9/18/2023 0 Comments Moon beam clock![]() ![]() The cesium beam tube part of the portable OPCB includes a vacuum tube, a cesium oven, a microwave cavity and two fluorescence collecting bowls ( Figure 1). It can be divided into three parts: cesium beam tube, optical part and circuits. The portable OPCB is a closed-loop feedback system, which can output the transition frequency of cesium atoms. Section 3 introduced the improvement of short-term and long-term frequency stability of portable OPCB. It is divided into the following parts: in the Section 2, the principle of portable OPCB is introduced. This paper introduces the improvement of the frequency stability of the portable OPCB in Peking University. In these years, the principle of the portable OPCB was improved, and the short-term frequency stability and long-term frequency stability were improved respectively. Its long-term frequency stability has gradually improved from 1-day frequency stability of 10 −13 to 5-day frequency stability of 7 × 10 −15, reaching the forefront of the portable cesium beam atomic clock field. The frequency stability at 1 s has gradually improved from the initial 10 −11 to 10 −12. The research on portable OPCB in Peking University began in 1990s, and now it has been nearly 30 years. The frequency stability of TA1000 from Chengdu Spaceon can reach 8.5 × 1 0 − 12 / τ. OSCAR and CS4 have also achieved good short-term frequency stability. GPS3 using commercial laser can reach 3.8 × 1 0 − 12 / τ. Researches on OPCB have been carried out both in China and abroad. OPCBs are expected to replace the existing magnetic state-selection cesium beam atomic clocks. The portable OPCB adopts the optical pumping technology, which can have both high performance and long life compared to magnetic state-selection cesium beam atomic clock. Due to the limitation of magnetic state-selection scheme, the frequency stability of magnetic state-selection cesium beam atomic clocks can hardly be further improved. The frequency stability of the magnetic state-selection cesium beam atomic clocks is approximately 8.5 × 1 0 − 12 / τ in short-term and can reach 1 × 10 −14 at several days. Compact magnetic state-selection cesium beam atomic clocks have commercial products and have been widely used, such as 5071A from the Microsemi, OSA3235B from Oscilloquartz and LIP-Cs3000 from China. Cesium beam atomic clocks can be divided into two types: magnetic state-selection and optically pumped. Its excellent medium and long-term frequency stability can not be completely replaced by other atomic clocks. The portable cesium beam atomic clock occupies an important position in the field of time and frequency. The compact optically pumped cesium beam atomic clock of Peking University is expected to contribute to the field of timing, positioning, navigation and high speed digital communication. The methods of obtaining the good long-term frequency stability are controlling the microwave power based on the atomic transition probability, controlling the C-field intensity based on Zeeman frequency and controlling the laser power using fluorescence. The optimization methods of the short-term frequency stability are using laser induced beam spectrum to stabilize the laser frequency, using cyclic transition to detect the atomic state and using a cesium oven with a collimator to generate the cesium atomic beam. At present, the short-term frequency stability is 3 × 10 − 12 / τ and the long-term (5-day) frequency stability can reach 7 × 10 −15. The research of optically pumped cesium beam atomic clock (OPCB) at Peking University has lasted for decades. ![]() 2Institute of Fundamental Experiment Education, Peking University, Beijing, China.1Institute of Quantum Electronics, Peking University, Beijing, China. ![]() Xuan He 1, Zhichao Yuan 1, Jiayuan Chen 1, Shengwei Fang 1, Xuzong Chen 1, Qing Wang 2* and Xianghui Qi 1* ![]()
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