AN OPTICAL FREQUENCY STANDARD WITH ULTRACOLD Ca-ATOMS

摘要

Optical frequency standards utilizing narrow atomic transitions with Q≈ 10~(12) and low sensitivities to external fields offer the possibility to reach relative uncertainties below 10~(-15). Using ensembles of more than 10~7 neutral alkaline earth atoms laser cooled in a magneto-optical trap, excellent short time stabilities below 10~(-16) in 1 s seem possible. In our optical Ca-frequency standard with an ensemble Doppler cooled to a temperature of 3 mK we have realized a relative uncertainty of 2·10~(-14) limited mainly by a residual Doppler effect of the atomic motion and by the effect of cold collisions. With a new quench cooling method we were able to reduce the temperature to below 10μK. First measurements showed the potential for a reduced uncertainty and an improved stability in utilizing these ultracold atoms in the frequency standard.