MAXIPOL: Cosmic Microwave Background Polarimetry Using a Rotating Half‐Wave Plate

The cosmic microwave background (CMB) is a rich source of cosmological information. Thanks to the simplicity and linearity of the theory of cosmological perturbations, observations of the CMB's polarization and temperature anisotropy can reveal the parameters which describe the contents, structure, and evolution of the cosmos. Temperature anisotropy is necessary but not sufficient to fully mine the CMB of its cosmological information as it is plagued with various parameter degeneracies. Fortunately, CMB polarization breaks many of these degeneracies and adds new information and increased precision. Of particular interest is the CMB's B-mode polarization which provides a handle on several cosmological parameters most notably the tensor-to-scalar ratio, r, and is sensitive to parameters which govern the growth of large scale structure (LSS) and evolution of the gravitational potential. These imprint CMB temperature anisotropy and cause E-to-B-mode polarization conversion via gravitational lensing. However, both primordial gravitational-wave-and secondary lensing-induced B-mode signals are very weak and therefore prone to various foregrounds and systematics. In this work we use Fisher-matrix-based estimations and apply, for the first time, Monte-Carlo Markov Chain (MCMC) simulations to determine the effect of beam systematics on the inferred cosmological parameters from five upcoming experiments: PLANCK, POLARBEAR, SPIDER, QUIET+CLOVER and CMBPOL. We consider beam systematics which couple the beam substructure to the gradient of temperature anisotropy and polarization (differential beamwidth, pointing offsets and ellipticity) and beam systematics due to differential beam normalization (differential gain) and orientation (beam rotation) of the polarization-sensitive axes (the latter two effects are insensitive to the beam substructure). We determine allowable levels of beam systematics for given tolerances on the induced parameter errors and check for possible biases in the inferred parameters concomitant with potential increases in the statistical uncertainty. All our results are scaled to the 'worst case scenario'. In this case, and for our tolerance levels the beam rotation should not exceed the few-degree to sub-degree level, typical ellipticity is required to be 1%, the differential gain allowed level is few parts in 10 3 to 10 4 , differential beam width upper limits are of the sub-percent level and differential pointing should not exceed the few-to sub-arc sec level.PACS numbers: 98.70.Vc INTRODUCTIONThe standard cosmological model accounts for a multitude of phenomena occurring over orders of magnitude of length and angular scales throughout the entire history of cosmological evolution. Remarkably, doing so only requires about a dozen parameters. Perhaps one of the most useful cosmological probes is cosmic microwave background (CMB) temperature anisotropy whose physics is well understood. Complementary cosmological probes can assist in breaking some of the degeneracies inherent in the CMB and further tighten...

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“…Hanany et al [16], Johnson et al [17], MacTavish et al [18]). These can operate in continuous or stepped rotation.…”

Section: Mathematical Formalismmentioning

confidence: 99%

CMB beam systematics: Impact on lensing parameter estimation

2009

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“…In MAXIPOL, instead, a DC motor outside the cryostat rotated a cryogenically cooled Half Wave Plate (HWP) by means of a fiberglass drive shaft crossing the cryostat shell and the tertiary mirror, mounted in the aperture stop of the optical system (Johnson et al 2007). …”

Section: Introductionmentioning

confidence: 99%

A cryogenic waveplate rotator for polarimetry at mm and submm wavelengths

Salatino

Bernardis

Masi

2011

A&A

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Context. Polarimetry at mm and submm wavelengths is the new frontier of research in cosmic microwave background and interstellar dust studies. Polarimeters working in the IR to MM range need to be operated at cryogenic temperatures to limit the systematic effects related to the emission of the polarization analyzer. Aims. We study the effect of the temperature of the different components of a waveplate polarimeter and describe a system able to rotate a birefringent crystal at 4 K in a completely automated way. Methods. We simulate the main systematic effects related to the temperature and non-ideality of the optical components in a Stokes polarimeter. To limit these effects, a cryogenic implementation of the polarimeter is mandatory. In our system, the rotation produced by a step motor running at room temperature is transmitted down to cryogenic temperatures by means of a long shaft and gears running on custom cryogenic bearings. Results. Our system is able to rotate a birefringent crystal at 4 K in a completely automated way and dissipates only a few mW in the cold environment. A readout system based on optical fibers allows us to control the rotation of the crystal to better than 0.1 • . Conclusions. This device fulfills the stringent requirements for operations in cryogenic space experiments, such as the forthcoming PILOT, BOOMERanG and LSPE.

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“…In this way, CMB polarization can be accurately measured and separated from ISD, taking advantage of their different spectral dependence (see e.g. 10,11,12 and references therein). The SWIPE instrument on LSPE has been optimized to cover with very high sensitivity the high frequency side of the CMB spectrum.…”

Section: The Science Case For Swipementioning

confidence: 99%

SWIPE: a bolometric polarimeter for the Large-Scale Polarization Explorer

et al. 2012

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The balloon-borne LSPE mission is optimized to measure the linear polarization of the Cosmic Microwave Background at large angular scales. The Short Wavelength Instrument for the Polarization Explorer (SWIPE) is composed of 3 arrays of multi-mode bolometers cooled at 0.3K , with optical components and filters cryogenically cooled below 4K to reduce the background on the detectors. Polarimetry is achieved by means of large rotating half-wave plates and wire-grid polarizers in front of the arrays. The polarization modulator is the first component of the optical chain, reducing significantly the effect of instrumental polarization. In SWIPE we trade angular resolution for sensitivity. The diameter of the entrance pupil of the refractive telescope is 45 cm, while the field optics is optimized to collect tens of modes for each detector, thus boosting the absorbed power. This approach results in a FWHM resolution of 1.8, 1.5, 1.2 degrees at 95, 145, 245 GHz respectively. The expected performance of the three channels is limited by photon noise, resulting in a final sensitivity around 0.1-0.2 μK per beam, for a 13 days survey covering 25% of the sky.

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MAXIPOL: Cosmic Microwave Background Polarimetry Using a Rotating Half‐Wave Plate

Cited by 85 publications

References 32 publications

CMB beam systematics: Impact on lensing parameter estimation

CMB beam systematics: Impact on lensing parameter estimation

A cryogenic waveplate rotator for polarimetry at mm and submm wavelengths

SWIPE: a bolometric polarimeter for the Large-Scale Polarization Explorer

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