QUBIC VI：低温半波片旋转器、设计和性能
QUBIC VI: cryogenic half wave plate rotator, design and performances
摘要：
暴胀重力波B模偏振探测是现代大角度尺度宇宙微波背景（CMB）实验的最终目标。一项巨大的努力正在进行，部署了许多地面、气球和卫星实验，使用不同的方法将这种微弱的偏振成分从入射辐射中分离出来。其中一种主要使用的技术是斯托克斯偏振测量法，其使用旋转半波片（HWP）和线偏振器来分离和调制具有低残余交叉偏振的偏振分量。本文介绍了QUBIC斯托克斯旋光仪的设计特点和性能。这些装置的一个共同系统是产生与旋转同步并与光学元件的发射率成比例的大的寄生信号。QUBIC Stokes旋光仪的一个关键特性是在低温下工作，以最大限度地减少这种不必要的分量。在低温下有效地移动这种大型光学元件构成了一个很大的工程挑战，以减少摩擦功耗。在设计阶段已经给予了很大的关注，以尽量减少部件之间的差异热收缩。旋转由放置在低温恒温器外部的步进电机驱动，以避免在低温温度下的热负载耗散。本工作中的测试和结果表明，QUBIC旋光仪可以轻松实现0.1°以下的定位精度，只需使用步进电机精度和光学绝对编码器。旋转仅在第二低温级（~ 8 K）上引起几mK的额外功率负载。
英文摘要：
Inflation Gravity Waves B-Modes polarization detection is the ultimate goal of modern large angular scale cosmic microwave background (CMB) experiments around the world. A big effort is undergoing with the deployment of many ground-based, balloon-borne and satellite experiments using different methods to separate this faint polarized component from the incoming radiation. One of the largely used technique is the Stokes Polarimetry that uses a rotating half-wave plate (HWP) and a linear polarizer to separate and modulate the polarization components with low residual cross-polarization. This paper describes the QUBIC Stokes Polarimeter highlighting its design features and its performances. A common systematic with these devices is the generation of large spurious signals synchronous with the rotation and proportional to the emissivity of the optical elements. A key feature of the QUBIC Stokes Polarimeter is to operate at cryogenic temperature in order to minimize this unwanted component. Moving efficiently this large optical element at low temperature constitutes a big engineering challenge in order to reduce friction power dissipation. Big attention has been given during the designing phase to minimize the differential thermal contractions between parts. The rotation is driven by a stepper motor placed outside the cryostat to avoid thermal load dissipation at cryogenic temperature. The tests and the results presented in this work show that the QUBIC polarimeter can easily achieve a precision below 0.1° in positioning simply using the stepper motor precision and the optical absolute encoder. The rotation induces only few mK of extra power load on the second cryogenic stage (~ 8 K).
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