Sub-kilohertz optical spectroscopy by time domain atom interferometry

Summary form only given, as follows. A time domain atom interferometer is used to compare the frequency of the Mg intercombination transition at 457 nm with an optical oscillator with sub-kHz resolution. An estimated accuracy of 2·10/sup -15/ is achieved with laser cooled and trapped atoms. The resolved line Q-factor is better than 10/sup 12/.