Millimeter-wave achromatic 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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“…The authors in Ref. 23 used the birefringent properties of sapphire to build achromatic half-wave plates. An isotropic material such as HDPE can also be used as an effectively anisotropic medium by staggering HDPE plates on top of each other with gaps in between (Fig.…”

Section: Figmentioning

confidence: 99%

Polarizer design for millimeter-wave plasma diagnostics

Leipold

Salewski

Jacobsen

et al. 2013

Review of Scientific Instruments

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Radiation from magnetized plasmas is in general elliptically polarized. In order to convert the elliptical polarization to linear polarization, mirrors with grooved surfaces are currently employed in our collective Thomson scattering diagnostic at ASDEX Upgrade. If these mirrors can be substituted by birefringent windows, the microwave receivers can be designed to be more compact at lower cost. Sapphire windows (a-cut) as well as grooved high density polyethylene windows can serve this purpose. The sapphire window can be designed such that the calculated transmission of the wave energy is better than 99%, and that of the high density polyethylene can be better than 97%.

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“…The Teflon filter has absorption greater than 90% at frequencies above 10 THz. An achromatic half-wave plate (HWP) [11,12] is mounted on the sky side of a 22 cm diameter aperture stop (Fig. 2).…”

Section: Overall Designmentioning

confidence: 99%

The Ebex Cryostat and Supporting Electronics

Sagiv

2012

The Twelfth Marcel Grossmann Meeting

Self Cite

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We describe the cryostat and supporting electronics for the EBEX experiment. EBEX is a balloon-borne polarimeter designed to measure the B-mode polarization of the cosmic microwave background radiation. The instrument includes a 1.5 meter Gregorian-type telescope and 1432 bolometric transition edge sensor detectors operating at 0.3 K. Electronics for monitoring temperatures and controlling cryostat refrigerators is read out over CANbus. A timing system ensures the data from all subsystems is accurately synchronized. EBEX completed an engineering test flight in June 2009 during which the cryogenics and supporting electronics performed according to predictions. The temperatures of the cryostat were stable, and an analysis of a subset of the data finds no scan synchronous signal in the cryostat temperatures. Preparations are underway for an Antarctic flight.

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Millimeter-wave achromatic half-wave plate

Cited by 40 publications

References 9 publications

CMB beam systematics: Impact on lensing parameter estimation

CMB beam systematics: Impact on lensing parameter estimation

Polarizer design for millimeter-wave plasma diagnostics

The Ebex Cryostat and Supporting Electronics

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