Polarbear Telescope

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Polarbear Telescope

• Huan T Tran
• UC Berkeley

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Polarbear Project

• Measure the Inflation-Induced Gravity wave signal
• Appears in the Polarization of the Cosmic
  Microwave Background
• Caused by primordial tensor modes
• Appears as a curl component of polarization maps
  (B-Modes)

• Polarbear
• 3m offset Gregorian
• Small enough for an effective ground shielding
• Sited at White mountain in Sierras CA (12,000
  ft)

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Collaboration
UC Berkeley Adrian T. Lee Paul Richards William
L. Holzapfel Martin White Greg Engargiola Huan
T. Tran Nils Halverson Hsiao-Me Cho Trevor
Lanting Mike Myers Roger O'Brient Zigmund
Kermish Kam Arnold Erin Quealy
Lawrence Berkeley National Lab Helmuth Spieler
Matt Dobbs Radek Stompr Julian Borrill
University of California at San Diego Brian
Keating George Fuller
UC-run WMRS
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Spectrum
arcmin
Degree-scale

• Gravity wave signal
• Bump at degree scales
• Very small- need 100X more sensitivity than WMAP

• Lensing Signal
• Another bump at arcminute scales
• Still small, but may dominate the overall signal
• Must be cleaned in order to see Gravity wave
  signal

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DetectorsDual-polarization Antenna-Coupled TES
Beam is normal to wafer plane
Multi-frequency array
Hemispherical Si Lens
Wafer
See Talk by Mike Myers This Afternoon
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Optical system-Telescope Camera

• Main Telescope
• Offset Gegorian
• Mizuguchi-Dragone condition
• Low Cross-pol (for middle pixel)
• Corrects for Astigmatism
• Large native FOV
• Highly curved focal plane
• Not telecentric
• inaccessible Aperture image

2m
3m
Aperture image
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Camera11 Re-imaging optics
All Lenses are HDPE
Aperture Lens/ Lyot Stop
Collimator
Field Lens
Gregorian Focus
Re-Image plane -Now telecentric and flat
HWP
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Performance
Full Field Spot diagram

• Aberration Performance
• Supports 1000 2-F-l pixels
• limited by Strehl (gt0.8) and
  
  
  Vignetting from Collimator lens

3.8 deg
Airy circle
Diffraction Limited Circle
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Beam overlap at the Primary
Footprint of beams on primary
Straight lenses give erect aperture image
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Beam overlap at the Primary
Footprint of beams on primary
Straight lenses give erect aperture image
Tilted lens tilts aperture image
Tilted Field lens fixes Non-Overlapping Beams
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Distortion
Distortion Grid

• Design is not Optimized for distortion
• May be the leading contribution to
  Cross-polarization
• Should remain stable
• Leading contribution should be an overall
  rotation

Input object
Output image
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Final note

• This design was primarily chosen because it
  supports a large FOV, is compact, and has a clear
  aperture.
• Polarization performance was a secondary concern,
  however
• Cross-pol mixes E-mode ? B-mode
• Instrumental-pol mixes T ?E,B-Modes dominant
• Instrumental-Pol is caused by
• Oblique reflections from metal
• Refraction
• Both should change slowly with time

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Final Note 2

• A large amount of Physical Optics analysis has
  been done, but with limited utility
• No Lenses
• Small number of simple elements
• Non-realistic feed pattern

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end
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Science