its orientation from parallel to the field (for f < fc), to perpendicular to it (f < fc). Hence DFLC can be used in modulating the light by switching the frequency of an externally applied voltage. We present in this work about application of DFLCs in full Stokes polarimetery. A polarization modulator has been worked out based on two DFLCs and two static retarders. The combination of DFLCs’ switching and static retarders are chosen such that more or less equal weightage is given to all the Stokes parameters. Initial results on the optimization of position angles of the modulators are presented towards the goal of achieving polychromatic modulator in the wavelength range 600-900 nm.
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