In this paper, artificial opals, made of 300-nm-diameter nanoporous SiO2 globules by sedimentation of a colloidal suspension and annealing at different temperatures in the range of 200–1500 °C, are studied as a promising material platform for terahertz (THz) optics. Our findings reveal that THz optical properties of such materials can be predictably varied in a wide range by annealing, while being a deterministic function of the material porosity. Thus, when increasing annealing temperature, the resultant material refractive index increases from 1.65 to 1.95 at 1.0 THz, while the material absorption coefficient (by field) reduces from 10 to 1 cm−1. The Bruggeman effective medium theory was then successfully applied to model optical properties of the nanoporous SiO2 at THz frequencies as a function of the material porosity and the annealing temperature. Finally, bulk nanoporous SiO2 were shaped using conventional grinding techniques into plates and cylindrical lenses to demonstrate robustness of the novel THz optical materials. A wide range of the nanoporous SiO2 refractive indices, their low-to-moderate THz-wave absorption, as well as their mechanical robustness make such materials a promising platform for THz optics.

中文翻译：

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基于退火人造蛋白石的纳米多孔 SiO2 作为太赫兹光学的有利材料平台

在本文中，人工蛋白石由直径为 300 nm 的纳米多孔 SiO2 球体通过胶体悬浮液的沉淀和在 200-1500 °C 范围内的不同温度下退火制成，被研究作为太赫兹 (THz) 的有前途的材料平台光学。我们的研究结果表明，这种材料的太赫兹光学特性可以通过退火在很宽的范围内进行可预测的变化，同时是材料孔隙率的确定性函数。因此，当提高退火温度时，所得材料的折射率在 1.0 THz 时从 1.65 增加到 1.95，而材料吸收系数（按场）从 10 减少到 1 cm-1。然后，布鲁格曼有效介质理论成功地应用于模拟纳米多孔 SiO2 在太赫兹频率下作为材料孔隙率和退火温度的函数的光学特性。最后，使用常规研磨技术将块状纳米多孔 SiO2 成型为板和柱面透镜，以证明新型太赫兹光学材料的稳健性。宽范围的纳米多孔 SiO2 折射率、低到中等的太赫兹波吸收以及它们的机械强度使此类材料成为太赫兹光学的有前途的平台。