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Frequency Stability in a Compact, Deployable Optical Atomic Clock

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Technical Report

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Charles Stark Draper Laboratory, Inc. Cambridge United States

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The advent of ultra-narrow lasers, ultra-fast lasers, and optical frequency combs in the last several decades have enabled a new generation of atomic clocks based on optical transitions as opposed to microwave transitions. While optical atomic clocks in the laboratory outperform microwave standards by orders of magnitude, their complexity, size, weight, and power have so far precluded their application to fielded, compact systems. Efforts described in this thesis to transfer optical atomic time keeping technology from the laboratory to the field and to improve analytic tools for spectroscopy with ultra-narrow lasers are motivated by a need to support GPS-denied operations a DARPA objective and to enable a broad range of positioning, navigation, and timing applications in civil, commercial, and defense sectors.Existing theoretical frameworks describing coupling strength for atom-laser interactions in optical atomic systems implicitly assume broad laser linewidths. This thesis explores possible spectroscopic implications of ultra-narrow lasers interacting with atoms. Additionally, a simple optical atomic clock architecture based on thermal calcium Ramsey-Bord R-B matter-wave interferometry is described. Experimental investigations in this thesis were carried out in two systems a compact, deployable Ca Beam Optical Timekeeping CaBOT clock, and a second-generation laboratory clock at NIST Ca-2. This thesis describes a performance evaluation of the CaBOT frequency reference exhibiting fractional frequency instability of 5.0x10-14 at one second. Measurement noise floor analyses revealed excess lasernoise to be the dominant performance limitation. With modest improvements, instability is projected to reach the 10-15 decade. In the Ca-2 system, temperature fluctuations were observed to drive instability for time scales 100s, and a temperature-frequency correlation study indicated that temperature control at the mK level would enable 10-16 instability

Subject Categories:

  • Test Facilities, Equipment and Methods
  • Optics

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