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      Full Stokes polarimetry using Dual-Frequency Liquid Crystals

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          Abstract

          In a dual-frequency liquid crystal (DFLC), when the frequency of the applied voltage is more than a critical value (\(f_c\)), 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 \(f < f_c\)), to perpendicular to it (\(f > f_c\)). 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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          Radiative Diagnostics in the Solar Photosphere and Chromosphere

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            Fast switching dual-frequency liquid crystal optical retarder, driven by an amplitude and frequency modulated voltage

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              Measurements of Photospheric and Chromospheric Magnetic Fields

              , , (2015)
              The Sun is replete with magnetic fields, with sunspots, pores and plage regions being their most prominent representatives on the solar surface. But even far away from these active regions, magnetic fields are ubiquitous. To a large extent, their importance for the thermodynamics in the solar photosphere is determined by the total magnetic flux. Whereas in low-flux quiet Sun regions, magnetic structures are shuffled around by the motion of granules, the high-flux areas like sunspots or pores effectively suppress convection, leading to a temperature decrease of up to 3000 K. The importance of magnetic fields to the conditions in higher atmospheric layers, the chromosphere and corona, is indisputable. Magnetic fields in both active and quiet regions are the main coupling agent between the outer layers of the solar atmosphere, and are therefore not only involved in the structuring of these layers, but also for the transport of energy from the solar surface through the corona to the interplanetary space. Consequently, inference of magnetic fields in the photosphere, and especially in the chromosphere, is crucial to deepen our understanding not only for solar phenomena such as chromospheric and coronal heating, flares or coronal mass ejections, but also for fundamental physical topics like dynamo theory or atomic physics. In this review, we present an overview of significant advances during the last decades in measurement techniques, analysis methods, and the availability of observatories, together with some selected results. We discuss the problems of determining magnetic fields at smallest spatial scales, connected with increasing demands on polarimetric sensitivity and temporal resolution, and highlight some promising future developments for their solution.
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                Author and article information

                Journal
                31 August 2018
                Article
                10.1117/12.2312503
                1808.10689
                b7750e74-3f1e-4f37-9877-d64d9fd815c6

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                History
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                Proc. SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII, 107024X (6 July 2018)
                7 pages, 3 figures
                astro-ph.IM

                Instrumentation & Methods for astrophysics
                Instrumentation & Methods for astrophysics

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