Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders

Harrington, David M.; Snik, Frans; Keller, Christoph U.; Sueoka, Stacey R.; Harten, Gerard van

doi:10.1117/1.jatis.3.4.048001

Cited by 16 publications

(34 citation statements)

References 47 publications

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“…The field dependence was at magnitudes of 0.02 in a Mueller matrix element across the 5 arcminute field. In the next two papers, 44,45 we explored polarization fringes caused by multi-crystal retarders and their dependence on retarder design, beam F/ number, thermal variation and thermal loading. The fringes are present at high spectral frequency, clearly resolvable by our instruments and with significant fringes in retardance, diattenuation and transmission.…”

Section: Introductionmentioning

confidence: 99%

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 4: calibration accuracy over field of view, retardance spatial uniformity, and achromat design sensitivity

Harrington

Sueoka

2018

J. Astron. Telesc. Instrum. Syst.

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Modern observatories and instruments require optics fabricated at larger sizes with more stringent performance requirements. The Daniel K. Inouye Solar Telescope (DKIST) will be the world's largest solar telescope at 4.0 m aperture delivering a 300 Watt beam and a 5 arc-minute field. Spatial variation of retardance is a limitation to calibration of the full field. Three polarimeters operate seven cameras simultaneously in narrow bandpasses from 380 nm to 1800 nm. The DKIST polarization calibration optics must be 120 mm in diameter at Gregorian focus to pass the beam and operate under high heat load, UV flux and environmental variability. Similar constraints apply to the three retarders for modulation within the instrument suite with large beams near focal planes at F/ 18 to F/ 62. We assess how design factors can produce more spatial and spectral errors simulating elliptical retardance caused by polishing errors. We measure over 5 • net circular retardance and spectral oscillations over ±2 • for optics specified as strictly linear retarders. Spatial variations on scales larger than 10 mm contain 90% of the variation. Different designs can be a factor of 2 more sensitive to polishing errors with dissimilar spatial distributions even when using identical retardance bias values and materials. The calibration for the on axis beam is not impacted once circular retardance is included. Calibration of the full field is limited by spatial retardance variation unless techniques account for this variation. We show calibration retarder variation at amplitudes of 1 • retardance for field angles greater than roughly one arc minute for both quartz and MgF 2 retarders at visible wavelengths with significant variation between the three DKIST calibration retarders. We present polishing error maps to inform new calibration techniques attempting to deliver absolute accuracy of system calibration below effective cross-talk levels of 1 • retardance.

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Section: Introductionmentioning

confidence: 99%

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 4: calibration accuracy over field of view, retardance spatial uniformity, and achromat design sensitivity

Harrington

Sueoka

2018

J. Astron. Telesc. Instrum. Syst.

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“…The Cryo-NIRSP feed optics and modulator properties are described in our prior references. 16,17,57,65 For the rest of the polarimetric instruments, the beam must propagate through the AO system as shown in Equation 4. The DL-NIRSP, ViSP and VTF all see M7, M8 and M9 as well as the tenth mirror as the adaptive optics system deformable mirror (DM = M10).…”

Section: Mirror Grouping Models Polarization and System Mueller Matricesmentioning

confidence: 99%

“…The optics are at 15 • incidence angle which does create polarization through the complex dichroic coatings on the front surfaces and also the broad-band anti-reflection coatings on the back surfaces. We modeled polarization fringes in two recent papers 13,68 and do not expect to observe significant fringing given the 0.5 • wedge angle in each of the FIDO beam splitters. There are presently five dichroics planned for fabrication as shown in Table 6.…”

Section: Dichroic Coatings: Polarization Performance and Fido Designsmentioning

confidence: 99%

“…We can implement the group model by combining the Mueller matrices derived for each mirror. We get the diattenuation and retardance using the Berreman calculus with the coating layer thicknesses in Table 8 and the theoretical equation for a flat fold mirror at a single incidence angle from Equation 13. We then apply the geometrical rotations between the groups of mirrors as the telescope rotates in azimuth, elevation and coudé laboratory table angle.…”

Section: A Dkist System Model For Polarization and Throughputmentioning

confidence: 99%

“…Retardance is denoted as δ which is the same as τ in the solar convention. In Equation 13 we show a common definition of the Mueller matrix for a mirror folded along the +Q plane. The II element is the average reflectivity.…”

