Absolute frequency measurement of the neutral 40Ca optical frequency standard at 657 nm based on microkelvin atoms

Published

March 14, 2007

Author(s)

G Wilpers, Christopher W. Oates, Scott A. Diddams, A Bartels, Tara M. Fortier, Windell Oskay, James C. Bergquist, Steven R. Jefferts, Thomas P. Heavner, Thomas E. Parker, Leo W. Hollberg

Abstract

We report an absolute frequency measurement of the optical clock transition at 657 nm in 40Ca with a relative uncertainty of 7.5x10^-15, the most accurate frequency measurement of a neutral atom optical transition to date. Relative instabilities of 2x10^-15 in 10 s of averaging time and 2x10^-16 in 1000 s were demonstrated by measuring relative to the single-ion ¹⁹⁹Hg⁺ optical frequency standard at NIST by means of a fs-laser-based frequency comb. The Hg⁺ frequency was simultaneously calibrated relative to the NIST Cs fountain via the NIST time scale for the absolute frequency measurement. The absolute frequency value of (455 986 240 494 135.8+/-3.4) Hz was measured by stabilizing a diode laser system to a thermal ensemble of about 106 atoms cooled in two stages to a temperature of 10 u K. A short cooling/spectroscopy cycle time of 25 ms led to a fractional frequency instability of ~2x10^-16 for an averaging time of 2000 s.

Citation

Metrologia

Volume

44

Pub Type

Journals

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Keywords

atomic clocks, high resolution spectroscopy, optical frequency standards

Citation

Wilpers, G. , Oates, C. , Diddams, S. , Bartels, A. , Fortier, T. , Oskay, W. , Bergquist, J. , Jefferts, S. , Heavner, T. , Parker, T. and Hollberg, L. (2007), Absolute frequency measurement of the neutral ⁴⁰Ca optical frequency standard at 657 nm based on microkelvin atoms, Metrologia, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50474 (Accessed October 2, 2025)