BICEP阵列中用于毫米波光学器件的塑料层压抗反射涂层
Plastic Laminate Antireflective Coatings for Millimeter-wave Optics in BICEP Array
AI总结：
针对BICEP阵列望远镜低温光学器件的抗反射涂层需求，研究人员设计制备了适配BA1接收器的30/40 GHz塑料层压抗反射涂层，测试了其反射率，并推进下一代涂层优化，为CMB第四阶段实验提供技术参考。
摘要：
BICEP/Keck系列实验旨在从南极以度级分辨率观测宇宙微波背景。未来几年，“第三阶段”BICEP阵列（BA）望远镜将把该项目的频率覆盖范围和对原初B模偏振的灵敏度提升一个数量级。阵列中的首个接收器BA1于2020年初开始在30/40 GHz频段进行观测。接下来的两个接收器BA2和BA3目前正在组装中，将在95 GHz至150 GHz的频率范围内绘制南天星空图。所有BA接收器的共同特点是采用折射式、同轴、低温光学设计，将微波辐射聚焦到布满天线耦合测辐射热计的焦平面上。光学链中的每个元件都需要孔径达760毫米的高性能抗反射涂层，且涂层必须能承受低至4 K的反复热循环。本文介绍了近期部署的BA1接收器所用30/40 GHz抗反射涂层的设计与制备，随后讨论了其反射率的实验室测量结果。我们回顾了这些折射率与多种聚乙烯、尼龙和氧化铝光学器件相匹配的单层及双层塑料涂层的层压方法。我们还描述了为下一代BA低温恒温器优化涂层的正在进行的工作，这可能为宇宙微波背景“第四阶段”实验未来的小口径望远镜的技术选择提供参考。
英文摘要：
The BICEP/Keck series of experiments target the Cosmic Microwave Background at degree-scale resolution from the South Pole. Over the next few years, the "Stage-3" BICEP Array (BA) telescope will improve the program's frequency coverage and sensitivity to primordial B-mode polarization by an order of magnitude. The first receiver in the array, BA1, began observing at 30/40 GHz in early 2020. The next two receivers, BA2 and BA3, are currently being assembled and will map the southern sky at frequencies ranging from 95 GHz to 150 GHz. Common to all BA receivers is a refractive, on-axis, cryogenic optical design that focuses microwave radiation onto a focal plane populated with antenna-coupled bolometers. High-performance antireflective coatings up to 760 mm in aperture are needed for each element in the optical chain, and must withstand repeated thermal cycles down to 4 K. Here we present the design and fabrication of the 30/40 GHz anti-reflection coatings for the recently deployed BA1 receiver, then discuss laboratory measurements of their reflectance. We review the lamination method for these single- and dual-layer plastic coatings with indices matched to various polyethylene, nylon and alumina optics. We also describe ongoing efforts to optimize coatings for the next BA cryostats, which may inform technological choices for future Small-Aperture Telescopes of the CMB "Stage 4" experiment.
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