Improved Evaluation of BBR and Collisional Frequency Shifts of NIM-Sr2 with 7.2 × 10<sup>−18</sup> Total Uncertainty
Bing-Kun Lu, Zhen Sun, Tao Yang, Yige Lin, Qiang Wang, Ye Li, Fei Meng, Bai-Ke Lin, Tianchu Li, Zhanjun Fang
Abstract
NIM-Sr2 optical lattice clock has been developed on the Changping campus of National Institute of Metrology (NIM). Considering the limitations in NIM-Sr1, several improved parts have been designed including a differential pumping stage in the vacuum system, a permanent magnet Zeeman slower, water-cooled anti-Helmholtz coils, an extended viewport for Zeeman slower, etc. A clock laser with a short-time stability better than 3 × 10 −16 is realized based on a self-designed 30-cm-long ultra-low expansion cavity. The systematic frequency shift has been evaluated to an uncertainty of 7.2 × 10 −18 , with the uncertainty of BBR shift and the collisional frequency shift being an order of magnitude lower than the last evaluation of NIM-Sr1.