Subhertz-linewidth infrared frequency source with a long-term instability below 5 × 10−15
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Distributing a stable, absolute optical reference frequency via fiber network would serve research and development in academia and industry. Lasers stabilized to high-finesse Fabry–Pérot cavities can achieve fractional frequency instabilities of less than 10−15 for periods up to several seconds. Their instabilities increase for longer averaging times due to a variable frequency drift, with a linear drift component of the order of 10…100 mHz/s. Hydrogen masers, on the other hand, yield an instability floor of a few parts in 10−15, but suffer from poor stabilities on short timescales. We demonstrate an infrared optical frequency source that combines a cavity-stabilized laser with a hydrogen maser to achieve a residual fractional frequency instability better than 5 × 10−15 for all averaging times from 0.4 up to 10,000 s. The frequency drift of the system over a period of 40,000 s is less than 30 µHz/s. For obtaining absolute frequency accuracy, the hydrogen maser is referenced to a primary frequency standard.
KeywordsBeat Frequency Frequency Drift Frequency Comb Fiber Link Slave Laser
The authors would like to thank A. Bauch for providing the maser signals and for very helpful comments and discussions, as well as S. Weyers for providing the cesium fountain data and for helpful comments. This work was supported by the European Metrological Research Programme EMRP under SIB-02 NEAT-FT and IND 014. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union. Support by the Centre of Quantum Engineering and Space-Time Research (QUEST) is gratefully acknowledged. Mention of specific products and trade names is for technical communication only and does not constitute an endorsement or recommendation by PTB.
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