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A Compact Optical Atomic Clock Based on a Two-Photon Transition in Rubidium

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Air Force Research Laboratory, Space Vehicles Directorate Kirtland AFB United States

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High stability clocks and oscillators play an integral role in many modern technologies such as navigation and communications 1. Laboratory-based primary frequency standards, which utilize RF transitions between atomic hyperfine levels, provide the highest degree of timing accuracy and are used to form international timescales 2, 3 in many cases, however, applications beyond timekeeping require clocks that are deployed outside the laboratory setting. One well-known case is that of global navigation satellite systems GNSS, which employ space-qualified frequency standards aboard satellites in medium earth orbit andor geosynchronous orbit 1, 4. While portable clocks are typically outpaced by their laboratory counterparts in terms of precision and accuracy, they nonetheless offer very low frequency instabilities in the case of rubidium atomic frequency standards, clocks are commercially available with a drift rate below 10expn -13day and a frequency noise floor less than 10expn -14 5. With the advent of fully stabilized optical frequency combs in 2000 68, optical frequency standards haverapidly surpassed the capabilities of RF clocks in both stability 9, 10 and systematic uncertainty 1113. However, these improvements have yet to make an impact on portable and deployable clocks. Much of the difficulty in developing compact and environmentally robust optical frequency standards lies with the complicated laser sources and optical systems required for laser cooling and interrogating an atomic sample. Moreover, given the high quality factor i.e. narrow spectral linewidth of typical optical clock transitions, laser pre-stabilization to a high-finesse Fabry-Perot cavity is generally required, which adds significant complexity to the system. Finally, optical frequency combs have historically not been sufficiently compact or robust to warrant an effort toward deployment.

Descriptive Note:

Technical Report,18 Aug 2015,08 Aug 2017



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Approved For Public Release;

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