CMB

The Cosmic Microwave Background (CMB) is background radiation coming from the era of the early universe. It is evidence of the Big Bang theory.

The linear polarization of CMB informs us further about the universe. The E-mode polarization could tell us about the optical depth. The sub-degree-scale B-mode polarization can inform the sum of neutrino mass via gravitational lensing. The degree-scale B-mode polarization can be used to test the theory of cosmological inflation.

List of papers

1. Characterization of a half-wave plate for cosmic microwave background circular polarization measurement with POLARBEAR
   • doi, arXiv
2. A Measurement of Atmospheric Circular Polarization with POLARBEAR
   • doi, arXiv
3. 博士論文 (Ph.D. thesis)
   • 連続回転半波長板による円偏光観測手法の開発とPOLARBEAR 実験での大気円偏光検出による検証
   • Development of circular polarization measurement method with continuously rotating half-wave plate and its validation with detection of atmospheric circular polarization with POLARBEAR
   • doi, Univ.

Half-Wave Plate

A half-wave plate (HWP) is an optical device that creates an optical path difference of half of the wavelength. In the CMB experiments, birefringent materials (e.g. Sapphire) are used. By observing a linear polarization signal with continuously rotating HWP, the signal is modulated by four times the HWP rotation frequency.

Moreover, we can search for the circular polarization signal by using the leakage between linear and circular polarization due to the frequency dependence of the HWP.

• Image of HWP
• Image of QWP
  • (source code: https://github.com/MeF0504/basic_setup/blob/master/misc/hwp_image.py )
• Table of HWP modulation
  • (source code: https://github.com/MeF0504/basic_setup/blob/master/misc/hwp_table.py )

List of Papers relating Circular Polarization of CMB

is here (I will update if I have time!)