期刊
METROLOGIA
卷 55, 期 6, 页码 789-805出版社
IOP PUBLISHING LTD
DOI: 10.1088/1681-7575/aae008
关键词
atomic fountain clocks; primary frequency standards; SI second; international atomic time; frequency metrology
资金
- European Metrology Research Programme (EMRP) in project [SIB55 ITOC]
- European Metrology Programme for Innovation and Research (EMPIR) [15SIB05 OFTEN]
- National Science Foundation
- EMRP/EMPIR participating countries within EURAMET
- European Union
Improvements of the systematic uncertainty, frequency instability, and long-term reliability of the two caesium fountain primary frequency standards CSF1 and CSF2 at PTB (Physikalisch-Technische Bundesanstalt) are described. We have further investigated many of the systematic effects and made a number of modifications of the fountains. With an optically stabilized microwave oscillator, the quantum projection noise limited frequency instabilities are improved to 7.2 x 10(-14) (tau/1 s)(-1/2) for CSF1 and 2.5 x 10(-14) (tau/1 s)(-1/2) for CSF2 at high atom density. The systematic uncertainties of CSF1 and CSF2 are reduced to 2.74 x 10(-16) and 1.71 x 10(-16), respectively. Both fountain clocks regularly calibrate the scale unit of International Atomic Time (TAI) and the local realization of Coordinated Universal Time, UTC(PTB), and serve as references to measure the frequencies of local and remote optical frequency standards.
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