Fujino T, Takakura S, Chinone Y, Hasegawa M, Hazumi M, Katayama N, Lee A T, Matsumura T, Minami Y, Nishino H
Graduate School of Engineering Science, Yokohama National University, Yokohama 240-8501, Japan.
Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, Colorado 80309, USA.
Rev Sci Instrum. 2023 Jun 1;94(6). doi: 10.1063/5.0140088.
A half-wave plate (HWP) is often used as a modulator to suppress systematic error in the measurements of cosmic microwave background (CMB) polarization. A HWP can also be used to measure circular polarization (CP) through its optical leakage from CP to linear polarization. The CP of the CMB is predicted from various sources, such as interactions in the Universe and extension of the standard model. Interaction with supernova remnants of population III stars is one of the brightest CP sources. Thus, the observation of the CP of CMB is a new tool for searching for population III stars. In this paper, we demonstrate the improved measurement of the leakage coefficient using the transmission measurement of an actual HWP in the laboratory. We measured the transmittance of linearly polarized light through the HWP used in Polarbear in the frequency range of 120-160 GHz. We evaluate the properties of the HWP by fitting the data with a physical model using the Markov Chain Monte Carlo method. We then estimate the band-averaged CP leakage coefficient using the physical model. We find that the leakage coefficient strongly depends on the spectra of CP sources. We thus calculate the maximum fractional leakage coefficient from CP to linear polarization as 0.133 ± 0.009 in the Rayleigh-Jeans spectrum. The nonzero value shows that Polarbear has a sensitivity to CP. Additionally, because we use the bandpass of detectors installed in the telescope to calculate the band-averaged values, we also consider systematic effects in the experiment.
半波片（HWP）常被用作调制器，以抑制宇宙微波背景（CMB）极化测量中的系统误差。半波片还可用于通过其从圆极化（CP）到线极化的光学泄漏来测量圆极化。CMB的圆极化是由各种来源预测的，例如宇宙中的相互作用和标准模型的扩展。与第三代恒星的超新星遗迹相互作用是最亮的圆极化源之一。因此，对CMB圆极化的观测是寻找第三代恒星的一种新工具。在本文中，我们展示了利用实验室中实际半波片的透射测量对泄漏系数进行的改进测量。我们测量了在120 - 160吉赫兹频率范围内通过Polarbear中使用的半波片的线偏振光的透过率。我们使用马尔可夫链蒙特卡罗方法通过将数据与物理模型拟合来评估半波片的特性。然后，我们使用该物理模型估计频带平均圆极化泄漏系数。我们发现泄漏系数强烈依赖于圆极化源的光谱。因此，我们计算出在瑞利 - 金斯光谱中从圆极化到线极化的最大分数泄漏系数为0.133±0.009。该非零值表明Polarbear对圆极化具有灵敏度。此外，由于我们使用安装在望远镜中的探测器的带通来计算频带平均值，所以我们也考虑了实验中的系统效应。