Section: Appendix D Antireflection Coatings: Spectral Oscillationsmentioning

confidence: 99%

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Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 5: impacts of enhanced mirror and dichroic coatings on system polarization calibration

Harrington

Sueoka

White

2019

J. Astron. Telesc. Instrum. Syst.

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The Daniel K. Inouye Solar Telescope (DKIST) is designed to deliver accurate spectro-polarimetric calibrations across a wide wavelength range and large field of view for solar disk, limb and coronal observations. DKIST instruments deliver spectral resolving powers up to 300,000 in multiple cameras of multiple instruments sampling nanometer scale bandpasses. We require detailed knowledge of optical coatings on all optics to ensure we can predict and calibrate the polarization behavior of the system. Optical coatings can be metals protected by many dielectric layers or several-micron thick dichroics. Strong spectral gradients up to 60 • retardance per nanometer wavelength and several percent diattenuation per nanometer wavelength are observed in such coatings. Often, optical coatings are not specified with spectral gradient targets for polarimetry in combination to both average and spectral threshold type specifications. DKIST has a suite of interchangeable dichroic beam splitters using up to 96 layers. We apply the Berreman formalism in open-source Python scripts to derive coating polarization behavior. We present high spectral resolution examples on dichroics where transmission can drop 10% with associated polarization changes over a 1 nm spectral bandpass in both mirrors and dichroics. We worked with a vendor to design dichroic coatings with relatively benign polarization properties that pass spectral gradient requirements and polarization requirements in addition to reflectivity. We now have the ability to fit multi-layer coating designs which allow us to predict system level polarization properties of mirrors, anti-reflection coatings and dichroics at arbitrary incidence angles, high spectral resolving power and on curved surfaces through optical modeling software packages. Performance predictions for polarization at large astronomical telescopes requires significant metrology efforts on individual optical components combined with systems-level modeling efforts. We show our custom-built laboratory spectropolarimeter and metrology efforts on protected metal mirrors, antireflection coatings and dichroic mirror samples.

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The Daniel K. Inouye Solar Telescope – Observatory Overview

et al. 2020

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We present an overview of the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST), its instruments, and support facilities. The 4 m aperture DKIST provides the highest-resolution observations of the Sun ever achieved. The large aperture of DKIST combined with state-of-the-art instrumentation provide the sensitivity to measure the vector magnetic field in the chromosphere and in the faint corona, i.e. for the first time with DKIST we will be able to measure and study the most important free-energy source in the outer solar atmosphere – the coronal magnetic field. Over its operational lifetime DKIST will advance our knowledge of fundamental astronomical processes, including highly dynamic solar eruptions that are at the source of space-weather events that impact our technological society. Design and construction of DKIST took over two decades. DKIST implements a fast (f/2), off-axis Gregorian optical design. The maximum available field-of-view is 5 arcmin. A complex thermal-control system was implemented in order to remove at prime focus the majority of the 13 kW collected by the primary mirror and to keep optical surfaces and structures at ambient temperature, thus avoiding self-induced local seeing. A high-order adaptive-optics system with 1600 actuators corrects atmospheric seeing enabling diffraction limited imaging and spectroscopy. Five instruments, four of which are polarimeters, provide powerful diagnostic capability over a broad wavelength range covering the visible, near-infrared, and mid-infrared spectrum. New polarization-calibration strategies were developed to achieve the stringent polarization accuracy requirement of 5×10−4. Instruments can be combined and operated simultaneously in order to obtain a maximum of observational information. Observing time on DKIST is allocated through an open, merit-based proposal process. DKIST will be operated primarily in “service mode” and is expected to on average produce 3 PB of raw data per year. A newly developed data center located at the NSO Headquarters in Boulder will initially serve fully calibrated data to the international users community. Higher-level data products, such as physical parameters obtained from inversions of spectro-polarimetric data will be added as resources allow.

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Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders

Abstract: Polarization modeling and predictions for DKIST part 2: application of the Berreman calculus to spectral polarization fringes of beamsplitters and crystal retarders,"

Cited by 16 publications

References 47 publications

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 4: calibration accuracy over field of view, retardance spatial uniformity, and achromat design sensitivity

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 4: calibration accuracy over field of view, retardance spatial uniformity, and achromat design sensitivity

Polarization modeling and predictions for Daniel K. Inouye Solar Telescope part 5: impacts of enhanced mirror and dichroic coatings on system polarization calibration

The Daniel K. Inouye Solar Telescope – Observatory Overview

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