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Appl Opt. 2020 Apr 1;59(10):3285-3295. doi: 10.1364/AO.383921.
We present two prescriptions for broadband ($ {\sim} 77 - 252;{\rm GHz} $), millimeter-wave antireflection coatings for cryogenic, sintered polycrystalline aluminum oxide optics: one for large-format (700 mm diameter) planar and plano-convex elements, the other for densely packed arrays of quasi-optical elements-in our case, 5 mm diameter half-spheres (called "lenslets"). The coatings comprise three layers of commercially available, polytetrafluoroethylene-based, dielectric sheet material. The lenslet coating is molded to fit the 150 mm diameter arrays directly, while the large-diameter lenses are coated using a tiled approach. We review the fabrication processes for both prescriptions, then discuss laboratory measurements of their transmittance and reflectance. In addition, we present the inferred refractive indices and loss tangents for the coating materials and the aluminum oxide substrate. We find that at 150 GHz and 300 K the large-format coating sample achieves $ (97 \pm 2)% $ transmittance, and the lenslet coating sample achieves $ (94 \pm 3)% $ transmittance.
我们展示了两种用于低温烧结多晶氧化铝光学器件的宽带（约77 - 252吉赫兹）毫米波减反射涂层配方：一种用于大幅面（直径700毫米）的平面和平凸元件，另一种用于紧密排列的准光学元件阵列——在我们的案例中，是直径5毫米的半球体（称为“小透镜”）。这些涂层由三层市售的基于聚四氟乙烯的介电片材组成。小透镜涂层直接模制成适合直径150毫米的阵列，而大直径透镜则采用平铺方式进行涂层处理。我们回顾了两种配方的制造工艺，然后讨论了它们的透过率和反射率的实验室测量结果。此外，我们还给出了涂层材料和氧化铝衬底的推断折射率和损耗角正切值。我们发现，在150吉赫兹和300开尔文时，大幅面涂层样品的透过率达到（97±2）%，小透镜涂层样品的透过率达到（94±3）%。
