Jie Zhang, Yingxin Luo, Bing Ouyang, Ke Deng, Zehuang Lu, and Jun Luo

Eur. Phys. J. D67, 46 (2013).

An ultra-stable optical reference cavity with re-entrant fused silica mirrors and a ULE (Ultra Low Expansion) spacer structure is designed for the ultra-narrow clock laser for an Al⁺optical standard. The designed cavity has a low thermal noise limit of 1´10⁻¹⁶and a flexible zero crossing temperature of the effective coefficient of thermal expansion (CTE). The CTE zero crossing temperature difference between a composite cavity and a pure ULE cavity can be tuned from −10^◦C to 23^◦C, which enables operation of the designed reference cavity near room temperature without worrying about the CTE zero crossing temperature of the ULE spacer. This design can also be applied to cavities with different lengths. Vibration immunity of the cavity is also achieved through structure optimization.