Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance

Casini, R.; Wijn, A. G. de; Judge, P. G.

doi:10.1088/0004-637x/757/1/45

Cited by 26 publications

(20 citation statements)

References 16 publications

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“…Modeling the fringes by a superposition of sine curves of various amplitudes and frequencies requires little computing time when compared to more involved approaches using wavelet analysis (Rojo & Harrington 2006) or 2D pattern recognition (Casini et al 2012). Drawbacks are the danger of removing or modifying an actual signal, that is a spectral line.…”

Section: Data Description and Analysismentioning

confidence: 99%

Magnetic fields of opposite polarity in sunspot penumbrae

Fränz

Collados

Bethge

et al. 2016

A&A

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Context. A significant part of the penumbral magnetic field returns below the surface in the very deep photosphere. For lines in the visible, a large portion of this return field can only be detected indirectly by studying its imprints on strongly asymmetric and three-lobed Stokes V profiles. Infrared lines probe a narrow layer in the very deep photosphere, providing the possibility of directly measuring the orientation of magnetic fields close to the solar surface. Aims. We study the topology of the penumbral magnetic field in the lower photosphere, focusing on regions where it returns below the surface. Methods. We analyzed 71 spectropolarimetric datasets from Hinode and from the GREGOR infrared spectrograph. We inferred the quality and polarimetric accuracy of the infrared data after applying several reduction steps. Techniques of spectral inversion and forward synthesis were used to test the detection algorithm. We compared the morphology and the fractional penumbral area covered by reversed-polarity and three-lobed Stokes V profiles for sunspots at disk center. We determined the amount of reversed-polarity and three-lobed Stokes V profiles in visible and infrared data of sunspots at various heliocentric angles. From the results, we computed center-to-limb variation curves, which were interpreted in the context of existing penumbral models. Results. Observations in visible and near-infrared spectral lines yield a significant difference in the penumbral area covered by magnetic fields of opposite polarity. In the infrared, the number of reversed-polarity Stokes V profiles is smaller by a factor of two than in the visible. For three-lobed Stokes V profiles the numbers differ by up to an order of magnitude.

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Section: Data Description and Analysismentioning

confidence: 99%

Magnetic fields of opposite polarity in sunspot penumbrae

Fränz

Collados

Bethge

et al. 2016

A&A

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“…Such variations, along with residual image motion of instrumental origin, may cause spurious polarization signals [I → Q, U , and V crosstalk] if one analyzes the modulated beam with a single linear polarizer. This problem is largely overcome if one simultaneously analyzes both s-and p-polarizations, and combines the results appropriately in a "dual-beam" polarimeter (Lites, 1987;Judge et al, 2004;Sankarasubramanian et al, 2006;Gosain, 2007;Casini, de Wijn, and Judge, 2012). The advantages of dual-beam polarimetry in the presence of rapid seeing fluctuations have been demonstrated by several ground-based polarimeters including the ASP, and by the IMaX balloon-borne instrument (Martínez Pillet et al, 2011).…”

Section: The Modified Savart Plate Polarization Analyzermentioning

confidence: 99%

The Hinode Spectro-Polarimeter

et al. 2013

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The joint Japan/US/UK Hinode mission includes the first large-aperture visiblelight solar telescope flown in space. One component of the Focal Plane Package of that telescope is a precision spectro-polarimeter designed to measure full Stokes spectra with the intent of using those spectra to infer the magnetic-field vector at high precision in the solar photosphere. This article describes the characteristics of the flight hardware of the Hinode Spectro-Polarimeter, and summarizes its in-flight performance.

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“…It has also been shown using numerical simulations 184 and measurements 39 that seeing-induced crosstalk considerably reduces, down to few times 0.01%, for modulation frequencies above 100 Hz, and drops below the detection limit in the kHz regime. 185 As a consequence of the above, instrumental developments using a temporal modulation scheme aim for a high modulation frequency to reduce jitter and seeing-induced artifacts. Most of the designs employ standard Charge Coupled Devices (CCDs) or Complementary Metal-Oxide Semiconductor (CMOS) architectures in a synchronous readout approach.…”

Section: Temporal Modulationmentioning

confidence: 99%

Instrumentation for solar spectropolarimetry: state of the art and prospects

Iglesias

Feller

2019

Opt. Eng.

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Given its unchallenged capabilities in terms of sensitivity and spatial resolution, the combination of imaging spectropolarimetry and numeric Stokes inversion represent the dominant technique currently used to remotely sense the physical properties of the solar atmosphere, and in particular, its important driving magnetic field. Solar magnetism manifests itself in a wide range of spatial, temporal and energetic scales. The ubiquitous but relatively small and weak fields of the so called quiet Sun are believed today to be crucial for answering many open questions in solar physics, some of which have substantial practical relevance due to the strong Sun-Earth connection. However, such fields are very challenging to detect because they require spectropolarimetric measurements with high spatial (subarcsec), spectral (< 100 m) and temporal (< 10 s) resolution along with high polarimetric sensitivity (< 0.1% of the intensity). In this review we collect and discuss both well-established and upcoming instrumental solutions developed during the last decades to push solar observations towards the above-mentioned parameter regime. This typically involves design trade-offs due to the high dimensionality of the data and signal-to-noise-ratio considerations, among others. We focus on the main three components that form a spectropolarimeter, namely, wavelength discriminators, the devices employed to encode the incoming polarization state into intensity images (polarization modulators), and the sensor technologies used to register them. We consider the instrumental solutions introduced to perform this kind of measurements at different optical wavelengths and from various observing locations, i.e., ground-based, from the stratosphere or near space.

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Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance

Cited by 26 publications

References 16 publications

Magnetic fields of opposite polarity in sunspot penumbrae

Magnetic fields of opposite polarity in sunspot penumbrae

The Hinode Spectro-Polarimeter

Instrumentation for solar spectropolarimetry: state of the art and prospects

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