AI 中文总结
加拿大银河辐射测绘仪（CGEM）是一款8-10 GHz射电望远镜，采用共轴喇叭馈源旋转体光学设计，通过新型框架优化光学系统以降低T→P泄漏，在轨性能与模拟波束模型吻合，旨在测绘北天极化信号以助力搜寻CMB的B模式。
AI 中文摘要
加拿大银河辐射测绘仪（CGEM）射电望远镜正在8-10 GHz频段测绘银河前景极化信号，以助力搜寻宇宙微波背景（CMB）中的B模式。本文描述了CGEM光学系统的设计及早期在轨表征情况。CGEM采用共轴喇叭馈源光学设计，属于旋转体（BOR）结构，具备优异的本征极化纯度。我们介绍了如何利用一种新型框架优化光学系统，该框架可直接最小化角功率谱空间内模拟强度到极化强度（T→P）的泄漏。经优化的光学系统，从8-10 GHz频段按比例缩放至CMB观测窗口附近的95 GHz时，模拟得到的T→P泄漏量级比r=10⁻³时预期的Cₗ^BB低数个数量级。我们还描述了该光学系统的机械设计，包括一种新型的二次镜支撑结构，其采用Astroquartz复合材料制成，具有低损耗、低介电常数的特点，且能保持光学系统的旋转体对称性。随后，我们展示了该光学系统的早期在轨性能，通过对太阳和卫星的观测，探测到了比峰值低40 dB的波束。基于电磁模拟构建的已部署CGEM光学系统的波束模型，与在轨数据高度吻合。
英文摘要
The Canadian Galactic Emission Mapper (CGEM) radio telescope is mapping polarized Galactic foregrounds from 8-10 GHz to aid in the search for B-modes in the Cosmic Microwave Background (CMB). Here we describe the design and early on-sky characterization of the CGEM optics. CGEM employs an on-axis, hat feed optical design that is a body of revolution (BOR) and exhibits excellent intrinsic polarization purity. We describe how we have optimized the optics with a novel framework that can directly minimize simulated intensity to polarized intensity ($T\rightarrow P$) leakage in angular power spectrum space. The optimized optics exhibit simulated $T\rightarrow P$ leakage that is orders of magnitude below anticipated $C_\ell^{BB}$ for $r = 10^{-3}$ when scaled from 8-10 GHz to the CMB observing window near 95 GHz. We go on to describe the mechanical design of the optics, including a novel secondary mirror support made from Astroquartz composite that has low loss, low dielectric constant, and preserves the BOR symmetry of the optics. We then showcase the early on-sky performance of the optics with observations of the Sun and satellites, which probe the beam to 40 dB down from the peak. A beam model for the deployed CGEM optics based on electromagnetic simulations is in excellent agreement with the on-sky data.
Comments27 pages, 11 figures, submitted to Proc. SPIE
