Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-Delay Polarization Modulators

Miller, Nathan J.; Chuss, David T.; Marriage, Tobias A.; Wollack, Edward J.; Appel, John W.; Bennett, C. L.; Eimer, Joseph; Essinger‐Hileman, T.; Fixsen, D. J.; Harrington, Kathleen; Moseley, S. H.; Rostem, Karwan; Switzer, Eric R.; Watts, Duncan J.

doi:10.3847/0004-637x/818/2/151

Cited by 27 publications

(29 citation statements)

References 59 publications

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“…Several current and planned experiments use either HWPs or Variable-delay Polarization Modulators (VPMs; Miller et al 2016), both of which can be used to measure V. Although the current limit is many orders of magnitude larger than the most optimistic signal predictions, these measurements provide an observational test of the standard cosmological model and a wide range of physical processes. Since this limit is still about four orders of magnitude above modern linear polarization measurements, a dedicated experiment with better V-coupling could make significant improvements using existing technology.…”

Section: Resultsmentioning

confidence: 99%

A New Limit on CMB Circular Polarization from SPIDER

Nagy

Ade

Amiri

et al. 2017

ApJ

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We present a new upper limit on cosmic microwave background (CMB) circular polarization from the 2015 flight of SPIDER, a balloon-borne telescope designed to search for B-mode linear polarization from cosmic inflation. Although the level of circular polarization in the CMB is predicted to be very small, experimental limits provide a valuable test of the underlying models. By exploiting the nonzero circular-to-linear polarization coupling of the half-wave plate polarization modulators, data from SPIDERʼs 2015 Antarctic flight provide a constraint on Stokes V at 95 and 150 GHz in the range ℓ 33 307 < <. No other limits exist over this full range of angular scales, and SPIDER improves on the previous limit by several orders of magnitude, providing 95% C.L. constraints on ℓ ℓ C 1 2 ℓ VV p + ( ) ( ) ranging from 141 to 255 μK 2 at 150 GHz for a thermal CMB spectrum. As linear CMB polarization experiments become increasingly sensitive, the techniques described in this paper can be applied to obtain even stronger constraints on circular polarization.

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Section: Resultsmentioning

confidence: 99%

A New Limit on CMB Circular Polarization from SPIDER

Nagy

Ade

Amiri

et al. 2017

ApJ

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“…We use the CMB survey data to map the Moon around each detector within a radius of 5 • to 90 • . 3 A destriping technique, used in generating the survey maps, allows us to recover features in the far- sidelobe maps (Delabrouille 1998;Burigana et al 1999;Kurki-Suonio et al 2009;Miller et al 2016). The destriped far-sidelobe maps are made in the detector coordinate system.…”

Section: Far Sidelobe Studymentioning

confidence: 99%

“…where I, Q, U, V are the Stokes parameters for the incoming radiation while I , Q , U , V are the Stokes parameters for the radiation leaving the VPM (Miller et al 2016;Harrington et al 2018). The transfer function depicts how the VPM transfers the sky polarization signal to the modulated TOD, and thus how to recover the original polarization signal.…”

Section: Polarization Data Processingmentioning

confidence: 99%

“…Multi-frequency observations enable CLASS to distinguish the CMB from Galactic foregrounds (Watts et al 2015). CLASS uses rapid front-end polarization modulation to recover the polarization signal at up to 90 • scales ( 2) (Miller et al 2016;Harrington et al 2018). This measurement will constrain the tensor B modes at the tensor-to-scalar ratio r ≈ 0.01 level (Watts et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

Brewer

Rojas

et al. 2020

ApJ

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The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background (CMB) over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the large angular scale (1 • θ 90 • ) CMB polarization to constrain the tensor-to-scalar ratio at the r ∼ 0.01 level and the optical depth to last scattering to the sample variance limit. This paper presents the optical characterization of the 40 GHz telescope during its first observation era, from September 2016 to February 2018. High signal-to-noise observations of the Moon establish the pointing and beam calibration. The telescope boresight pointing variation is < 0.023 • (< 1.6% of the beam's full width at half maximum (FWHM)). We estimate beam parameters per detector and in aggregate, as in the CMB survey maps. The aggregate beam has a FWHM of 1.579 • ± .001 • and a solid angle of 838 ± 6 µsr, consistent with physical optics simulations. The corresponding beam window function has sub-percent error per multipole at < 200. An extended 90 • beam map reveals no significant far sidelobes. The observed Moon polarization shows that the instrument polarization angles are consistent with the optical model and that the temperature-topolarization leakage fraction is < 10 −4 (95% C.L.). We find that the Moon-based results are consistent with measurements of M42, RCW 38, and Tau A from CLASS's CMB survey data. In particular, Tau A measurements establish degree-level precision for instrument polarization angles.

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“…The combination of instrument stability and systematics rejection due to the front-end polarization modulation with a VPM enables the recovery of the largest angular scales of the CMB polarization from a ground based telescope. 6 These proceedings cover the requirements, design, implementation, and performance of the VPMs for the first two CLASS telescopes (Q-band and the first W-band telescope). The Q-band VPM was installed at the CLASS site in the Spring of 2016 and was on sky until the Spring of 2018, when it was removed and re-installed.…”

Section: Introductionmentioning

confidence: 99%

Variable-delay polarization modulators for the CLASS telescopes

Harrington

Eimer

Chuss

et al. 2018

Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX

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The search for inflationary primordial gravitational waves and the measurement of the optical depth to reionization, both through their imprint on the large angular scale correlations in the polarization of the cosmic microwave background (CMB), has created the need for high sensitivity measurements of polarization across large fractions of the sky at millimeter wavelengths. These measurements are subject to instrumental and atmospheric 1/f noise, which has motivated the development of polarization modulators to facilitate the rejection of these large systematic effects.Variable-delay polarization modulators (VPMs) are used in the Cosmology Large Angular Scale Surveyor (CLASS) telescopes as the first element in the optical chain to rapidly modulate the incoming polarization. VPMs consist of a linearly polarizing wire grid in front of a movable flat mirror. Varying the distance between the grid and the mirror produces a changing phase shift between polarization states parallel and perpendicular to the grid which modulates Stokes U (linear polarization at 45 • ) and Stokes V (circular polarization). The CLASS telescopes have VPMs as the first optical element from the sky; this simultaneously allows a lock-in style polarization measurement and the separation of sky polarization from any instrumental polarization further along in the optical path.The CLASS VPM wire grids use 50 µm copper-plated tungsten wire with a 160 µm spacing across a 60 cm clear aperture. The mirror is mounted on a flexure system with one degree of translational freedom, enabling the required mirror motion while maintaining excellent parallelism with respect to the wire grid. The wire grids and mirrors are held parallel to each other to better than 80 µm, and the wire grids have RMS flatness errors below 50 µm across the 60 cm aperture. The Q-band CLASS VPM was the first VPM to begin observing the CMB full time, starting in the Spring of 2016. The first W-band CLASS VPM was installed in the Spring of 2018. * The modulation functions are the top row of the Mueller matrix for the combined VPM plus detector system, this takes polarization from the sky and returns the power observed by the detector. † † The mirror-off position or the zero current position is defined as the position the MTM sags to when the telescope is pointed at 45 • elevation and the voice coils are unpowered.

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Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-Delay Polarization Modulators

Cited by 27 publications

References 59 publications

A New Limit on CMB Circular Polarization from SPIDER

A New Limit on CMB Circular Polarization from SPIDER

Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: 40 GHz Telescope Pointing, Beam Profile, Window Function, and Polarization Performance

Variable-delay polarization modulators for the CLASS telescopes

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