Influence of chirped excitation pulses in an optical clock with ultracold calcium atoms

We have investigated the influence of frequency chirps of the excitation pulses in a time-domain optical Ramsey-Borde/spl acute/ atom-interferometer used in an optical clock with ultracold calcium atoms. With optical interferometry, we identify a ringing in the excitation pulses to be responsible for the observed frequency shifts. Using these results, the uncertainty of the latest frequency measurement could be reduced to 1.2/spl middot/10/sup -14/.