用于引力波探测器的TiO₂掺杂GeO₂非晶光学涂层的本征缺陷
Intrinsic Defects in Amorphous Optical Coatings of TiO$_2$-doped GeO$_2$ for Gravitational-wave Detectors
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中文总结 AI 辅助
本研究针对TiO₂掺杂GeO₂非晶光学涂层的残余吸收问题，通过模拟与测量确定富Ti缺氧环境为缺陷来源，提出可通过控制氧化学计量比缓解该问题。
中文摘要 AI 辅助
未来引力波探测器的激光功率提升，要求反射镜涂层的光吸收低于每反射镜0.1 ppm。TiO₂掺杂GeO₂是目前降低室温涂层热噪声的最佳高折射率材料，即便在将外部污染降至最低后，仍表现出ppm级的吸收。通过从头算模拟和吸收测量，我们确定富Ti缺氧环境是这种残余吸收的来源。我们发现，非晶网络中的普通结构无序可局域电子态，但不会产生能吸收1064 nm光的缺陷；相比之下，致密富Ti环境中的氧空位会产生类Ti³⁺-Ti³⁺极化子对或混合Ti极化子态，其跃迁接近1064 nm。光热测量显示，干/惰性退火后吸收增加，支持这些还原敏感缺陷的形成。这些结果表明，残余吸收并非TiO₂掺杂GeO₂的本征限制，而是与工艺相关的缺陷，可通过控制沉积和退火过程中的氧化学计量比来缓解。
英文摘要
The increased laser power of future gravitational-wave detectors will require mirror coatings with optical absorption below 0.1 ppm per mirror. TiO$_2$-doped GeO$_2$, currently the best high-index material for reducing room-temperature coating thermal noise, still exhibits ppm-level absorption even after extrinsic contamination is minimized. Using ab-initio simulations and absorption measurements, we identify oxygen-deficient Ti-rich environments as the origin of this residual absorption. We find that ordinary structural disorder in the amorphous network can localize electronic states but does not produce defects capable of absorbing 1064-nm light. In contrast, oxygen vacancies in compact Ti-rich environments create localized Ti$^{3+}$--Ti$^{3+}$-like polaron-pair or mixed Ti-polaron states states with transitions near 1064 nm. Photothermal measurements show increased absorption after dry/inert annealing, supporting the formation of these reduction-sensitive defects. These results show that the residual absorption is not an intrinsic limitation of TiO$_2$-doped GeO$_2$, but a process-dependent defect that may be mitigated through control of oxygen stoichiometry during deposition and annealing.
