Precision in ground-based solar polarimetry: simulating the role of adaptive optics

Nagaraju, K.; Feller, A.

doi:10.1364/ao.51.007953

Cited by 12 publications

(8 citation statements)

References 20 publications

(32 reference statements)

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“…For ground-based solar polarimetry, one should particularly pay attention to the atmospheric seeing, since it will introduce spurious polarization signals. With most of the seeing power contained in the 1-100 Hz frequency range (Judge et al 2004), a modulation frequency of the order of 100 Hz is required to reliably reconstruct the four polarization components I, Q, U and V (Krishnappa & Feller 2012). Consequently, seeing-induced crosstalk can be eliminated by using a very high modulation frequency in a single-beam polarimeter.…”

Section: Theorymentioning

confidence: 99%

Design and calibration of a high-sensitivity and high-accuracy polarimeter based on liquid crystal variable retarders

Guo

Ren

Liu

et al. 2017

Res. Astron. Astrophys.

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Polarimetry plays an important role in the measurement of solar magnetic fields. We developed a high-sensitivity and high-accuracy polarimeter (HHP) based on nematic liquid crystal variable retarders (LCVRs), which has a compact setup and no mechanical moving parts. The system design and calibration methods are discussed in detail. The azimuth error of the transmission axis of the polarizer as well as the fast axes of the two LCVRs and the quarter-wave plate were determined using dedicated procedures. Linearly and circularly polarized light were employed to evaluate the performance of the HHP. The experimental results indicate that a polarimetric sensitivity of better than 5.7 × 10 −3 can be achieved by using a single short-exposure image, while an accuracy on the order of 10 −5 can be reached by using a large number of short-exposure images. This makes the HHP a high-performance system to be used with ground-based solar telescope for high-precision solar magnetic field investigations.

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Section: Theorymentioning

confidence: 99%

Design and calibration of a high-sensitivity and high-accuracy polarimeter based on liquid crystal variable retarders

Guo

Ren

Liu

et al. 2017

Res. Astron. Astrophys.

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“…The typical time scales of seeing evolution for daytime observations in competitive observing sites are of the order of 10 ms, 183 making this a suitable exposure time if post-facto image restoration wants to be used to reduce aberrations. 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.…”

Section: Temporal Modulationmentioning

confidence: 91%

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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“…Thus, the residual seeing effects still remain, introducing seeing-induced cross-talk (Krishnappa and Feller 2012). Higher modulation frequencies help to reduce the seeing-induced crosstalk (Judge et al 2004;Gandorfer et al 2004;Ramelli et al 2010;Casini et al 2012;Krishnappa and Feller 2012).…”

Section: Image Correction In Real Timementioning

confidence: 99%

Measurements of Photospheric and Chromospheric Magnetic Fields

et al. 2015

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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.Comment: Accepted for publication in "Space Science Reviews"; 42 pages, 16 figure

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Precision in ground-based solar polarimetry: simulating the role of adaptive optics

Cited by 12 publications

References 20 publications

Design and calibration of a high-sensitivity and high-accuracy polarimeter based on liquid crystal variable retarders

Design and calibration of a high-sensitivity and high-accuracy polarimeter based on liquid crystal variable retarders

Instrumentation for solar spectropolarimetry: state of the art and prospects

Measurements of Photospheric and Chromospheric Magnetic Fields

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