The making of robust and highly performing imaging spectropolarimeters for large solar telescopes

Abstract

We discuss the requirements, concepts, simulations, implementation, and calibration of two dual Fabry-Perot based imaging spectropolarimeters, CRISP and CHROMIS, at the Swedish 1-meter Solar Telescope, and CRISP2 that is under construction. These instruments use a combination of a high-resolution and a low-resolution etalon together with an order-sorting prefilter to define the bandpass. The overall design is made robust and stable by tailoring the low-resolution etalon reflectivity to accommodate expected cavity errors from both etalons, and by using a compact optical design that eliminates the need for folding mirrors. By using a telecentric design based on lenses rather than mirrors, image degradation by the FPI system is negligible, as shown in a previous publication, and the throughput of the system is maximised. Initial alignment, and maintaining that alignment over time, is greatly simplified. The telecentric design allows full calibration and/or modelling of essential system parameters to be carried out without interfering with the optical setup. We also discuss briefly the polarimeters developed for CRISP and CHROMIS. The high performance of CRISP and CHROMIS has been demonstrated in an earlier publication through measurements of the granulation contrast and comparisons with similar measurements simultaneously made through broadband continuum filters. Here, we focus on the aspects of the design that are central to enabling high performance and robustness, but also discuss the calibration and processing of the data, and use a few examples of processed data to demonstrate the achievable image and data quality. We put forward a proposal for a similar conceptual design for the European Solar Telescope and conclude by discussing potential problems of the proposed approach to designs of this type. Some aspects of these FPI systems may be of interest also outside the solar community.

arXiv commentAccepted for publication in Astronomy & Astrophysics (A&A). 24 pages

References in corpus (34)

• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• The Imaging Magnetograph eXperiment (IMaX) for the Sunrise balloon-borne solar observatory
• CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
• The Polarimetric and Helioseismic Imager on Solar Orbiter
• Physical Properties of a Sunspot Chromosphere with Umbral Flashes
• The European Solar Telescope
• Radiative diagnostics in the solar photosphere and chromosphere
• SSTRED: Data- and metadata-processing pipeline for CHROMIS and CRISP
• Stokes imaging polarimetry using image restoration at the Swedish 1-m Solar Telescope
• Chromospheric condensations and magnetic field in a C3.6-class flare studied via He I D3 spectro-polarimetry
• Wavelength-Diverse Polarization Modulators for Stokes Polarimetry
• The GREGOR Fabry-Pérot Interferometer
• Is the solar spectrum latitude dependent? An investigation with SST/TRIPPEL
• An observationally-constrained model of strong magnetic reconnection in the solar chromosphere. Atmospheric stratification and estimates of heating rates
• Is the sky the limit? Performance of the revamped Swedish 1-m Solar Telescope and its blue- and red-beam re-imaging systems
• Stratification of physical parameters in a C-class solar flare using multi-line observations
• Observationally based models of penumbral microjets
• Spatio-temporal analysis of chromospheric heating in a plage region
• Analysis of Seeing-Induced Polarization Cross-Talk and Modulation Scheme Performance
• Image restoration of solar spectra
• Inversions of synthetic umbral flashes: effects of the scanning time on the inferred atmospheres
• Physical properties of bright Ca II K fibrils in the solar chromosphere
• Heating of the solar chromosphere through current dissipation
• High-resolution observations of recurrent jets from an arch filament system
• Design and Performance Analysis of a Highly Efficient Polychromatic Full-Stokes Polarization Modulator for the CRISP Imaging Spectrometer
• Small-scale magnetic flux emergence preceding a chain of energetic solar atmospheric events
• Estimating the longitudinal magnetic field in the chromosphere of quiet-Sun magnetic concentrations
• Magnetic field inference in active region coronal loops using coronal rain clumps
• High flow speeds and transition-region like temperatures in the solar chromosphere during flux emergence
• Improved reconstruction of solar magnetic fields from imaging spectropolarimetry through spatio-temporal regularisation
• Diagnosing the solar atmosphere through the Mg I b${}_2$ 5173 Å line. I. Nonlocal thermodynamic equilibrium inversions versus traditional inferences
• Coronal kink oscillations and photospheric driving: combining SolO/EUI and SST/CRISP high-resolution observations
• A prototype of a large tunable Fabry-Perot interferometer for solar spectroscopy
• Observations of umbral flashes in the resonant sunspot chromosphere

Cited by in corpus (1)

• The magnetic sensitivity of the Ca II H and K lines