Instrumentation for solar spectropolarimetry: state of the art and prospects

Abstract

Given its unchallenged capabilities in terms of sensitivity and spatial resolution, the combination of imaging spectropolarimetry and numeric Stokes inversion represents 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 (sub-arcsec), spectral (<100 mA), and temporal (<10 s) resolution along with high polarimetric sensitivity (<0.001 of the intensity). We collect and discuss both well-established and upcoming instrumental solutions developed during the last decades to push solar observations toward 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 spectro-polarimeter, 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.

Invited Review

References in corpus (14)

• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
• Inversion of the radiative transfer equation for polarized light
• The European Solar Telescope
• Magnetic properties of G-band bright points in a sunspot moat
• First Detection of Chromospheric Magnetic Field Changes During an X1-Flare
• A 3-D sunspot model derived from an inversion of spectropolarimetric observations and its implications for the penumbral heating
• Vector magnetic field measurements along a cooled stereo-imaged coronal loop
• Imaging Spectropolarimetry with IBIS: Evolution of Bright Points in the Quiet Sun
• Multi-line Stokes inversion for prominence magnetic-field diagnostics
• Image restoration of solar spectra
• First flight of the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) instrument
• Magnetic Properties and Flow Angle of the Inverse Evershed Flow at Its Downflow Points
• Full Stokes observations in the He I 1083 nm spectral region covering an M3.2 flare

Cited by in corpus (9)

• The European Solar Telescope
• The Visible Spectro-Polarimeter of the Daniel K. Inouye Solar Telescope
• Design and Performance Analysis of a Highly Efficient Polychromatic Full-Stokes Polarization Modulator for the CRISP Imaging Spectrometer
• A Practical Calibration Method for RGB Micro-Grid Polarimetric Cameras
• A Model-based Technique for Ad Hoc Correction of Instrumental Polarization in Solar Spectropolarimetry
• A nonlinear solar magnetic field calibration method for the filter-based magnetograph by the residual network
• Designing wavelength sampling for Fabry-Pérot observations. Information-based spectral sampling
• Multi-wavelength spectropolarimetric observations of AR13724 performed by GRIS
• Multi-height probing of horizontal flows in the solar photosphere