Direct comparison of two cold-atom-based optical frequency standards by using a femtosecond-laser comb.
With a fiber-broadened, femtosecond-laser frequency comb, the 76-THz interval between two laser-cooled optical frequency standards was measured with a statistical uncertainty of 2x10(-13) in 5 s , to our knowledge the best short-term instability thus far reported for an optical frequency measurement. One standard is based on the calcium intercombination line at 657 nm, and the other, on the mercury ion electric-quadrupole transition at 282 nm. By linking this measurement to the known Ca frequency, we report a new frequency value for the Hg(+) clock transition with an improvement in accuracy of ~10(5) compared with its best previous measurement.
Vogel
K R
KR
Diddams
S A
SA
Oates
C W
CW
Curtis
E A
EA
Rafac
R J
RJ
Itano
W M
WM
Bergquist
J C
JC
Fox
R W
RW
Lee
W D
WD
Wells
J S
JS
Hollberg
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L