Improved short-term stability of optical frequency standards: approaching 1 Hz in 1 s with the Ca standard at 657 nm.
For a neutral (40)Ca-based optical frequency standard we report a fractional frequency instability of 4 x 10(-15) in 1 s, which represents a fivefold improvement over existing atomic frequency standards. Using the technique of optical Bordé-Ramsey spectroscopy with a sample of 10(7) trapped atoms, we have resolved linewidths as narrow as 200 Hz (FWHM). With colder atoms this system could potentially achieve an instability as low as 2 x 10(-16) in 1 s. Such low instabilities are important for frequency standards and precision tests of fundamental physics.
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Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80303, USA.
Curtis
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Hollberg
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