OPTICAL RAMSEY INTERFERENCES ON LASER COOLED AND TRAPPED ATOMS, DETECTED BY ELECTRON SHELVING

Based on a new detection scheme optical Ramsey fringes on the magnesiu m intercombination transition (lambda = 45 7 nm) have been demonstrate d with a resolution of 4 kHz and an accuracy of 1 Hz (DELTAv/v almost- equal-to 2 x 10(-15)) using laser cooled and trapped atoms. Applying a pulsed excitation scheme to the trapped ensemble, the Ramsey signals are nearly undisturbed by the relativistic Doppler effect and phase er rors of the Ramsey zones. The detection is based on the quantum amplif ication due to the electron shelving effect in cooperation with the tr ap dynamics, monitored as decrease of the trap fluorescence induced by the fast trapping transition. Simultaneously recorded Ramsey interfer ences on a thermal atomic beam allowed a direct measurement of the sec ond order Doppler shift. The relevance of the experiment to future opt ical frequency standards achieving a stability and an accuracy of bett er than 10(-15) as well as applications of this system for atom interf erometry are discussed.